InfoMagic Internet Tools 1995 April/Internet Tools.iso/dos_win/winsock/wsock11/winsock.txt

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                               Windows
                               Sockets







                           Windows Sockets
                        An Open Interface for
                      Network Programming under
                         Microsoft  Windows

                             Version 1.1

                           20 January 1993


                             Martin Hall
                             Mark Towfiq
                             Geoff Arnold
                           David Treadwell
                            Henry Sanders



             Copyright  1992 by Martin Hall, Mark Towfiq
           Geoff Arnold, David Treadwell and Henry Sanders

                         All rights reserved.

          This document may be  freely redistributed in  any
          form, electronic or otherwise, provided that it is
          distributed in its entirety and that the copyright
          and  this  notice  are  included.    Comments   or
          questions may be submitted via electronic mail  to
          [e-mail].   Requests to  be added  to
          the  Windows  Sockets   mailing  list  should   be
          addressed to [e-mail].   This
          specification, archives of  the mailing list,  and
          other information on Windows Sockets are available
          via anonymous  FTP  from the  host  microdyne.com,
          directory /pub/winsock.  Questions about products
          conforming  to   this  specification   should   be
          addressed to the vendors of the products.

          Portions of the Windows Sockets specification  are
          derived from material which is Copyright (c) 1982-
          1986  by  the   Regents  of   the  University   of
          California.    All  rights  are  reserved.     The
          Berkeley Software License Agreement specifies  the
          terms and conditions for redistribution.


          Revision history:
          1.0 Rev.A June 11, 1992
          1.0 Rev.B June 16, 1992
          1.0 Rev. C     October 12, 1992
          1.1       January, 1993

























                                  ii                           Windows Sockets
                             Version 1.1
ACKNOWLEDGMENTS..........................................1
1.  INTRODUCTION.........................................3
     1.1 What is Windows Sockets?........................3
     1.2 Berkeley Sockets................................3
     1.3 Microsoft Windows and Windows-specific extensions 3
     1.4 The Status of this Specification................4
     1.5 Revision History................................4
          1.5.1 Windows Sockets Version 1.0..............4
          1.5.2 Windows Sockets Version 1.1..............4
2.  PROGRAMMING WITH SOCKETS.............................6
     2.1 Windows Sockets Stack Installation Checking.....6
     2.2 Sockets.........................................6
          2.2.1 Basic concepts...........................6
          2.2.2 Client-server model......................6
          2.2.3 Out-of-band data.........................7
          2.2.4 Broadcasting.............................7
     2.3 Byte Ordering...................................8
     2.4 Socket Options..................................8
     2.5 Database Files..................................9
     2.6 Deviation from Berkeley Sockets.................9
          2.6.1 socket data type and error values........10
          2.6.2 select() and FD_*........................10
          2.6.3 Error codes - errno, h_errno & WSAGetLastError()
          ...............................................10
          2.6.4 Pointers.................................11
          2.6.5 Renamed functions........................11
               2.6.5.1 close() & closesocket()...........11
               2.6.5.1 ioctl() & ioctlsocket()...........11
          2.6.6 Blocking routines & EINPROGRESS..........11
          2.6.7 Maximum number of sockets supported......11
          2.6.8 Include files............................12
          2.6.9 Return values on API failure.............12
          2.6.10 Raw Sockets.............................12
     2.7 Windows Sockets in Multithreaded Versions of Windows
     ....................................................12
3.  SOCKET LIBRARY OVERVIEW..............................14
     3.1 Socket Functions................................14
          3.1.1 Blocking/Non blocking & Data Volatility..14
     3.2 Database Functions..............................15
     3.3 Microsoft Windows-specific Extension Functions..16
          3.3.1 Asynchronous select() Mechanism..........17
          3.3.2 Asynchronous Support Routines............17
          3.3.3 Hooking Blocking Methods.................17
          3.3.4 Error Handling...........................18
          3.3.5 Accessing a Windows Sockets DLL from an
          Intermediate DLL...............................18
          3.3.6 Internal use of Messages by Windows Sockets
          Implementations................................18
          3.3.7 Private API Interfaces...................19
4.  SOCKET LIBRARY REFERENCE.............................20
     4.1 Socket Routines.................................20
          4.1.1 accept().................................21
          4.1.2 bind()...................................23
          4.1.3 closesocket()............................25
          4.1.4 connect()................................27
          4.1.5 getpeername()............................29
          4.1.6 getsockname()............................30
          4.1.7 getsockopt().............................31
          4.1.8 htonl()..................................33
          4.1.9 htons()..................................34
                                 iii          4.1.10 inet_addr().............................35
          4.1.11 inet_ntoa().............................36
          4.1.12 ioctlsocket()...........................37
          4.1.13 listen()................................39
          4.1.14 ntohl().................................41
          4.1.15 ntohs().................................42
          4.1.16 recv()..................................43
          4.1.17 recvfrom()..............................45
          4.1.18 select()................................48
          4.1.19 send()..................................50
          4.1.20 sendto()................................52
          4.1.21 setsockopt()............................55
          4.1.22 shutdown()..............................58
          4.1.23 socket()................................60
     4.2 Database Routines...............................62
          4.2.1 gethostbyaddr()..........................62
          4.2.2 gethostbyname()..........................64
          4.2.3 gethostname()............................65
          4.2.4 getprotobyname().........................66
          4.2.5 getprotobynumber().......................68
          4.2.6 getservbyname()..........................69
          4.2.7 getservbyport()..........................71
     4.3 Microsoft Windows-specific Extensions...........72
          4.3.1 WSAAsyncGetHostByAddr()..................72
          4.3.2 WSAAsyncGetHostByName()..................75
          4.3.3 WSAAsyncGetProtoByName().................78
          4.3.4 WSAAsyncGetProtoByNumber()...............81
          4.3.5 WSAAsyncGetServByName()..................84
          4.3.6 WSAAsyncGetServByPort()..................87
          4.3.7 WSAAsyncSelect().........................90
          4.3.8 WSACancelAsyncRequest()..................96
          4.3.9 WSACancelBlockingCall()..................98
          4.3.10 WSACleanup()............................100
          4.3.11 WSAGetLastError().......................102
          4.3.12 WSAIsBlocking().........................103
          4.3.13 WSASetBlockingHook()....................104
          4.3.14 WSASetLastError().......................106
          4.3.15 WSAStartup()............................107
          4.3.16 WSAUnhookBlockingHook().................111
Appendix A.  Error Codes and Header Files................112
     A.1 Error Codes.....................................112
     A.2 Header Files....................................114
          A.2.1 Berkeley Header Files....................114
          A.2.2 Windows Sockets Header File - winsock.h..115
Appendix B.  Notes for Windows Sockets Suppliers.........127
     B.1 Introduction....................................127
     B.2 Windows Sockets Components......................127
          B.2.1 Development Components...................127
          B.2.2 Run Time Components......................127
     B.3 Multithreadedness and blocking routines.........127
     B.4 Database Files..................................128
     B.5 FD_ISSET........................................128
     B.6 Error Codes.....................................128
     B.7 DLL Ordinal Numbers.............................128
     B.8 Validation Suite................................129
Appendix C.  For Further Reference.......................131
Appendix D.  Background Information......................131
     D.1 Legal Status of Windows Sockets.................131
     D.2 The Story Behind the Windows Sockets Icon.......131



                                  iv


                                                        Introduction 1


ACKNOWLEDGMENTS

The authors would like to thank their companies for allowing them the
time and resources to make this specification possible:  JSB
Corporation, Microdyne Corporation, FTP Software, Sun Microsystems,
and Microsoft Corporation.

Special thanks should also be extended to the other efforts
contributing to the success of Windows Sockets. The original draft was
heavily influenced by existing specifications offered and detailed by
JSB Corporation and Net Manage, Inc. The "version 1.0 debate" hosted
by Microsoft in Seattle allowed many of the members of the working
group to hash out final details for 1.0 vis-a-vis.

Sun Microsystems was kind enough to allow first time implementors to
"plug and play" beta software during the first Windows Sock-A-Thon of
Windows Sockets application  and implementation                           s                     at Interop                                               s            Fall '92.
Microsoft has shared WSAT (the Windows Sockets API Tester) with other
Windows Sockets implementors as a standard Windows Sockets test suite
to aid in testing their implementations. Finally, Sun Microsystems and
FTP Software plan to host the Windows Sock-A-Thon II in Boston
February '93.

Without the contributions of the individuals and corporations involved
in the working group, Windows Sockets would never have been as
thoroughly reviewed and completed as quickly. In just one year,
several
competitors in the networking business developed a useful
specification with something to show for it! Many thanks to all which
participated, either in person or on e-mail to the Windows Sockets
effort. The authors would like to thank everyone who participated in
any way, and apologize in advance for anyone we have omitted.

List of contributors:

Martin Hall    (Chairman)     JSB Corporation
     [e-mail]
Mark Towfiq    (Coordinator)  Microdyne Corporation
     [e-mail]
Geoff Arnold   (Editor 1.0)   Sun Microsystems
     [e-mail]
David Treadwell     (Editor 1.1)   Microsoft Corporation
     [e-mail]
Henry Sanders            Microsoft Corporation
     [e-mail]

J. Allard           Microsoft           jallard@microsoft.
                    Corporation         com
Chris Arap-Bologna  Distinct            [e-mail]
Larry Backman       FTP Software        [e-mail]
Alistair Banks      Microsoft           alistair@microsoft
                    Corporation         .com
Rob Barrow          JSB Corporation     [e-mail]
Carl Beame          Beame & Whiteside   beame@mcmaster,ca
Dave Beaver         Microsoft           dbeaver@microsoft.
                    Corporation         com
                                  1


2 Introduction

Amatzia BenArtzi    NetManage, Inc.     amatzia@netmanage.
                                        com
Mark Beyer          Ungermann-Bass      [e-mail]
Nelson Bolyard      Silicon Graphics,   [e-mail]
                    Inc.
Pat Bonner          Hewlett-Packard     [e-mail]
                                        m
Derek Brown         FTP Software        [e-mail]
Malcolm Butler      ICL                 [e-mail].
                                        uk
Mike Calbaum        Fronteir            mike@frontiertech.
                    Technologies        com
Isaac Chan          Microsoft           isaacc@microsoft.c
                    Corporation         om
Khoji Darbani       Informix            [e-mail]
Nestor Fesas        Hughes LAN Systems  [e-mail]
Karanja Gakio       FTP Software        [e-mail]
Vikas Garg          Distinct            [e-mail]
Gary Gere           Gupta               [e-mail]
Jim Gilroy          Microsoft           jamesg@microsoft.c
                    Corporation         om
Bill Hayes          Hewlett-Packard     [e-mail].
                                        hp.com
Paul Hill           MIT                 [e-mail]
Tmima Koren         Net Manage, Inc.    [e-mail]
                                        m
Hoek Law            Citicorp            [e-mail]
Graeme Le Roux      Moresdawn P/L       -
Kevin Lewis         Novell              [e-mail]
Roger Lin           3Com                roger_lin@3mail.3c
                                        om.com
Terry Lister        Hewlett-Packard     [e-mail]
Jeng Long Jiang     Wollongong          [e-mail]
Lee Murach          Network Research    [e-mail]
Pete Ostenson       Microsoft           [e-mail]
                    Corporation         m
David Pool          Spry, Inc.          [e-mail]
Bob Quinn           FTP Software        [e-mail]
Glenn Reitsma       Hughes LAN Systems  [e-mail]
Brad Rice           Age                 [e-mail]
Allen Rochkind      3Com                -
Jonathan Rosen      IBM                 [e-mail]
                                        m
Steve Stokes        Novell              [e-mail]
Joseph Tsai         3Com                joe_tsai@3mail.3co
                                        m.com
James Van Bokkelen  FTP Software        [e-mail]
Miles Wu            Wollongong          [e-mail]
Boris Yanovsky      NetManage, Inc.     [e-mail]
                                        m


                                                        Introduction 3

1.  INTRODUCTION

1.1 What is Windows Sockets?
The Windows Sockets specification defines a network programming
interface for Microsoft Windows1 which is based on the "socket"
paradigm popularized in the Berkeley Software Distribution (BSD) from
the University of California at Berkeley.  It encompasses both
familiar Berkeley socket style routines and a set of Windows-specific
extensions designed to allow the programmer to take advantage of the
message-driven nature of Windows.

The Windows Sockets Specification is intended to provide a single API
to which application developers can program and multiple network
software vendors can conform.  Furthermore, in the context of a
particular version of Microsoft Windows, it defines a binary interface
(ABI) such that an application written to the Windows Sockets API can
work with a conformant protocol implementation from any network
software vendor.  This specification thus defines the library calls
and associated semantics to which an application developer can program
and which a network software vendor can implement.

Network software which conforms to this Windows Sockets specification
will be considered "Windows Sockets Compliant".  Suppliers of
interfaces which are "Windows Sockets Compliant" shall be referred to
as "Windows Sockets Suppliers".  To be Windows Sockets Compliant, a
vendor must implement 100% of this Windows Sockets specification.

Applications which are capable of operating with any "Windows Sockets
Compliant" protocol implementation will be considered as having a
"Windows Sockets Interface" and will be referred to as "Windows
Sockets Applications".

This version of the Windows Sockets specification defines and
documents the use of the API in conjunction with the Internet Protocol
Suite (IPS, generally referred to as TCP/IP).  Specifically, all
Windows Sockets implementations support both stream (TCP) and datagram
(UDP) sockets.

While the use of this API with alternative protocol stacks is not
precluded (and is expected to be the subject of future revisions of
the specification), such usage is beyond the scope of this version of
the specification.


1.2 Berkeley Sockets
The Windows Sockets Specification has been built upon the Berkeley
Sockets programming model which is the de facto standard for TCP/IP
networking.  It is intended to provide a high degree of familiarity
for programmers who are used to programming with sockets in UNIX2 and
other environments, and to simplify the task of porting existing
sockets-based source code.  The Windows Sockets API is consistent with
release 4.3 of the Berkeley Software Distribution (4.3BSD).



1 Windows is a trademark of Microsoft Corporation.
2 UNIX is a trademark of Unix System Laboratories, Inc.
                                  3


4 Introduction

Portions of the Windows Sockets specification are derived from
material which is Copyright (c) 1982-1986 by the Regents of the
University of California.  All rights are reserved.  The Berkeley
Software License Agreement specifies the terms and conditions for
redistribution.


1.3 Microsoft Windows and Windows-specific extensions
This API is intended to be usable within all implementations and
versions of Microsoft Windows from Microsoft Windows Version 3.0
onwards.  It thus provides for Windows Sockets implementations and
Windows Sockets applications in both 16 and 32 bit operating
environments.

Windows Sockets makes provisions for multithreaded Windows processes.
A process contains one or more threads of execution.  In the Windows
3.1 non-multithreaded world, a task corresponds to a process with a
single thread.  All references to threads in this document refer to
actual "threads" in multithreaded Windows environments.  In non
multithreaded environments (such as Windows 3.0), use of the term
thread refers to a Windows process.

The Microsoft Windows extensions included in Windows Sockets are
provided to allow application developers to create software which
conforms to the Windows programming model.  It is expected that this
will facilitate the creation of robust and high-performance
applications, and will improve the cooperative multitasking of
applications within non-preemptive versions of Windows.  With the
exception of WSAStartup() and WSACleanup() their use is not mandatory.


1.4 The Status of this Specification

Windows Sockets is an independent specification which was created and
exists for the benefit of application developers and network vendors
and, indirectly, computer users. Each published (non-draft) version of
this specification  represents a fully workable API for implementation
by network vendors and programming use by application developers.
Discussion of this specification and  suggested improvements continue
and are welcomed. Such discussion occurs mainly via the Internet
electronic mail forum [e-mail]. Meetings of  interested
parties occur on an irregular basis. Details of these meetings are
publicized to the electronic mail forum.


1.5 Revision History
1.5.1 Windows Sockets Version 1.0
Windows Sockets Version 1.0 represented the results of considerable
work within  the vendor and user community as discussed in Appendix C.
This version of  the specification was released in order that network
software suppliers and  application developers could begin to
construct implementations and
applications  which conformed to the Windows Sockets standard.

1.5.2 Windows Sockets Version 1.1
Windows Sockets Version 1.1 follows the guidelines and structure laid
out by version 1.0, making changes only where absolutely necessary as


                                                        Introduction 5

indicated by the experiences of a number of companies that created
Windows Sockets implementations based on the version 1.0
specification.  Version 1.1 contains several clarifications and minor
fixes to version 1.0.  Additionally, the following more significant
changes were incorporated into version 1.1:

     o Inclusion of the gethostname() routine to simplify retrieval of
     the host's name and address.

     o Definition of DLL ordinal values below 1000 as reserved for
     Windows Sockets and ordinals above 1000 as unrestricted.  This
     allows Windows Sockets vendors to include private interfaces to
     their DLLs without risking that the ordinals chosen will conflict
     with a future version of Windows Sockets.

     o Addition of a reference count to WSAStartup() and WSACleanup(),
     requiring correspondences between the calls.  This allows
     applications and third-party DLLs to make use of a Windows
     Sockets implementation without being concerned about the calls to
     these APIs made by the other.

     o Change of return type of inet_addr() from struct in_addr to
     unsigned long.  This was required due to different handling of
     four-byte structure returns between the Microsoft and Borland C
     compilers.

     o Change of WSAAsyncSelect() semantics from "edge-triggered" to
     "level-triggered".  The level-triggered semantics significantly
     simplify an application's use of this routine.

     o Change the ioctlsocket() FIONBIO semantics to fail if a
     WSAAsyncSelect() call is outstanding on the socket.

     o Addition of the TCP_NODELAY socket option for RFC 1122
     conformance.

All changes between the 1.0 and 1.1 specifications are flagged with
change bars at the left of the page.



















                                  5


6 Programming with Sockets


2.  PROGRAMMING WITH SOCKETS

2.1 Windows Sockets Stack Installation Checking
To detect the presence of one (or many) Windows Sockets
implementations on a system, an application which has been linked with
the Windows Sockets Import Library may simply call the WSAStartup()
routine.  If an application wishes to be a little more sophisticated
it can examine the $PATH environment variable and search for instances
of Windows Sockets implementations (WINSOCK.DLL).  For each instance
it can issue a LoadLibrary() call and use the WSAStartup() routine to
discover implementation specific data.

This version of the Windows Sockets specification does not attempt to
address explicitly the issue of multiple concurrent Windows Sockets
implementations.  Nothing in the specification should be interpreted
as restricting multiple Windows Sockets DLLs from being present and
used concurrently by one or more Windows Sockets applications.

For further details of where to obtain Windows Sockets components, see
Appendix B.2.


2.2 Sockets
The following material is derived from the document "An Advanced
4.3BSD Interprocess Communication Tutorial" by Samuel J. Leffler,
Robert S. Fabry, William N. Joy, Phil Lapsley, Steve Miller, and Chris
Torek.

2.2.1 Basic concepts
The basic building block for communication is the socket.  A socket is
an endpoint of communication to which a name may be bound.  Each
socket in use has a type and an associated process.  Sockets exist
within communication domains.  A communication domain is an
abstraction introduced to bundle common properties of threads
communicating through sockets.  Sockets normally exchange data only
with sockets in the same domain (it may be possible to cross domain
boundaries, but only if some translation process is performed).  The
Windows Sockets facilities support a single communication domain: the
Internet domain, which is used by processes which communicate using
the Internet Protocol Suite.  (Future versions of this specification
may include additional domains.)

Sockets are typed according to the communication properties visible to
a user.  Applications are presumed to communicate only between sockets
of the same type, although there is nothing that prevents
communication between sockets of different types should the underlying
communication protocols support this.

Two types of sockets currently are available to a user.  A stream
socket provides for the bi-directional, reliable, sequenced, and
unduplicated flow of data without record boundaries.

A datagram socket supports bi-directional flow of data which is not
promised to be sequenced, reliable, or unduplicated.  That is, a
process receiving messages on a datagram socket may find messages
duplicated, and, possibly, in an order different from the order in


                                            Programming with Sockets 7

which it was sent.  An important characteristic of a datagram socket
is that record boundaries in data are preserved.  Datagram sockets
closely model the facilities found in many contemporary packet
switched networks such as Ethernet.

2.2.2 Client-server model
The most commonly used paradigm in constructing distributed
applications is the client/server model.  In this scheme client
applications request services from a server application.  This implies
an asymmetry in establishing communication between the client and
server.

The client and server require a well-known set of conventions before
service may be rendered (and accepted).  This set of conventions
comprises a protocol which must be implemented at both ends of a
connection.  Depending on the situation, the protocol may be symmetric
or asymmetric.  In a symmetric protocol, either side may play the
master or slave roles.  In an asymmetric protocol, one side is
immutably recognized as the master, with the other as the slave.  An
example of a symmetric protocol is the TELNET protocol used in the
Internet for remote terminal emulation.  An example of an asymmetric
protocol is the Internet file transfer protocol, FTP.  No matter
whether the specific protocol used in obtaining a service is symmetric
or asymmetric, when accessing a service there is a "client process''
and a "server process''.

A server application normally listens at a well-known address for
service requests.  That is, the server process remains dormant until a
connection is requested by a client's connection to the server's
address.  At such a time the server process "wakes up'' and services
the client, performing whatever appropriate actions the client
requests of it.  While connection-based services are the norm, some
services are based on the use of datagram sockets.

2.2.3 Out-of-band data



Note: The following discussion of out-of-band data, also referred to
as TCP Urgent data,  follows the model used in the Berkeley software
distribution.  Users and implementors should be aware of the fact that
there are at present two conflicting interpretations of RFC 793 (in
which the concept is introduced), and that the implementation of out-
of-band data in the Berkeley Software Distribution does not conform to
the Host Requirements laid down in RFC 1122.  To minimize
interoperability problems, applications writers are advised not to use
out-of-band data unless this is required in order to interoperate with
an existing service.  Windows Sockets suppliers are urged to document
the out-of-band semantics (BSD or RFC 1122) which their product
implements.  It is beyond the scope of this specification to mandate a
particular set of semantics for out-of-band data handling.




The stream socket abstraction includes the notion of "out of band''
data.  Out-of-band data is a logically independent transmission
                                  7


8 Programming with Sockets

channel associated with each pair of connected stream sockets.  Out-
of-band data is delivered to the user independently of normal data.
The abstraction defines that the out-of-band data facilities must
support the reliable delivery of at least one out-of-band message at a
time.  This message may contain at least one byte of data, and at
least one message may be pending delivery to the user at any one time.
For communications protocols which support only in-band signaling
(i.e.  the urgent data is delivered in sequence with the normal data),
the system normally extracts the data from the normal data stream and
stores it separately.  This allows users to choose between receiving
the urgent data in order and receiving it out of sequence without
having to buffer all the intervening data.  It is possible to "peek''
at out-of-band data.

An application may prefer to process out-of-band data "in-line", as
part of the normal data stream.  This is achieved by setting the
socket option SO_OOBINLINE (see section 4.1.21, setsockopt()).  In
this case, the application may wish to determine whether any of the
unread data is "urgent" (the term usually applied to in-line out-of-
band data).  To facilitate this, the Windows Sockets implementation
will maintain a logical "mark" in the data stream indicate the point
at which the out-of-band data was sent.  An application can use the
SIOCATMARK ioctlsocket() command (see section 4.1.12) to determine
whether there is any unread data preceding the mark.  For example, it
might use this to resynchronize with its peer by ensuring that all
data up to the mark in the data stream is discarded when appropriate.

The WSAAsyncSelect() routine is particularly well suited to handling
notification of the presence of out-of-band-data.

2.2.4 Broadcasting
By using a datagram socket, it is possible to send broadcast packets
on many networks supported by the system.  The network itself must
support broadcast: the system provides no simulation of broadcast in
software.  Broadcast messages can place a high load on a network,
since they force every host on the network to service them.
Consequently, the ability to send broadcast packets has been limited
to sockets which are explicitly marked as allowing broadcasting.
Broadcast is typically used for one of two reasons: it is desired to
find a resource on a local network without prior knowledge of its
address, or important functions such as routing require that
information be sent to all accessible neighbors.

The destination address of the message to be broadcast depends on the
network(s) on which the message is to be broadcast.  The Internet
domain supports a shorthand notation for broadcast on the local
network, the address INADDR_BROADCAST.  Received broadcast messages
contain the senders address and port, as datagram sockets must be
bound before use.

Some types of network support the notion of different types of
broadcast.  For example, the IEEE 802.5 token ring architecture
supports the use of link-level broadcast indicators, which control
whether broadcasts are forwarded by bridges.  The Windows Sockets
specification does not provide any mechanism whereby an application
can determine the type of underlying network, nor any way to control
the semantics of broadcasting.


                                            Programming with Sockets 9



2.3 Byte Ordering
The Intel byte ordering is like that of the DEC VAX3, and therefore
differs from the Internet and 680004-type processor byte ordering.
Thus care must be taken to ensure correct orientation.

Any reference to IP addresses or port numbers passed to or from a
Windows Sockets routine must be in network order.  This includes the
IP address and port fields of a struct sockaddr_in (but not the
sin_family field).

Consider an application which normally contacts a server on the TCP
port corresponding to the "time" service, but which provides a
mechanism for the user to specify that an alternative port is to be
used.  The port number returned by getservbyname() is already in
network order, which is the format required constructing an address,
so no translation is required.  However if the user elects to use a
different port, entered as an integer, the application must convert
this from host to network order (using the htons() function) before
using it to construct an address.  Conversely, if the application
wishes to display the number of the port within an address (returned
via, e.g., getpeername()), the port number must be converted from
network to host order (using ntohs()) before it can be displayed.

Since the Intel and Internet byte orders are different, the
conversions described above are unavoidable.  Application writers are
cautioned that they should use the standard conversion functions
provided as part of the Windows Sockets API rather than writing their
own conversion code, since future implementations of Windows Sockets
are likely to run on systems for which the host order is identical to
the network byte order.  Only applications which use the standard
conversion functions are likely to be portable.


2.4 Socket Options
The socket options supported by Windows Sockets are listed in the
pages describing setsockopt() and getsockopt().  A Windows Sockets
implementation must recognize all of these options, and (for
getsockopt()) return plausible values for each.  The default value for
each option is shown in the following table.














3 VAX is a trademark of Digital Equipment Corporation.
4 68000 is a trademark of Motorola, Inc.
                                  9


10 Programming with Sockets


Value        Type     Meaning             Default      Not
                                                       e



SO_ACCEPTCO  BOOL     Socket is           FALSE
 NN                     listen()ing.        unless a
                                          listen()
                                          has been
                                          performed

SO_BROADCAS  BOOL     Socket is           FALSE
T                     configured for the
                      transmission of
                      broadcast
                      messages.

SO_DEBUG     BOOL     Debugging is        FALSE        (i)
                      enabled.

SO_DONTLING  BOOL     If true, the        TRUE
ER                    SO_LINGER option
                      is disabled.

SO_DONTROUT  BOOL     Routing is          FALSE        (i)
E                     disabled.

SO_ERROR     int      Retrieve error      0
                      status and clear.

SO_KEEPALIV  BOOL     Keepalives are      FALSE
E                     being sent.

SO_LINGER    struct   Returns the         l_onoff is
             linger   current linger      0
             FAR *    options.

SO_OOBINLIN  BOOL     Out-of-band data    FALSE
E                     is being received
                      in the normal data
                      stream.

SO_RCVBUF    int      Buffer size for     Implementat  (i)
                      receives            ion
                                          dependent

SO_REUSEADD  BOOL     The address to      FALSE
R                     which this socket
                      is bound can be
                      used by others.

SO_SNDBUF    int      Buffer size for     Implementat  (i)
                      sends               ion
                                          dependent


                                           Programming with Sockets 11


SO_TYPE      int      The type of the     As created
                      socket (e.g.        via
                      SOCK_STREAM).       socket()

TCP_NODELAY  BOOL     Disables the Nagle  Implementat
                      algorithm for send  ion
                      coalescing.         dependent


Notes:
(i)       An implementation may silently ignore this option on
          setsockopt() and return a constant value for getsockopt(),
          or it may accept a value for setsockopt() and return the
          corresponding value in getsockopt() without using the value
          in any way.



2.5 Database Files
The getXbyY()  and WSAAsyncGetXByY() classes of routines are provided             5
for retrieving network specific information.  The getXbyY() routines
were originally designed (in the first Berkeley UNIX releases) as
mechanisms for looking up information in text databases.  Although the
information may be retrieved by the Windows Sockets implementation in
different ways, a Windows Sockets application requests such
information in a consistent manner through either the getXbyY() or the
WSAAsyncGetXByY() class of routines.


2.6 Deviation from Berkeley Sockets
There are a few limited instances where the Windows Sockets API has
had to divert from strict adherence to the Berkeley conventions,
usually because of difficulties of implementation in a Windows
environment.

2.6.1 socket data type and error values
A new data type, SOCKET, has been defined.  The definition of this
type was necessary for future enhancements to the Windows Sockets
specification, such as being able to use sockets as file handles in
Windows NT .  Definition of this type also facilitates porting of          6
applications to a Win/32 environment, as the type will automatically
be promoted from 16 to 32 bits.

In UNIX, all handles, including socket handles, are small, non-
negative integers, and some applications make assumptions that this
will be true.  Windows Sockets handles have no restrictions, other
than that the value INVALID_SOCKET is not a valid socket.  Socket
handles may take any value in the range 0 to INVALID_SOCKET-1.




  This specification uses the function name getXbyY() to represent the5
set of routines gethostbyaddr(), gethostbyname(), etc. Similarly
WSAAsyncGetXByY() represents WSAAsyncGetHostByAddr(), etc.
  NT and Windows/NT are trademarks of Microsoft Corporation.6
                                  11


12 Programming with Sockets

Because the SOCKET type is unsigned, compiling existing source code
from, for example, a UNIX environment may lead to compiler warnings
about signed/unsigned data type mismatches.

