Aminet 1 (Walnut Creek)/Aminet - June 1993 [Walnut Creek].iso/aminet/comm/misc/xpr_2_0.lha/DocXProtocol.doc

Text File | 1989-09-11 | 91KB | 2,328 lines

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Trademarks:
Amiga is a trademark of Commodore Business Machines.
A-Talk III is a trademark of Felsina Software.
Manx is a trademark of Manx Software Systems.
Lattice is a trademark of Lattice, Inc.




        XPR: External File Transfer Protocols as Amiga Libraries.
        =========================================================

                    Version 2.0 - 11 September 1989

                       (C) Copyright 1989 by

                         W.G.J. Langeveld

                 Stanford Linear Accelerator Center


                              ABSTRACT
                              ========

             This  document  describes a  standard method
             of using  Amiga  shared  libraries  for  the
             implementation  of  external  file  transfer
             protocols  (XPR's), as  implemented  in  the
             Amiga  terminal  emulators  A-Talk  III  and
             VLT.  The  method  can  also be  used to im-
             plement external terminal emulations (XEM's).



1. Introduction.
================

        One of the most frequently asked questions of the author of a
communications program is "Why don't you implement this wonderful file transfer
protocol in addition to the 25 you already have?". Clearly, implementing more
FTP's leads to larger code size and to increased product development time and
customer support requirements, unless there is a way to have the additional
protocols available as separate entities. One obvious way is to put the
additional FTP's in overlays, but that only mitigates the code size problem and
does not allow protocols to be used with communications programs of different
vendors. Better is to open the serial device as a shared port and to have a
completely separate program access it at the same time. However, this method has
the disadvantage that shared use of a single serial port can lead to
unpredictable results unless there is a well-established priority system
enforcing which program is allowed to write to the device at which time. The
advantage is that the FTP can now be developed separately and even by someone
other than the author of the communications program. There are variations
involving inter-process communication to add access control to the latter
system, but I will not go into further detail.
        The system described here is based on Amiga shared libraries. The
library implements a small number of primary functions, such as "Send File(s)"
and "Receive File(s)". These functions are called with a single argument, a
pointer to an XPR_IO structure. This structure contains a number of things, the
more obvious one being a pointer to a null terminated string indicating which
files are to be sent or received and addresses of "call-back" functions inside
the code of the communications program to access the serial device, which is
opened typically in exclusive access. The scheme described here opens the
possibility for the Amiga community to write a multitude of file transfer
protocols, all rather small in size because they don't contain any overhead,
that work with any communications program following the rules outlined in this
document.
        Possible problems with shared libraries are that they should be
reentrant and that they should, if possible, not open dos.library [1]. On the
other hand, these problems can easily be turned into advantages: for one,
reentrancy is not hard to accomplish and in addition when there are multiple
serial ports in use all of them can use the FTP with a single copy of the code.
Not having to open dos.library can be accomplished by having call-back functions
that provide all the DOS access needed in the original communications program.
Typically these DOS functions are already linked into the original code anyway,
and call-backs have to be provided for serial port access in any case.
        For the sake of reentrancy across calls to the external protocol library
(XPR), a field for storing a pointer to a data area is added for use by the XPR
internally.

        Section 2 explains the library structure itself. Section 3 covers the
XPR_IO structure and defines all the call-back functions. Section 4 describes an
example library for a simple ASCII transfer without bells or whistles and will
show how to code the library part of the call-backs. Section 5 shows how to set
up a partial interface on the communications program side, sufficient to work
with the ASCII example. Note: Sections 2 through 5 only describe the
functionality of the specification that was present in the first public release.
Section 6, finally, describes a number of extensions that were added later.

        Note: the examples are all for Manx C and assembler but should be easily
modifyable for Lattice or any other language. Not all source files are given in
this document. This archive, however, contains the example library plus all
files needed to link it and interface to it, for Manx. Specifically, the
routines that interface to XPR from VLT are in the "comm-program" subdirectory,
and the sources to the library are in the "library" subdirectory. Also note,
that both communications program and XPR implementers can only count on the
the arguments passed in the registers as indicated. While it may appear from
some of the code that the arguments are also available on the stack, this can
not be relied on.

        I would like to thank Marco Papa of Felsina Software for his help in
working out some of the details of the XPR standard, and Rick Huebner for his
comments and debugging in the later stages.

        Neither this document, nor the XPR standard, nor the other files in this
archive are in the public domain, but they may be freely distributed and used
for any purpose bearing in mind the stipulations given in the disclaimer above,
and with the proviso that in case of further distribution all files of this
archive must remain together and unchanged.


Reference:
[1] Jim Mackraz says that opening dos.library inside a library is not a good
    idea.


2. XPR libraries.
=================

        Each external FTP is implemented as a separate library which lives in
the libs: directory. It is mandatory that the names of XPR libraries start with
the three letters "xpr" so that they are easily identified. The template for the
name is xpr<protocol-name>.library, where <protocol-name> is a descriptive name
of the protocol that is implemented. Obvious examples would be xprkermit.library
and xprxmodem.library, but xprmykermit.library would be fine for a
user-customized kermit implementation. When thinking of a name, the  implementer
of an XPR library should keep in mind that communication programs will likely
use the <protocol-name> part in their XPR requester.
        Each XPR library in turn has four mandatory public functions. The
functions are:

        XProtocolCleanup()
        XProtocolSetup()
        XProtocolSend()    and
        XProtocolReceive()

in addition to the usual open, close expunge and reserved vectors. The library
skeleton is given in Appendix A.
        Two more library functions, XProtocolHostMon() and XProtocolUserMon(),
are optional, see chapter 6.
        Typically, a session with a terminal emulator using external protocols
would consist of

        1. Selecting an external protocol (Using e.g. a file requester
           showing only those files in libs: starting with "xpr").
        2. Retrieving the library base XProtocolBase of the selected protocol
           using OpenLibrary().
        3. (Allocating and) initializing an XPR_IO structure.
        4. Optionally calling XProtocolSetup() with the initialized structure.
        5. Optionally Calling XProtocolSend() and/or XprotocolReceive() once or
           multiple times to transfer files.
        6. Optionally calling XProtocolSetup() to change parameters or to send
           special commands. Perhaps repeat 5.
        7. Calling XprotocolCleanup() to deallocate any resources allocated by
           XProtocolSetup(). (Deallocate the XPR_IO structure if needed).
        8. Closing the library using CloseLibrary().
        9. Repeat the process, or
       10. Exit.

        All four XPR functions take a single argument, a pointer to an XPR_IO
structure, properly initialized as described in section 5, and passed in
register A0. After XProtocolSetup() has been called, the same XPR_IO structure
should be used for calls to any of the other functions. Only the xpr_filename
field is allowed to be changed between  calls. In particular, the xpr_data field
is for internal use by the XPR library only! It should be initialized to NULL
before calling XProtocolSetup() and should not be changed by the communications
program. XProtocolSetup() should be called once right after opening the library
and subsequently only at the request of the user. XProtocolCleanup() should
always be called before the library is closed.
        In the form of a sample program, the rules above look like this:

/** MyWonderFullCommProgram.c
*
*   Just an example. An actual implementation would likely look different.
*
**/
#include <stdio.h>
#include <functions.h>
#include "xproto.h"

struct Library *XProtocolBase = NULL;

#define SEND 1
#define RECEIVE 2
#define INITIALIZE 3

main()
{
   struct XPR_IO io;
   int user_said, Waiting_for_user_input();

   XProtocolBase = OpenLibrary("xprascii.library", 0L);
   if (XProtocolBase == NULL) {
      printf("protocol not found\n");
      exit(10);
   }

/*
*   Initialize structure (see later).
*/
   xpr_setup(io);
/*
*   Retrieve the initalization string
*/
   Get_init_string_from_user_or_wherever(buffer);
   io->xpr_filename = buffer;
   XProtocolSetup(io);

   while (user_said = Waiting_for_user_input(filename)) {
      if (user_said == SEND) {
         io->xpr_filename = filename;
         XProtocolSend(io);
      }
      else if (user_said == RECEIVE) {
         io->xpr_filename = filename;
         XProtocolReceive(io);
      }
      else if (user_said == INITIALIZE) {
         io->xpr_filename = NULL;
         XProtocolSetup(io);
      }
   }

   XProtocolCleanup(io);

   CloseLibrary(XProtocolBase);

   exit(0);
}

        Clearly, only one FTP can be active at any particular instant in the
life of the session of the communications program. However, this is not really a
limitation in practice, and can be worked around at the cost of some amount of
programming effort.
        XProtocolSetup(), XProtocolSend(), XProtocolReceive() and
XProtocolCleanup() return 0L on failure, non-zero on success. Note to XPR
implementers: the vanilla success return code should be 1L. Other bits in the
return code may have special meaning, see section 6.