This means, for example, that checking for errors when the socket()
and accept() routines return should not be done by comparing the
return value with -1, or seeing if the value is negative (both common,
and legal, approaches in BSD).  Instead, an application should use the
manifest constant INVALID_SOCKET as defined in winsock.h.  For
example:
     TYPICAL BSD STYLE:
          s = socket(...);
          if (s == -1)   /* or s < 0 */
               {...}

     PREFERRED STYLE:
          s = socket(...);
          if (s == INVALID_SOCKET)
               {...}

2.6.2 select() and FD_*
Because a SOCKET is no longer represented by the UNIX-style "small
non-negative integer", the implementation of the select() function was
changed in the Windows Sockets API.  Each set of sockets is still
represented by the fd_set type, but instead of being stored as a
bitmask the set is implemented as an array of SOCKETs.  To avoid
potential problems, applications must adhere to the use of the FD_XXX
macros to set, initialize, clear, and check the fd_set structures.

2.6.3 Error codes - errno, h_errno & WSAGetLastError()
Error codes set by the Windows Sockets implementation are NOT made
available via the errno variable.  Additionally, for the getXbyY()
class of functions, error codes are NOT made available via the h_errno
variable.  Instead, error codes are accessed by using the
WSAGetLastError() API described in section 4.3.11.  This function is
provided in Windows Sockets as a precursor (and eventually an alias)
for the Win32 function GetLastError().  This is intended to provide a
reliable way for a thread in a multi-threaded process to obtain per-
thread error information.

For compatibility with BSD, an application may choose to include a
line of the form:

          #define errno WSAGetLastError()

This will allow networking code which was written to use the global
errno to work correctly in a single-threaded environment.  There are,
obviously, some drawbacks.  If a source file includes code which
inspects errno for both socket and non-socket functions, this
mechanism cannot be used.  Furthermore, it is not possible for an
application to assign a new value to errno.  (In Windows Sockets the
function WSASetLastError() may be used for this purpose.)


                                           Programming with Sockets 13

     TYPICAL BSD STYLE:
          r = recv(...);
          if (r == -1
              && errno == EWOULDBLOCK)
               {...}

     PREFERRED STYLE:
          r = recv(...);
          if (r == -1       /* (but see below) */
              && WSAGetLastError() == EWOULDBLOCK)
               {...}

Although error constants consistent with 4.3 Berkeley Sockets are
provided for compatibility purposes, applications should, where
possible, use the "WSA" error code definitions.  For example, a more
accurate version of the above source code fragment is:

          r = recv(...);
          if (r == -1       /* (but see below) */
              && WSAGetLastError() == WSAEWOULDBLOCK)
               {...}

2.6.4 Pointers
All pointers used by applications with Windows Sockets should be FAR.
To facilitate this, data type definitions such as LPHOSTENT are
provided.

2.6.5 Renamed functions
In two cases it was necessary to rename functions which are used in
Berkeley Sockets in order to avoid clashes with other APIs.

2.6.5.1 close() & closesocket()
In Berkeley Sockets, sockets are represented by standard file
descriptors, and so the close() function can be used to close sockets
as well as regular files.  While nothing in the Windows Sockets API
prevents an implementation from using regular file handles to identify
sockets, nothing requires it either.  Socket descriptors are not
presumed to correspond to regular file handles, and file operations
such as read(), write(), and close() cannot be assumed to work
correctly when applied to sockets.  Sockets must be closed by using
the closesocket() routine.  Using the close() routine to close a
socket is incorrect and the effects of doing so are undefined by this
specification.

2.6.5.1 ioctl() & ioctlsocket()
Various C language run-time systems use the ioctl() routine for
purposes unrelated to Windows Sockets.  For this reason we have
defined the routine ioctlsocket() which is used to handle socket
functions which in the Berkeley Software Distribution are performed
using ioctl() and fcntl().

2.6.6 Blocking routines & EINPROGRESS
Although blocking operations on sockets are supported under Windows
Sockets, their use is strongly discouraged.  Programmers who are
constrained to use blocking mode  for example, as part of an existing
application which is to be ported  should be aware of the semantics

                                  13


14 Programming with Sockets

of blocking operations in Windows Sockets.  See section 3.1.1 for more
details.

2.6.7 Maximum number of sockets supported
The maximum number of sockets supported by a particular Windows
Sockets supplier is implementation specific.  An application should
make no assumptions about the availability of a certain number of
sockets.  This topic is addressed further in section 4.3.15,
WSAStartup().  However, independent of the number of sockets supported
by a particular implementation is the issue of the maximum number of
sockets which an application can actually make use of.

The maximum number of sockets which a Windows Sockets application can
make use of is determined at compile time by the manifest constant
FD_SETSIZE.  This value is used in constructing the fd_set structures
used in select() (see section 4.1.18).  The default value in winsock.h
is 64.  If an application is designed to be capable of working with
more than 64 sockets, the implementor should define the manifest
FD_SETSIZE in every source file before including winsock.h.  One way
of doing this may be to include the definition within the compiler
options in the makefile, for example adding  -DFD_SETSIZE=128 as an
option to the compiler command line for Microsoft C.  It must be
emphasized that defining FD_SETSIZE as a particular value has no
effect on the actual number of sockets provided by a Windows Sockets
implementation.

2.6.8 Include files
For ease of portability of existing Berkeley sockets based source
code, a number of standard Berkeley include files are supported.
However, these Berkeley header files merely include the winsock.h
include file, and it is therefore sufficient (and recommended) that
Windows Sockets application source files should simply include
winsock.h.

2.6.9 Return values on API failure
The manifest constant SOCKET_ERROR is provided for checking API
failure.  Although use of this constant is not mandatory, it is
recommended.  The following example illustrates the use of the
SOCKET_ERROR constant:

     TYPICAL BSD STYLE:
          r = recv(...);
          if (r == -1     /* or r < 0 */
              && errno == EWOULDBLOCK)
               {...}
     PREFERRED STYLE:
          r = recv(...);
          if (r == SOCKET_ERROR
              && WSAGetLastError() == WSAEWOULDBLOCK)
               {...}

2.6.10 Raw Sockets
The Windows Sockets specification does not mandate that a Windows
Sockets DLL support raw sockets, that is, sockets opened with
SOCK_RAW.  However, a Windows Sockets DLL is allowed and encouraged to
supply raw socket support.  A Windows Sockets-compliant application
that wishes to use raw sockets should attempt to open the socket with


                                           Programming with Sockets 15

the socket() call (see section 4.1.23), and if it fails either attempt
to use another socket type or indicate the failure to the user.


2.7 Windows Sockets in Multithreaded Versions of Windows
The Windows Sockets interface is designed to work for both single-
threaded versions of Windows (such as Windows 3.1) and preemptive
multithreaded versions of Windows (such as Windows NT).  In a
multithreaded environment the sockets interface is basically the same,
but the author of a multithreaded application must be aware that it is
the responsibility of the application, not the Windows Sockets
implementation, to synchronize access to a socket between threads.
This is the same rule as applies to other forms of I/O such as file
I/O.  Failure to synchronize calls on a socket leads to unpredictable
results; for example if there are two simultaneous calls to send(),
there is no guarantee as to the order in which the data will be sent.

Closing a socket in one thread that has an outstanding blocking call
on the same socket in another thread will cause the blocking call to
fail with WSAEINTR, just as if the operation were canceled.  This also
applies if there is a select() call outstanding and the application
closes one of the sockets being selected.

There is no default blocking hook installed in preemptive
multithreaded versions of Windows.  This is because the machine will
not be blocked if a single application is waiting for an operation to
complete and hence not calling PeekMessage() or GetMessage() which
cause the application to yield in nonpremptive Windows.  However, for
backwards compatibility the WSASetBlockingHook() call is implemented
in multithreaded versions of Windows, and any application whose
behavior depends on the default blocking hook may install their own
blocking hook which duplicates the default hook's semantics, if
desired.
























                                  15


16 Socket Library Overview


3.  SOCKET LIBRARY OVERVIEW

3.1 Socket Functions
The Windows Sockets specification includes the following Berkeley-
style socket routines:


                                            Socket Library Overview 17


accept() *            An incoming connection is
                      acknowledged and associated with
                      an immediately created socket.
                      The original socket is returned
                      to the listening state.

bind()                Assign a local name to an unnamed
                      socket.

closesocket() *       Remove a socket from the per-
                      process object reference table.
                      Only blocks if SO_LINGER is set.

connect() *           Initiate a connection on the
                      specified socket.

getpeername()         Retrieve the name of the peer
                      connected to the specified
                      socket.

getsockname()         Retrieve the current name for the
                      specified socket

getsockopt()          Retrieve options associated with
                      the specified socket.

htonl()               Convert a 32-bit quantity from
                      host byte order to network byte
                      order.

htons()               Convert a 16-bit quantity from
                      host byte order to network byte
                      order.

inet_addr()           Converts a character string
                      representing a number in the
                      Internet standard ".'' notation
                      to an Internet address value.

inet_ntoa()           Converts an Internet address
                      value to an ASCII string in ".''
                      notation i.e.  "a.b.c.d''.

ioctlsocket()         Provide control for sockets.

listen()              Listen for incoming connections
                      on a specified socket.

ntohl()               Convert a 32-bit quantity from
                      network byte order to host byte
                      order.

ntohs()               Convert a 16-bit quantity from
                      network byte order to host byte
                      order.

                                  17


18 Socket Library Overview


recv() *              Receive data from a connected
                      socket.

recvfrom() *          Receive data from either a
                      connected or unconnected socket.

select() *            Perform synchronous I/O
                      multiplexing.

send() *              Send data to a connected socket.

sendto() *            Send data to either a connected
                      or unconnected socket.

setsockopt()          Store options associated with the
                      specified socket.

shutdown()            Shut down part of a full-duplex
                      connection.

socket()              Create an endpoint for
                      communication and return a
                      socket.


* = The routine can block if acting on a blocking socket.

3.1.1 Blocking/Non blocking & Data Volatility
One major issue in porting applications from a Berkeley sockets
environment to a Windows environment involves "blocking"; that is,
invoking a function which does not return until the associated
operation is completed.  The problem arises when the operation may
take an arbitrarily long time to complete: an obvious example is a
recv() which may block until data has been received from the peer
system.  The default behavior within the Berkeley sockets model is for
a socket to operate in a blocking mode unless the programmer
explicitly requests that operations be treated as non-blocking.  It is
strongly recommended that programmers use the nonblocking
(asynchronous) operations if at all possible, as they work
significantly better within the nonpreemptive Windows environment.
Use blocking operations only if absolutely necessary, and carefully
read and understand this section if you must use blocking operations.

Even on a blocking socket, some operations (e.g. bind(), getsockopt(),
getpeername()) can be completed immediately.  For such operations
there is no difference between blocking and non-blocking operation.
Other operations (e.g. recv()) may be completed immediately or may
take an arbitrary time to complete, depending on various transport
conditions.  When applied to a blocking socket, these operations are
referred to as blocking operations.  All routines which can block are
listed with an asterisk in the tables above and below.

Within a Windows Sockets implementation, a blocking operation which
cannot be completed immediately is handled as follows.  The DLL
initiates the operation, and then enters a loop in which it dispatches
any Windows messages (yielding the processor to another thread if


                                            Socket Library Overview 19

necessary) and then checks for the completion of the Windows Sockets
function.  If the function has completed, or if
WSACancelBlockingCall() has been invoked, the blocking function
completes with an appropriate result.  Refer to section 4.3.13,
WSASetBlockingHook(), for a complete description of this mechanism,
including pseudocode for the various functions.

If a Windows message is received for a process for which a blocking
operation is in progress, there is a risk that the application will
attempt to issue another Windows Sockets call.  Because of the
difficulty of managing this condition safely, the Windows Sockets
specification does not support such application behavior.  Two
functions are provided to assist the programmer in this situation.
WSAIsBlocking() may be called to determine whether or not a blocking
Windows Sockets call is in progress.  WSACancelBlockingCall() may be
called to cancel an in-progress blocking call, if any.  Any other
Windows Sockets function which is called in this situation will fail
with the error WSAEINPROGRESS.  It should be emphasized that this
restriction applies to both blocking and non-blocking operations.

Although this mechanism is sufficient for simple applications, it
cannot support the complex message-dispatching requirements of more
advanced applications (for example, those using the MDI model).  For
such applications, the Windows Sockets API includes the function
WSASetBlockingHook(), which allows the programmer to define a special
routine which will be called instead of the default message dispatch
routine described above.

The Windows Sockets DLL calls the blocking hook only if all of the
following are true: the routine is one which is defined as being able
to block, the specified socket is a blocking socket, and the request
cannot be completed immediately.  (A socket is set to blocking by
default, but the IOCTL FIONBIO and  WSAAsyncSelect() both set a socket
to nonblocking mode.)  If an application uses only non-blocking
sockets and uses the WSAAsyncSelect() and/or the WSAAsyncGetXByY()
routines instead of select() and the getXbyY() routines, then the
blocking hook will never be called and the application does not need
to be concerned with the reentrancy issues the blocking hook can
introduce.

If an application invokes an asynchronous or non-blocking operation
which takes a pointer to a memory object (e.g. a buffer, or a global
variable) as an argument, it is the responsibility of the application
to ensure that the object is available to the Windows Sockets
implementation throughout the operation.  The application must not
invoke any Windows function which might affect the mapping or
addressability of the memory involved.  In a multithreaded system, the
application is also responsible for coordinating access to the object
using appropriate synchronization mechanisms.  A Windows Sockets
implementation cannot, and will not, address these issues.  The
possible consequences of failing to observe these rules are beyond the
scope of this specification.


3.2 Database Functions
The Windows Sockets specification defines the following "database"
routines.  As noted earlier, a Windows Sockets supplier may choose to
                                  19


20 Socket Library Overview

implement these in a manner which does not depend on local database
files.  The pointer returned by certain database routines such as
gethostbyname() points to a structure which is allocated by the
Windows Sockets library.  The data which is pointed to is volatile and
is good only until the next Windows Sockets API call from that thread.
Additionally, the application must never attempt to modify this
structure or to free any of its components.  Only one copy of this
structure is allocated for a thread, and so the application should
copy any information which it needs before issuing any other Windows
Sockets API calls.



gethostbyaddr() *     Retrieve the name(s) and address
                      corresponding to a network
                      address.

gethostbyname() *     Retrieve the name(s) and address
                      corresponding to a host name.

gethostname()         Retrieve the name of the local
                      host.

getprotobyname() *    Retrieve the protocol name and
                      number corresponding to a
                      protocol name.

getprotobynumber() *  Retrieve the protocol name and
                      number corresponding to a
                      protocol number.

getservbyname() *     Retrieve the service name and
                      port corresponding to a service
                      name.

getservbyport() *     Retrieve the service name and
                      port corresponding to a port.




* = The routine can block under some circumstances.


3.3 Microsoft Windows-specific Extension Functions
The Windows Sockets specification provides a number of extensions to
the standard set of Berkeley Sockets routines.  Principally, these
extended APIs allow message-based, asynchronous access to network
events.  While use of this extended API set is not mandatory for
socket-based programming  (with the exception of WSAStartup() and
WSACleanup()), it is recommended for conformance with the Microsoft
Windows programming paradigm.


                                            Socket Library Overview 21


WSAAsyncGetHostByAdd  A set of functions which provide
r()                   asynchronous

WSAAsyncGetHostByNam  versions of the standard Berkeley
e()

WSAAsyncGetProtoByNa  getXbyY() functions.  For
me()                  example, the

WSAAsyncGetProtoByNu  WSAAsyncGetHostByName() function
mber()                provides an

WSAAsyncGetServByNam  asynchronous message based
e()                   implementation of

WSAAsyncGetServByPor  the standard Berkeley
t()                   gethostbyname() function.

WSAAsyncSelect()      Perform asynchronous version of
                      select()

WSACancelAsyncReques  Cancel an outstanding instance of
t()                   a WSAAsyncGetXByY() function.

WSACancelBlockingCal  Cancel an outstanding "blocking"
l()                   API call

WSACleanup()          Sign off from the underlying
                      Windows Sockets DLL.

WSAGetLastError()     Obtain details of last Windows
                      Sockets API error

WSAIsBlocking()       Determine if the underlying
                      Windows Sockets DLL is already
                      blocking an existing call for
                      this thread

WSASetBlockingHook()  "Hook" the blocking method used
                      by the underlying Windows Sockets
                      implementation

WSASetLastError()     Set the error to be returned by a
                      subsequent WSAGetLastError()

WSAStartup()          Initialize the underlying Windows
                      Sockets DLL.

WSAUnhookBlockingHoo  Restore the original blocking
k()                   function


3.3.1 Asynchronous select() Mechanism
The WSAAsyncSelect() API allows an application to register an interest
in one or many network events.  This API is provided to supersede the
need to do polled network I/O.  Any situation in which select() or
                                  21


22 Socket Library Overview

non-blocking I/O routines (such as send() and recv()) are either
already used or are being considered is usually a candidate for the
WSAAsyncSelect() API.  When declaring interest in such condition(s),
you supply a window handle to be used for notification.  The
corresponding window then receives message-based notification of the
conditions in which you declared an interest.

WSAAsyncSelect() allows interest to be declared in the following
conditions for a particular socket:
     Socket readiness for reading
     Socket readiness for writing
     Out-of-band data ready for reading
     Socket readiness for accepting incoming connection
     Completion of non-blocking connect()
     Connection closure

3.3.2 Asynchronous Support Routines
The asynchronous "database" functions allow applications to request
information in an asynchronous manner.  Some network implementations
and/or configurations perform network based operations to resolve such
requests.  The WSAAsyncGetXByY() functions allow application
developers to request services which would otherwise block the
operation of the whole Windows environment if the standard Berkeley
function were used.  The WSACancelAsyncRequest() function allows an
application to cancel any outstanding asynchronous request.

3.3.3 Hooking Blocking Methods
As noted in section 3.1.1 above, Windows Sockets implements blocking
operations in such a way that Windows message processing can continue,
which may result in the application which issued the call receiving a
Windows message.  In certain situations an application may want to
influence or change the way in which this pseudo-blocking process is
implemented.  The WSASetBlockingHook() provides the ability to
substitute a named routine which the Windows Sockets implementation is
to use when relinquishing the processor during a "blocking" operation.

3.3.4 Error Handling
For compatibility with thread-based environments, details of API
errors are obtained through the WSAGetLastError() API.  Although the
accepted "Berkeley-Style" mechanism for obtaining socket-based network
errors is via "errno", this mechanism cannot guarantee the integrity
of an error ID in a multi-threaded environment.  WSAGetLastError()
allows you to retrieve an error code on a per thread basis.

WSAGetLastError() returns error codes which avoid conflict with
standard Microsoft C error codes.  Certain error codes returned by
certain Windows Sockets routines fall into the standard range of error
codes as defined by Microsoft C.  If you are NOT using an application
development environment which defines error codes consistent with
Microsoft C, you are advised to use the Windows Sockets error codes
prefixed by "WSA" to ensure accurate error code detection.

Note that this specification defines a recommended set of error codes,
and lists the possible errors which may be returned as a result of
each function.  It may be the case in some implementations that other
Windows Sockets error codes will be returned in addition to those
listed, and applications should be prepared to handle errors other


                                            Socket Library Overview 23

than those enumerated under each API description.  However a Windows
Sockets implementation must not return any value which is not
enumerated in the table of legal Windows Sockets errors given in
Appendix A.1.

3.3.5 Accessing a Windows Sockets DLL from an Intermediate DLL
A Windows Sockets DLL may be accessed both directly from an
application and through an "intermediate" DLL.  An example of such an
intermediate DLL would be a virtual network API layer that supports
generalized network functionality for applications and uses Windows
Sockets.  Such a DLL could be used by several applications
simultaneously, and the DLL must take special precautions with respect
to the WSAStartup() and WSACleanup() calls to ensure that these
routines are called in the context of each task that will make Windows
Sockets calls.  This is because the Windows Sockets DLL will need a
call to WSAStartup() for each task in order to set up task-specific
data structures, and a call to WSACleanup() to free any resources
allocated for the task.

There are (at least) two ways to accomplish this.  The simplest method
is for the intermediate DLL to have calls similar to WSAStartup() and
WSACleanup() that applications call as appropriate.  The DLL would
then call WSAStartup() or WSACleanup()  from within these routines.
Another mechanism is for the intermediate DLL to build a table of task
handles, which are obtained from the GetCurrentTask() Windows API, and
at each entry point into the intermediate DLL check whether
WSAStartup() has been called for the current task, then call
WSAStartup() if necessary.

If a DLL makes a blocking call and does not install its own blocking
hook, then the DLL author must be aware that control may be returned
to the application either by an application-installed blocking hook or
by the default blocking hook.  Thus, it is possible that the
application will cancel the DLL's blocking operation via
WSACancelBlockingCall().  If this occurs, the DLL's blocking operation
will fail with the error code WSAEINTR, and the DLL must return
control to the calling task as quickly as possible, as the used has
likely pressed a cancel or close button and the task has requested
control of the CPU.  It is recommended that DLLs which make blocking
calls install their own blocking hooks with WSASetBlockingHook() to
prevent unforeseen interactions between the application and the DLL.

Note that this is not necessary for DLLs in Windows NT because of its
different process and DLL structure.  Under Windows NT, the
intermediate DLL could simply call WSAStartup() in its DLL
initialization routine, which is called whenever a new process which
uses the DLL starts.

3.3.6 Internal use of Messages by Windows Sockets Implementations
In order to implement Windows Sockets purely as a DLL, it may be
necessary for the DLL to post messages internally for communication
and timing.  This is perfectly legal; however, a Windows Sockets DLL
must not post messages to a window handle opened by a client
application except for those messages requested by the application.  A
Windows Sockets DLL that needs to use messages for its own purposes
must open a hidden window and post any necessary messages to the
handle for that window.
                                  23


24 Socket Library Overview


3.3.7 Private API Interfaces
The winsock.def file in Appendix B.7 lists the ordinals defined for
the Windows Sockets APIs.  In addition to the ordinal values listed,
all ordinals 999 and below are reserved for future Windows Sockets
use.  It may be convenient for a Windows Sockets implementation to
export additional, private interfaces from the Windows Sockets DLL.
This is perfectly acceptable, as long as the ordinals for these
exports are above 1000.  Note that any application that uses a
particular Windows Sockets DLL's private APIs will most likely not
work on any other vendor's Windows Sockets implementation.  Only the
APIs defined in this document are guaranteed to be present in every
Windows Sockets implementation.

If an application uses private interfaces of a particular vendor's
Windows Sockets DLL, it is recommended that the DLL not be statically
linked with the application but rather dynamically loaded with the
Windows routines LoadLibrary() and GetProcAddress().  This allows the
application to give an informative error message if it is run on a
system with a Windows Sockets DLL that does not support the same set
of extended functionality.


                                           Socket Library Reference 25


4.  SOCKET LIBRARY REFERENCE

4.1 Socket Routines
This chapter presents the socket library routines in alphabetical
order, and describes each routine in detail.

In each routine it is indicated that the header file winsock.h must be
included.  Appendix A.2 lists the Berkeley-compatible header files
which are supported.  These are provided for compatibility purposes
only, and each of them will simply include winsock.h.  The Windows
header file windows.h is also needed, but winsock.h will include it if
necessary.


26 accept

4.1.1 accept()
Description    Accept a connection on a socket.

          #include <winsock.h>

          SOCKET PASCAL FAR accept ( SOCKET s, struct sockaddr FAR *
          addr,
          int FAR * addrlen );


          s         A descriptor identifying a socket which is
                    listening for connections after a listen().

          addr      An optional pointer to a buffer which receives the
                    address of the connecting entity, as known to the
                    communications layer.  The exact format of the
                    addr argument is determined by the address family
                    established when the socket was created.

          addrlen   An optional pointer to an integer which contains
                    the length of the address addr.

Remarks   This routine extracts the first connection on the queue of
          pending connections on s, creates a new socket with the same
          properties as s and returns a handle to the new socket.  If
          no pending connections are present on the queue, and the
          socket is not marked as non-blocking, accept() blocks the
          caller until a connection is present.  If the socket is
          marked non-blocking and no pending connections are present
          on the queue, accept() returns an error as described below.
          The accepted socket may not be used to accept more
          connections.  The original socket remains open.

          The argument addr is a result parameter that is filled in
          with the address of the connecting entity, as known to the
          communications layer.  The exact format of the addr
          parameter is determined by the address family in which the
          communication is occurring.  The addrlen is a value-result
          parameter; it should initially contain the amount of space
          pointed to by addr; on return it will contain the actual
          length (in bytes) of the address returned.  This call is
          used with connection-based socket types such as SOCK_STREAM.
          If addr and/or addrlen are equal to NULL, then no
          information about the remote address of the accepted socket
          is returned.


Return Value   If no error occurs, accept() returns a value of type
          SOCKET which is a descriptor for the accepted packet.
          Otherwise, a value of INVALID_SOCKET is returned, and a
          specific error code may be retrieved by calling
          WSAGetLastError().

          The integer referred to by addrlen initially contains the
          amount of space pointed to by addr.  On return it will
          contain the actual length in bytes of the address returned.


                                                             accept 27

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEFAULT           The addrlen argument is too small (less
                              than the sizeof a struct sockaddr).

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().

          WSAEINPROGRESS      A blocking Windows Sockets call is in
                              progress.

          WSAEINVAL           listen() was not invoked prior to
                              accept().

          WSAEMFILE           The queue is empty upon entry to
                              accept() and there are no descriptors
                              available.

          WSAENOBUFS          No buffer space is available.

          WSAENOTSOCK         The descriptor is not a socket.

          WSAEOPNOTSUPP       The referenced socket is not a type that
                              supports connection-oriented service.

          WSAEWOULDBLOCK      The socket is marked as non-blocking and
                              no connections are present to be
                              accepted.

See Also  bind(), connect(), listen(), select(), socket(),
          WSAAsyncSelect()


28 bind

4.1.2 bind()
Description    Associate a local address with a socket.

          #include <winsock.h>

          int PASCAL FAR bind ( SOCKET s, const struct sockaddr FAR *
          name, int namelen );


          s         A descriptor identifying an unbound socket.

          name      The address to assign to the socket.  The sockaddr
                    structure is defined as follows:

                    struct sockaddr {
                         u_short   sa_family;
                         char sa_data[14];
                    };

          namelen   The length of the name.

Remarks   This routine is used on an unconnected datagram or stream
          socket, before subsequent connect()s or listen()s.  When a
          socket is created with socket(), it exists in a name space
          (address family), but it has no name assigned.  bind()
          establishes the local association (host address/port number)
          of the socket by assigning a local name to an unnamed
          socket.

          In the Internet address family, a name consists of several
          components.  For SOCK_DGRAM and SOCK_STREAM, the name
          consists of three parts: a host address, the protocol number
          (set implicitly to UDP or TCP, respectively), and a port
          number which identifies the application.  If an application
          does not care what address is assigned to it, it may specify
          an Internet address equal to INADDR_ANY, a port equal to 0,
          or both.  If the Internet address is equal to INADDR_ANY,
          any appropriate network interface will be used; this
          simplifies application programming in the presence of multi-
          homed hosts.  If the port is specified as 0, the Windows
          Sockets implementation will assign a unique port to the
          application with a value between 1024 and 5000.  The
          application may use getsockname() after bind() to learn the
          address that has been assigned to it, but note that
          getsockname() will not necessarily fill in the Internet
          address until the socket is connected, since several
          Internet addresses may be valid if the host is multi-homed.

          If an application desires to bind to an arbitrary port
          outside of the range 1024 to 5000, such as the case of rsh
          which must bind to any reserved port, code similar to the
          following may be used:

              SOCKADDR_IN sin;
              SOCKET s;
              u_short alport = IPPORT_RESERVED;


                                                               bind 29

              sin.sin_family = AF_INET;
              sin.sin_addr.s_addr = 0;
              for (;;) {
                  sin.sin_port = htons(alport);
                  if (bind(s, (LPSOCKADDR)&sin, sizeof (sin)) == 0) {
                      /* it worked */
                  }
                  if ( GetLastError() != WSAEADDRINUSE) {
                      /* fail */
                  }
                  alport--;
                  if (alport == IPPORT_RESERVED/2 ) {
                      /* fail--all unassigned reserved ports are */
                      /* in use. */
                  }
              }





Return Value   If no error occurs, bind() returns 0.  Otherwise, it
          returns SOCKET_ERROR, and a specific error code may be
          retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEADDRINUSE       The specified address is already in use.
                              (See the SO_REUSEADDR socket option
                              under setsockopt().)

          WSAEFAULT           The namelen argument is too small (less
                              than the size of a struct sockaddr).

          WSAEINPROGRESS      A blocking Windows Sockets call is in
                              progress.

          WSAEAFNOSUPPORT     The specified address family is not
                              supported by this protocol.

          WSAEINVAL           The socket is already bound to an
                              address.

          WSAENOBUFS          Not enough buffers available, too many
                              connections.

          WSAENOTSOCK         The descriptor is not a socket.

See Also  connect(), listen(), getsockname(), setsockopt(), socket(),
          WSACancelBlockingCall().


30 closesocket

4.1.3 closesocket()
Description    Close a socket.

          #include <winsock.h>

          int PASCAL FAR closesocket ( SOCKET s );


          s         A descriptor identifying a socket.

Remarks   This function closes a socket.  More precisely, it releases
          the socket descriptor s, so that further references to s
          will fail with the error WSAENOTSOCK.  If this is the last
          reference to the underlying socket, the associated naming
          information and queued data are discarded.

          The semantics of closesocket() are affected by the socket
          options SO_LINGER and SO_DONTLINGER as follows:

          Option         Interval       Type of close  Wait for close?
          SO_DONTLINGER  Don't care     Graceful       No
          SO_LINGER      Zero      Hard      No
          SO_LINGER      Non-zero  Graceful       Yes

          If SO_LINGER is set (i.e. the l_onoff field of the linger
          structure is non-zero; see sections 2.4,  4.1.7 and 4.1.21)
          with a zero timeout interval (l_linger is zero),
          closesocket() is not blocked even if queued data has not yet
          been sent or acknowledged.  This is called a "hard" or
          "abortive" close, because the socket's virtual circuit is
          reset immediately, and any unsent data is lost.  Any recv()
          call on the remote side of the circuit will fail with
          WSAECONNRESET.

          If SO_LINGER is set with a non-zero timeout interval, the
          closesocket() call blocks until the remaining data has been
          sent or until the timeout expires.  This is called a
          graceful disconnect.  Note that if the socket is set to non-
          blocking and SO_LINGER is set to a non-zero timeout, the
          call to closesocket() will fail with an error of
          WSAEWOULDBLOCK.

          If SO_DONTLINGER is set on a stream socket (i.e. the l_onoff
          field of the linger structure is zero; see sections 2.4,
          4.1.7 and 4.1.21), the closesocket() call will return
          immediately.  However, any data queued for transmission will
          be sent if possible before the underlying socket is closed.
          This is also called a graceful disconnect.  Note that in
          this case the Windows Sockets implementation may not release
          the socket and other resources for an arbitrary period,
          which may affect applications which expect to use all
          available sockets.


Return Value   If no error occurs, closesocket() returns 0.
          Otherwise, a value of SOCKET_ERROR is returned, and a


                                                        closesocket 31

          specific error code may be retrieved by calling
          WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAENOTSOCK         The descriptor is not a socket.

          WSAEINPROGRESS      A blocking Windows Sockets call is in
                              progress.

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().

          WSAEWOULDBLOCK      The socket is marked as nonblocking and
                              SO_LINGER is set to a nonzero timeout
                              value.


See Also  accept(), socket(), ioctlsocket(), setsockopt(),
          WSAAsyncSelect().


32 connect

4.1.4 connect()
Description    Establish a connection to a peer.

          #include <winsock.h>

          int PASCAL FAR connect ( SOCKET s, const struct sockaddr FAR
          * name,
          int namelen );


          s         A descriptor identifying an unconnected socket.

          name      The name of the peer to which the socket is to be
                    connected.

          namelen   The length of the name.

Remarks   This function is used to create a connection to the
          specified foreign association.  The parameter s specifies an
          unconnected datagram or stream socket  If the socket is
          unbound, unique values are assigned to the local association
          by the system, and the socket is marked as bound.  Note that
          if the address field of the name structure is all zeroes,
          connect() will return the error WSAEADDRNOTAVAIL.

          For stream sockets (type SOCK_STREAM), an active connection
          is initiated to the foreign host using name (an address in
          the name space of the socket).  When the socket call
          completes successfully, the socket is ready to send/receive
          data.

          For a datagram socket (type SOCK_DGRAM), a default
          destination is set, which will be used on subsequent send()
          and recv() calls.


Return Value   If no error occurs, connect() returns 0.  Otherwise, it
          returns SOCKET_ERROR, and a specific error code may be
          retrieved by calling WSAGetLastError().

          On a blocking socket, the return value indicates success or
          failure of the connection attempt.

          On a non-blocking socket, if the return value is
          SOCKET_ERROR an application should call WSAGetLastError().
          If this indicates an error code of WSAEWOULDBLOCK, then your
          application can either:

          1. Use select() to determine the completion of the
          connection request by checking if the socket is writeable,
          or

          2. If your application is using the message-based
          WSAAsyncSelect() to indicate interest in connection events,
          then your application will receive an FD_CONNECT message
          when the connect operation is complete.


                                                            connect 33

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEADDRINUSE       The specified address is already in use.

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().

          WSAEINPROGRESS      A blocking Windows Sockets call is in
                              progress.

          WSAEADDRNOTAVAIL    The specified address is not available
                              from the local machine.

          WSAEAFNOSUPPORT     Addresses in the specified family cannot
                              be used with this socket.

          WSAECONNREFUSED     The attempt to connect was forcefully
                              rejected.

          WSAEDESTADDREQ      A destination address is required.

          WSAEFAULT           The namelen argument is incorrect.

          WSAEINVAL           The socket is not already bound to an
                              address.

          WSAEISCONN          The socket is already connected.

          WSAEMFILE           No more file descriptors are available.

          WSAENETUNREACH      The network can't be reached from this
                              host at this time.

          WSAENOBUFS          No buffer space is available.  The
                              socket cannot be connected.

          WSAENOTSOCK         The descriptor is not a socket.

          WSAETIMEDOUT        Attempt to connect timed out without
                              establishing a connection

          WSAEWOULDBLOCK      The socket is marked as non-blocking and
                              the connection cannot be completed
                              immediately.  It is possible to select()
                              the socket while it is connecting by
                              select()ing it for writing.

See Also  accept(), bind(), getsockname(), socket(), select() and
          WSAAsyncSelect()..


34 getpeername

4.1.5 getpeername()
Description    Get the address of the peer to which a socket is
          connected.

          #include <winsock.h>

          int PASCAL FAR getpeername ( SOCKET s, struct sockaddr FAR *
          name, int FAR * namelen );


          s         A descriptor identifying a connected socket.

          name      The structure which is to receive the name of the
                    peer.

          namelen   A pointer to the size of the name structure.

Remarks   getpeername() retrieves the name of the peer connected to
          the socket s and stores it in the struct sockaddr identified
          by name.  It is used on a connected datagram or stream
          socket.

          On return, the namelen argument contains the actual size of
          the name returned in bytes.


Return Value   If no error occurs, getpeername() returns 0.
          Otherwise, a value of SOCKET_ERROR is returned, and a
          specific error code may be retrieved by calling
          WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEFAULT           The namelen argument is not large
                              enough.

          WSAEINPROGRESS      A blocking Windows Sockets call is in
                              progress.

          WSAENOTCONN         The socket is not connected.

          WSAENOTSOCK         The descriptor is not a socket.

See Also  bind(), socket(), getsockname().


                                                        getsockname 35

4.1.6 getsockname()
Description    Get the local name for a socket.

          #include <winsock.h>

          int PASCAL FAR getsockname ( SOCKET s, struct sockaddr FAR *
          name,
          int FAR * namelen );


          s         A descriptor identifying a bound socket.

          name      Receives the address (name) of the socket.

          namelen    The size of the name buffer.

Remarks   getsockname() retrieves the current name for the specified
          socket descriptor in name.  It is used on a bound and/or
          connected socket specified by the s parameter.  The local
          association is returned.  This call is especially useful
          when a connect() call has been made without doing a bind()
          first; this call provides the only means by which you can
          determine the local association which has been set by the
          system.

          On return, the namelen argument contains the actual size of
          the name returned in bytes.

          If a socket was bound to INADDR_ANY, indicating that any of
          the host's IP addresses should be used for the socket,
          getsockname() will not necessarily return information about
          the host IP address, unless the socket has been connected
          with connect() or accept().  A Windows Sockets application
          must not assume that the IP address will be changed from
          INADDR_ANY unless the socket is connected.  This is because
          for a multi-homed host the IP address that will be used for
          the socket is unknown unless the socket is connected.

Return Value   If no error occurs, getsockname() returns 0.
          Otherwise, a value of SOCKET_ERROR is returned, and a
          specific error code may be retrieved by calling
          WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEFAULT           The namelen argument is not large
                              enough.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.


36 getsockname

          WSAENOTSOCK         The descriptor is not a socket.

          WSAEINVAL           The socket has not been bound to an
                              address with bind().

See Also  bind(), socket(), getpeername().


                                                         getsockopt 37

4.1.7 getsockopt()
Description    Retrieve a socket option.

          #include <winsock.h>

              PASCAL FAR           int            getsockopt ( SOCKET s, int level, int
          optname,
          char FAR * optval, int FAR * optlen );


          s         A descriptor identifying a socket.

          level     The level at which the option is defined; the only
                    supported level  are                                                                         s     SOL_SOCKET and IPPROTO_TCP.

          optname   The socket option for which the value is to be
                    retrieved.

          optval    A pointer to the buffer in which the value for the
                    requested option is to be returned.

          optlen    A pointer to the size of the optval buffer.

Remarks   getsockopt() retrieves the current value for a socket option
          associated with a socket of any type, in any state, and
          stores the result in optval.  Options may exist at multiple
          protocol levels, but they are always present at the
          uppermost "socket'' level.  Options affect socket
          operations, such as whether an operation blocks or not, the
          routing of packets, out-of-band data transfer, etc.

          The value associated  with the selected option is returned
          in the buffer optval.  The integer pointed to by  optlen
          should originally contain the size of this buffer; on
          return, it will be set to the size of the value returned.
          For SO_LINGER, this will be the size of  a struct linger;
          for all other options it will be the size of an integer.

          If the option was never set with setsockopt(), then
          getsockopt() returns the default value for the option.

          The following options are supported for getsockopt().  The
          Type identifies the type of data addressed by optval.  The
          TCP_NODELAY option uses level IPPROTO_TCP; all other options
          use level SOL_SOCKET.

               Value        Type     Meaning
               SO_ACCEPTCO  BOOL     Socket is listen()ing.
                N               N
               SO_BROADCAS  BOOL     Socket is configured for the
               T                     transmission of broadcast
                                     messages.
               SO_DEBUG     BOOL     Debugging is enabled.
               SO_DONTLING  BOOL     If true, the SO_LINGER
               ER                    option is disabled.
               SO_DONTROUT  BOOL     Routing is disabled.
               E


38 getsockopt

               SO_ERROR     int      Retrieve error status and
                                     clear.
               SO_KEEPALIV  BOOL     Keepalives are being sent.
               E
               SO_LINGER    struct   Returns the current linger
                            linger   options.
                            FAR *
               SO_OOBINLIN  BOOL     Out-of-band data is being
               E                     received in the normal data
                                     stream.
               SO_RCVBUF    int      Buffer size for receives
               SO_REUSEADD  BOOL     The socket may be bound to
               R                     an address which is already
                                     in use.
               SO_SNDBUF    int      Buffer size for sends
               SO_TYPE      int      The type of the socket (e.g.
                                     SOCK_STREAM).
               TCP_NODELAY  BOOL     Disables the Nagle algorithm
                                     for send coalescing.

               BSD options not supported for getsockopt() are:

               Value        Type     Meaning
               SO_RCVLOWAT  int      Receive low water mark
               SO_RCVTIMEO  int      Receive timeout
               SO_SNDLOWAT  int      Send low water mark
               SO_SNDTIMEO  int      Send timeout
               IP_OPTIONS            Get options in IP header.
               TCP_MAXSEG   int      Get TCP maximum segment
                                     size.


          Calling getsockopt() with an unsupported option will result
          in an error code of WSAENOPROTOOPT being returned from
          WSAGetLastError().



Return Value   If no error occurs, getsockopt() returns 0.  Otherwise,
          a value of SOCKET_ERROR is returned, and a specific error
          code may be retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEFAULT           The optlen argument was invalid.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.


                                                         getsockopt 39

          WSAENOPROTOOPT      The option is unknown or unsupported.
                              In particular, SO_BROADCAST is not
                              supported on sockets of type
                              SOCK_STREAM, while SO_ACCEPTCONN,
                              SO_DONTLINGER, SO_KEEPALIVE, SO_LINGER
                              and SO_OOBINLINE are not supported on
                              sockets of type SOCK_DGRAM.

          WSAENOTSOCK         The descriptor is not a socket.

See Also  setsockopt(), WSAAsyncSelect(), socket().


40 htonl

4.1.8 htonl()
Description    Convert a u_long from host to network byte order.

          #include <winsock.h>

          u_long PASCAL FAR htonl ( u_long hostlong );


          hostlong  A 32-bit number in host byte order.

Remarks   This routine takes a 32-bit number in host byte order and
          returns a 32-bit number in network byte order.


Return Value   htonl() returns the value in network byte order.

See Also  htons(), ntohl(), ntohs().


                                                              htons 41

4.1.9 htons()
Description    Convert a u_short from host to network byte order.

          #include <winsock.h>

          u_short PASCAL FAR htons ( u_short hostshort );


          hostshort A 16-bit number in host byte order.

Remarks   This routine takes a 16-bit number in host byte order and
          returns a 16-bit number in network byte order.


Return Value   htons() returns the value in network byte order.

See Also  htonl(), ntohl(), ntohs().


42 inet_addr

4.1.10 inet_addr()
Description    Convert a string containing a dotted address into an
          in_addr.

          #include <winsock.h>

          unsigned long PASCAL FAR inet_addr ( const char FAR * cp );


          cp        A character string representing a number expressed
                    in the Internet standard ".'' notation.

Remarks   This function interprets the character string specified by
          the cp parameter.  This string represents a numeric Internet
          address expressed in the Internet standard ".'' notation.
          The value returned is a number suitable for use as an
          Internet address.  All Internet addresses are returned in
          network order (bytes ordered from left to right).

          Internet Addresses

          Values specified using the ".'' notation take one of the
          following forms:

          a.b.c.d   a.b.c     a.b  a

          When four parts are specified, each is interpreted as a byte
          of data and assigned, from left to right, to the four bytes
          of an Internet address.  Note that when an Internet address
          is viewed as a 32-bit integer quantity on the Intel
          architecture, the bytes referred to above appear as
          "d.c.b.a''.  That is, the bytes on an Intel processor are
          ordered from right to left.

          Note: The following notations are only used by Berkeley, and
          nowhere else on the Internet.  In the interests of
          compatibility with their software, they are supported as
          specified.

          When a three part address is specified, the last part is
          interpreted as a 16-bit quantity and placed in the right
          most two bytes of the network address.  This makes the three
          part address format convenient for specifying Class B
          network addresses as "128.net.host''.

          When a two part address is specified, the last part is
          interpreted as a 24-bit quantity and placed in the right
          most three bytes of the network address.  This makes the two
          part address format convenient for specifying Class A
          network addresses as "net.host''.

          When only one part is given, the value is stored directly in
          the network address without any byte rearrangement.


Return Value   If no error occurs, inet_addr() returns an unsigned
          long containing a suitable binary representation of the


                                                          inet_addr 43

          Internet address given.  If the passed-in string does not
          contain a legitimate Internet address, for example if a
          portion of an "a.b.c.d" address exceeds 255, inet_addr()
          returns the value INADDR_NONE.

See Also  inet_ntoa()


44 inet_ntoa

4.1.11 inet_ntoa()
Description    Convert a network address into a string in dotted
          format.

          #include <winsock.h>

          char FAR * PASCAL FAR inet_ntoa ( struct in_addr in );


          in        A structure which represents an Internet host
                    address.

Remarks   This function takes an Internet address structure specified
          by the in parameter.  It returns an ASCII string
          representing the address in ".''  notation as "a.b.c.d''.
          Note that the string returned by inet_ntoa() resides in
          memory which is allocated by the Windows Sockets
          implementation.  The application should not make any
          assumptions about the way in which the memory is allocated.
          The data is guaranteed to be valid until the next Windows
          Sockets API call within the same thread, but no longer.


Return Value   If no error occurs, inet_ntoa() returns a char pointer
          to a static buffer containing the text address in standard
          ".'' notation.  Otherwise, it returns NULL.  The data should
          be copied before another Windows Sockets call is made.

See Also  inet_addr().


                                                        ioctlsocket 45

4.1.12 ioctlsocket()
Description    Control the mode of a socket.

          #include <winsock.h>

          int PASCAL FAR ioctlsocket ( SOCKET s, long cmd, u_long FAR
          * argp );


          s         A descriptor identifying a socket.

          cmd       The command to perform on the socket s.

          argp      A pointer to a parameter for cmd.

Remarks   This routine may be used on any socket in any state.  It is
          used to get or retrieve operating parameters associated with
          the socket, independent of the protocol and communications
          subsystem.  The following commands are supported:

          Command   Semantics

          FIONBIO   Enable or disable non-blocking mode on the socket
                    s.  argp points at an unsigned long, which is non-
                    zero if non-blocking mode is to be enabled and
                    zero if it is to be disabled.  When a socket is
                    created, it operates in blocking mode (i.e. non-
                    blocking mode is disabled).  This is consistent
                    with BSD sockets.

                    The WSAAsyncSelect() routine automatically sets a
                    socket to nonblocking mode.  If WSAAsyncSelect()
                    has been issued on a socket, then any attempt to
                    use ioctlsocket() to set the socket back to
                    blocking mode will fail with WSAEINVAL.  To set
                    the socket back to blocking mode, an application
                    must first disable WSAAsyncSelect() by calling
                    WSAAsyncSelect() with the lEvent parameter equal
                    to 0.

          FIONREAD  Determine the amount of data which can be read
                    atomically from socket s.  argp points at an
                    unsigned long in which ioctlsocket() stores the
                    result.  If s is of type SOCK_STREAM, FIONREAD
                    returns the total amount of data which may be read
                    in a single recv(); this is normally the same as
                    the total amount of data queued on the socket.  If
                    s is of type SOCK_DGRAM, FIONREAD returns the size
                    of the first datagram queued on the socket.

          SIOCATMARK     Determine whether or not all out-of-band data
                    has been read.  This applies only to a socket of
                    type SOCK_STREAM which has been configured for in-
                    line reception of any out-of-band data
                    (SO_OOBINLINE).  If no out-of-band data is waiting
                    to be read,  the operation returns TRUE.
                    Otherwise it returns FALSE, and the next recv() or


46 ioctlsocket

                    recvfrom() performed on the socket will retrieve
                    some or all of the data preceding the "mark"; the
                    application should use the SIOCATMARK operation to
                    determine whether any remains.  If there is any
                    normal data preceding the "urgent" (out of band)
                    data, it will be received in order.  (Note that a
                    recv() or recvfrom() will never mix out-of-band
                    and normal data in the same call.)  argp points at
                    a BOOL in which ioctlsocket() stores the result.

Compatibility  This function is a subset of ioctl() as used in
          Berkeley sockets.  In particular, there is no command which
          is equivalent to FIOASYNC, while SIOCATMARK is the only
          socket-level command which is supported.


Return Value   Upon successful completion, the ioctlsocket() returns
          0.  Otherwise, a value of SOCKET_ERROR is returned, and a
          specific error code may be retrieved by calling
          WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINVAL           cmd is not a valid command, or argp is
                              not an acceptable parameter for cmd, or
                              the command is not applicable to the
                              type of socket supplied

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAENOTSOCK         The descriptor s is not a socket.


See Also  socket(), setsockopt(), getsockopt(), WSAAsyncSelect().


                                                             listen 47

4.1.13 listen()
Description    Establish a socket to listen for incoming connection.

          #include <winsock.h>

          int PASCAL FAR listen ( SOCKET s, int backlog );

          s         A descriptor identifying a bound, unconnected
                    socket.

          backlog   The maximum length to which the queue of pending
                    connections may grow.

Remarks   To accept connections, a socket is first created with
          socket(), a backlog for incoming connections is specified
          with listen(), and then the connections are accepted with
          accept().  listen() applies only to sockets that support
          connections, i.e. those of type SOCK_STREAM.  The socket s
          is put into "passive'' mode where incoming connections are
          acknowledged and queued pending acceptance by the process.

          This function is typically used by servers that could have
          more than one connection request at a time: if a connection
          request arrives with the queue full, the client will receive
          an error with an indication of WSAECONNREFUSED.

          listen() attempts to continue to function rationally when
          there are no available descriptors.  It will accept
          connections until the queue is emptied.  If descriptors
          become available, a later call to listen() or accept() will
          re-fill the queue to the current or most recent "backlog'',
          if possible, and resume listening for incoming connections.

Compatibility  backlog is currently limited (silently) to 5.  As in
          4.3BSD, illegal values (less than 1 or greater than 5) are
          replaced by the nearest legal value.

Return Value   If no error occurs, listen() returns 0.  Otherwise, a
          value of SOCKET_ERROR is returned, and a specific error code
          may be retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEADDRINUSE       An attempt has been made to listen() on
                              an address in use.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEINVAL           The socket has not been bound with
                              bind() or is already connected.


48 listen


          WSAEISCONN          The socket is already connected.

          WSAEMFILE           No more file descriptors are available.

          WSAENOBUFS          No buffer space is available.

          WSAENOTSOCK         The descriptor is not a socket.

          WSAEOPNOTSUPP       The referenced socket is not of a type
                              that supports the listen() operation.

See Also  accept(),  connect(), socket().


                                                              ntohl 49

4.1.14 ntohl()
Description    Convert a u_long from network to host byte order.

          #include <winsock.h>

          u_long PASCAL FAR ntohl ( u_long netlong );


          netlong   A 32-bit number in network byte order.

Remarks   This routine takes a 32-bit number in network byte order and
          returns a 32-bit number in host byte order.


Return Value   ntohl() returns the value in host byte order.

See Also  htonl(), htons(), ntohs().


50 ntohs

4.1.15 ntohs()
Description    Convert a u_short from network to host byte order.

          #include <winsock.h>

          u_short PASCAL FAR ntohs ( u_short netshort );


          netshort  A 16-bit number in network byte order.

Remarks   This routine takes a 16-bit number in network byte order and
          returns a 16-bit number in host byte order.


Return Value   ntohs() returns the value in host byte order.

See Also  htonl(), htons(), ntohl().


                                                               recv 51

4.1.16 recv()
Description    Receive data from a socket.

          #include <winsock.h>

          int PASCAL FAR recv ( SOCKET s, char FAR * buf, int len, int
          flags );


          s         A descriptor identifying a connected socket.

          buf       A buffer for the incoming data.

          len       The length of buf.

          flags     Specifies the way in which the call is made.

Remarks   This function is used on connected datagram or stream
          sockets specified by the s parameter and is used to read
          incoming data.

          For sockets of type SOCK_STREAM, as much information as is
          currently available up to the size of the buffer supplied is
          returned.  If the socket has been configured for in-line
          reception of out-of-band data (socket option SO_OOBINLINE)
          and out-of-band data is unread, only out-of-band data will
          be returned.  The application may use the ioctlsocket()
          SIOCATMARK to determine whether any more out-of-band data
          remains to be read.

          For datagram sockets, data is extracted from the first
          enqueued datagram, up to the size of the buffer supplied.
          If the datagram is larger than the buffer supplied, the
          buffer is filled with the first part of the datagram, the
          excess data is lost, and recv() returns the error
          WSAEMSGSIZE.

          If no incoming data is available at the socket, the recv()
          call waits for data to arrive unless the socket is non-
          blocking.  In this case a value of SOCKET_ERROR is returned
          with the error code set to WSAEWOULDBLOCK.  The select() or
          WSAAsyncSelect() calls may be used to determine when more
          data arrives.

          If the socket is of type SOCK_STREAM and the remote side has
          shut down the connection gracefully, a recv() will complete
          immediately with 0 bytes received.  If the connection has
          been reset, a recv() will fail with the error WSAECONNRESET.

          Flags may be used to influence the behavior of the function
          invocation beyond the options specified for the associated
          socket.  That is, the semantics of this function are
          determined by the socket options and the flags parameter.
          The latter is constructed by or-ing any of the following
          values:

          Value     Meaning


52 recv

          MSG_PEEK  Peek at the incoming data.  The data is copied
                    into the buffer but is not removed from the input
                    queue.

          MSG_OOB   Process out-of-band data (See section 2.2.3 for a
                    discussion of this topic.)



Return Value   If no error occurs, recv() returns the number of bytes
          received.  If the connection has been closed, it returns 0.
          Otherwise, a value of SOCKET_ERROR is returned, and a
          specific error code may be retrieved by calling
          WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAENOTCONN         The socket is not connected.

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAENOTSOCK         The descriptor is not a socket.

          WSAEOPNOTSUPP       MSG_OOB was specified, but the socket is
                              not of type SOCK_STREAM.

          WSAESHUTDOWN        The socket has been shutdown; it is not
                              possible to recv() on a socket after
                              shutdown() has been invoked with how set
                              to 0 or 2.

          WSAEWOULDBLOCK      The socket is marked as non-blocking and
                              the receive operation would block.

          WSAEMSGSIZE         The datagram was too large to fit into
                              the specified buffer and was truncated.

          WSAEINVAL           The socket has not been bound with
                              bind().

          WSAECONNABORTED     The virtual circuit was aborted due to
                              timeout or other failure.

          WSAECONNRESET       The virtual circuit was reset by the
                              remote side.


                                                               recv 53

See Also  recvfrom(), read(), ,recv(), send(), select(),
          WSAAsyncSelect(), socket()


54 recvfrom

4.1.17 recvfrom()
Description    Receive a datagram and store the source address.

          #include <winsock.h>

          int PASCAL FAR recvfrom ( SOCKET s, char FAR * buf, int len,
          int flags,
          struct sockaddr FAR * from, int FAR * fromlen );


          s         A descriptor identifying a bound socket.

          buf       A buffer for the incoming data.

          len       The length of buf.

          flags     Specifies the way in which the call is made.

          from      An optional pointer to a buffer which will hold
                    the source address upon return.

          fromlen   An optional pointer to the size of the from
                    buffer.

Remarks   This function is used to read incoming data on a (possibly
          connected) socket and capture the address from which the
          data was sent.

          For sockets of type SOCK_STREAM, as much information as is
          currently available up to the size of the buffer supplied is
          returned.  If the socket has been configured for in-line
          reception of out-of-band data (socket option SO_OOBINLINE)
          and out-of-band data is unread, only out-of-band data will
          be returned.  The application may use the ioctlsocket()
          SIOCATMARK to determine whether any more out-of-band data
          remains to be read.  The from and fromlen parameters are
          ignored for SOCK_STREAM sockets.

          For datagram sockets, data is extracted from the first
          enqueued datagram, up to the size of the buffer supplied.
          If the datagram is larger than the buffer supplied, the
          buffer is filled with the first part of the message, the
          excess data is lost, and recvfrom() returns the error code
          WSAEMSGSIZE.

          If from is non-zero, and the socket is of type SOCK_DGRAM,
          the network address of the peer which sent the data is
          copied to the corresponding struct sockaddr.  The value
          pointed to by fromlen is initialized to the size of this
          structure, and is modified on return to indicate the actual
          size of the address stored there.

          If no incoming data is available at the socket, the
          recvfrom() call waits for data to arrive unless the socket
          is non-blocking.  In this case a value of SOCKET_ERROR is
          returned with the error code set to WSAEWOULDBLOCK.  The


                                                           recvfrom 55

          select() or WSAAsyncSelect() calls may be used to determine
          when more data arrives.

          If the socket is of type SOCK_STREAM and the remote side has
          shut down the connection gracefully, a recvfrom() will
          complete immediately with 0 bytes received.  If the
          connection has been reset recv() will fail with the error
          WSAECONNRESET.

          Flags may be used to influence the behavior of the function
          invocation beyond the options specified for the associated
          socket.  That is, the semantics of this function are
          determined by the socket options and the flags parameter.
          The latter is constructed by or-ing any of the following
          values:

          Value     Meaning
          MSG_PEEK  Peek at the incoming data.  The data is copied
                    into the buffer but is not removed from the input
                    queue.

          MSG_OOB   Process out-of-band data (See section 2.2.3 for a
                    discussion of this topic.)



Return Value   If no error occurs, recvfrom() returns the number of
          bytes received.  If the connection has been closed, it
          returns 0.  Otherwise, a value of SOCKET_ERROR is returned,
          and a specific error code may be retrieved by calling
          WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEFAULT           The fromlen argument was invalid: the
                              from buffer was too small to accommodate
                              the peer address.

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEINVAL           The socket has not been bound with
                              bind().

          WSAENOTCONN         The socket is not connected (SOCK_STREAM
                              only).

          WSAENOTSOCK         The descriptor is not a socket.


56 recvfrom


          WSAEOPNOTSUPP       MSG_OOB was specified, but the socket is
                              not of type SOCK_STREAM.

          WSAESHUTDOWN        The socket has been shutdown; it is not
                              possible to recvfrom() on a socket after
                              shutdown() has been invoked with how set
                              to 0 or 2.

          WSAEWOULDBLOCK      The socket is marked as non-blocking and
                              the recvfrom() operation would block.

          WSAEMSGSIZE         The datagram was too large to fit into
                              the specified buffer and was truncated.

          WSAECONNABORTED     The virtual circuit was aborted due to
                              timeout or other failure.

          WSAECONNRESET       The virtual circuit was reset by the
                              remote side.


See Also  recv(), send(), socket(), WSAAsyncSelect().


                                                             select 57

4.1.18 select()
Description    Determine the status of one or more sockets, waiting if
          necessary.

          #include <winsock.h>

          int PASCAL FAR select ( int nfds, fd_set FAR * readfds,
          fd_set FAR * writefds,
          fd_set FAR * exceptfds, const struct timeval FAR * timeout
          );


          nfds      This argument is ignored and included only for the
                    sake of compatibility.

          readfds   An optional pointer to a set of sockets to be
                    checked for readability.

          writefds  An optional pointer to a set of sockets to be
                    checked for writability

          exceptfds An optional pointer to a set of sockets to be
                    checked for errors.

          timeout   The maximum time for select() to wait, or NULL for
                    blocking operation.

Remarks   This function is used to determine the status of one or more
          sockets.  For each socket, the caller may request
          information on read, write or error status.  The set of
          sockets for which a given status is requested is indicated
          by an fd_set structure.  Upon return, the structure is
          updated to reflect the subset of these sockets which meet
          the specified condition, and select() returns the number of
          sockets meeting the conditions.  A set of macros is provided
          for manipulating an fd_set.  These macros are compatible
          with those used in the Berkeley software, but the underlying
          representation is completely different.