3. The XPR_IO structure.
========================

        The XPR_IO structure definition is given in Appendix B. The reader
should keep in mind that the callback functions are to be implemented by the
author of the communications program, not by the author of the external
protocol. However, most communications programs already have functions that
perform the operations listed here, so the implementation should not be too
difficult. Also, the communications program author is not required, strictly
speaking, to implement any of the functions: functions that are not implemented
should be indicated by initializing the corresponding XPR_IO field to NULL.
Obviously, a minimum set of functions must be implemented in order to be useful.
On the other hand, it is up to the implementer of the external protocol to
determine if the given set of functions is sufficient to perform the protocol
transfer. In case of missing functions (indicated by NULL fields in the XPR_IO
structure) suitable default actions should be taken.

        We will now examine all the fields of XPR_IO in detail.


3.1     char  *xpr_filename;
----------------------------

        The xpr_filename field is used primarily to pass null-terminated strings
containing a file name (or file names specified by wild cards) to the functions
XProtocolSend() or XProtocolReceive(). The XPR implementer may elect to support
wild cards in the file name. Call-backs for finding the first and next filename
matching the pattern are provided in the XPR_IO structure, but on the other hand
XPR implementers should take care to check that these call-backs are implemented
by the communications program by testing the corresponding XPR_IO fields for
NULL. Never assume that all call-backs are implemented! If a particular
call-back without which the XPR cannot function is not implemented, the XPR
should fail gracefully.

        The xpr_filename field can also be used to pass an initialization string
to XProtocolSetup(). Typically, if this field is left NULL in a call to
XProtocolSetup(), it would be the duty of XProtocolSetup() to query the user for
initialization information, using e.g. the xpr_gets function (see later). If an
initialization string is present, XProtocolSetup() should NOT query the user,
but this is left to the discretion of the implementer of the protocol, as is the
precise form of the initialization string. It is the duty of the communications
program to determine any default initialization strings for the protocol in
question. Suggested is the use of environment variables named for the protocols
they refer to, containing the initialization string. For the simple Ascii
protocol shown later, the user might have a statement like

        set xprascii=50

in his startup sequence, or with AmigaDOS 1.3, a file called xprascii in his
env: directory containing the letters "50" (50 referring here to the number of
ticks delay between 80-character packets - obviously more extensive
initialization might be needed).
        Given the presence of such default information, XProtocolSetup() should
always be called using the default initialization string right after opening the
library. Conversely, a mechanism (menu option) should be present in the
communications program to change the settings by calling XProtocolSetup() with a
NULL value for this field. On the other hand, if no default initialization
string is present, the legal situation can arise that XProtocolSetup() is never
called.
        It should be noted that XProtocolSetup() can be used to implement any
commands not directly related to sending or receiving files. Examples that come
to mind are Kermit Bye and Finish. One should keep in mind, that typically the
communications program does not know what protocol it is running, much less what
commands that protocol might support. When the user asks to "setup" the external
protocol, XProtocolSetup() should be called with a NULL xpr_filename field,
and the external protocol should request a command, as stated before. In the
case of an external Kermit protocol, the user might type a Bye or Finish, and
the external protocol could act accordingly. See section 6 for additional
information.

        The xpr_filename field is ignored by the XProtocolCleanup() function.


3.2    long (*xpr_fopen)();
---------------------------

        The xpr_fopen() call-back function works in most respects identically to
the stdio function fopen(). Calling sequence:

        long fp = (*xpr_fopen)(char *filename, char *accessmode)
        D0                     A0              A1

The result is a FILE structure, but one should not count on it being a
particular one, since it may be compiler dependent. The return value should only
be used in calls to other stdio functions. The only accesmodes available are
"r"  (read-only)
"w"  (write-only, create new file if none exists, truncate existing file)
"a"  (write-only, create new file if none exists, append to existing file)
"r+" (same as "r", but may also write)
"w+" (same as "w", but may also read)
"a+" (same as "a", but may also read).
        An error return is indicated when the function returns NULL.
        Note that the arguments must be passed in registers A0 and A1
respectively. See also section 4.