          The parameter readfds identifies those sockets which are to
          be checked for readability.  If the socket is currently
          listen()ing, it will be marked as readable if an incoming
          connection request has been received, so that an accept() is
          guaranteed to complete without blocking.  For other sockets,
          readability means that queued data is available for reading
          or, for sockets of type SOCK_STREAM, that the virtual socket
          corresponding to the socket has been closed, so that a
          recv() or recvfrom() is guaranteed to complete without
          blocking.  If the virtual circuit was closed gracefully,
          then a recv() will return immediately with 0 bytes read; if
          the virtual circuit was reset, then a recv() will complete
          immediately with the error code WSAECONNRESET. The presence
          of out-of-band data will be checked if the socket option
          SO_OOBINLINE has been enabled (see setsockopt()).

          The parameter writefds identifies those sockets which are to
          be checked for writability.   If a socket is connect()ing


58 select

          (non-blocking), writability means that the connection
          establishment successfully completed.  If the socket is not
          in the process of connect()ing, writability means that a
          send() or sendto() will complete without blocking.  [It is
          not specified how long this guarantee can be assumed to be
          valid, particularly in a multithreaded environment.]

          The parameter exceptfds identifies those sockets which are
          to be checked for the presence of out-of-band data or any
          exceptional error conditions.  Note that out-of-band data
          will only be reported in this way if the option SO_OOBINLINE
          is FALSE.  For a SOCK_STREAM, the breaking of the connection
          by the peer or due to KEEPALIVE failure will be indicated as
          an exception.  This specification does not define which
          other errors will be included.  If a socket is connect()ing
          (non-blocking), failure of the connect attempt is indicated
          in exceptfds.

          Any of readfds, writefds, or exceptfds may be given as NULL
          if no descriptors are of interest.

          Four macros are defined in the header file winsock.h for
          manipulating the descriptor sets.  The variable FD_SETSIZE
          determines the maximum number of descriptors in a set.  (The
          default value of FD_SETSIZE is 64, which may be modified by
          #defining FD_SETSIZE to another value before #including
          winsock.h.)  Internally, an fd_set is represented as an
          array of SOCKETs; the last valid entry is followed by an
          element set to INVALID_SOCKET.  The macros are:

          FD_CLR(s, *set)     Removes the descriptor s from set.

          FD_ISSET(s, *set)   Nonzero if s is a member of the set,
                    zero otherwise.

          FD_SET(s, *set)          Adds descriptor s to set.

          FD_ZERO(*set)       Initializes the set to the NULL set.

          The parameter timeout controls how long the select() may
          take to complete.  If timeout is a null pointer, select()
          will block indefinitely until at least one descriptor meets
          the specified criteria.  Otherwise, timeout points to a
          struct timeval which specifies the maximum time that
          select() should wait before returning.  If the timeval is
          initialized to {0, 0}, select() will return immediately;
          this is used to "poll" the state of the selected sockets.
          If this is the case, then the select() call is considered
          nonblocking and the standard assumptions for nonblocking
          calls apply.  For example, the blocking hook must not be
          called, and the Windows Sockets implementation must not
          yield.

Return Value   select() returns the total number of descriptors which
          are ready and contained in the fd_set structures, 0 if the
          time limit expired, or SOCKET_ERROR if an error occurred.


                                                             select 59

          If the return value is SOCKET_ERROR, WSAGetLastError() may
          be used to retrieve a specific error code.

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINVAL           The timeout value is not valid.

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAENOTSOCK         One of the descriptor sets contains an
                              entry which is not a socket.

See Also  WSAAsyncSelect(), accept(), connect(), recv(), recvfrom(),
          send().


60 send

4.1.19 send()
Description    Send data on a connected socket.

          #include <winsock.h>

          int PASCAL FAR send ( SOCKET s, const char FAR * buf, int
          len, int flags );


          s         A descriptor identifying a connected socket.

          buf       A buffer containing the data to be transmitted.

          len       The length of the data in buf.

          flags     Specifies the way in which the call is made.

Remarks   send() is used on connected datagram or stream sockets and
          is used to write outgoing data on a socket.  For datagram
          sockets, care must be taken not to exceed the maximum IP
          packet size of the underlying subnets, which is given by the
          iMaxUdpDg element in the WSAData structure returned by
          WSAStartup().  If the data is too long to pass atomically
          through the underlying protocol the error WSAEMSGSIZE is
          returned, and no data is transmitted.

          Note that the successful completion of a send() does not
          indicate that the data was successfully delivered.

          If no buffer space is available within the transport system
          to hold the data to be transmitted, send() will block unless
          the socket has been placed in a non-blocking I/O mode.  On
          non-blocking SOCK_STREAM sockets, the number of bytes
          written may be between 1 and the requested length, depending
          on buffer availability on both the local and foreign hosts.
          The select() call may be used to determine when it is
          possible to send more data.

          Flags may be used to influence the behavior of the function
          invocation beyond the options specified for the associated
          socket.  That is, the semantics of this function are
          determined by the socket options and the flags parameter.
          The latter is constructed by or-ing any of the following
          values:

          Value     Meaning
          MSG_DONTROUTE
                    Specifies that the data should not be subject to
                    routing.  A Windows Sockets supplier may choose to
                    ignore this flag; see also the discussion of the
                    SO_DONTROUTE option in section 2.4.

          MSG_OOB   Send out-of-band data (SOCK_STREAM only; see also
                    section 2.2.3)


                                                               send 61

Return Value   If no error occurs, send() returns the total number of
          characters sent.  (Note that this may be less than the
          number indicated by len.) Otherwise, a value of SOCKET_ERROR
          is returned, and a specific error code may be retrieved by
          calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEACCES           The requested address is a broadcast
                              address, but the appropriate flag was
                              not set.

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEFAULT           The buf argument is not in a valid part
                              of the user address space.

          WSAENETRESET        The connection must be reset because the
                              Windows Sockets implementation dropped
                              it.

          WSAENOBUFS          The Windows Sockets implementation
                              reports a buffer deadlock.

          WSAENOTCONN         The socket is not connected.

          WSAENOTSOCK         The descriptor is not a socket.

          WSAEOPNOTSUPP       MSG_OOB was specified, but the socket is
                              not of type SOCK_STREAM.

          WSAESHUTDOWN        The socket has been shutdown; it is not
                              possible to send() on a socket after
                              shutdown() has been invoked with how set
                              to 1 or 2.

          WSAEWOULDBLOCK      The socket is marked as non-blocking and
                              the requested operation would block.

          WSAEMSGSIZE         The socket is of type SOCK_DGRAM, and
                              the datagram is larger than the maximum
                              supported by the Windows Sockets
                              implementation.

          WSAEINVAL           The socket has not been bound with
                              bind().


62 send

          WSAECONNABORTED     The virtual circuit was aborted due to
                              timeout or other failure.

          WSAECONNRESET       The virtual circuit was reset by the
                              remote side.


See Also  recv(), recvfrom(), socket(), sendto(), WSAStartup().


                                                             sendto 63

4.1.20 sendto()
Description    Send data to a specific destination.

          #include <winsock.h>

          int PASCAL FAR sendto ( SOCKET s, const char FAR * buf, int
          len, int flags,
          const struct sockaddr FAR * to, int tolen );


          s         A descriptor identifying a socket.

          buf       A buffer containing the data to be transmitted.

          len       The length of the data in buf.

          flags     Specifies the way in which the call is made.

          to        An optional pointer to the address of the target
                    socket.

          tolen     The size of the address in to.

Remarks   sendto() is used on datagram or stream sockets and is used
          to write outgoing data on a socket.  For datagram sockets,
          care must be taken not to exceed the maximum IP packet size
          of the underlying subnets, which is given by the iMaxUdpDg
          element in the WSAData structure returned by WSAStartup().
          If the data is too long to pass atomically through the
          underlying protocol the error WSAEMSGSIZE is returned, and
          no data is transmitted.

          Note that the successful completion of a sendto() does not
          indicate that the data was successfully delivered.

          sendto() is normally used on a SOCK_DGRAM socket to send a
          datagram to a specific peer socket identified by the to
          parameter.  On a SOCK_STREAM socket, the to and tolen
          parameters are ignored; in this case the sendto() is
          equivalent to send().

          To send a broadcast (on a SOCK_DGRAM only), the address in
          the to parameter should be constructed using the special IP
          address INADDR_BROADCAST (defined in winsock.h) together
          with the intended port number.  It is generally inadvisable
          for a broadcast datagram to exceed the size at which
          fragmentation may occur, which implies that the data portion
          of the datagram (excluding headers) should not exceed 512
          bytes.

          If no buffer space is available within the transport system
          to hold the data to be transmitted, sendto() will block
          unless the socket has been placed in a non-blocking I/O
          mode.  On non-blocking SOCK_STREAM sockets, the number of
          bytes written may be between 1 and the requested length,
          depending on buffer availability on both the local and


64 sendto

          foreign hosts.  The select() call may be used to determine
          when it is possible to send more data.

          Flags may be used to influence the behavior of the function
          invocation beyond the options specified for the associated
          socket.  That is, the semantics of this function are
          determined by the socket options and the flags parameter.
          The latter is constructed by or-ing any of the following
          values:

          Value     Meaning
          MSG_DONTROUTE
                    Specifies that the data should not be subject to
                    routing.  A Windows Sockets supplier may choose to
                    ignore this flag; see also the discussion of the
                    SO_DONTROUTE option in section .

          MSG_OOB   Send out-of-band data (SOCK_STREAM only; see also
                    section )


Return Value   If no error occurs, sendto() returns the total number
          of characters sent.  (Note that this may be less than the
          number indicated by len.) Otherwise, a value of SOCKET_ERROR
          is returned, and a specific error code may be retrieved by
          calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEACCES           The requested address is a broadcast
                              address, but the appropriate flag was
                              not set.

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEFAULT           The buf or to parameters are not part of
                              the user address space, or the to
                              argument is too small (less than the
                              sizeof a struct sockaddr).

          WSAENETRESET        The connection must be reset because the
                              Windows Sockets implementation dropped
                              it.

          WSAENOBUFS          The Windows Sockets implementation
                              reports a buffer deadlock.


                                                             sendto 65

          WSAENOTCONN         The socket is not connected (SOCK_STREAM
                              only).

          WSAENOTSOCK         The descriptor is not a socket.

          WSAEOPNOTSUPP       MSG_OOB was specified, but the socket is
                              not of type SOCK_STREAM.

          WSAESHUTDOWN        The socket has been shutdown; it is not
                              possible to sendto() on a socket after
                              shutdown() has been invoked with how set
                              to 1 or 2.

          WSAEWOULDBLOCK      The socket is marked as non-blocking and
                              the requested operation would block.

          WSAEMSGSIZE         The socket is of type SOCK_DGRAM, and
                              the datagram is larger than the maximum
                              supported by the Windows Sockets
                              implementation.

          WSAECONNABORTED     The virtual circuit was aborted due to
                              timeout or other failure.

          WSAECONNRESET       The virtual circuit was reset by the
                              remote side.

          WSAEADDRNOTAVAIL    The specified address is not available
                              from the local machine.

          WSAEAFNOSUPPORT     Addresses in the specified family cannot
                              be used with this socket.

          WSAEDESTADDRREQ     A destination address is required.

          WSAENETUNREACH      The network can't be reached from this
                              host at this time.

See Also  recv(), recvfrom(), socket(), send(), WSAStartup().


66 setsockopt

4.1.21 setsockopt()
Description    Set a socket option.

          #include <winsock.h>

          int PASCAL FAR setsockopt ( SOCKET s, int level, int
          optname,
          const char FAR * optval, int optlen );


          s         A descriptor identifying a socket.

          level     The level at which the option is defined; the only
                    supported levels are SOL_SOCKET and IPPROTO_TCP.

          optname   The socket option for which the value is to be
                    set.

          optval    A pointer to the buffer in which the value for the
                    requested option is supplied.

          optlen    The size of the optval buffer.

Remarks   setsockopt() sets the current value for a socket option
          associated with a socket of any type, in any state.
          Although options may exist at multiple protocol levels, this
          specification only defines options that exist at the
          uppermost "socket'' level.  Options affect socket
          operations, such as whether expedited data is received in
          the normal data stream, whether broadcast messages may be
          sent on the socket, etc.

          There are two types of socket options: Boolean options that
          enable or disable a feature or behavior, and options which
          require an integer value or structure.  To enable a Boolean
          option, optval points to a nonzero integer.  To disable the
          option optval points to an integer equal to zero.  optlen
          should be equal to sizeof(int) for Boolean options.  For
          other options, optval points to the an integer or structure
          that contains the desired value for the option, and optlen
          is the length of the integer or structure.

          SO_LINGER controls the action taken when unsent data is
          queued on a socket and a closesocket() is performed.  See
          closesocket() for a description of the way in which the
          SO_LINGER settings affect the semantics of closesocket().
          The application sets the desired behavior by creating a
          struct linger (pointed to by the optval argument) with the
          following elements:

          struct linger {
               int  l_onoff;
               int  l_linger;
          }

          To enable SO_LINGER, the application should set l_onoff to a
          non-zero value, set l_linger to 0 or the desired timeout (in


                                                         setsockopt 67

          seconds), and call setsockopt().  To enable SO_DONTLINGER
          (i.e. disable SO_LINGER) l_onoff should be set to zero and
          setsockopt() should be called.

          By default, a socket may not be bound (see bind()) to a
          local address which is already in use.  On occasions,
          however, it may be desirable to "re-use" an address in this
          way.  Since every connection is uniquely identified by the
          combination of local and remote addresses, there is no
          problem with having two sockets bound to the same local
          address as long as the remote addresses are different.  To
          inform the Windows Sockets implementation that a bind() on a
          socket should not be disallowed because the desired address
          is already in use by another socket, the application should
          set the SO_REUSEADDR socket option for the socket before
          issuing the bind().  Note that the option is interpreted
          only at the time of the bind(): it is therefore unnecessary
          (but harmless) to set the option on a socket which is not to
          be bound to an existing address, and setting or resetting
          the option after the bind() has no effect on this or any
          other socket.

          An application may request that the Windows Sockets
          implementation enable the use of "keep-alive" packets on TCP
          connections by turning on the SO_KEEPALIVE socket option.  A
          Windows Sockets implementation need not support the use of
          keep-alives: if it does, the precise semantics are
          implementation-specific but should conform to section
          4.2.3.6 of RFC 1122: Requirements for Internet Hosts --
          Communication Layers.  If a connection is dropped as the
          result of "keep-alives" the error code WSAENETRESET is
          returned to any calls in progress on the socket, and any
          subsequent calls will fail with WSAENOTCONN.

          The TCP_NODELAY option disables the Nagle algorithm.  The
          Nagle algorithm is used to reduce the number of small
          packets sent by a host by buffering unacknowledged send data
          until a full-size packet can be sent.  However, for some
          applications this algorithm can impede performance, and
          TCP_NODELAY may be used to turn it off.  Application writers
          should not set TCP_NODELAY unless the impact of doing so is
          well-understood and desired, since setting TCP_NODELAY can
          have a significant negative impact of network performance.
          TCP_NODELAY is the only supported socket option which uses
          level IPPROTO_TCP; all other options use level SOL_SOCKET.

          Windows Sockets suppliers are encouraged (but not required)
          to supply output debug information if the SO_DEBUG option is
          set by an application.  The mechanism for generating the
          debug information and the form it takes are beyond the scope
          of this specification.

          The following options are supported for setsockopt().  The
          Type identifies the type of data addressed by optval.

               Value        Type     Meaning


68 setsockopt

               SO_BROADCAS  BOOL     Allow transmission of
               T                     broadcast messages on the
                                     socket.
               SO_DEBUG     BOOL     Record debugging
                                     information.
               SO_DONTLING  BOOL     Don't block close waiting
               ER                    for unsent data to be sent.
                                     Setting this option is
                                     equivalent to setting
                                     SO_LINGER with l_onoff set
                                     to zero.
               SO_DONTROUT  BOOL     Don't route: send directly
               E                     to interface.
               SO_KEEPALIV  BOOL     Send keepalives
               E
               SO_LINGER    struct   Linger on close if unsent
                            linger   data is present
                            FAR *
               SO_OOBINLIN  BOOL     Receive out-of-band data in
               E                     the normal data stream.
               SO_RCVBUF    int      Specify buffer size for
                                     receives
               SO_REUSEADD  BOOL     Allow the socket to be bound
               R                     to an address which is
                                     already in use.  (See
                                     bind().)
               SO_SNDBUF    int      Specify buffer size for
                                     sends.
               TCP_NODELAY  BOOL     Disables the Nagle algorithm
                                     for send coalescing.

               BSD options not supported for setsockopt() are:

               Value        Type     Meaning
               SO_ACCEPTCO  BOOL     Socket is listening
               NN
               SO_ERROR     int      Get error status and clear
               SO_RCVLOWAT  int      Receive low water mark
               SO_RCVTIMEO  int      Receive timeout
               SO_SNDLOWAT  int      Send low water mark
               SO_SNDTIMEO  int      Send timeout
               SO_TYPE      int      Type of the socket
               IP_OPTIONS            Set options field in IP
                                     header.

Return Value   If no error occurs, setsockopt() returns 0.  Otherwise,
          a value of SOCKET_ERROR is returned, and a specific error
          code may be retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.


                                                         setsockopt 69

          WSAEFAULT           optval is not in a valid part of the
                              process address  space.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEINVAL           level is not valid, or the information
                              in optval is not valid.

          WSAENETRESET        Connection has timed out when
                              SO_KEEPALIVE is set.

          WSAENOPROTOOPT      The option is unknown or unsupported.
                              In particular, SO_BROADCAST is not
                              supported on sockets of type
                              SOCK_STREAM, while SO_DONTLINGER,
                              SO_KEEPALIVE, SO_LINGER and SO_OOBINLINE
                              are not supported on sockets of type
                              SOCK_DGRAM.

          WSAENOTCONN         Connection has been reset when
                              SO_KEEPALIVE is set.

          WSAENOTSOCK         The descriptor is not a socket.

See Also  bind(), getsockopt(), ioctlsocket(), socket(),
          WSAAsyncSelect().


70 shutdown

4.1.22 shutdown()
Description    Disable sends and/or receives on a socket.

          #include <winsock.h>

          int PASCAL FAR shutdown ( SOCKET s, int how );


          s         A descriptor identifying a socket.

          how       A flag that describes what types of operation will
                    no longer be allowed.

Remarks   shutdown() is used on all types of sockets to disable
          reception, transmission, or both.

          If how is 0, subsequent receives on the socket will be
          disallowed.  This has no effect on the lower protocol
          layers.  For TCP, the TCP window is not changed and incoming
          data will be accepted (but not acknowledged) until the
          window is exhausted.  For UDP, incoming datagrams are
          accepted and queued.  In no case will an ICMP error packet
          be generated.

          If how is 1, subsequent sends are disallowed.  For TCP
          sockets, a FIN will be sent.

          Setting how to 2 disables both sends and receives as
          described above.

          Note that shutdown() does not close the socket, and
          resources attached to the socket will not be freed until
          closesocket() is invoked.


Comments  shutdown() does not block regardless of the SO_LINGER
          setting on the socket.

          An application should not rely on being able to re-use a
          socket after it has been shut down.  In particular, a
          Windows Sockets implementation is not required to support
          the use of connect() on such a socket.

Return Value   If no error occurs, shutdown() returns 0.  Otherwise, a
          value of SOCKET_ERROR is returned, and a specific error code
          may be retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINVAL           how is not valid.


                                                           shutdown 71

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAENOTCONN         The socket is not connected (SOCK_STREAM
                              only).

          WSAENOTSOCK         The descriptor is not a socket.

See Also  connect(), socket().


72 socket

4.1.23 socket()
Description    Create a socket.

          #include <winsock.h>

          SOCKET PASCAL FAR socket ( int af, int type, int protocol );


          af        An address format specification.  The only format
                    currently supported is PF_INET, which is the ARPA
                    Internet address format.

          type      A type specification for the new socket.

          protocol  A particular protocol to be used with the socket,
                    or 0 if the caller does not wish to specify a
                    protocol.

Remarks   socket() allocates a socket descriptor of the specified
          address family, data type and protocol, as well as related
          resources.  If a protocol is not specified (i.e. equal to
          0), the default for the specified connection mode is used.

          Only a single protocol exists to support a particular socket
          type using a given address format.  However, the address
          family may be given as AF_UNSPEC (unspecified), in which
          case the protocol parameter must be specified.  The protocol
          number to use is particular to the "communication domain''
          in which communication is to take place.

          The following type specifications are supported:

               Type           Explanation
               SOCK_STREAM    Provides sequenced, reliable, two-way,
                              connection-based byte streams with an
                              out-of-band data transmission mechanism.
                              Uses TCP for the Internet address
                              family.

               SOCK_DGRAM     Supports datagrams, which are
                              connectionless, unreliable buffers of a
                              fixed (typically small) maximum length.
                              Uses UDP for the Internet address
                              family.


          Sockets of type SOCK_STREAM are full-duplex byte streams.  A
          stream socket must be in a connected state before any data
          may be sent or received on it.  A connection to another
          socket is created with a connect() call.  Once connected,
          data may be transferred using send() and recv() calls.  When
          a session has been completed, a closesocket() must be
          performed.  Out-of-band data may also be transmitted as
          described in send() and received as described in recv().

          The communications protocols used to implement a SOCK_STREAM
          ensure that data is not lost or duplicated.  If data for


                                                             socket 73

          which the peer protocol has buffer space cannot be
          successfully transmitted within a reasonable length of time,
          the connection is considered broken and subsequent calls
          will fail with the error code set to WSAETIMEDOUT.

          SOCK_DGRAM sockets allow sending and receiving of datagrams
          to and from arbitrary peers using sendto() and recvfrom().
          If such a socket is connect()ed to a specific peer,
          datagrams may be send to that peer send() and may be
          received from (only) this peer using recv().


Return Value   If no error occurs, socket() returns a descriptor
          referencing the new socket.  Otherwise, a value of
          INVALID_SOCKET is returned, and a specific error code may be
          retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEAFNOSUPPORT     The specified address family is not
                              supported.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEMFILE           No more file descriptors are available.

          WSAENOBUFS          No buffer space is available.  The
                              socket cannot be created.

          WSAEPROTONOSUPPORT  The specified protocol is not supported.

          WSAEPROTOTYPE       The specified protocol is the wrong type
                              for this socket.

          WSAESOCKTNOSUPPORT  The specified socket type is not
                              supported in this address family.

See Also  accept(), bind(), connect(), getsockname(), getsockopt(),
          setsockopt(), listen(), recv(), recvfrom(), select(),
          send(), sendto(), shutdown(), ioctlsocket().


74 gethostbyaddr


4.2 Database Routines
4.2.1 gethostbyaddr()
Description    Get host information corresponding to an address.

          #include <winsock.h>

          struct hostent FAR * PASCAL FAR gethostbyaddr ( const char
          FAR * addr, int len,  int type );


          addr      A pointer to an address in network byte order.

          len       The length of the address, which must be 4 for
                    PF_INET addresses.

          type      The type of the address, which must be PF_INET.

Remarks   gethostbyaddr() returns a pointer to the following structure
          which contains the name(s) and address which correspond to
          the given address.

          struct hostent {
               char FAR *     h_name;
               char FAR * FAR *    h_aliases;
               short     h_addrtype;
               short     h_length;
               char FAR * FAR *    h_addr_list;
          };

          The members of this structure are:
          Element   Usage
          h_name    Official name of the host (PC).
          h_aliases A NULL-terminated array of alternate names.
          h_addrtype     The type of address being returned; for
                    Windows Sockets this is always PF_INET.
          h_length  The length, in bytes, of each address; for
                    PF_INET, this is always 4.
          h_addr_list    A NULL-terminated list of addresses for the
                    host.  Addresses are returned in network byte
                    order.

          The macro h_addr is defined to be h_addr_list[0] for
          compatibility with older software.

          The pointer which is returned points to a structure which is
          allocated by the Windows Sockets implementation.  The
          application must never attempt to modify this structure or
          to free any of its components.  Furthermore, only one copy
          of this structure is allocated per thread, and so the
          application should copy any information which it needs
          before issuing any other Windows Sockets API calls.


Return Value   If no error occurs, gethostbyaddr() returns a pointer
          to the hostent structure described above.  Otherwise it


                                                      gethostbyaddr 75

          returns a NULL pointer and a specific error number may be
          retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAHOST_NOT_FOUND   Authoritative Answer Host not found.

          WSATRY_AGAIN        Non-Authoritative Host not found, or
                              SERVERFAIL.

          WSANO_RECOVERY      Non recoverable errors, FORMERR,
                              REFUSED, NOTIMP.

          WSANO_DATA          Valid name, no data record of requested
                              type.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().

See Also  WSAAsyncGetHostByAddr(), gethostbyname(),


76 gethostbyname

4.2.2 gethostbyname()
Description    Get host information corresponding to a hostname.

          #include <winsock.h>

          struct hostent FAR * PASCAL FAR gethostbyname ( const char
          FAR * name );


          name      A pointer to the name of the host.

Remarks   gethostbyname() returns a pointer to a hostent structure as
          described under gethostbyaddr().  The contents of this
          structure correspond to the hostname name.

          The pointer which is returned points to a structure which is
          allocated by the Windows Sockets implementation.  The
          application must never attempt to modify this structure or
          to free any of its components.  Furthermore, only one copy
          of this structure is allocated per thread, and so the
          application should copy any information which it needs
          before issuing any other Windows Sockets API calls.

          A gethostbyname() implementation must not resolve IP address
          strings passed to it.  Such a request should be treated
          exactly as if an unknown host name were passed.  An
          application with an IP address string to resolve should use
          inet_addr() to convert the string to an IP address, then
          gethostbyaddr() to obtain the hostent structure.


Return Value   If no error occurs, gethostbyname() returns a pointer
          to the hostent structure described above.  Otherwise it
          returns a NULL pointer and a specific error number may be
          retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAHOST_NOT_FOUND   Authoritative Answer Host not found.

          WSATRY_AGAIN        Non-Authoritative Host not found, or
                              SERVERFAIL.

          WSANO_RECOVERY      Non recoverable errors, FORMERR,
                              REFUSED, NOTIMP.

          WSANO_DATA          Valid name, no data record of requested
                              type.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.


                                                        gethostname 77


          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().


See Also  WSAAsyncGetHostByName(), gethostbyaddr()


78 gethostbyname


4.2.3 gethostname()
Description    Return the standard host name for the local machine.

          #include <winsock.h>

          int PASCAL FAR gethostname ( char FAR * name, int namelen );

          name      A pointer to a buffer that will receive the host
                    name.

          namelen   The length of the buffer.

Remarks   This routine returns the name of the local host into the
          buffer specified by the name parameter.  The host name is
          returned as a null-terminated string.  The form of the host
          name is dependent on the Windows Sockets implementation--it
          may be a simple host name, or it may be a fully qualified
          domain name.  However, it is guaranteed that the name
          returned will be successfully parsed by gethostbyname() and
          WSAAsyncGetHostByName().

Return Value   If no error occurs, gethostname() returns 0, otherwise
          it returns SOCKET_ERROR and a specific error code may be
          retrieved by calling WSAGetLastError().

Error Codes                   WSAEFAULT The namelen parameter is too
                              small

          WSANOTINITIALISED   A successful WSAStartup() must occur
                              before using this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

See Also  gethostbyname(), WSAAsyncGetHostByName().


                                                     getprotobyname 79

4.2.4 getprotobyname()
Description    Get protocol information corresponding to a protocol
          name.

          #include <winsock.h>

          struct protoent FAR * PASCAL FAR getprotobyname ( const char
          FAR * name );


          name      A pointer to a protocol name.

Remarks   getprotobyname() returns a pointer to the following
          structure which contains the name(s) and protocol number
          which correspond to the given protocol name.

          struct protoent {
               char FAR *     p_name;
               char FAR * FAR *    p_aliases;
               short     p_proto;
          };

          The members of this structure are:
          Element   Usage
          p_name    Official name of the protocol.
          p_aliases A NULL-terminated array of alternate names.
          p_proto   The protocol number, in host byte order.

          The pointer which is returned points to a structure which is
          allocated by the Windows Sockets library.  The application
          must never attempt to modify this structure or to free any
          of its components.  Furthermore only one copy of this
          structure is allocated per thread, and so the application
          should copy any information which it needs before issuing
          any other Windows Sockets API calls.


Return Value   If no error occurs, getprotobyname() returns a pointer
          to the protoent structure described above.  Otherwise it
          returns a NULL pointer and a specific error number may be
          retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSANO_RECOVERY      Non recoverable errors, FORMERR,
                              REFUSED, NOTIMP.

          WSANO_DATA          Valid name, no data record of requested
                              type.


80 getprotobyname

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().


See Also  WSAAsyncGetProtoByName(), getprotobynumber()


                                                   getprotobynumber 81

4.2.5 getprotobynumber()
Description    Get protocol information corresponding to a protocol
          number.

          #include <winsock.h>

          struct protoent FAR * PASCAL FAR getprotobynumber ( int
          number );


          number    A protocol number, in host byte order.

Remarks   This function returns a pointer to a protoent structure as
          described above in getprotobyname().  The contents of the
          structure correspond to the given protocol number.

          The pointer which is returned points to a structure which is
          allocated by the Windows Sockets implementation.  The
          application must never attempt to modify this structure or
          to free any of its components.  Furthermore, only one copy
          of this structure is allocated per thread, and so the
          application should copy any information which it needs
          before issuing any other Windows Sockets API calls.


Return Value   If no error occurs, getprotobynumber() returns a
          pointer to the protoent structure described above.
          Otherwise it returns a NULL pointer and a specific error
          number may be retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSANO_RECOVERY      Non recoverable errors, FORMERR,
                              REFUSED, NOTIMP.

          WSANO_DATA          Valid name, no data record of requested
                              type.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().

See Also  WSAAsyncGetProtoByNumber(), getprotobyname()


82 getservbyname

4.2.6 getservbyname()
Description    Get service information corresponding to a service name
          and protocol.

          #include <winsock.h>

          struct servent FAR * PASCAL FAR getservbyname ( const char
          FAR * name,
          const char FAR * proto );


          name      A pointer to a service name.

          proto     An optional pointer to a protocol name.  If this
                    is NULL, getservbyname() returns the first service
                    entry for which the name matches the s_name or one
                    of the s_aliases.  Otherwise getservbyname()
                    matches both the name and the proto.

Remarks   getservbyname() returns a pointer to the following structure
          which contains the name(s) and service number which
          correspond to the given service name.

          struct servent {
               char FAR *     s_name;
               char FAR * FAR *    s_aliases;
               short     s_port;
               char FAR *     s_proto;
          };

          The members of this structure are:
          Element   Usage
          s_name    Official name of the service.
          s_aliases A NULL-terminated array of alternate names.
          s_port    The port number at which the service may be
                    contacted.  Port numbers are returned in network
                    byte order.
          s_proto   The name of the protocol to use when contacting
                    the service.

          The pointer which is returned points to a structure which is
          allocated by the Windows Sockets library.  The application
          must never attempt to modify this structure or to free any
          of its components.  Furthermore only one copy of this
          structure is allocated per thread, and so the application
          should copy any information which it needs before issuing
          any other Windows Sockets API calls.


Return Value   If no error occurs, getservbyname() returns a pointer
          to the servent structure described above.  Otherwise it
          returns a NULL pointer and a specific error number may be
          retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.


                                                      getservbyname 83


          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSANO_RECOVERY      Non recoverable errors, FORMERR,
                              REFUSED, NOTIMP.

          WSANO_DATA          Valid name, no data record of requested
                              type.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().


See Also  WSAAsyncGetServByName(), getservbyport()


84 getservbyport

4.2.7 getservbyport()
Description    Get service information corresponding to a port and
          protocol.

          #include <winsock.h>

          struct servent FAR * PASCAL FAR getservbyport ( int port,
          const char FAR * proto );


          port      The port for a service, in network byte order.

          proto     An optional pointer to a protocol name.  If this
                    is NULL, getservbyport() returns the first service
                    entry for which the port matches the s_port.
                    Otherwise getservbyport() matches both the port
                    and the proto.

Remarks   getservbyport() returns a pointer a servent structure as
          described above for getservbyname().

          The pointer which is returned points to a structure which is
          allocated by the Windows Sockets implementation.  The
          application must never attempt to modify this structure or
          to free any of its components.  Furthermore, only one copy
          of this structure is allocated per thread, and so the
          application should copy any information which it needs
          before issuing any other Windows Sockets API calls.


Return Value   If no error occurs, getservbyport() returns a pointer
          to the servent structure described above.  Otherwise it
          returns a NULL pointer and a specific error number may be
          retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSANO_RECOVERY      Non recoverable errors, FORMERR,
                              REFUSED, NOTIMP.

          WSANO_DATA          Valid name, no data record of requested
                              type.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEINTR            The (blocking) call was canceled via
                              WSACancelBlockingCall().


See Also  WSAAsyncGetServByPort(), getservbyname()


                                              WSAAsyncGetHostByAddr 85


4.3 Microsoft Windows-specific Extensions
4.3.1 WSAAsyncGetHostByAddr()
Description    Get host information corresponding to an address -
          asynchronous version.

          #include <winsock.h>

          HANDLE PASCAL FAR WSAAsyncGetHostByAddr ( HWND hWnd,
          unsigned int wMsg,  const char FAR * addr, int len, int
          type, char FAR * buf, int buflen );


          hWnd      The handle of the window which should receive a
                    message when the asynchronous request completes.

          wMsg      The message to be received when the asynchronous
                    request completes.

          addr      A pointer to the network address for the host.
                    Host addresses are stored in network byte order.

          len       The length of the address, which must be 4 for
                    PF_INET.

          type      The type of the address, which must be PF_INET.

          buf       A pointer to the data area to receive the hostent
                    data.  Note that this must be larger than the size
                    of a hostent structure.  This is because the data
                    area supplied is used by the Windows Sockets
                    implementation to contain not only a hostent
                    structure but any and all of the data which is
                    referenced by members of the hostent structure.
                    It is recommended that you supply a buffer of
                    MAXGETHOSTSTRUCT bytes.

          buflen    The size of data area buf above.

Remarks   This function is an asynchronous version of gethostbyaddr(),
          and is used to retrieve host name and address information
          corresponding to a network address.  The Windows Sockets
          implementation initiates the operation and returns to the
          caller immediately, passing back an asynchronous task handle
          which the application may use to identify the operation.
          When the operation is completed, the results (if any) are
          copied into the buffer provided by the caller and a message
          is sent to the application's window.

          When the asynchronous operation is complete the
          application's window hWnd receives message wMsg.  The wParam
          argument contains the asynchronous task handle as returned
          by the original function call.  The high 16 bits of lParam
          contain any error code.  The error code may be any error as
          defined in winsock.h.  An error code of zero indicates
          successful completion of the asynchronous operation.  On
          successful completion, the buffer supplied to the original


86 WSAAsyncGetHostByAddr

          function call contains a hostent structure.  To access the
          elements of this structure, the original buffer address
          should be cast to a hostent structure pointer and accessed
          as appropriate.

          Note that if the error code is WSAENOBUFS, it indicates that
          the size of the buffer specified by buflen in the original
          call was too small to contain all the resultant information.
          In this case, the low 16 bits of lParam contain the size of
          buffer required to supply ALL the requisite information.  If
          the application decides that the partial data is inadequate,
          it may reissue the WSAAsyncGetHostByAddr() function call
          with a buffer large enough to receive all the desired
          information (i.e.  no smaller than the low 16 bits of
          lParam).

          The error code and buffer length should be extracted from
          the lParam using the macros  WSAGETASYNCERROR and
          WSAGETASYNCBUFLEN, defined in winsock.h as:

          #define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
          #define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)

          The use of these macros will maximize the portability of the
          source code for the application.

Return Value   The return value specifies whether or not the
          asynchronous operation was successfully initiated.  Note
          that it does not imply success or failure of the operation
          itself.

          If the operation was successfully initiated,
          WSAAsyncGetHostByAddr() returns a nonzero value of type
          HANDLE which is the asynchronous task handle for the
          request.  This value can be used in two ways.  It can be
          used to cancel the operation using WSACancelAsyncRequest().
          It can also be used to match up asynchronous operations and
          completion messages, by examining the wParam message
          argument.

          If the asynchronous operation could not be initiated,
          WSAAsyncGetHostByAddr() returns a zero value, and a specific
          error number may be retrieved by calling WSAGetLastError().

Comments  The buffer supplied to this function is used by the Windows
          Sockets implementation to construct a hostent structure
          together with the contents of data areas referenced by
          members of the same hostent structure.  To avoid the
          WSAENOBUFS error noted above, the application should provide
          a buffer of at least MAXGETHOSTSTRUCT bytes (as defined in
          winsock.h).

Notes For
Windows Sockets
Suppliers It is the responsibility of the Windows Sockets
          implementation to ensure that messages are successfully
          posted to the application.  If a PostMessage() operation


                                              WSAAsyncGetHostByAddr 87

          fails, the Windows Sockets implementation must re-post that
          message as long as the window exists.

          Windows Sockets suppliers should use the WSAMAKEASYNCREPLY
          macro when constructing the lParam in the message.

Error Codes    The following error codes may be set when an
          application window receives a message.  As described above,
          they may be extracted from the lParam in the reply message
          using the WSAGETASYNCERROR macro.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAENOBUFS          No/insufficient buffer space is
                              available

          WSAHOST_NOT_FOUND   Authoritative Answer Host not found.

          WSATRY_AGAIN        Non-Authoritative Host not found, or
                              SERVERFAIL.

          WSANO_RECOVERY      Non recoverable errors, FORMERR,
                              REFUSED, NOTIMP.

          WSANO_DATA          Valid name, no data record of requested
                              type.

          The following errors may occur at the time of the function
          call, and indicate that the asynchronous operation could not
          be initiated.

          WSANOTINITIALISED   A successful WSAStartup() must occur
                              before using this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEWOULDBLOCK      The asynchronous operation cannot be
                              scheduled at this time due to resource
                              or other constraints within the Windows
                              Sockets implementation.

See Also  gethostbyaddr(), WSACancelAsyncRequest()


88 WSAAsyncGetHostByName

4.3.2 WSAAsyncGetHostByName()
Description    Get host information corresponding to a hostname -
          asynchronous version.

          #include <winsock.h>

          HANDLE PASCAL FAR WSAAsyncGetHostByName ( HWND hWnd,
          unsigned int wMsg,  const char FAR * name, char FAR * buf,
          int buflen );


          hWnd      The handle of the window which should receive a
                    message when the asynchronous request completes.

          wMsg      The message to be received when the asynchronous
                    request completes.

          name      A pointer to the name of the host.

          buf       A pointer to the data area to receive the hostent
                    data.  Note that this must be larger than the size
                    of a hostent structure.  This is because the data
                    area supplied is used by the Windows Sockets
                    implementation to contain not only a hostent
                    structure but any and all of the data which is
                    referenced by members of the hostent structure.
                    It is recommended that you supply a buffer of
                    MAXGETHOSTSTRUCT bytes.

          buflen    The size of data area buf above.

Remarks   This function is an asynchronous version of gethostbyname(),
          and is used to retrieve host name and address information
          corresponding to a hostname.  The Windows Sockets
          implementation initiates the operation and returns to the
          caller immediately, passing back an asynchronous task handle
          which the application may use to identify the operation.
          When the operation is completed, the results (if any) are
          copied into the buffer provided by the caller and a message
          is sent to the application's window.

          When the asynchronous operation is complete the
          application's window hWnd receives message wMsg.  The wParam
          argument contains the asynchronous task handle as returned
          by the original function call.  The high 16 bits of lParam
          contain any error code.  The error code may be any error as
          defined in winsock.h.  An error code of zero indicates
          successful completion of the asynchronous operation.  On
          successful completion, the buffer supplied to the original
          function call contains a hostent structure.  To access the
          elements of this structure, the original buffer address
          should be cast to a hostent structure pointer and accessed
          as appropriate.

          Note that if the error code is WSAENOBUFS, it indicates that
          the size of the buffer specified by buflen in the original
          call was too small to contain all the resultant information.


                                              WSAAsyncGetHostByName 89

          In this case, the low 16 bits of lParam contain the size of
          buffer required to supply ALL the requisite information.  If
          the application decides that the partial data is inadequate,
          it may reissue the WSAAsyncGetHostByName() function call
          with a buffer large enough to receive all the desired
          information (i.e. no smaller than the low 16 bits of
          lParam).

          The error code and buffer length should be extracted from
          the lParam using the macros  WSAGETASYNCERROR and
          WSAGETASYNCBUFLEN, defined in winsock.h as:

          #define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
          #define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)

          The use of these macros will maximize the portability of the
          source code for the application.


Return Value   The return value specifies whether or not the
          asynchronous operation was successfully initiated.  Note
          that it does not imply success or failure of the operation
          itself.

          If the operation was successfully initiated,
          WSAAsyncGetHostByName() returns a nonzero value of type
          HANDLE which is the asynchronous task handle for the
          request.  This value can be used in two ways.  It can be
          used to cancel the operation using WSACancelAsyncRequest().
          It can also be used to match up asynchronous operations and
          completion messages, by examining the wParam message
          argument.

          If the asynchronous operation could not be initiated,
          WSAAsyncGetHostByName() returns a zero value, and a specific
          error number may be retrieved by calling WSAGetLastError().

Comments  The buffer supplied to this function is used by the Windows
          Sockets implementation to construct a hostent structure
          together with the contents of data areas referenced by
          members of the same hostent structure.  To avoid the
          WSAENOBUFS error noted above, the application should provide
          a buffer of at least MAXGETHOSTSTRUCT bytes (as defined in
          winsock.h).

Notes For
Windows Sockets
Suppliers It is the responsibility of the Windows Sockets
          implementation to ensure that messages are successfully
          posted to the application.  If a PostMessage() operation
          fails, the Windows Sockets implementation must re-post that
          message as long as the window exists.

          Windows Sockets suppliers should use the WSAMAKEASYNCREPLY
          macro when constructing the lParam in the message.


90 WSAAsyncGetHostByName

Error Codes    The following error codes may be set when an
          application window receives a message.  As described above,
          they may be extracted from the lParam in the reply message
          using the WSAGETASYNCERROR macro.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAENOBUFS          No/insufficient buffer space is
                              available

          WSAHOST_NOT_FOUND   Authoritative Answer Host not found.

          WSATRY_AGAIN        Non-Authoritative Host not found, or
                              SERVERFAIL.

          WSANO_RECOVERY      Non recoverable errors, FORMERR,
                              REFUSED, NOTIMP.

          WSANO_DATA          Valid name, no data record of requested
                              type.

          The following errors may occur at the time of the function
          call, and indicate that the asynchronous operation could not
          be initiated.

          WSANOTINITIALISED   A successful WSAStartup() must occur
                              before using this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEWOULDBLOCK      The asynchronous operation cannot be
                              scheduled at this time due to resource
                              or other constraints within the Windows
                              Sockets implementation.

See Also  gethostbyname(), WSACancelAsyncRequest()


                                             WSAAsyncGetProtoByName 91

4.3.3 WSAAsyncGetProtoByName()
Description    Get protocol information corresponding to a protocol
          name - asynchronous version.

          #include <winsock.h>

          HANDLE PASCAL FAR WSAAsyncGetProtoByName ( HWND hWnd,
          unsigned int wMsg,  const char FAR * name, char FAR * buf,
          int buflen );


          hWnd      The handle of the window which should receive a
                    message when the asynchronous request completes.

          wMsg      The message to be received when the asynchronous
                    request completes.

          name      A pointer to the protocol name to be resolved.

          buf       A pointer to the data area to receive the protoent
                    data.  Note that this must be larger than the size
                    of a protoent structure.  This is because the data
                    area supplied is used by the Windows Sockets
                    implementation to contain not only a protoent
                    structure but any and all of the data which is
                    referenced by members of the protoent structure.
                    It is recommended that you supply a buffer of
                    MAXGETHOSTSTRUCT bytes.

          buflen    The size of data area buf above.

Remarks   This function is an asynchronous version of
          getprotobyname(), and is used to retrieve the protocol name
          and number corresponding to a protocol name.  The Windows
          Sockets implementation initiates the operation and returns
          to the caller immediately, passing back an asynchronous task
          handle which the application may use to identify the
          operation.  When the operation is completed, the results (if
          any) are copied into the buffer provided by the caller and a
          message is sent to the application's window.

          When the asynchronous operation is complete the
          application's window hWnd receives message wMsg.  The wParam
          argument contains the asynchronous task handle as returned
          by the original function call.  The high 16 bits of lParam
          contain any error code.  The error code may be any error as
          defined in winsock.h.  An error code of zero indicates
          successful completion of the asynchronous operation.  On
          successful completion, the buffer supplied to the original
          function call contains a protoent structure.  To access the
          elements of this structure, the original buffer address
          should be cast to a protoent structure pointer and accessed
          as appropriate.

          Note that if the error code is WSAENOBUFS, it indicates that
          the size of the buffer specified by buflen in the original
          call was too small to contain all the resultant information.


92 WSAAsyncGetProtoByName

          In this case, the low 16 bits of lParam contain the size of
          buffer required to supply ALL the requisite information.  If
          the application decides that the partial data is inadequate,
          it may reissue the WSAAsyncGetProtoByName() function call
          with a buffer large enough to receive all the desired
          information (i.e.  no smaller than the low 16 bits of
          lParam).

          The error code and buffer length should be extracted from
          the lParam using the macros  WSAGETASYNCERROR and
          WSAGETASYNCBUFLEN, defined in winsock.h as:

          #define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
          #define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)

          The use of these macros will maximize the portability of the
          source code for the application.


Return Value   The return value specifies whether or not the
          asynchronous operation was successfully initiated.  Note
          that it does not imply success or failure of the operation
          itself.

          If the operation was successfully initiated,
          WSAAsyncGetProtoByName() returns a nonzero value of type
          HANDLE which is the asynchronous task handle for the
          request.  This value can be used in two ways.  It can be
          used to cancel the operation using WSACancelAsyncRequest().
          It can also be used to match up asynchronous operations and
          completion messages, by examining the wParam message
          argument.

          If the asynchronous operation could not be initiated,
          WSAAsyncGetProtoByName() returns a zero value, and a
          specific error number may be retrieved by calling
          WSAGetLastError().

Comments  The buffer supplied to this function is used by the Windows
          Sockets implementation to construct a protoent structure
          together with the contents of data areas referenced by
          members of the same protoent structure.  To avoid the
          WSAENOBUFS error noted above, the application should provide
          a buffer of at least MAXGETHOSTSTRUCT bytes (as defined in
          winsock.h).

Notes For
Windows Sockets
Suppliers It is the responsibility of the Windows Sockets
          implementation to ensure that messages are successfully
          posted to the application.  If a PostMessage() operation
          fails, the Windows Sockets implementation must re-post that
          message as long as the window exists.

          Windows Sockets suppliers should use the WSAMAKEASYNCREPLY
          macro when constructing the lParam in the message.


                                             WSAAsyncGetProtoByName 93

Error Codes    The following error codes may be set when an
          application window receives a message.  As described above,
          they may be extracted from the lParam in the reply message
          using the WSAGETASYNCERROR macro.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAENOBUFS          No/insufficient buffer space is
                              available

          WSAHOST_NOT_FOUND   Authoritative Answer Host not found.

          WSATRY_AGAIN        Non-Authoritative Host not found, or
                              SERVERFAIL.

          WSANO_RECOVERY      Non recoverable errors, FORMERR,
                              REFUSED, NOTIMP.

          WSANO_DATA          Valid name, no data record of requested
                              type.

          The following errors may occur at the time of the function
          call, and indicate that the asynchronous operation could not
          be initiated.

          WSANOTINITIALISED   A successful WSAStartup() must occur
                              before using this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEWOULDBLOCK      The asynchronous operation cannot be
                              scheduled at this time due to resource
                              or other constraints within the Windows
                              Sockets implementation.

See Also  getprotobyname(), WSACancelAsyncRequest()


94 WSAAsyncGetProtoByNumber

4.3.4 WSAAsyncGetProtoByNumber()
Description    Get protocol information corresponding to a protocol
          number - asynchronous version.

          #include <winsock.h>

          HANDLE PASCAL FAR WSAAsyncGetProtoByNumber ( HWND hWnd,
          unsigned int wMsg,  int number, char FAR * buf, int buflen
          );


          hWnd      The handle of the window which should receive a
                    message when the asynchronous request completes.

          wMsg      The message to be received when the asynchronous
                    request completes.

          number    The protocol number to be resolved, in host byte
                    order.

          buf       A pointer to the data area to receive the protoent
                    data.  Note that this must be larger than the size
                    of a protoent structure.  This is because the data
                    area supplied is used by the Windows Sockets
                    implementation to contain not only a protoent
                    structure but any and all of the data which is
                    referenced by members of the protoent structure.
                    It is recommended that you supply a buffer of
                    MAXGETHOSTSTRUCT bytes.

          buflen    The size of data area buf above.

Remarks   This function is an asynchronous version of
          getprotobynumber(), and is used to retrieve the protocol
          name and number corresponding to a protocol number.  The
          Windows Sockets implementation initiates the operation and
          returns to the caller immediately, passing back an
          asynchronous task handle which the application may use to
          identify the operation.  When the operation is completed,
          the results (if any) are copied into the buffer provided by
          the caller and a message is sent to the application's
          window.

          When the asynchronous operation is complete the
          application's window hWnd receives message wMsg.  The wParam
          argument contains the asynchronous task handle as returned
          by the original function call.  The high 16 bits of lParam
          contain any error code.  The error code may be any error as
          defined in winsock.h.  An error code of zero indicates
          successful completion of the asynchronous operation.  On
          successful completion, the buffer supplied to the original
          function call contains a protoent structure.  To access the
          elements of this structure, the original buffer address
          should be cast to a protoent structure pointer and accessed
          as appropriate.


                                           WSAAsyncGetProtoByNumber 95

          Note that if the error code is WSAENOBUFS, it indicates that
          the size of the buffer specified by buflen in the original
          call was too small to contain all the resultant information.
          In this case, the low 16 bits of lParam contain the size of
          buffer required to supply ALL the requisite information.  If
          the application decides that the partial data is inadequate,
          it may reissue the WSAAsyncGetProtoByNumber() function call
          with a buffer large enough to receive all the desired
          information (i.e. no smaller than the low 16 bits of
          lParam).

          The error code and buffer length should be extracted from
          the lParam using the macros  WSAGETASYNCERROR and
          WSAGETASYNCBUFLEN, defined in winsock.h as:

          #define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
          #define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)

          The use of these macros will maximize the portability of the
          source code for the application.


Return Value   The return value specifies whether or not the
          asynchronous operation was successfully initiated.  Note
          that it does not imply success or failure of the operation
          itself.

          If the operation was successfully initiated,
          WSAAsyncGetProtoByNumber() returns a nonzero value of type
          HANDLE which is the asynchronous task handle for the
          request.  This value can be used in two ways.  It can be
          used to cancel the operation using WSACancelAsyncRequest().
          It can also be used to match up asynchronous operations and
          completion messages, by examining the wParam message
          argument.

          If the asynchronous operation could not be initiated,
          WSAAsyncGetProtoByNumber() returns a zero value, and a
          specific error number may be retrieved by calling
          WSAGetLastError().

Comments  The buffer supplied to this function is used by the Windows
          Sockets implementation to construct a protoent structure
          together with the contents of data areas referenced by
          members of the same protoent structure.  To avoid the
          WSAENOBUFS error noted above, the application should provide
          a buffer of at least MAXGETHOSTSTRUCT bytes (as defined in
          winsock.h).

Notes For
Windows Sockets
Suppliers It is the responsibility of the Windows Sockets
          implementation to ensure that messages are successfully
          posted to the application.  If a PostMessage() operation
          fails, the Windows Sockets implementation must re-post that
          message as long as the window exists.


96 WSAAsyncGetProtoByNumber

          Windows Sockets suppliers should use the WSAMAKEASYNCREPLY
          macro when constructing the lParam in the message.

Error Codes    The following error codes may be set when an
          application window receives a message.  As described above,
          they may be extracted from the lParam in the reply message
          using the WSAGETASYNCERROR macro.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAENOBUFS          No/insufficient buffer space is
                              available

          WSAHOST_NOT_FOUND   Authoritative Answer Host not found.

          WSATRY_AGAIN        Non-Authoritative Host not found, or
                              SERVERFAIL.

          WSANO_RECOVERY      Non recoverable errors, FORMERR,
                              REFUSED, NOTIMP.

          WSANO_DATA          Valid name, no data record of requested
                              type.

          The following errors may occur at the time of the function
          call, and indicate that the asynchronous operation could not
          be initiated.

          WSANOTINITIALISED   A successful WSAStartup() must occur
                              before using this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEWOULDBLOCK      The asynchronous operation cannot be
                              scheduled at this time due to resource
                              or other constraints within the Windows
                              Sockets implementation.
See Also  getprotobynumber(), WSACancelAsyncRequest()


                                              WSAAsyncGetServByName 97

4.3.5 WSAAsyncGetServByName()
Description    Get service information corresponding to a service name
          and port - asynchronous version.

          #include <winsock.h>

          HANDLE PASCAL FAR WSAAsyncGetServByName ( HWND hWnd,
          unsigned int wMsg,  const char FAR * name, const char FAR *
          proto, char FAR * buf,  int buflen );


          hWnd      The handle of the window which should receive a
                    message when the asynchronous request completes.

          wMsg      The message to be received when the asynchronous
                    request completes.

          name      A pointer to a service name.

          proto     A pointer to a protocol name.  This may be NULL,
                    in which case WSAAsyncGetServByName() will search
                    for the first service entry for which s_name or
                    one of the s_aliases matches the given name.
                    Otherwise WSAAsyncGetServByName() matches both
                    name and proto.

          buf       A pointer to the data area to receive the servent
                    data.  Note that this must be larger than the size
                    of a servent structure.  This is because the data
                    area supplied is used by the Windows Sockets
                    implementation to contain not only a servent
                    structure but any and all of the data which is
                    referenced by members of the servent structure.
                    It is recommended that you supply a buffer of
                    MAXGETHOSTSTRUCT bytes.

          buflen    The size of data area buf above.

Remarks   This function is an asynchronous version of getservbyname(),
          and is used to retrieve service information corresponding to
          a service name.  The Windows Sockets implementation
          initiates the operation and returns to the caller
          immediately, passing back an asynchronous task handle which
          the application may use to identify the operation.  When the
          operation is completed, the results (if any) are copied into
          the buffer provided by the caller and a message is sent to
          the application's window.

          When the asynchronous operation is complete the
          application's window hWnd receives message wMsg.  The wParam
          argument contains the asynchronous task handle as returned
          by the original function call.  The high 16 bits of lParam
          contain any error code.  The error code may be any error as
          defined in winsock.h.  An error code of zero indicates
          successful completion of the asynchronous operation.  On
          successful completion, the buffer supplied to the original
          function call contains a hostent structure.  To access the


98 WSAAsyncGetServByName

          elements of this structure, the original buffer address
          should be cast to a hostent structure pointer and accessed
          as appropriate.

          Note that if the error code is WSAENOBUFS, it indicates that
          the size of the buffer specified by buflen in the original
          call was too small to contain all the resultant information.
          In this case, the low 16 bits of lParam contain the size of
          buffer required to supply ALL the requisite information.  If
          the application decides that the partial data is inadequate,
          it may reissue the WSAAsyncGetServByName() function call
          with a buffer large enough to receive all the desired
          information (i.e. no smaller than the low 16 bits of
          lParam).

          The error code and buffer length should be extracted from
          the lParam using the macros  WSAGETASYNCERROR and
          WSAGETASYNCBUFLEN, defined in winsock.h as:

          #define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
          #define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)

          The use of these macros will maximize the portability of the
          source code for the application.


Return Value   The return value specifies whether or not the
          asynchronous operation was successfully initiated.  Note
          that it does not imply success or failure of the operation
          itself.

          If the operation was successfully initiated,
          WSAAsyncGetServByName() returns a nonzero value of type
          HANDLE which is the asynchronous task handle for the
          request.  This value can be used in two ways.  It can be
          used to cancel the operation using WSACancelAsyncRequest().
          It can also be used to match up asynchronous operations and
          completion messages, by examining the wParam message
          argument.

          If the asynchronous operation could not be initiated,
          WSAAsyncServByName() returns a zero value, and a specific
          error number may be retrieved by calling WSAGetLastError().

Comments  The buffer supplied to this function is used by the Windows
          Sockets implementation to construct a hostent structure
          together with the contents of data areas referenced by
          members of the same hostent structure.  To avoid the
          WSAENOBUFS error noted above, the application should provide
          a buffer of at least MAXGETHOSTSTRUCT bytes (as defined in
          winsock.h).

Notes For
Windows Sockets
Suppliers It is the responsibility of the Windows Sockets
          implementation to ensure that messages are successfully
          posted to the application.  If a PostMessage() operation


                                              WSAAsyncGetServByName 99

          fails, the Windows Sockets implementation must re-post that
          message as long as the window exists.

          Windows Sockets suppliers should use the WSAMAKEASYNCREPLY
          macro when constructing the lParam in the message.

Error Codes    The following error codes may be set when an
          application window receives a message.  As described above,
          they may be extracted from the lParam in the reply message
          using the WSAGETASYNCERROR macro.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAENOBUFS          No/insufficient buffer space is
                              available

          WSAHOST_NOT_FOUND   Authoritative Answer Host not found.

          WSATRY_AGAIN        Non-Authoritative Host not found, or
                              SERVERFAIL.

          WSANO_RECOVERY      Non recoverable errors, FORMERR,
                              REFUSED, NOTIMP.

          WSANO_DATA          Valid name, no data record of requested
                              type.

          The following errors may occur at the time of the function
          call, and indicate that the asynchronous operation could not
          be initiated.

          WSANOTINITIALISED   A successful WSAStartup() must occur
                              before using this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEWOULDBLOCK      The asynchronous operation cannot be
                              scheduled at this time due to resource
                              or other constraints within the Windows
                              Sockets implementation.

See Also  getservbyname(), WSACancelAsyncRequest()


100 WSAAsyncGetServByPort

4.3.6 WSAAsyncGetServByPort()
Description    Get service information corresponding to a port and
          protocol - asynchronous version.

          #include <winsock.h>

          HANDLE PASCAL FAR WSAAsyncGetServByPort ( HWND hWnd,
          unsigned int wMsg,  int port, const char FAR * proto, char
          FAR * buf, int buflen );


          hWnd      The handle of the window which should receive a
                    message when the asynchronous request completes.

          wMsg      The message to be received when the asynchronous
                    request completes.

          port      The port for the service, in network byte order.

          proto     A pointer to a protocol name.  This may be NULL,
                    in which case WSAAsyncGetServByPort() will search
                    for the first service entry for which s_port match
                    the given port.  Otherwise WSAAsyncGetServByPort()
                    matches both port and proto.

          buf       A pointer to the data area to receive the servent
                    data.  Note that this must be larger than the size
                    of a servent structure.  This is because the data
                    area supplied is used by the Windows Sockets
                    implementation to contain not only a servent
                    structure but any and all of the data which is
                    referenced by members of the servent structure.
                    It is recommended that you supply a buffer of
                    MAXGETHOSTSTRUCT bytes.

          buflen    The size of data area buf above.

Remarks   This function is an asynchronous version of getservbyport(),
          and is used to retrieve service information corresponding to
          a port number.  The Windows Sockets implementation initiates
          the operation and returns to the caller immediately, passing
          back an asynchronous task handle which the application may
          use to identify the operation.  When the operation is
          completed, the results (if any) are copied into the buffer
          provided by the caller and a message is sent to the
          application's window.