3.3     long (*xpr_fclose)();
-----------------------------

        The xpr_fclose() call-back function works in most respects identically
to the stdio function fclose(). Calling sequence:

        (*xpr_fclose)(long filepointer)
                      A0

Note that the argument must be passed in register A0.


3.4     long (*xpr_fread)();
----------------------------

        The xpr_fread() call-back function works in most respects identically to
the stdio function fread(). Calling sequence:

        long count = (*xpr_fread)(char *buffer, long size, long count,
        D0                        A0            D0         D1

                                  long fileptr)
                                  A1

The function returns the actual number items read. The size argument is in bytes.
The function returns 0 on error or end of file.


3.5     long (*xpr_fwrite)();
-----------------------------

        The xpr_fwrite() call-back function works in most respects identically
to the stdio function fwrite(). Calling sequence:

        long count = (*xpr_fwrite)(char *buffer, long size, long count,
        D0                         A0            D0         D1

                                  long fileptr)
                                  A1

The function returns the actual number items written. The size argument is in
bytes. The function returns 0 on failure.


3.6     long (*xpr_sread)();
----------------------------

        The xpr_sread() call-back function has the following calling sequence:

        long count = (*xpr_sread)(char *buffer, long size, long timeout)
        D0                        A0            D0         D1

The first argument is a pointer to a buffer to receive the characters from the
serial port, with a size specified in the second argument. The third item is a
timeout in microseconds. The function returns the actual number of characters
put into the buffer, or -1L on error. When the timeout argument is non-zero, the
function will return when one of three events occurs: (1) the timeout period
has expired, or (2) the buffer has been filled with  exactly "size" characters,
or (3) an error occurs.
        Specifically, when the routine is called, a timer is started and set to
the value contained in timeout. The routine now starts collecting data from the
serial port and stores them in buffer. If the timer times out before size
characters are received, the routine returns immediately with count set to the
actual number of characters received. In case no characters at all are received,
it will return count = 0L. If the buffer is full before the timer has expired,
the routine returns immediately with count = size. It is up to the XPR to set
the  timeout long enough to ensure that at the current baud rate the buffer can
actually be filled to the specified size within the timeout period. The routine
can also return with count set to -1L. This might happen, for example, when the
carrier is lost. The XPR should then fairly quickly get around to checking
the abort status using the xpr_chkabort() function: BBS programs will want to
regain control quickly after the carrier is dropped.
        The timeout may be set to 0L if the objective is to just read any
characters that may currently be available. In this case, the function will not
start up a timer, but will instead check the serial device for currently
available characters and return them in the usual fashion, and return as quickly
as possible. Note: the value 0L for the timeout argument is a special case.
Remember that AmigaDOS 1.3 may have problems with small non-zero values for
timeouts.
    Further notes on the implementation of xpr_sread() can be found in the
discussion about XProtocolHostMon in section 6.3.1.


3.7     long (*xpr_swrite)();
-----------------------------

        The xpr_swrite() call-back function has the following calling sequence:

        long status = (*xpr_swrite)(char *buffer, long size)
        D0                          A0            D0

This function writes a buffer with the given size to the serial port. It returns
0L on success, non-zero on failure.

3.8     long (*xpr_sflush)();
----------------------------

        The xpr_sflush call-back function has the following calling sequence:

        long status = (*xpr_sflush)()
        D0

This function flushes all the data in the serial port input buffer.  It is
typically used to recover after a protocol error. The function returns 0L on
success, non-zero on failure.