          When the asynchronous operation is complete the
          application's window hWnd receives message wMsg.  The wParam
          argument contains the asynchronous task handle as returned
          by the original function call.  The high 16 bits of lParam
          contain any error code.  The error code may be any error as
          defined in winsock.h.  An error code of zero indicates
          successful completion of the asynchronous operation.  On
          successful completion, the buffer supplied to the original
          function call contains a servent structure.  To access the
          elements of this structure, the original buffer address


                                             WSAAsyncGetServByPort 101

          should be cast to a servent structure pointer and accessed
          as appropriate.

          Note that if the error code is WSAENOBUFS, it indicates that
          the size of the buffer specified by buflen in the original
          call was too small to contain all the resultant information.
          In this case, the low 16 bits of lParam contain the size of
          buffer required to supply ALL the requisite information.  If
          the application decides that the partial data is inadequate,
          it may reissue the WSAAsyncGetServByPort() function call
          with a buffer large enough to receive all the desired
          information (i.e. no smaller than the low 16 bits of
          lParam).

          The error code and buffer length should be extracted from
          the lParam using the macros  WSAGETASYNCERROR and
          WSAGETASYNCBUFLEN, defined in winsock.h as:

          #define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
          #define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)

          The use of these macros will maximize the portability of the
          source code for the application.


Return Value   The return value specifies whether or not the
          asynchronous operation was successfully initiated.  Note
          that it does not imply success or failure of the operation
          itself.

          If the operation was successfully initiated,
          WSAAsyncGetServByPort() returns a nonzero value of type
          HANDLE which is the asynchronous task handle for the
          request.  This value can be used in two ways.  It can be
          used to cancel the operation using WSACancelAsyncRequest().
          It can also be used to match up asynchronous operations and
          completion messages, by examining the wParam message
          argument.

          If the asynchronous operation could not be initiated,
          WSAAsyncGetServByPort() returns a zero value, and a specific
          error number may be retrieved by calling WSAGetLastError().

Comments  The buffer supplied to this function is used by the Windows
          Sockets implementation to construct a servent structure
          together with the contents of data areas referenced by
          members of the same servent structure.  To avoid the
          WSAENOBUFS error noted above, the application should provide
          a buffer of at least MAXGETHOSTSTRUCT bytes (as defined in
          winsock.h).

Notes For
Windows Sockets
Suppliers It is the responsibility of the Windows Sockets
          implementation to ensure that messages are successfully
          posted to the application.  If a PostMessage() operation


102 WSAAsyncGetServByPort

          fails, the Windows Sockets implementation must re-post that
          message as long as the window exists.

          Windows Sockets suppliers should use the WSAMAKEASYNCREPLY
          macro when constructing the lParam in the message.

Error Codes    The following error codes may be set when an
          application window receives a message.  As described above,
          they may be extracted from the lParam in the reply message
          using the WSAGETASYNCERROR macro.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAENOBUFS          No/insufficient buffer space is
                              available

          WSAHOST_NOT_FOUND   Authoritative Answer Host not found.

          WSATRY_AGAIN        Non-Authoritative Host not found, or
                              SERVERFAIL.

          WSANO_RECOVERY      Non recoverable errors, FORMERR,
                              REFUSED, NOTIMP.

          WSANO_DATA          Valid name, no data record of requested
                              type.

          The following errors may occur at the time of the function
          call, and indicate that the asynchronous operation could not
          be initiated.

          WSANOTINITIALISED   A successful WSAStartup() must occur
                              before using this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEWOULDBLOCK      The asynchronous operation cannot be
                              scheduled at this time due to resource
                              or other constraints within the Windows
                              Sockets implementation.

See Also  getservbyport(), WSACancelAsyncRequest()


                                                    WSAAsyncSelect 103

4.3.7 WSAAsyncSelect()
Description    Request event notification for a socket.

          #include <winsock.h>

          int PASCAL FAR WSAAsyncSelect ( SOCKET s, HWND hWnd,
          unsigned int wMsg,  long lEvent );


          s         A descriptor identifying the socket for which
                    event notification is required.

          hWnd      A handle identifying the window which should
                    receive a message when a network event occurs.

          wMsg      The message to be received when a network event
                    occurs.

          lEvent    A bitmask which specifies a combination of network
                    events in which the application is interested.

Remarks   This function is used to request that the Windows Sockets
          DLL should send a message to the window hWnd whenever it
          detects any of the network events specified by the lEvent
          parameter.  The message which should be sent is specified by
          the wMsg parameter.  The socket for which notification is
          required is identified by s.

          This function automatically sets socket s to non-blocking
          mode.

          The lEvent parameter is constructed by or'ing any of the
          values specified in the following list.

               Value     Meaning
               FD_READ   Want to receive notification of readiness for
                         reading
               FD_WRITE  Want to receive notification of readiness for
                         writing
               FD_OOB    Want to receive notification of the arrival
                         of out-of-band data
               FD_ACCEPT Want to receive notification of incoming
                         connections
               FD_CONNECT     Want to receive notification of
                         completed connection
               FD_CLOSE  Want to receive notification of socket
                         closure

          Issuing a WSAAsyncSelect() for a socket cancels any previous
          WSAAsyncSelect() for the same socket.  For example, to
          receive notification for both reading and writing, the
          application must call WSAAsyncSelect() with both FD_READ and
          FD_WRITE, as follows:

          rc = WSAAsyncSelect(s, hWnd, wMsg, FD_READ|FD_WRITE);


104 WSAAsyncSelect

          It is not possible to specify different messages for
          different events.  The following code will not work; the
          second call will cancel the effects of the first, and only
          FD_WRITE events will be reported with message wMsg2:

          rc = WSAAsyncSelect(s, hWnd, wMsg1, FD_READ);
          rc = WSAAsyncSelect(s, hWnd, wMsg2, FD_WRITE);

          To cancel all notification  i.e., to indicate that the
          Windows Sockets implementation should send no further
          messages related to network events on the socket  lEvent
          should be set to zero.

          rc = WSAAsyncSelect(s, hWnd, 0, 0);

          Although in this instance WSAAsyncSelect() immediately
          disables event message posting for the socket, it is
          possible that messages may be waiting in the application's
          message queue.  The application must therefore be prepared
          to receive network event messages even after cancellation.
          Closing a socket with closesocket() also cancels
          WSAAsyncSelect() message sending, but the same caveat about
          messages in the queue prior to the closesocket() still
          applies.

          Since an accept()'ed socket has the same properties as the
          listening socket used to accept it, any WSAAsyncSelect()
          events set for the listening socket apply to the accepted
          socket.  For example, if a listening socket has
          WSAAsyncSelect() events FD_ACCEPT, FD_READ, and FD_WRITE,
          then any socket accepted on that listening socket will also
          have FD_ACCEPT, FD_READ, and FD_WRITE events with the same
          wMsg value used for messages.  If a different wMsg or events
          are desired, the application should call WSAAsyncSelect(),
          passing the accepted socket and the desired new
          information.7

          When one of the nominated network events occurs on the
          specified socket s, the application's window hWnd receives
          message wMsg.  The wParam argument identifies the socket on
          which a network event has occurred.  The low word of lParam
          specifies the network event that has occurred.  The high
          word of lParam contains any error code.  The error code be
          any error as defined in winsock.h.

          The error and event codes may be extracted from the lParam
          using the macros WSAGETSELECTERROR and WSAGETSELECTEVENT,
          defined in winsock.h as:

7Note that there is a timing window between the accept()                                                 accept()                                                 accept() call and the
call to WSAAsyncSelect()         WSAAsyncSelect()         WSAAsyncSelect() to change the events or wMsg.  An application
which desires a different wMsg for the listening and accept()                                                     accept()                                                     accept()'ed
sockets should ask for only FD_ACCEPT events on the listening socket,
then set appropriate events after the accept()                                      accept()                                      accept().  Since FD_ACCEPT is
never sent for a connected socket and FD_READ, FD_WRITE, FD_OOB, and
FD_CLOSE are never sent for listening sockets, this will not impose
difficulties.


                                                    WSAAsyncSelect 105


          #define WSAGETSELECTERROR(lParam)            HIWORD(lParam)
          #define WSAGETSELECTEVENT(lParam)            LOWORD(lParam)

          The use of these macros will maximize the portability of the
          source code for the application.

          The possible network event codes which may be returned are
          as follows:

               Value     Meaning
               FD_READ   Socket s ready for reading
               FD_WRITE  Socket s ready for writing
               FD_OOB    Out-of-band data ready for reading on socket
                         s.
               FD_ACCEPT Socket s ready for accepting a new incoming
                         connection
               FD_CONNECT     Connection on socket s completed
               FD_CLOSE  Connection identified by socket s has been
                         closed


Return Value   The return value is 0 if the application's declaration
          of interest in the network event set was successful.
          Otherwise the value SOCKET_ERROR is returned, and a specific
          error number may be retrieved by calling WSAGetLastError().

Comments  Although WSAAsyncSelect() can be called with interest in
          multiple events, the application window will receive a
          single message for each network event.

          As in the case of the select() function, WSAAsyncSelect()
          will frequently be used to determine when a data transfer
          operation (send() or recv()) can be issued with the
          expectation of immediate success.  Nevertheless, a robust
          application must be prepared for the possibility that it may
          receive a message and issue a Windows Sockets API call which
          returns WSAEWOULDBLOCK immediately.  For example, the
          following sequence of events is possible:

          (i)       data arrives on socket s; Windows Sockets posts
                    WSAAsyncSelect message
          (ii)      application processes some other message
          (iii)     while processing, application issues an
                    ioctlsocket(s, FIONREAD...) and notices that there
                    is data ready to be read
          (iv)      application issues a recv(s,...) to read the data
          (v)       application  loops to process next message,
                    eventually reaching the WSAAsyncSelect message
                    indicating that data is ready to read
          (vi)      application issues recv(s,...), which fails with
                    the error WSAEWOULDBLOCK.

          Other sequences are possible.

          The Windows Sockets DLL will not continually flood an
          application with messages for a particular network event.


106 WSAAsyncSelect

          Having successfully posted notification of a particular
          event to an application window, no further message(s) for
          that network event will be posted to the application window
          until the application makes the function call which
          implicitly reenables notification of that network event.

          Event          Re-enabling function
          FD_READ        recv() or recvfrom()
          FD_WRITE       send() or sendto()
          FD_OOB         recv()
          FD_ACCEPT      accept()
          FD_CONNECT     NONE
          FD_CLOSE       NONE

          Any call to the reenabling routine, even one which fails,
          results in reenabling of message posting for the relevant
          event.

          For FD_READ, FD_OOB, and FD_ACCEPT events, message posting
          is "level-triggered."  This means that if the reenabling
          routine is called and the relevant event is still valid
          after the call, a WSAAsyncSelect() message is posted to the
          application.  This allows an application to be event-driven
          and not concern itself with the amount of data that arrives
          at any one time.  Consider the following sequence:

          (i)       Windows Sockets DLL receives 100 bytes of data on
                    socket s and posts an FD_READ message.
          (ii)      The application issues recv( s, buffptr, 50, 0) to
                    read 50 bytes.
          (iii)     The Windows Sockets DLL posts another FD_READ
                    message since there is still data to be read.

          With these semantics, an application need not read all
          available data in response to an FD_READ message--a single
          recv() in response to each FD_READ message is appropriate.
          If an application issues multiple recv() calls in response
          to a single FD_READ, it may receive multiple FD_READ
          messages.  Such an application may wish to disable FD_READ
          messages before starting the recv() calls by calling
          WSAAsyncSelect() with the FD_READ event not set.

          If an event is true when the application initially calls
          WSAAsyncSelect() or when the reenabling function is called,
          then a message is posted as appropriate.  For example, if an
          application calls listen(), a connect attempt is made, then
          the application calls WSAAsyncSelect() specifying that it
          wants to receive FD_ACCEPT messages for the socket, the
          Windows Sockets implementation posts an FD_ACCEPT message
          immediately.

          The FD_WRITE event is handled slightly differently.  An
          FD_WRITE message is posted when a socket is first connected
          with connect() or accepted with accept(), and then after a
          send() or sendto() fails with WSAEWOULDBLOCK and buffer
          space becomes available.  Therefore, an application can
          assume that sends are possible starting from the first


                                                    WSAAsyncSelect 107

          FD_WRITE message and lasting until a send returns
          WSAEWOULDBLOCK.  After such a failure the application will
          be notified that sends are again possible with an FD_WRITE
          message.

          The FD_OOB event is used only when a socket is configured to
          receive out-of-band data separately.  If the socket is
          configured to receive out-of-band data in-line, the out-of-
          band (expedited) data is treated as normal data and the
          application should register an interest in, and will
          receive, FD_READ events, not FD_OOB events.  An application
          may set or inspect the way in which out-of-band data is to
          be handled by using setsockopt() or getsockopt() for the
          SO_OOBINLINE option.

          The error code in an FD_CLOSE message indicates whether the
          socket close was graceful or abortive.  If the error code is
          0, then the close was graceful; if the error code is
          WSAECONNRESET, then the socket's virtual socket was reset.
          This only applies to sockets of type SOCK_STREAM.

          The FD_CLOSE message is posted when a close indication is
          received for the virtual circuit corresponding to the
          socket.  In TCP terms, this means that the FD_CLOSE is
          posted when the connection goes into the FIN WAIT or CLOSE
          WAIT states.  This results from the remote end performing a
          shutdown() on the send side or a closesocket().

          Please note your application will receive ONLY an FD_CLOSE
          message to indicate closure of a virtual circuit. It will
          NOT receive an FD_READ message to indicate this condition.

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINVAL           Indicates that one of the specified
                              parameters was invalid

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          Additional error codes may be set when an application window
          receives a message.  This error code is extracted from the
          lParam in the reply message using the WSAGETSELECTERROR
          macro.  Possible error codes for each network event are:
          Event: FD_CONNECT
          Error Code          Meaning
          WSAEADDRINUSE       The specified address is already in use.

          WSAEADDRNOTAVAIL    The specified address is not available
                              from the local machine.


108 WSAAsyncSelect

          WSAEAFNOSUPPORT     Addresses in the specified family cannot
                              be used with this socket.

          WSAECONNREFUSED     The attempt to connect was forcefully
                              rejected.

          WSAEDESTADDRREQ     A destination address is required.

          WSAEFAULT           The namelen argument is incorrect.

          WSAEINVAL           The socket is already bound to an
                              address.

          WSAEISCONN          The socket is already connected.

          WSAEMFILE           No more file descriptors are available.

          WSAENETUNREACH      The network can't be reached from this
                              host at this time.

          WSAENOBUFS          No buffer space is available.  The
                              socket cannot be connected.

          WSAENOTCONN         The socket is not connected.

          WSAENOTSOCK         The descriptor is a file, not a socket.

          WSAETIMEDOUT        Attempt to connect timed out without
                              establishing a connection

          Event: FD_CLOSE
          Error Code          Meaning
          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAECONNRESET       The connection was reset by the remote
                              side.

          WSAECONNABORTED     The connection was aborted due to
                              timeout or other failure.

          Event: FD_READ
          Event: FD_WRITE
          Event: FD_OOB
          Event: FD_ACCEPT
          Error Code          Meaning
          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

Notes For
Windows Sockets
Suppliers It is the responsibility of the Windows Sockets Supplier to
          ensure that messages are successfully posted to the
          application.  If a PostMessage() operation fails, the


                                                    WSAAsyncSelect 109

          Windows Sockets implementation MUST re-post that message as
          long as the window exists.

          Windows Sockets suppliers should use the WSAMAKESELECTREPLY
          macro when constructing the lParam in the message.

          When a socket is closed, the Windows Sockets Supplier should
          purge any messages remaining for posting to the application
          window.  However the application must be prepared to
          receive, and discard, any messages which may have been
          posted prior to the closesocket().

See Also  select()


110 WSACancelAsyncRequest

4.3.8 WSACancelAsyncRequest()
Description    Cancel an incomplete asynchronous operation.

          #include <winsock.h>

          int PASCAL FAR WSACancelAsyncRequest ( HANDLE
          hAsyncTaskHandle );


          hAsyncTaskHandle    Specifies the asynchronous operation to
                    be canceled.

Remarks   The WSACancelAsyncRequest() function is used to cancel an
          asynchronous operation which was initiated by one of the
          WSAAsyncGetXByY() functions such as WSAAsyncGetHostByName().
          The operation to be canceled is identified by the
          hAsyncTaskHandle parameter, which should be set to the
          asynchronous task handle as returned by the initiating
          function.


Return Value   The value returned by WSACancelAsyncRequest() is 0 if
          the operation was successfully canceled.  Otherwise the
          value SOCKET_ERROR is returned, and a specific error number
          may be retrieved by calling WSAGetLastError().

Comments  An attempt to cancel an existing asynchronous
          WSAAsyncGetXByY() operation can fail with an error code of
          WSAEALREADY for two reasons.  First, the original operation
          has already completed and the application has dealt with the
          resultant message.  Second, the original operation has
          already completed but the resultant message is still waiting
          in the application window queue.

Notes For
Windows Sockets
Suppliers It is unclear whether the application can usefully
          distinguish between WSAEINVAL and WSAEALREADY, since in both
          cases the error indicates that there is no asynchronous
          operation in progress with the indicated handle.  [Trivial
          exception: 0 is always an invalid asynchronous task handle.]
          The Windows Sockets specification does not prescribe how a
          conformant Windows Sockets implementation should distinguish
          between the two cases.  For maximum portability, a Windows
          Sockets application should treat the two errors as
          equivalent.

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINVAL           Indicates that the specified
                              asynchronous task handle was invalid


                                             WSACancelAsyncRequest 111


          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

          WSAEALREADY         The asynchronous routine being canceled
                              has already completed.


See Also  WSAAsyncGetHostByAddr(), WSAAsyncGetHostByName(),
          WSAAsyncGetProtoByNumber(), WSAAsyncGetProtoByName(),
          WSAAsyncGetHostByName(), WSAAsyncGetServByPort(),
          WSAAsyncGetServByName().


112 WSACancelBlockingCall

4.3.9 WSACancelBlockingCall()
Description    Cancel a blocking call which is currently in progress.

          #include <winsock.h>

          int PASCAL FAR WSACancelBlockingCall ( void );

Remarks   This function cancels any outstanding blocking operation for
          this task.  It is normally used in two situations:

          (1) An application is processing a message which has been
          received while a blocking call is in progress.  In this
          case, WSAIsBlocking() will be true.

          (2) A blocking call is in progress, and Windows Sockets has
          called back to the application's "blocking hook" function
          (as established by WSASetBlockingHook()).

          In each case, the original blocking call will terminate as
          soon as possible with the error WSAEINTR.  (In (1), the
          termination will not take place until Windows message
          scheduling has caused control to revert to the blocking
          routine in Windows Sockets.  In (2), the blocking call will
          be terminated as soon as the blocking hook function
          completes.)

          In the case of a blocking connect() operation, the Windows
          Sockets implementation will terminate the blocking call as
          soon as possible, but it may not be possible for the socket
          resources to be released until the connection has completed
          (and then been reset) or timed out.  This is likely to be
          noticeable only if the application immediately tries to open
          a new socket (if no sockets are available), or to connect()
          to the same peer.

          Cancelling an accept() or a select() call does not adversely
          impact the sockets passed to these calls.  Only the
          particular call fails; any operation that was legal before
          the cancel is legal after the cancel, and the state of the
          socket is not affected in any way.

          Cancelling any operation other than accept() and select()
          can leave the socket in an indeterminate state.  If an
          application cancels a blocking operation on a socket, the
          only operation that the application can depend on being able
          to perform on the socket is a call to closesocket(),
          although other operations may work on some Windows Sockets
          implementations.  If an application desires maximum
          portability, it must be careful not to depend on performing
          operations after a cancel.  An application may reset the
          connection by setting the timeout on SO_LINGER to 0.

          If a cancel operation compromised the integrity of a
          SOCK_STREAM's data stream in any way, the Windows Sockets
          implementation must reset the connection and fail all future
          operations other than closesocket() with WSAECONNABORTED.


                                             WSACancelBlockingCall 113

Return Value   The value returned by WSACancelBlockingCall() is 0 if
          the operation was successfully canceled.  Otherwise the
          value SOCKET_ERROR is returned, and a specific error number
          may be retrieved by calling WSAGetLastError().

Comments  Note that it is possible that the network operation
          completes before the WSACancelBlockingCall()  is processed,
          for example if data is received into the user buffer at
          interrupt time while the application is in a blocking hook.
          In this case, the blocking operation will return
          successfully as if WSACancelBlockingCall() had never been
          called.  Note that the WSACancelBlockingCall() still
          succeeds in this case; the only way to know with certainty
          that an operation was actually canceled is to check for a
          return code of WSAEINTR from the blocking call.

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINVAL           Indicates that there is no outstanding
                              blocking call.


114 WSACleanup

4.3.10 WSACleanup()
Description    Terminate use of the Windows Sockets DLL.

          #include <winsock.h>

          int PASCAL FAR WSACleanup ( void );

Remarks   An application or DLL is required to perform a (successful)
          WSAStartup() call before it can use Windows Sockets
          services.  When it has completed the use of Windows Sockets,
          the application or DLL must call WSACleanup() to deregister
          itself from a Windows Sockets implementation and allow the
          implementation to free any resources allocated on behalf of
          the application or DLL.  Any open SOCK_STREAM sockets that
          are connected when WSACleanup() is called are reset; sockets
          which have been closed with closesocket() but which still
          have pending data to be sent are not affected--the pending
          data is still sent.

          There must be a call to WSACleanup() for every call to
          WSAStartup() made by a task.  Only the final WSACleanup()
          for that task does the actual cleanup; the preceding calls
          simply decrement an internal reference count in the Windows
          Sockets DLL.  A naive application may ensure that
          WSACleanup() was called enough times by calling WSACleanup()
          in a loop until it returns WSANOTINITIALISED.

Return Value   The return value is 0 if the operation was successful.
          Otherwise the value SOCKET_ERROR is returned, and a specific
          error number may be retrieved by calling WSAGetLastError().

Comments  Attempting to call WSACleanup() from within a blocking hook
          and then failing to check the return code is a common
          Windows Sockets programming error.  If an application needs
          to quit while a blocking call is outstanding, the
          application must first cancel the blocking call with
          WSACancelBlockingCall() then issue the WSACleanup() call
          once control has been returned to the application.

Notes For
Windows Sockets
Suppliers Well-behaved Windows Sockets applications will make a
          WSACleanup() call to indicate deregistration from a Windows
          Sockets implementation.  This function can thus, for
          example, be utilized to free up resources allocated to the
          specific application.

          A Windows Sockets implementation must be prepared to deal
          with an application which terminates without invoking
          WSACleanup() - for example, as a result of an error.

          In a multithreaded environment, WSACleanup() terminates
          Windows Sockets operations for all threads.

          A Windows Sockets implementation must ensure that
          WSACleanup() leaves things in a state in which the


                                                        WSACleanup 115

          application can invoke WSAStartup() to re-establish Windows
          Sockets usage.

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

See Also  WSAStartup()


116 WSAGetLastError

4.3.11 WSAGetLastError()
Description    Get the error status for the last operation which
          failed.

          #include <winsock.h>

          int PASCAL FAR WSAGetLastError ( void );

Remarks   This function returns the last network error that occurred.
          When a particular Windows Sockets API function indicates
          that an error has occurred, this function should be called
          to retrieve the appropriate error code.

Return Value   The return value indicates the error code for the last
          Windows Sockets API routine performed by this thread.

Notes For
Windows Sockets
Suppliers The use of the WSAGetLastError() function to retrieve the
          last error code, rather than relying on a global error
          variable (cf. errno), is required in order to provide
          compatibility with future multi-threaded environments.

          Note that in a nonpreemptive Windows environment
          WSAGetLastError() is used to retrieve only Windows Sockets
          API errors.  In a preemptive environment, WSAGetLastError()
          will invoke GetLastError(), which is used to retrieve the
          error status for all Win32 API functions on a per-thread
          basis.  For portability, an application should use
          WSAGetLastError() immediately after the Windows Sockets API
          function which failed.

See Also  WSASetLastError()


                                                     WSAIsBlocking 117

4.3.12 WSAIsBlocking()
Description    Determine if a blocking call is in progress.

          #include <winsock.h>

          BOOL PASCAL FAR WSAIsBlocking ( void );

Remarks   This function allows a task to determine if it is executing
          while waiting for a previous blocking call to complete.

Return Value   The return value is TRUE if there is an outstanding
          blocking function awaiting completion.  Otherwise, it is
          FALSE.

Comments  Although a call issued on a blocking socket appears to an
          application program as though it "blocks", the Windows
          Sockets DLL has to relinquish the processor to allow other
          applications to run.  This means that it is possible for the
          application which issued the blocking call to be re-entered,
          depending on the message(s) it receives.  In this instance,
          the WSAIsBlocking() function can be used to ascertain
          whether the task has been re-entered while waiting for an
          outstanding blocking call to complete.  Note that Windows
          Sockets prohibits more than one outstanding call per thread.

Notes For
Windows Sockets
Suppliers A Windows Sockets implementation must prohibit more than one
          outstanding blocking call per thread.


118 WSASetBlockingHook

4.3.13 WSASetBlockingHook()
Description    Establish an application-specific blocking hook
          function.

          #include <winsock.h>

          FARPROC PASCAL FAR WSASetBlockingHook ( FARPROC lpBlockFunc
          );


          lpBlockFunc    A pointer to the procedure instance address
                    of the blocking function to be installed.

Remarks   This function installs a new function which a Windows
          Sockets implementation should use to implement blocking
          socket function calls.

          A Windows Sockets implementation includes a default
          mechanism by which blocking socket functions are
          implemented.  The function WSASetBlockingHook() gives the
          application the ability to execute its own function at
          "blocking" time in place of the default function.

          When an application invokes a blocking Windows Sockets API
          operation, the Windows Sockets implementation initiates the
          operation and then enters a loop which is similar to the
          following pseudocode:

          for(;;) {
               /* flush messages for good user response */
               while(BlockingHook())
                    ;
               /* check for WSACancelBlockingCall() */
               if(operation_cancelled())
                    break;
               /* check to see if operation completed */
               if(operation_complete())
                    break;     /* normal completion */
          }

          Note that Windows Sockets implementations may perform the
          above steps in a different order; for example, the check for
          operation complete may occur before calling the blocking
          hook.  The default BlockingHook() function is equivalent to:

          BOOL DefaultBlockingHook(void) {
               MSG msg;
               BOOL ret;
               /* get the next message if any */
               ret = (BOOL)PeekMessage(&msg,NULL,0,0,PM_REMOVE);
               /* if we got one, process it */
               if (ret) {
                    TranslateMessage(&msg);
                    DispatchMessage(&msg);
               }
               /* TRUE if we got a message */
               return ret;


                                                WSASetBlockingHook 119

          }

          The WSASetBlockingHook() function is provided to support
          those applications which require more complex message
          processing - for example, those employing the MDI (multiple
          document interface) model.  It is not intended as a
          mechanism for performing general applications functions.  In
          particular, the only Windows Sockets API function which may
          be issued from a custom blocking hook function is
          WSACancelBlockingCall(), which will cause the blocking loop
          to terminate.

          This function must be implemented on a per-task basis for
          non-multithreaded versions of Windows and on a per-thread
          basis for multithreaded versions of Windows such as Windows
          NT.  It thus provides for a particular task or thread to
          replace the blocking mechanism without affecting other tasks
          or threads.

          In multithreaded versions of Windows, there is no default
          blocking hook--blocking calls block the thread that makes
          the call.  However, an application may install a specific
          blocking hook by calling WSASetBlockingHook().
          This allows easy portability of applications that depend on
          the blocking hook behavior.

Return Value   The return value is a pointer to the procedure-instance
          of the previously installed blocking function.  The
          application or library that calls the WSASetBlockingHook ()
          function should save this return value so that it can be
          restored if necessary.  (If "nesting" is not important, the
          application may simply discard the value returned by
          WSASetBlockingHook() and eventually use
          WSAUnhookBlockingHook() to restore the default mechanism.)
          If the operation fails, a NULL pointer is returned, and a
          specific error number may be retrieved by calling
          WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

          WSAENETDOWN         The Windows Sockets implementation has
                              detected that the network subsystem has
                              failed.

          WSAEINPROGRESS      A blocking Windows Sockets operation is
                              in progress.

See Also  WSAUnhookBlockingHook()


120 WSASetLastError

4.3.14 WSASetLastError()
Description    Set the error code which can be retrieved by
          WSAGetLastError().

          #include <winsock.h>

          void PASCAL FAR WSASetLastError ( int iError );

Remarks   This function allows an application to set the error code to
          be returned by a subsequent WSAGetLastError() call for the
          current thread.  Note that any subsequent Windows Sockets
          routine called by the application will override the error
          code as set by this routine.


          iError    Specifies the error code to be returned by a
                    subsequent WSAGetLastError() call.

Notes For
Windows Sockets
Suppliers In a Win32 environment, this function will invoke
SetLastError().

Return Value   None.

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

See Also  WSAGetLastError()


                                                        WSAStartup 121

4.3.15 WSAStartup()
Description

          #include <winsock.h>

          int PASCAL FAR WSAStartup ( WORD wVersionRequested,
          LPWSADATA lpWSAData );


          wVersionRequested   The highest version of Windows Sockets
                         API support that the caller can use.  The
                         high order byte specifies the minor version
                         (revision) number; the low-order byte
                         specifies the major version number.

          lpWSAData      A pointer to the WSADATA data structure that
                         is to receive details of the Windows Sockets
                         implementation.

Remarks   This function MUST be the first Windows Sockets function
          called by an application or DLL.  It allows an application
          or DLL  to specify the version of Windows Sockets API
          required and to retrieve details of the specific Windows
          Sockets implementation.  The application or DLL may only
          issue further Windows Sockets API functions after a
          successful WSAStartup() invocation.

          In order to support future Windows Sockets implementations
          and applications which may have functionality differences
          from Windows Sockets 1.1, a negotiation takes place in
          WSAStartup().  The caller of WSAStartup() and the Windows
          Sockets DLL indicate to each other the highest version that
          they can support, and each confirms that the other's highest
          version is acceptable.  Upon entry to WSAStartup(), the
          Windows Sockets DLL examines the version requested by the
          application.  If this version is higher than the lowest
          version supported by the DLL, the call succeeds and the DLL
          returns in wHighVersion the highest version it supports and
          in wVersion the minimum of its high version and
          wVersionRequested.  The Windows Sockets DLL then assumes
          that the application will use wVersion.  If the wVersion
          field of the WSADATA structure is unacceptable to the
          caller, it should call WSACleanup() and either search for
          another Windows Sockets DLL or fail to initialize.

          This negotiation allows both a Windows Sockets DLL and a
          Windows Sockets application to support a range of Windows
          Sockets versions.  An application can successfully utilize a
          Windows Sockets DLL if there is any overlap in the version
          ranges.  The following chart gives examples of how
          WSAStartup() works in conjunction with different application
          and Windows Sockets DLL versions:


122 WSAStartup



App versions DLL Versions wVersionRequested wVersion wHighVersion End Result

1.1          1.1          1.1               1.1      1.1          use 1.1

1.0 1.1      1.0          1.1               1.0      1.0          use 1.0

1.0          1.0 1.1      1.0               1.0      1.1          use 1.0

1.1          1.0 1.1      1.1               1.1      1.1          use 1.1

1.1          1.0          1.1               1.0      1.0          Application fails

1.0          1.1          1.0               ---      ---          WSAVERNOTSUPPORTED

1.0 1.1      1.0 1.1      1.1               1.1      1.1          use 1.1

1.1 2.0      1.1          2.0               1.1      1.1          use 1.1

2.0          1.1          2.0               1.1      1.1          Application fails


          The following code fragment demonstrates how an application
          which supports only version 1.1 of Windows Sockets makes a
          WSAStartup() call:

          WORD wVersionRequested;
          WSADATA wsaData;
          int err;

          wVersionRequested = MAKEWORD( 1, 1 );

          err = WSAStartup( wVersionRequested, &wsaData );
          if ( err != 0 ) {
              /* Tell the user that we couldn't find a useable */
              /* winsock.dll.                                  */
              return;
          }

          /* Confirm that the Windows Sockets DLL supports 1.1.*/
          /* Note that if the DLL supports versions greater    */


                                                        WSAStartup 123

          /* than 1.1 in addition to 1.1, it will still return */
          /* 1.1 in wVersion since that is the version we      */
          /* requested.                                        */

          if ( LOBYTE( wsaData.wVersion ) != 1 ||
                   HIBYTE( wsaData.wVersion ) != 1 ) {
              /* Tell the user that we couldn't find a useable */
              /* winsock.dll.                                  */
              WSACleanup( );
              return;
          }

          /* The Windows Sockets DLL is acceptable.  Proceed.  */

          And this code fragment demonstrates how a Windows Sockets
          DLL which supports only version 1.1 performs the
          WSAStartup() negotiation:

          /* Make sure that the version requested is >= 1.1.   */
          /* The low byte is the major version and the high    */
          /* byte is the minor version.                        */

          if ( LOBYTE( wVersionRequested ) < 1 ||
               ( LOBYTE( wVersionRequested ) == 1 &&
                 HIBYTE( wVersionRequested ) < 1 ) {
              return WSAVERNOTSUPPORTED;
          }

          /* Since we only support 1.1, set both wVersion and  */
          /* wHighVersion to 1.1.                              */

          lpWsaData->wVersion = MAKEWORD( 1, 1 );
          lpWsaData->wHighVersion = MAKEWORD( 1, 1 );

          Once an application or DLL has made a successful
          WSAStartup() call, it may proceed to make other Windows
          Sockets API calls as needed.  When it has finished using the
          services of the Windows Sockets DLL, the application or DLL
          must call WSACleanup() in order to allow the Windows Sockets
          DLL to free any resources for the application.

          Details of the actual Windows Sockets implementation are
          described in the WSAData structure defined as follows:

          struct WSAData {
               WORD           wVersion;
               WORD           wHighVersion;
               char
               szDescription[WSADESCRIPTION_LEN+1];
               char           szSystemStatus[WSASYSSTATUS_LEN+1];
               unsigned short iMaxSockets;
               unsigned short iMaxUdpDg;
               char FAR *          lpVendorInfo;
          };

          The members of this structure are:
          Element   Usage


124 WSAStartup

          wVersion  The version of the Windows Sockets specification
                    that the Windows Sockets DLL expects the caller to
                    use.
          wHighVersion   The highest version of the Windows Sockets
                    specification that this DLL can support (also
                    encoded as above).  Normally this will be the same
                    as wVersion.
          szDescription  A null-terminated ASCII string into which the
                    Windows Sockets DLL copies a description of the
                    Windows Sockets implementation, including vendor
                    identification.  The text (up to 256 characters in
                    length) may contain any characters, but vendors
                    are cautioned against including control and
                    formatting characters: the most likely use that an
                    application will put this to is to display it
                    (possibly truncated) in a status message.
          szSystemStatus A null-terminated ASCII string into which the
                    Windows Sockets DLL copies relevant status or
                    configuration information.  The Windows Sockets
                    DLL should use this field only if the information
                    might be useful to the user or  support staff: it
                    should not be considered as an extension of the
                    szDescription field.
          iMaxSockets    The maximum number of sockets which a single
                    process can potentially open.  A Windows Sockets
                    implementation may provide a global pool of
                    sockets for allocation to any process;
                    alternatively it may allocate per-process
                    resources for sockets.  The number may well
                    reflect the way in which the Windows Sockets DLL
                    or the networking software was configured.
                    Application writers may use this number as a crude
                    indication of whether the Windows Sockets
                    implementation is usable by the application.  For
                    example, an X Windows server might check
                    iMaxSockets when first started: if it is less than
                    8, the application would display an error message
                    instructing the user to reconfigure the networking
                    software.  (This is a situation in which the
                    szSystemStatus text might be used.)  Obviously
                    there is no guarantee that a particular
                    application can actually allocate iMaxSockets
                    sockets, since there may be other Windows Sockets
                    applications in use.
          iMaxUdpDg The size in bytes of the largest UDP datagram that
                    can be sent or received by a Windows Sockets
                    application.  If the implementation imposes no
                    limit, iMaxUdpDg is zero.  In many implementations
                    of Berkeley sockets, there is an implicit limit of
                    8192 bytes on UDP datagrams (which are fragmented
                    if necessary).  A Windows Sockets implementation
                    may impose a limit based, for instance, on the
                    allocation of fragment reassembly buffers.  The
                    minimum value of iMaxUdpDg for a compliant Windows
                    Sockets implementation is 512.  Note that
                    regardless of the value of iMaxUdpDg, it is
                    inadvisable to attempt to send a broadcast


                                                        WSAStartup 125

                    datagram which is larger than the Maximum
                    Transmission Unit (MTU) for the network.  (The
                    Windows Sockets API does not provide a mechanism
                    to discover the MTU, but it must be no less than
                    512 bytes.)
          lpVendorInfo   A far pointer to a vendor-specific data
                    structure.  The definition of this structure (if
                    supplied) is beyond the scope of this
                    specification.

          An application or DLL may call WSAStartup() more than once
          if it needs to obtain the WSAData structure information more
          than once.  However, the wVersionRequired parameter is
          assumed to be the same on all calls to WSAStartup(); that
          is, an application or DLL cannot change the version of
          Windows Sockets it expects after the initial call to
          WSAStartup().

          There must be one WSACleanup() call corresponding to every
          WSAStartup() call to allow third-party DLLs to make use of a
          Windows Sockets DLL on behalf of an application.  This
          means, for example, that if an application calls
          WSAStartup() three times, it must call WSACleanup() three
          times.  The first two calls to WSACleanup() do nothing
          except decrement an internal counter; the final WSACleanup()
          call for the task does all necessary resource deallocation
          for the task.


Return Value   WSAStartup() returns zero if successful.  Otherwise it
          returns one of the error codes listed below.  Note that the
          normal mechanism whereby the application calls
          WSAGetLastError() to determine the error code cannot be
          used, since the Windows Sockets DLL may not have established
          the client data area where the "last error" information is
          stored.

Notes For
Windows Sockets
Suppliers Each Windows Sockets application MUST make a WSAStartup()
          call before issuing any other Windows Sockets API calls.
          This function can thus be utilized for initialization
          purposes.

          Further issues are discussed in the notes for WSACleanup().

Error Codes                   WSASYSNOTREADY Indicates that the
                              underlying network subsystem is not
                              ready for network communication.

          WSAVERNOTSUPPORTED
                              The version of Windows Sockets API
                              support requested is not provided by
                              this particular Windows Sockets
                              implementation.


126 WSAStartup

          WSAEINVAL           The Windows Sockets version specified by
                              the application is not supported by this
                              DLL.

See Also  send(), sendto(), WSACleanup()


                                             WSAUnhookBlockingHook 127

4.3.16 WSAUnhookBlockingHook()
Description    Restore the default blocking hook function.

          #include <winsock.h>

          int PASCAL FAR WSAUnhookBlockingHook ( void );

Remarks   This function removes any previous blocking hook that has
          been installed and reinstalls the default blocking
          mechanism.

          WSAUnhookBlockingHook() will always install the default
          mechanism, not the previous mechanism.  If an application
          wish to nest blocking hooks - i.e. to establish a temporary
          blocking hook function and then revert to the previous
          mechanism (whether the default or one established by an
          earlier WSASetBlockingHook()) - it must save and restore the
          value returned by WSASetBlockingHook(); it cannot use
          WSAUnhookBlockingHook().

          In multithreaded versions of Windows such as Windows NT,
          there is no default blocking hook.  Calling
          WSAUnhookBlockingHook() disables any blocking hook installed
          by the application and any blocking calls made block the
          thread which made the call.

Return Value   The return value is 0 if the operation was successful.
          Otherwise the value SOCKET_ERROR is returned, and a specific
          error number may be retrieved by calling WSAGetLastError().

Error Codes                   WSANOTINITIALISED   A successful
                              WSAStartup() must occur before using
                              this API.

See Also  WSASetBlockingHook()


128 Appendix A1: Error Codes


Appendix A.  Error Codes and Header Files

A.1 Error Codes
The following is a list of possible error codes returned by the
WSAGetLastError() call, along with their explanations.  The error
numbers are consistently set across all Windows Sockets-compliant
implementations.


                                          Appendix A1: Error Codes 129


Windows        Berkeley       Err  Interpretation
Sockets code   equivalent     or



WSAEINTR       EINTR               As in standard C                              100
                              04
WSAEBADF       EBADF               As in standard C                              100
                              09
WSAEACCES      EACCES              As in standard C                              100
                              13
WSAEFAULT      EFAULT              As in standard C                              100
                              14
WSAEINVAL      EINVAL              As in standard C                              100
                              22
WSAEMFILE      EMFILE              As in standard C                              100
                              24

WSAEWOULDBLOC  EWOULDBLOCK         As in BSD                              100
K                             35
WSAEINPROGRES  EINPROGRESS         This error is returned                              100
S                                  if any                              36
                                   Windows Sockets API
                                   function is
                                   called while a blocking
                                   function is
                                   in progress.
WSAEALREADY    EALREADY            As in BSD                              100
                              37
WSAENOTSOCK    ENOTSOCK            As in BSD                              100
                              38
WSAEDESTADDRR  EDESTADDRREQ   100  As in BSD
EQ                            39
WSAEMSGSIZE    EMSGSIZE            As in BSD                              100
                              40
WSAEPROTOTYPE  EPROTOTYPE          As in BSD                              100
                              41
WSAENOPROTOOP  ENOPROTOOPT         As in BSD                              100
T                             42
WSAEPROTONOSU  EPROTONOSUPPO  100  As in BSD
PPORT          RT             43
WSAESOCKTNOSU  ESOCKTNOSUPPO       As in BSD                              100
PPORT          RT             44
WSAEOPNOTSUPP  EOPNOTSUPP          As in BSD                              100
                              45
WSAEPFNOSUPPO  EPFNOSUPPORT   100  As in BSD
RT                            46
WSAEAFNOSUPPO  EAFNOSUPPORT   100  As in BSD
RT                            47
WSAEADDRINUSE  EADDRINUSE     100  As in BSD
                              48
WSAEADDRNOTAV  EADDRNOTAVAIL       As in BSD                              100
AIL                           49


130 Appendix A1: Error Codes

WSAENETDOWN    ENETDOWN            As in BSD.  This error                              100
                              50   may be reported at any
                                   time if the Windows
                                   Sockets implementation
                                   detects an underlying
                                   failure.
WSAENETUNREAC  ENETUNREACH         As in BSD                              100
H                             51
WSAENETRESET   ENETRESET           As in BSD                              100
                              52
WSAECONNABORT  ECONNABORTED        As in BSD                              100
ED                            53
WSAECONNRESET  ECONNRESET          As in BSD                              100
                              54
WSAENOBUFS     ENOBUFS             As in BSD                              100
                              55
WSAEISCONN     EISCONN             As in BSD                              100
                              56
WSAENOTCONN    ENOTCONN            As in BSD                              100
                              57
WSAESHUTDOWN   ESHUTDOWN           As in BSD                              100
                              58
WSAETOOMANYRE  ETOOMANYREFS        As in BSD                              100
FS                            59
WSAETIMEDOUT   ETIMEDOUT      100  As in BSD
                              60
WSAECONNREFUS  ECONNREFUSED        As in BSD                              100
ED                            61
WSAELOOP       ELOOP               As in BSD                              100
                              62
WSAENAMETOOLO  ENAMETOOLONG        As in BSD                              100
NG                            63
WSAEHOSTDOWN   EHOSTDOWN           As in BSD                              100
                              64
WSAEHOSTUNREA  EHOSTUNREACH        As in BSD                              100
CH                            65

WSASYSNOTREAD                      Returned by                              100
Y                             91   WSAStartup()
                                   indicating that the
                                   network subsystem is
                                   unusable.
WSAVERNOTSUPP                      Returned by                              100
ORTED                         92   WSAStartup()
                                   indicating that the
                                   Windows Sockets
                                   DLL cannot support this
                                   app.
WSANOTINITIAL                      Returned by any                              100
ISED                               function except                              93
                                   WSAStartup() indicating
                                   that a successful
                                   WSAStartup() has not
                                   yet been performed.

WSAHOST_NOT_F  HOST_NOT_FOUN       As in BSD.                              110
OUND           D              01


                                          Appendix A1: Error Codes 131

WSATRY_AGAIN   TRY_AGAIN           As in BSD                              110
                              02
WSANO_RECOVER  NO_RECOVERY         As in BSD                              110
Y                             03
WSANO_DATA     NO_DATA             As in BSD                              110
                              04



The first set of definitions is present to resolve contentions between
standard C error codes which may be defined inconsistently between
various C compilers.

The second set of definitions provides Windows Sockets versions of
regular Berkeley Sockets error codes.

The third set of definitions consists of extended Windows Sockets-
specific error codes.

The fourth set of errors are returned by Windows Sockets getXbyY() and
WSAAsyncGetXByY() functions, and correspond to the errors which in
Berkeley software would be returned in the h_errno variable.  They
correspond to various failures which may be returned by the Domain
Name Service.  If the Windows Sockets implementation  does not use the
DNS, it will use the most appropriate code.  In general, a Windows
Sockets application should interpret WSAHOST_NOT_FOUND and WSANO_DATA
as indicating that the key (name, address, etc.) was not found,, while
WSATRY_AGAIN and WSANO_RECOVERY suggest that the name service itself
is non-operational.

The error numbers are derived from the winsock.h header file listed in
section A.2.2, and are based on the fact that Windows Sockets error
numbers are computed by adding 10000 to the "normal" Berkeley error
number.

Note that this table does not include all of the error codes defined
in winsock.h.  This is because it includes only errors which might
reasonably be returned by a Windows Sockets implementation: winsock.h,
on the other hand, includes a full set of BSD definitions to ensure
compatibility with ported software.


132 Appendix A2: Header Files


A.2 Header Files
A.2.1 Berkeley Header Files
A Windows Sockets supplier who provides a development kit to support
the development of Windows Sockets applications must supply a set of
vestigial header files with names that match a number of the header
files in the Berkeley software distribution.  These files are provided
for source code compatibility only, and each consists of three lines:

#ifndef _WINSOCKAPI_
#include <winsock.h>
#endif

The header files provided for compatibility are:
netdb.h
arpa/inet.h
sys/time.h
sys/socket.h
netinet/in.h

The file winsock.h contains all of the type and structure definitions,
constants, macros, and function prototypes used by the Windows Sockets
specification.  An application writer may choose to ignore the
compatibility headers and include winsock.h in each source file.


                                                         winsock.h 133


A.2.2 Windows Sockets Header File - winsock.h

The winsock.h header file includes a number of types and definitions
from the standard Windows header file windows.h.  The windows.h in the
Windows 3.0 SDK (Software Developer's Kit) lacks a #include guard, so
if you need to include windows.h as well as winsock.h, you should
define the symbol _INC_WINDOWS before #including winsock.h, as
follows:
          #include <windows.h>
          #define _INC_WINDOWS
          #include <winsock.h>
Users of the SDK for Windows 3.1 and later need not do this.

A Windows Sockets DLL vendor MUST NOT make any modifications to this
header file which could impact binary compatibility of Windows Sockets
applications.  The constant values, function parameters and return
codes, and the like must remain consistent across all Windows Sockets
DLL vendors.


/* WINSOCK.H--definitions to be used with the WINSOCK.DLL
 *
 * This header file corresponds to version 1.1 of the Windows Sockets specification.
 *
 * This file includes parts which are Copyright (c) 1982-1986 Regents
 * of the University of California.  All rights reserved.  The
 * Berkeley Software License Agreement specifies the terms and
 * conditions for redistribution.
 */

#ifndef _WINSOCKAPI_
#define _WINSOCKAPI_

/*
 * Pull in WINDOWS.H if necessary
 */
#ifndef _INC_WINDOWS
#include <windows.h>
#endif /* _INC_WINDOWS */

/*
 * Basic system type definitions, taken from the BSD file sys/types.h.
 */
typedef unsigned char   u_char;
typedef unsigned short  u_short;
typedef unsigned int    u_int;
typedef unsigned long   u_long;

/*
 * The new type to be used in all
 * instances which refer to sockets.
 */
typedef u_int           SOCKET;

/*
 * Select uses arrays of SOCKETs.  These macros manipulate such
 * arrays.  FD_SETSIZE may be defined by the user before including
 * this file, but the default here should be >= 64.
 *
 * CAVEAT IMPLEMENTOR and USER: THESE MACROS AND TYPES MUST BE
 * INCLUDED IN WINSOCK.H EXACTLY AS SHOWN HERE.
 */
#ifndef FD_SETSIZE
#define FD_SETSIZE      64
#endif /* FD_SETSIZE */

typedef struct fd_set {
        u_short fd_count;               /* how many are SET? */
        SOCKET  fd_array[FD_SETSIZE];   /* an array of SOCKETs */
} fd_set;

extern int PASCAL FAR __WSAFDIsSet(SOCKET, fd_set FAR *);

#define FD_CLR(fd, set) do { \
    u_int __i; \
    for (__i = 0; __i < ((fd_set FAR *)(set))->fd_count ; __i++) { \
        if (((fd_set FAR *)(set))->fd_array[__i] == fd) { \
            while (__i < ((fd_set FAR *)(set))->fd_count-1) { \
                ((fd_set FAR *)(set))->fd_array[__i] = \
                    ((fd_set FAR *)(set))->fd_array[__i+1]; \
                __i++; \
            } \
            ((fd_set FAR *)(set))->fd_count--; \
            break; \
        } \
    } \
} while(0)

#define FD_SET(fd, set) do { \
    if (((fd_set FAR *)(set))->fd_count < FD_SETSIZE) \
        ((fd_set FAR *)(set))->fd_array[((fd_set FAR *)(set))->fd_count++]=fd;\
} while(0)

#define FD_ZERO(set) (((fd_set FAR *)(set))->fd_count=0)

#define FD_ISSET(fd, set) __WSAFDIsSet((SOCKET)fd, (fd_set FAR *)set)

/*
 * Structure used in select() call, taken from the BSD file sys/time.h.
 */
struct timeval {
        long    tv_sec;         /* seconds */
        long    tv_usec;        /* and microseconds */
};

/*
 * Operations on timevals.
 *
 * NB: timercmp does not work for >= or <=.
 */
#define timerisset(tvp)         ((tvp)->tv_sec || (tvp)->tv_usec)
#define timercmp(tvp, uvp, cmp) \
        ((tvp)->tv_sec cmp (uvp)->tv_sec || \
         (tvp)->tv_sec == (uvp)->tv_sec && (tvp)->tv_usec cmp (uvp)->tv_usec)
#define timerclear(tvp)         (tvp)->tv_sec = (tvp)->tv_usec = 0

/*
 * Commands for ioctlsocket(),  taken from the BSD file fcntl.h.
 *
 *
 * Ioctl's have the command encoded in the lower word,
 * and the size of any in or out parameters in the upper
 * word.  The high 2 bits of the upper word are used
 * to encode the in/out status of the parameter; for now
 * we restrict parameters to at most 128 bytes.
 */
#define IOCPARM_MASK    0x7f            /* parameters must be < 128 bytes */
#define IOC_VOID        0x20000000      /* no parameters */
#define IOC_OUT         0x40000000      /* copy out parameters */
#define IOC_IN          0x80000000      /* copy in parameters */
#define IOC_INOUT       (IOC_IN|IOC_OUT)
                                        /* 0x20000000 distinguishes new &
                                           old ioctl's */
#define _IO(x,y)        (IOC_VOID|(x<<8)|y)

#define _IOR(x,y,t)     (IOC_OUT|(((long)sizeof(t)&IOCPARM_MASK)<<16)|(x<<8)|y)

#define _IOW(x,y,t)     (IOC_IN|(((long)sizeof(t)&IOCPARM_MASK)<<16)|(x<<8)|y)

#define FIONREAD    _IOR('f', 127, u_long) /* get # bytes to read */
#define FIONBIO     _IOW('f', 126, u_long) /* set/clear non-blocking i/o */
#define FIOASYNC    _IOW('f', 125, u_long) /* set/clear async i/o */

/* Socket I/O Controls */
#define SIOCSHIWAT  _IOW('s',  0, u_long)  /* set high watermark */
#define SIOCGHIWAT  _IOR('s',  1, u_long)  /* get high watermark */
#define SIOCSLOWAT  _IOW('s',  2, u_long)  /* set low watermark */
#define SIOCGLOWAT  _IOR('s',  3, u_long)  /* get low watermark */
#define SIOCATMARK  _IOR('s',  7, u_long)  /* at oob mark? */

/*
 * Structures returned by network data base library, taken from the
 * BSD file netdb.h.  All addresses are supplied in host order, and
 * returned in network order (suitable for use in system calls).
 */

struct  hostent {
        char    FAR * h_name;           /* official name of host */
        char    FAR * FAR * h_aliases;  /* alias list */
        short   h_addrtype;             /* host address type */
        short   h_length;               /* length of address */
        char    FAR * FAR * h_addr_list; /* list of addresses */
#define h_addr  h_addr_list[0]          /* address, for backward compat */
};

/*
 * It is assumed here that a network number
 * fits in 32 bits.
 */
struct  netent {
        char    FAR * n_name;           /* official name of net */
        char    FAR * FAR * n_aliases;  /* alias list */
        short   n_addrtype;             /* net address type */
        u_long  n_net;                  /* network # */
};

struct  servent {
        char    FAR * s_name;           /* official service name */
        char    FAR * FAR * s_aliases;  /* alias list */
        short   s_port;                 /* port # */
        char    FAR * s_proto;          /* protocol to use */
};

struct  protoent {
        char    FAR * p_name;           /* official protocol name */
        char    FAR * FAR * p_aliases;  /* alias list */
        short   p_proto;                /* protocol # */
};

/*
 * Constants and structures defined by the internet system,
 * Per RFC 790, September 1981, taken from the BSD file netinet/in.h.
 */

/*
 * Protocols
 */
#define IPPROTO_IP              0               /* dummy for IP */
#define IPPROTO_ICMP            1               /* control message protocol */
#define IPPROTO_GGP             2               /* gateway^2 (deprecated) */
#define IPPROTO_TCP             6               /* tcp */
#define IPPROTO_PUP             12              /* pup */
#define IPPROTO_UDP             17              /* user datagram protocol */
#define IPPROTO_IDP             22              /* xns idp */
#define IPPROTO_ND              77              /* UNOFFICIAL net disk proto */

#define IPPROTO_RAW             255             /* raw IP packet */
#define IPPROTO_MAX             256

/*
 * Port/socket numbers: network standard functions
 */
#define IPPORT_ECHO             7
#define IPPORT_DISCARD          9
#define IPPORT_SYSTAT           11
#define IPPORT_DAYTIME          13
#define IPPORT_NETSTAT          15
#define IPPORT_FTP              21
#define IPPORT_TELNET           23
#define IPPORT_SMTP             25
#define IPPORT_TIMESERVER       37
#define IPPORT_NAMESERVER       42
#define IPPORT_WHOIS            43
#define IPPORT_MTP              57

/*
 * Port/socket numbers: host specific functions
 */
#define IPPORT_TFTP             69
#define IPPORT_RJE              77
#define IPPORT_FINGER           79
#define IPPORT_TTYLINK          87
#define IPPORT_SUPDUP           95

/*
 * UNIX TCP sockets
 */
#define IPPORT_EXECSERVER       512
#define IPPORT_LOGINSERVER      513
#define IPPORT_CMDSERVER        514
#define IPPORT_EFSSERVER        520

/*
 * UNIX UDP sockets
 */
#define IPPORT_BIFFUDP          512
#define IPPORT_WHOSERVER        513
#define IPPORT_ROUTESERVER      520
                                        /* 520+1 also used */

/*
 * Ports < IPPORT_RESERVED are reserved for
 * privileged processes (e.g. root).
 */
#define IPPORT_RESERVED         1024

/*
 * Link numbers
 */
#define IMPLINK_IP              155
#define IMPLINK_LOWEXPER        156
#define IMPLINK_HIGHEXPER       158

/*
 * Internet address (old style... should be updated)
 */
struct in_addr {
        union {
                struct { u_char s_b1,s_b2,s_b3,s_b4; } S_un_b;
                struct { u_short s_w1,s_w2; } S_un_w;
                u_long S_addr;
        } S_un;
#define s_addr  S_un.S_addr
                                /* can be used for most tcp & ip code */
#define s_host  S_un.S_un_b.s_b2
                                /* host on imp */
#define s_net   S_un.S_un_b.s_b1
                                /* network */
#define s_imp   S_un.S_un_w.s_w2
                                /* imp */
#define s_impno S_un.S_un_b.s_b4
                                /* imp # */
#define s_lh    S_un.S_un_b.s_b3
                                /* logical host */
};

/*
 * Definitions of bits in internet address integers.
 * On subnets, the decomposition of addresses to host and net parts
 * is done according to subnet mask, not the masks here.
 */
#define IN_CLASSA(i)            (((long)(i) & 0x80000000) == 0)
#define IN_CLASSA_NET           0xff000000
#define IN_CLASSA_NSHIFT        24
#define IN_CLASSA_HOST          0x00ffffff
#define IN_CLASSA_MAX           128

#define IN_CLASSB(i)            (((long)(i) & 0xc0000000) == 0x80000000)
#define IN_CLASSB_NET           0xffff0000
#define IN_CLASSB_NSHIFT        16
#define IN_CLASSB_HOST          0x0000ffff
#define IN_CLASSB_MAX           65536

#define IN_CLASSC(i)            (((long)(i) & 0xc0000000) == 0xc0000000)
#define IN_CLASSC_NET           0xffffff00
#define IN_CLASSC_NSHIFT        8
#define IN_CLASSC_HOST          0x000000ff

#define INADDR_ANY              (u_long)0x00000000
#define INADDR_LOOPBACK         0x7f000001
#define INADDR_BROADCAST        (u_long)0xffffffff
#define INADDR_NONE             0xffffffff

/*
 * Socket address, internet style.
 */
struct sockaddr_in {
        short   sin_family;
        u_short sin_port;
        struct  in_addr sin_addr;
        char    sin_zero[8];
};

#define WSADESCRIPTION_LEN      256
#define WSASYS_STATUS_LEN       128

typedef struct WSAData {
        WORD                    wVersion;
        WORD                    wHighVersion;
        char                    szDescription[WSADESCRIPTION_LEN+1];
        char                    szSystemStatus[WSASYS_STATUS_LEN+1];
        unsigned short          iMaxSockets;
        unsigned short          iMaxUdpDg;
        char FAR *              lpVendorInfo;
} WSADATA;

typedef WSADATA FAR *LPWSADATA;

/*
 * Options for use with [gs]etsockopt at the IP level.
 */
#define IP_OPTIONS      1               /* set/get IP per-packet options */

/*
 * Definitions related to sockets: types, address families, options,
 * taken from the BSD file sys/socket.h.
 */

/*
 * This is used instead of -1, since the
 * SOCKET type is unsigned.
 */
#define INVALID_SOCKET  (SOCKET)(~0)
#define SOCKET_ERROR            (-1)

/*
 * Types
 */
#define SOCK_STREAM     1               /* stream socket */
#define SOCK_DGRAM      2               /* datagram socket */
#define SOCK_RAW        3               /* raw-protocol interface */
#define SOCK_RDM        4               /* reliably-delivered message */
#define SOCK_SEQPACKET  5               /* sequenced packet stream */