3.9     long (*xpr_update)();
-----------------------------

        The xpr_update() call-back function has the following calling sequence:

        (*xpr_update)(struct XPR_UPDATE *updatestruct)
                      A0
where:

struct XPR_UPDATE {     long  xpru_updatemask;
                        char *xpru_protocol;
                        char *xpru_filename;
                        long  xpru_filesize;
                        char *xpru_msg;
                        char *xpru_errormsg;
                        long  xpru_blocks;
                        long  xpru_blocksize;
                        long  xpru_bytes;
                        long  xpru_errors;
                        long  xpru_timeouts;
                        long  xpru_packettype;
                        long  xpru_packetdelay;
                        long  xpru_chardelay;
                        char *xpru_blockcheck;
                        char *xpru_expecttime;
                        char *xpru_elapsedtime;
                        long  xpru_datarate;
                        long  xpru_reserved1;
                        long  xpru_reserved2;
                        long  xpru_reserved3;
                        long  xpru_reserved4;
                        long  xpru_reserved5;
                   }

This function is intended to communicate a variety of values and strings from
the external protocol to the communications program for display. Hence, the
display format itself (requester, text-I/O) is left to the implementer of the
communications program.
        The mask xpru_updatemask indicates which of the other fields are valid,
i.e. have had their value updated. It is possible to update a single or multiple
values. Values that the external protocol does not use can be indicated by a
NULL for pointers and -1L for longs.
        The possible bit values for the xpru_updatemask are:

                #define XPRU_PROTOCOL           0x00000001L
                #define XPRU_FILENAME           0x00000002L
                #define XPRU_FILESIZE           0x00000004L
                #define XPRU_MSG                0x00000008L
                #define XPRU_ERRORMSG           0x00000010L
                #define XPRU_BLOCKS             0x00000020L
                #define XPRU_BLOCKSIZE          0x00000040L
                #define XPRU_BYTES              0x00000080L
                #define XPRU_ERRORS             0x00000100L
                #define XPRU_TIMEOUTS           0x00000200L
                #define XPRU_PACKETTYPE         0x00000400L
                #define XPRU_PACKETDELAY        0x00000800L
                #define XPRU_CHARDELAY          0x00001000L
                #define XPRU_BLOCKCHECK         0x00002000L
                #define XPRU_EXPECTTIME         0x00004000L
                #define XPRU_ELAPSEDTIME        0x00008000L
                #define XPRU_DATARATE           0x00010000L

        The other fields of the XPR_UPDATE structure have the following
meaning:

xpru_protocol    -- a string that indicates the name of the protocol used
xpru_filename    -- the name of the file currently sent or received
xpru_filesize    -- the size of the file
xpru_msg         -- a "generic" message (50 characters or less)
xpru_errormsg    -- an "error" message  (50 characters or less)
xpru_blocks      -- number of transferred blocks
xpru_blocksize   -- size of most recently transferred block (bytes)
xpru_bytes       -- number of transferred bytes
xpru_errors      -- number of errors
xpru_timeouts    -- number of timeouts
xpru_packettype  -- type of packet (e.g. Kermit 'D'-packet)
xpru_packetdelay -- delay between packets in msec
xpru_chardelay   -- delay between characters in msec
xpru_blockcheck  -- block check type (e.g. "Checksum", "CRC-16", "CRC-32")
xpru_expecttime  -- expected transfer time (e.g. "5 min 20 sec", "00:05:30")
xpru_elapsedtime -- elapsed time from start of transfer (see xpru_expecttime)
xpru_datarate    -- rate of data transfer expressed in characters per second.
xpru_reserved1   -- for further expansion
 ...         .   --  ...
xpru_reserved5   -- for further expansion

        The communications program is free to ignore any field and to only update
the ones it can handle.
        If xpru_updatemask is equal to -1L, then ALL fields are either valid or
are unambiguously valued to indicate they are unused: NULL for pointers and -1L
for longs.
        When writing an external protocol, it is advisable to keep any strings
as short as possible, and not longer than about 50 characters. Remember, if your
strings are too long, they may overflow whatever display mechanism the
communications program has chosen. It is also advisable to fill in as many
fields as you can, since the communications program may not choose to display
the ones you favor. When writing a communications program interface to XPR, on
the other hand, remember that strings can be as much as 50 characters long. If
you don't receive your favorite variables, it may be possible to compute them
from those that are given. It is good practice for the external protocol to call
xpr_update before starting the transfer with a message in the xpru_msg field
indicating whether the protocol is sending or receiving a file.
        The XPR_UPDATE structure must be provided by the external protocol, and
must, of course be allocated either on the stack (as a local variable) or using
AllocMem or malloc(). This is needed to ensure reentrancy. In general, it is a
good idea to keep the entire library reentrant, since more than one
communications program may be using the same code simultaneously. (If you use
malloc(), make sure your implementation of malloc() is reentrant!).