/*
 * Option flags per-socket.
 */
#define SO_DEBUG        0x0001          /* turn on debugging info recording */
#define SO_ACCEPTCONN   0x0002          /* socket has had listen() */
#define SO_REUSEADDR    0x0004          /* allow local address reuse */
#define SO_KEEPALIVE    0x0008          /* keep connections alive */
#define SO_DONTROUTE    0x0010          /* just use interface addresses */
#define SO_BROADCAST    0x0020          /* permit sending of broadcast msgs */
#define SO_USELOOPBACK  0x0040          /* bypass hardware when possible */
#define SO_LINGER       0x0080          /* linger on close if data present */
#define SO_OOBINLINE    0x0100          /* leave received OOB data in line */

#define SO_DONTLINGER   (u_int)(~SO_LINGER)

/*
 * Additional options.
 */
#define SO_SNDBUF       0x1001          /* send buffer size */
#define SO_RCVBUF       0x1002          /* receive buffer size */
#define SO_SNDLOWAT     0x1003          /* send low-water mark */
#define SO_RCVLOWAT     0x1004          /* receive low-water mark */
#define SO_SNDTIMEO     0x1005          /* send timeout */
#define SO_RCVTIMEO     0x1006          /* receive timeout */
#define SO_ERROR        0x1007          /* get error status and clear */
#define SO_TYPE         0x1008          /* get socket type */

/*
 * TCP options.
 */
#define TCP_NODELAY     0x0001

/*
 * Address families.
 */
#define AF_UNSPEC       0               /* unspecified */
#define AF_UNIX         1               /* local to host (pipes, portals) */
#define AF_INET         2               /* internetwork: UDP, TCP, etc. */
#define AF_IMPLINK      3               /* arpanet imp addresses */
#define AF_PUP          4               /* pup protocols: e.g. BSP */
#define AF_CHAOS        5               /* mit CHAOS protocols */
#define AF_NS           6               /* XEROX NS protocols */
#define AF_ISO          7               /* ISO protocols */
#define AF_OSI          AF_ISO          /* OSI is ISO */
#define AF_ECMA         8               /* european computer manufacturers */
#define AF_DATAKIT      9               /* datakit protocols */
#define AF_CCITT        10              /* CCITT protocols, X.25 etc */
#define AF_SNA          11              /* IBM SNA */
#define AF_DECnet       12              /* DECnet */
#define AF_DLI          13              /* Direct data link interface */
#define AF_LAT          14              /* LAT */
#define AF_HYLINK       15              /* NSC Hyperchannel */
#define AF_APPLETALK    16              /* AppleTalk */
#define AF_NETBIOS      17              /* NetBios-style addresses */

#define AF_MAX          18

/*
 * Structure used by kernel to store most
 * addresses.
 */
struct sockaddr {
        u_short sa_family;              /* address family */
        char    sa_data[14];            /* up to 14 bytes of direct address */
};

/*
 * Structure used by kernel to pass protocol
 * information in raw sockets.
 */
struct sockproto {
        u_short sp_family;              /* address family */
        u_short sp_protocol;            /* protocol */
};

/*
 * Protocol families, same as address families for now.
 */
#define PF_UNSPEC       AF_UNSPEC
#define PF_UNIX         AF_UNIX
#define PF_INET         AF_INET
#define PF_IMPLINK      AF_IMPLINK
#define PF_PUP          AF_PUP
#define PF_CHAOS        AF_CHAOS
#define PF_NS           AF_NS
#define PF_ISO          AF_ISO
#define PF_OSI          AF_OSI
#define PF_ECMA         AF_ECMA
#define PF_DATAKIT      AF_DATAKIT
#define PF_CCITT        AF_CCITT
#define PF_SNA          AF_SNA
#define PF_DECnet       AF_DECnet
#define PF_DLI          AF_DLI
#define PF_LAT          AF_LAT
#define PF_HYLINK       AF_HYLINK
#define PF_APPLETALK    AF_APPLETALK

#define PF_MAX          AF_MAX

/*
 * Structure used for manipulating linger option.
 */
struct  linger {
        u_short l_onoff;                /* option on/off */
        u_short l_linger;               /* linger time */
};

/*
 * Level number for (get/set)sockopt() to apply to socket itself.
 */
#define SOL_SOCKET      0xffff          /* options for socket level */

/*
 * Maximum queue length specifiable by listen.
 */
#define SOMAXCONN       5

#define MSG_OOB         0x1             /* process out-of-band data */
#define MSG_PEEK        0x2             /* peek at incoming message */
#define MSG_DONTROUTE   0x4             /* send without using routing tables */

#define MSG_MAXIOVLEN   16

/*
 * Define constant based on rfc883, used by gethostbyxxxx() calls.
 */
#define MAXGETHOSTSTRUCT        1024

/*
 * Define flags to be used with the WSAAsyncSelect() call.
 */
#define FD_READ         0x01
#define FD_WRITE        0x02
#define FD_OOB          0x04
#define FD_ACCEPT       0x08
#define FD_CONNECT      0x10
#define FD_CLOSE        0x20

/*
 * All Windows Sockets error constants are biased by WSABASEERR from
 * the "normal"
 */
#define WSABASEERR              10000
/*
 * Windows Sockets definitions of regular Microsoft C error constants
 */
#define WSAEINTR                (WSABASEERR+4)
#define WSAEBADF                (WSABASEERR+9)
#define WSAEACCES               (WSABASEERR+13)
#define WSAEFAULT               (WSABASEERR+14)
#define WSAEINVAL               (WSABASEERR+22)
#define WSAEMFILE               (WSABASEERR+24)

/*
 * Windows Sockets definitions of regular Berkeley error constants
 */
#define WSAEWOULDBLOCK          (WSABASEERR+35)
#define WSAEINPROGRESS          (WSABASEERR+36)
#define WSAEALREADY             (WSABASEERR+37)
#define WSAENOTSOCK             (WSABASEERR+38)
#define WSAEDESTADDRREQ         (WSABASEERR+39)
#define WSAEMSGSIZE             (WSABASEERR+40)
#define WSAEPROTOTYPE           (WSABASEERR+41)
#define WSAENOPROTOOPT          (WSABASEERR+42)
#define WSAEPROTONOSUPPORT      (WSABASEERR+43)
#define WSAESOCKTNOSUPPORT      (WSABASEERR+44)
#define WSAEOPNOTSUPP           (WSABASEERR+45)
#define WSAEPFNOSUPPORT         (WSABASEERR+46)
#define WSAEAFNOSUPPORT         (WSABASEERR+47)
#define WSAEADDRINUSE           (WSABASEERR+48)
#define WSAEADDRNOTAVAIL        (WSABASEERR+49)
#define WSAENETDOWN             (WSABASEERR+50)
#define WSAENETUNREACH          (WSABASEERR+51)
#define WSAENETRESET            (WSABASEERR+52)
#define WSAECONNABORTED         (WSABASEERR+53)
#define WSAECONNRESET           (WSABASEERR+54)
#define WSAENOBUFS              (WSABASEERR+55)
#define WSAEISCONN              (WSABASEERR+56)
#define WSAENOTCONN             (WSABASEERR+57)
#define WSAESHUTDOWN            (WSABASEERR+58)
#define WSAETOOMANYREFS         (WSABASEERR+59)
#define WSAETIMEDOUT            (WSABASEERR+60)
#define WSAECONNREFUSED         (WSABASEERR+61)
#define WSAELOOP                (WSABASEERR+62)
#define WSAENAMETOOLONG         (WSABASEERR+63)
#define WSAEHOSTDOWN            (WSABASEERR+64)
#define WSAEHOSTUNREACH         (WSABASEERR+65)
#define WSAENOTEMPTY            (WSABASEERR+66)
#define WSAEPROCLIM             (WSABASEERR+67)
#define WSAEUSERS               (WSABASEERR+68)
#define WSAEDQUOT               (WSABASEERR+69)
#define WSAESTALE               (WSABASEERR+70)
#define WSAEREMOTE              (WSABASEERR+71)

/*
 * Extended Windows Sockets error constant definitions
 */
#define WSASYSNOTREADY          (WSABASEERR+91)
#define WSAVERNOTSUPPORTED      (WSABASEERR+92)
#define WSANOTINITIALISED       (WSABASEERR+93)

/*
 * Error return codes from gethostbyname() and gethostbyaddr()
 * (when using the resolver). Note that these errors are
 * retrieved via WSAGetLastError() and must therefore follow
 * the rules for avoiding clashes with error numbers from
 * specific implementations or language run-time systems.
 * For this reason the codes are based at WSABASEERR+1001.
 * Note also that [WSA]NO_ADDRESS is defined only for
 * compatibility purposes.
 */

#define h_errno         WSAGetLastError()

/* Authoritative Answer: Host not found */
#define WSAHOST_NOT_FOUND       (WSABASEERR+1001)
#define HOST_NOT_FOUND          WSAHOST_NOT_FOUND

/* Non-Authoritative: Host not found, or SERVERFAIL */
#define WSATRY_AGAIN            (WSABASEERR+1002)
#define TRY_AGAIN               WSATRY_AGAIN

/* Non recoverable errors, FORMERR, REFUSED, NOTIMP */
#define WSANO_RECOVERY          (WSABASEERR+1003)
#define NO_RECOVERY             WSANO_RECOVERY

/* Valid name, no data record of requested type */
#define WSANO_DATA              (WSABASEERR+1004)
#define NO_DATA                 WSANO_DATA

/* no address, look for MX record */
#define WSANO_ADDRESS           WSANO_DATA
#define NO_ADDRESS              WSANO_ADDRESS

/*
 * Windows Sockets errors redefined as regular Berkeley error constants
 */
#define EWOULDBLOCK             WSAEWOULDBLOCK
#define EINPROGRESS             WSAEINPROGRESS
#define EALREADY                WSAEALREADY
#define ENOTSOCK                WSAENOTSOCK
#define EDESTADDRREQ            WSAEDESTADDRREQ
#define EMSGSIZE                WSAEMSGSIZE
#define EPROTOTYPE              WSAEPROTOTYPE
#define ENOPROTOOPT             WSAENOPROTOOPT
#define EPROTONOSUPPORT         WSAEPROTONOSUPPORT
#define ESOCKTNOSUPPORT         WSAESOCKTNOSUPPORT
#define EOPNOTSUPP              WSAEOPNOTSUPP
#define EPFNOSUPPORT            WSAEPFNOSUPPORT
#define EAFNOSUPPORT            WSAEAFNOSUPPORT
#define EADDRINUSE              WSAEADDRINUSE
#define EADDRNOTAVAIL           WSAEADDRNOTAVAIL
#define ENETDOWN                WSAENETDOWN
#define ENETUNREACH             WSAENETUNREACH
#define ENETRESET               WSAENETRESET
#define ECONNABORTED            WSAECONNABORTED
#define ECONNRESET              WSAECONNRESET
#define ENOBUFS                 WSAENOBUFS
#define EISCONN                 WSAEISCONN
#define ENOTCONN                WSAENOTCONN
#define ESHUTDOWN               WSAESHUTDOWN
#define ETOOMANYREFS            WSAETOOMANYREFS
#define ETIMEDOUT               WSAETIMEDOUT
#define ECONNREFUSED            WSAECONNREFUSED
#define ELOOP                   WSAELOOP
#define ENAMETOOLONG            WSAENAMETOOLONG
#define EHOSTDOWN               WSAEHOSTDOWN
#define EHOSTUNREACH            WSAEHOSTUNREACH
#define ENOTEMPTY               WSAENOTEMPTY
#define EPROCLIM                WSAEPROCLIM
#define EUSERS                  WSAEUSERS
#define EDQUOT                  WSAEDQUOT
#define ESTALE                  WSAESTALE
#define EREMOTE                 WSAEREMOTE

/* Socket function prototypes */

#ifdef __cplusplus
extern "C" {
#endif

SOCKET PASCAL FAR accept (SOCKET s, struct sockaddr FAR *addr,
                          int FAR *addrlen);

int PASCAL FAR bind (SOCKET s, const struct sockaddr FAR *addr, int namelen);

int PASCAL FAR closesocket (SOCKET s);

int PASCAL FAR connect (SOCKET s, const struct sockaddr FAR *name, int namelen);

int PASCAL FAR ioctlsocket (SOCKET s, long cmd, u_long FAR *argp);

int PASCAL FAR getpeername (SOCKET s, struct sockaddr FAR *name,
                            int FAR * namelen);

int PASCAL FAR getsockname (SOCKET s, struct sockaddr FAR *name,
                            int FAR * namelen);

int PASCAL FAR getsockopt (SOCKET s, int level, int optname,
                           char FAR * optval, int FAR *optlen);

u_long PASCAL FAR htonl (u_long hostlong);

u_short PASCAL FAR htons (u_short hostshort);

unsigned long PASCAL FAR inet_addr (const char FAR * cp);

char FAR * PASCAL FAR inet_ntoa (struct in_addr in);

int PASCAL FAR listen (SOCKET s, int backlog);

u_long PASCAL FAR ntohl (u_long netlong);

u_short PASCAL FAR ntohs (u_short netshort);

int PASCAL FAR recv (SOCKET s, char FAR * buf, int len, int flags);

int PASCAL FAR recvfrom (SOCKET s, char FAR * buf, int len, int flags,
                         struct sockaddr FAR *from, int FAR * fromlen);

int PASCAL FAR select (int nfds, fd_set FAR *readfds, fd_set FAR *writefds,
                       fd_set FAR *exceptfds, const struct timeval FAR *timeout);

int PASCAL FAR send (SOCKET s, const char FAR * buf, int len, int flags);

int PASCAL FAR sendto (SOCKET s, const char FAR * buf, int len, int flags,
                       const struct sockaddr FAR *to, int tolen);

int PASCAL FAR setsockopt (SOCKET s, int level, int optname,
                           const char FAR * optval, int optlen);

int PASCAL FAR shutdown (SOCKET s, int how);

SOCKET PASCAL FAR socket (int af, int type, int protocol);

/* Database function prototypes */

struct hostent FAR * PASCAL FAR gethostbyaddr(const char FAR * addr,
                                              int len, int type);

struct hostent FAR * PASCAL FAR gethostbyname(const char FAR * name);

int PASCAL FAR gethostname (char FAR * name, int namelen);

struct servent FAR * PASCAL FAR getservbyport(int port, const char FAR * proto);

struct servent FAR * PASCAL FAR getservbyname(const char FAR * name,
                                              const char FAR * proto);

struct protoent FAR * PASCAL FAR getprotobynumber(int proto);

struct protoent FAR * PASCAL FAR getprotobyname(const char FAR * name);

/* Microsoft Windows Extension function prototypes */

int PASCAL FAR WSAStartup(WORD wVersionRequired, LPWSADATA lpWSAData);

int PASCAL FAR WSACleanup(void);

void PASCAL FAR WSASetLastError(int iError);

int PASCAL FAR WSAGetLastError(void);

BOOL PASCAL FAR WSAIsBlocking(void);

int PASCAL FAR WSAUnhookBlockingHook(void);

FARPROC PASCAL FAR WSASetBlockingHook(FARPROC lpBlockFunc);

int PASCAL FAR WSACancelBlockingCall(void);

HANDLE PASCAL FAR WSAAsyncGetServByName(HWND hWnd, u_int wMsg,
                                        const char FAR * name,
                                        const char FAR * proto,
                                        char FAR * buf, int buflen);

HANDLE PASCAL FAR WSAAsyncGetServByPort(HWND hWnd, u_int wMsg, int port,
                                        const char FAR * proto, char FAR * buf,
                                        int buflen);

HANDLE PASCAL FAR WSAAsyncGetProtoByName(HWND hWnd, u_int wMsg,
                                         const char FAR * name, char FAR * buf,
                                         int buflen);

HANDLE PASCAL FAR WSAAsyncGetProtoByNumber(HWND hWnd, u_int wMsg,
                                           int number, char FAR * buf,
                                           int buflen);

HANDLE PASCAL FAR WSAAsyncGetHostByName(HWND hWnd, u_int wMsg,
                                        const char FAR * name, char FAR * buf,
                                        int buflen);

HANDLE PASCAL FAR WSAAsyncGetHostByAddr(HWND hWnd, u_int wMsg,
                                        const char FAR * addr, int len, int type,
                                        const char FAR * buf, int buflen);

int PASCAL FAR WSACancelAsyncRequest(HANDLE hAsyncTaskHandle);

int PASCAL FAR WSAAsyncSelect(SOCKET s, HWND hWnd, u_int wMsg,
                               long lEvent);

#ifdef __cplusplus
}
#endif

/* Microsoft Windows Extended data types */
typedef struct sockaddr SOCKADDR;
typedef struct sockaddr *PSOCKADDR;
typedef struct sockaddr FAR *LPSOCKADDR;

typedef struct sockaddr_in SOCKADDR_IN;
typedef struct sockaddr_in *PSOCKADDR_IN;
typedef struct sockaddr_in FAR *LPSOCKADDR_IN;

typedef struct linger LINGER;
typedef struct linger *PLINGER;
typedef struct linger FAR *LPLINGER;

typedef struct in_addr IN_ADDR;
typedef struct in_addr *PIN_ADDR;
typedef struct in_addr FAR *LPIN_ADDR;

typedef struct fd_set FD_SET;
typedef struct fd_set *PFD_SET;
typedef struct fd_set FAR *LPFD_SET;

typedef struct hostent HOSTENT;
typedef struct hostent *PHOSTENT;
typedef struct hostent FAR *LPHOSTENT;

typedef struct servent SERVENT;
typedef struct servent *PSERVENT;
typedef struct servent FAR *LPSERVENT;

typedef struct protoent PROTOENT;
typedef struct protoent *PPROTOENT;
typedef struct protoent FAR *LPPROTOENT;

typedef struct timeval TIMEVAL;
typedef struct timeval *PTIMEVAL;
typedef struct timeval FAR *LPTIMEVAL;

/*
 * Windows message parameter composition and decomposition
 * macros.
 *
 * WSAMAKEASYNCREPLY is intended for use by the Windows Sockets implementation
 * when constructing the response to a WSAAsyncGetXByY() routine.
 */
#define WSAMAKEASYNCREPLY(buflen,error)     MAKELONG(buflen,error)
/*
 * WSAMAKESELECTREPLY is intended for use by the Windows Sockets implementation
 * when constructing the response to WSAAsyncSelect().
 */
#define WSAMAKESELECTREPLY(event,error)     MAKELONG(event,error)
/*
 * WSAGETASYNCBUFLEN is intended for use by the Windows Sockets application
 * to extract the buffer length from the lParam in the response
 * to a WSAGetXByY().
 */
#define WSAGETASYNCBUFLEN(lParam)           LOWORD(lParam)
/*
 * WSAGETASYNCERROR is intended for use by the Windows Sockets application
 * to extract the error code from the lParam in the response
 * to a WSAGetXByY().
 */
#define WSAGETASYNCERROR(lParam)            HIWORD(lParam)
/*
 * WSAGETSELECTEVENT is intended for use by the Windows Sockets application
 * to extract the event code from the lParam in the response
 * to a WSAAsyncSelect().
 */
#define WSAGETSELECTEVENT(lParam)           LOWORD(lParam)
/*
 * WSAGETSELECTERROR is intended for use by the Windows Sockets application
 * to extract the error code from the lParam in the response
 * to a WSAAsyncSelect().
 */
#define WSAGETSELECTERROR(lParam)           HIWORD(lParam)

#endif  /* _WINSOCKAPI_ */


                   Appendix B: Notes for Windows Sockets Suppliers 149


Appendix B.  Notes for Windows Sockets Suppliers

B.1 Introduction
A Windows Sockets implementation must implement ALL the functionality
described in the Windows Sockets documentation.  Validation of
compliance is discussed in section B.8.

Windows Sockets Version 1.1 implementations must support both TCP and
UDP type sockets.  An implementation may support raw sockets (of type
SOCK_RAW), but their use is deprecated.

Certain APIs documented above have special notes for Windows Sockets
implementors.  A Windows Sockets implementation should pay special
attention to conforming to the API as documented.  The Special Notes
are provided for assistance and clarification.


B.2 Windows Sockets Components
B.2.1 Development Components
The Windows Sockets development components for use by Windows Sockets
application developers will be provided by each Windows Sockets
supplier.  These Windows Sockets development components are:

Component           Description
Windows Sockets Documentation This document
WINSOCK.LIB file    Windows Sockets API Import Library
WINSOCK.H file      Windows Sockets Header File
NETDB.H file        Berkeley Compatible Header File
ARPA/INET.H file    Berkeley Compatible Header File
SYS/TIME.H file     Berkeley Compatible Header File
SYS/SOCKET.H file   Berkeley Compatible Header File
NETINET/IN.H file   Berkeley Compatible Header File

B.2.2 Run Time Components
The run time component provided by each Windows Sockets supplier is:

Component           Description
WINSOCK.DLL         The Windows Sockets API implementation DLL


B.3 Multithreadedness and blocking routines.
Data areas returned by, for example, the getXbyY() routines MUST be on
a per thread basis.

Note that an application MUST be prevented from making multiple nested
Windows Sockets function calls.  Only one outstanding function call
will be allowed for a particular task.  Any Windows Sockets call
performed when an existing blocking call is already outstanding will
fail with an error code of WSAEINPROGRESS.  There are two exceptions
to this restriction: WSACancelBlockingCall() and WSAIsBlocking() may
be called at any time.  Windows Sockets suppliers should note that
although preliminary drafts of this specification indicated that the
restriction only applied to blocking function calls, and that it would
be permissible to make non-blocking calls while a blocking call was in
progress, this is no longer true.


150 Appendix B: Notes for Windows Sockets Suppliers

Regarding the implementation of blocking routines, the solution in
Windows Sockets is to simulate the blocking mechanism by having each
routine call PeekMessage() as it waits for the completion of its
operation.  In anticipation of this, the function WSASetBlockingHook()
is provided to allow the programmer to define a special routine to be
called instead of the default PeekMessage() loop.  The blocking hook
functions are discussed in more detail in 4.3.13,
WSASetBlockingHook().


B.4 Database Files
The database routines in the getXbyY() family (gethostbyaddr(), etc.)
were originally designed (in the first Berkeley UNIX releases) as
mechanisms for looking up information in text databases.  A Windows
Sockets supplier may choose to employ local files OR a name service to
provide some or all of this information.  If local files exist, the
format of the files must be identical to that used in BSD UNIX,
allowing for the differences in text file formats.


B.5 FD_ISSET
It is necessary to implement the FD_ISSET Berkeley macro using a
supporting function: __WSAFDIsSet().  It is the responsibility of a
Windows Sockets implementation to make this available as part of the
Windows Sockets API.  Unlike the other functions exported by a Windows
Sockets DLL, however, this function is not intended to be invoked
directly by Windows Sockets applications: it should be used only to
support the FD_ISSET macro.  The source code for this function is
listed below:

int FAR
__WSAFDIsSet(SOCKET fd, fd_set FAR *set)
{
    int i = set->fd_count;

    while (i--)
     if (set->fd_array[i] == fd)
         return 1;

    return 0;
}


B.6 Error Codes
In order to avoid conflict between various compiler environments
Windows Sockets implementations MUST return the error codes listed in
the API specification, using the manifest constants beginning with
"WSA".  The Berkeley-compatible error code definitions are provided
solely for compatibility purposes for applications which are being
ported from other platforms.


B.7 DLL Ordinal Numbers
The winsock.def file for use by every Windows Sockets implementation
is as follows.  Ordinal values starting at 1000 are reserved for
Windows Sockets implementors to use for exporting private interfaces
to their DLLs.  A Windows Sockets implementation must not use any


                   Appendix B: Notes for Windows Sockets Suppliers 151

ordinals 999 and below except for those APIs listed below.  An
application which wishes to work with any Windows Sockets DLL must use
only those routines listed below; using a private export makes an
application dependent on a particular Windows Sockets implementation.

;
;         File: winsock.def
;       System: MS-Windows 3.x
;      Summary: Module definition file for Windows Sockets DLL.
;

LIBRARY         WINSOCK         ; Application's module name

DESCRIPTION     'BSD Socket API for Windows'

EXETYPE         WINDOWS         ; required for all windows
applications

STUB            'WINSTUB.EXE'   ; generates error message if
application
                                ; is run without Windows

;CODE can be FIXED in memory because of potential upcalls
CODE            PRELOAD         FIXED

;DATA must be SINGLE and at a FIXED location since this is a DLL
DATA            PRELOAD         FIXED           SINGLE

HEAPSIZE        1024
STACKSIZE       16384

; All functions that will be called by any Windows routine
; must be exported.  Any additional exports beyond those defined
; here must have ordinal numbers 1000 or above.

EXPORTS
        accept                         @1
        bind                           @2
        closesocket                    @3
        connect                        @4
        getpeername                    @5
        getsockname                    @6
        getsockopt                     @7
        htonl                          @8
        htons                          @9
        inet_addr                      @10
        inet_ntoa                      @11
        ioctlsocket                    @12
        listen                         @13
        ntohl                          @14
        ntohs                          @15
        recv                           @16
        recvfrom                       @17
        select                         @18
        send                           @19
        sendto                         @20
        setsockopt                     @21


152 Appendix B: Notes for Windows Sockets Suppliers

        shutdown                       @22
        socket                         @23

        gethostbyaddr                  @51
        gethostbyname                  @52
        getprotobyname                 @53
        getprotobynumber               @54
        getservbyname                  @55
        getservbyport                  @56
        gethostname                    @57

        WSAAsyncSelect                 @101
        WSAAsyncGetHostByAddr          @102
        WSAAsyncGetHostByName          @103
        WSAAsyncGetProtoByNumber       @104
        WSAAsyncGetProtoByName         @105
        WSAAsyncGetServByPort          @106
        WSAAsyncGetServByName          @107
        WSACancelAsyncRequest          @108
        WSASetBlockingHook             @109
        WSAUnhookBlockingHook          @110
        WSAGetLastError                @111
        WSASetLastError                @112
        WSACancelBlockingCall          @113
        WSAIsBlocking                  @114
        WSAStartup                     @115
        WSACleanup                     @116

        __WSAFDIsSet                   @151

        WEP                            @500    RESIDENTNAME

;eof


B.8 Validation Suite

An alpha version of the Windows Sockets Test and Validation Suite to
ensure Windows Sockets compatibility will be available at Fall 1992
Interop from Microsoft.  This alpha version includes functionality
testing of the Windows Sockets interface and is supported by a
comprehensive scripting language.  The final version of the suite is
expected to be available in January 1993, and it will include a more
sophisticated user interface.  Beta versions may be available in the
interim.  Further documentation on the test suite is available from
Microsoft.


                   Appendix B: Notes for Windows Sockets Suppliers 153


Appendix C.  For Further Reference

This specification is intended to cover the Windows Sockets interface
to TCP/IP in detail.  Many details of TCP/IP and Windows, however, are
intentionally omitted in the interest of brevity, and this
specification often assumes background knowledge of these topics.  For
more information, the following references may be helpful:

Braden, R.[1989], RFC 1122, Requirements for Internet Hosts--
          Communication Layers, Internet Engineering Task Force.

Comer, D. [1991], Internetworking with TCP/IP Volume I: Principles,
          Protocols, and Architecture, Prentice Hall, Englewood
          Cliffs, New Jersey.

Comer, D. and Stevens, D. [1991], Internetworking with TCP/IP Volume
          II: Design, Implementation, and Internals, Prentice Hall,
          Englewood Cliffs, New Jersey.

Comer, D. and Stevens, D. [1991], Internetworking with TCP/IP Volume
          III: Client-Server Programming and Applications, Prentice
          Hall, Englewood Cliffs, New Jersey.

Leffler, S. et al., An Advanced 4.3BSD Interprocess Communication
          Tutorial.

Petzold, C. [1992], Programming Windows 3.1, Microsoft Press, Redmond,
          Washington.

Stevens, W.R. [1990], Unix Network Programming, Prentice Hall,
          Englewood Cliffs, New Jersey.



Appendix D.  Background Information

D.1 Legal Status of Windows Sockets

The copyright for the Windows Sockets specification is owned by the
specification authors listed on the title page.  Permission is granted
to redistribute this specification in any form, provided that the
contents of the specification are not modified.  Windows Sockets
implementors are encouraged to include this specification with their
product documentation.

The Windows Sockets logo on the title page of this document is meant
for use on both Windows Sockets implementations and for applications
that use the Windows Sockets interface.  Use of the logo is encouraged
on packaging, documentation, collateral, and advertising.  The logo is
available on microdyne.com in pub/winsock as winsock.bmp.  The
suggested color for the logo's title bar is blue, the electrical
socket grey, and the text and outline black.



D.2 The Story Behind the Windows Sockets Icon


154 Appendix B: Notes for Windows Sockets Suppliers


(by Alistair Banks, Microsoft Corporation)

We thought we'd do a "Wind Sock" at one stage--but you try to get that
into 32x32 bits! It would have had to look wavy and colorful, and...
well, it just didn't work. Also, our graphics designers have
"opinions"
about the icons truly representing what they are--people would have
thought this was "The colorful wavy tube specification 1.0!"

I tried to explain "API" "Programming Interface" to the artist--we
ended up with toolbox icons with little flying windows

Then we came to realise that we should be going after the shortened
form of the name, rather the name in full... Windows Sockets... And so
we went for that - so she drew (now remember I'm English and you're
probably American) "Windows Spanner", a.k.a. a socket wrench.  In the
U.S. you'd have been talking about the "Windows Socket spec" OK, but
in England that would have been translated as "Windows Spanner Spec
1.0" - so we went to Electrical sockets - well the first ones came out
looking like "Windows Pignose Spec 1.0"!!!!

So how do you use 32x32, get an international electrical socket! You
take the square type (American & English OK, Europe & Australia are
too rounded)--you choose the American one, because it's on the wall in
front of you (and it's more compact (but less safe, IMHO) and then you
turn it upside down, thereby compromising its nationality!

[IMHO = "In My Humble Opinion"--ed.]