3.10     long (*xpr_chkabort)();
-------------------------------

        The xpr_chkabort() call-back function has no arguments:

        long status = (*xpr_chkabort)()
        D0

When it returns non-zero, it means that the user has requested an abort. It is
possible to implement levels of abort by returning 1L, 2L, 3L, etc, depending on
the user's actions. The highest level of abort is -1L, which should be
interpreted to mean stop all actions and return. The chkabort function should be
called reasonably frequently.


3.11    long (*xpr_chkmisc)();
------------------------------

        The xpr_chkmisc() call-back function has no arguments and returns
nothing.

        (*xpr_chkmisc)()

It is intended to give the communications program that is currently executing
the external protocol transfer a chance to service its various message ports and
to respond to user actions. It should be called on a regular basis.


3.12    long (*xpr_gets)();
---------------------------

        The xpr_gets() call-back function works somewhat like the stdio function
gets(). Calling sequence:

        long status = (*xpr_gets)(char *prompt, char *buffer)
        D0                        A0            A1

The first argument is a pointer to a string containing a prompt, to be displayed
by the communications program in any manner it sees fit. The second argument
should be a pointer to a buffer to receive the user's response. It should have a
size of at least 256 bytes. The function returns 0L on failure or user
cancellation, non-zero on success. The buffer has to be supplied by the XPR.


3.13    long (*xpr_setserial)();
--------------------------------

        The xpr_setserial() call-back function has the following calling
sequence:

        long oldstatus = (*xpr_setserial)(long newstatus)
        D0                                D0

This function returns the current serial device status in encoded form. If the
newstatus argument is -1L, the serial device status will not be changed.
Otherwise the serial device status will be changed to newstatus. If oldstatus
is returned as -1L, the call failed and the serial status was not changed.
        Note: if the serial device status is changed with this function, the
external protocol must change the status back to oldstatus before returning.

        serial status longword:
        .......................

        byte 0:         as the SerFlags field in IOExtSer structure.
                bit 0:  - parity on if set
                bit 1:  - parity odd if set
                bit 2:  - 7-wire protocol enabled if set
                bit 3:  - queued break if set
                bit 4:  - rad-boogie if set
                bit 5:  - shared if set
                bit 6:  - EOF mode if set
                bit 7:  - Xon/Xoff disabled if set
        byte 1:         summary of other settings
                bit 0:  - enable mark/space parity if set
                bit 1:  - parity mark if set, space otherwise
                bit 2:  - 2 stop bits if set, 1 otherwise
                bit 3:  - read wordlength is 7 if set, 8 otherwise
                bit 4:  - write wordlength is 7 if set, 8 otherwise
                bit 5:  - not used
                bit 6:  - not used
                bit 7:  - not used
        byte 2:         specifies one of a limited set of baud rates, as in
                        preferences.h.
                        -    110 baud =  0
                        -    300 baud =  1
                        -   1200 baud =  2
                        -   2400 baud =  3
                        -   4800 baud =  4
                        -   9600 baud =  5
                        -  19200 baud =  6
                        -   midi      =  7
                        -  38400 baud =  8
                        -  57600 baud =  9
                        -  76800 baud = 10
                        - 115200 baud = 11
        byte 3:         not used


3.14    long (*xpr_ffirst)();
-----------------------------

        The xpr_ffirst() call-back function has the calling sequence:

        long stateinfo = (*xpr_ffirst)(char *buffer, char *pattern)
        D0                             A0            A1

The first argument is a buffer to receive the first filename that matches the
pattern in the second argument. The function returns 0L if no file matching the
pattern was found, non-zero otherwise. The buffer should have a size of at least
256 bytes and is provided by the XPR. See also 3.14.


3.15    long (*xpr_fnext)();
----------------------------

        The xpr_fnext() call-back function has the calling sequence:

        long stateinfo = (*xpr_fnext)(long oldstate, char *buffer, char *pattern)
        D0                            D0             A0            A1

The first argument is a buffer to receive the next filename that matches the
pattern in the second argument. The function returns 0L if no further file
matching the pattern was found, non-zero otherwise. The buffer should have a
size of at least 256 bytes and is provided by the XPR.
        Note: the value returned by xpr_ffirst and xpr_fnext may be used by the
implementing communications program to maintain state information, but the
mechanism is up to the implementer. If reentrancy is not required, state
information may be kept in global variables by the implementer, and the oldstate
argument can be ignored. However, the external protocol implementation must pass
the stateinfo variable returned by ffirst or fnext to the next invocation of
fnext.


3.16    long (*xpr_finfo)();
----------------------------

        The xpr_finfo() call-back function has the calling sequence:

        long info = (*xpr_finfo)(char *filename, long typeofinfo)
        D0                       A0              D0

This function returns information about a file given its name and the type of
information requested. Notice that some information may not be accessible if
the file is already write locked. Therefore, you should call this function
(where appropriate) before opening the file.

        typeofinfo value:       resulting info:              on failure:
        ..................................................................

        1L                      file size (bytes)            0L

        2L                      file type: 1L is binary,     0L
                                           2L is text.

        (other values)          (to be determined)


3.17    long  *xpr_fseek();
---------------------------

        The xpr_fseek() call-back function works in most respects identically to
the stdio function fseek(). Calling sequence:

        long status = (*xpr_fseek)(long fileptr, long offset, long origin)
        D0                         A0            D0           D1

This function sets the current position of a file to "offset" from the
beginning (origin = 0), current position (origin = 1) or end (origin = 2) of
the file.
The function returns 0 on success.


3.18    long  *xpr_extension;
-----------------------------

        This field indicates how many extension fields follow this structure.
Before using any of those functions or fields (as defined in section 6), the
XPR must check that the desired function is indeed present by ensuring that
xpr_extension is larger than the position of the function beyond the xpr_data
field.


3.19    long  *xpr_data;
------------------------

        This field is for internal use by the external protocol. Typically the
field is initialized to point to a structure containing information extracted
from the initialization string handed to or retrieved by the XProtocolSetup()
function, see section 2. The structure should be deallocated and the field
restored to NULL by the XProtocolCleanup() function. The communications program
should never access this field, except when initializing the XPR_IO structure:
the field should be initialized to NULL.






4. An example protocol.
=======================

        The following is an annotated listing of an ascii upload protocol.
Notice that the files supplied in this archive are likely more up to date and
more extensive than the example given here.

/** xprascii.c
*
*   These are the protocol transfer routines for a simple ASCII upload.
*
**/
#include <exec/exec.h>
#include <functions.h>
#include <stdio.h>
/*
*   xproto.h is the include file given in Appendix B.
*/
#include "xproto.h"
/*
*   The following two strings must exist.
*/
char  XPRname[]   = "xprascii.library";
char  XPRid[]     = "xprascii 0.9 (May 89)\r\n";
UWORD XPRrevision = 9;

long atol();
/*
*   The callxx...() routines are described later. They provide the
*   assembler interface from the XPR library to the call-back routines.
*/
long calla(), callaa(), callad(), calladd(), calladda();

char *malloc();


/**
*
*   Send a file
*
**/
long XProtocolSend(IO)
struct XPR_IO *IO;
{
   long fp, r, i;
   long brkflag = 0, fl = 0L, sd = 0L;
   long (*xupdate)(), (*xswrite)(), (*xfopen)(), (*xfclose)(), (*xfread)(),
        (*xsread)(),  (*xchkabort)();
   unsigned char *buff = NULL, *serbuff = NULL;
   struct XPR_UPDATE xpru;

/*
*   These are the call-backs we need. If any of them isn't provided, quit.
*   Could do some error reporting if at least xupdate is there.
*/
   if ((xupdate    = IO->xpr_update)   == NULL) return(0L);
   if ((xswrite    = IO->xpr_swrite)   == NULL) return(0L);
   if ((xfopen     = IO->xpr_fopen)    == NULL) return(0L);
   if ((xfclose    = IO->xpr_fclose)   == NULL) return(0L);
   if ((xfread     = IO->xpr_fread)    == NULL) return(0L);
   if ((xsread     = IO->xpr_sread)    == NULL) return(0L);
   if ((xchkabort  = IO->xpr_chkabort) == NULL) return(0L);
/*
*   Allocate a few buffers.
*/
   buff    = (unsigned char *) malloc(80);
   serbuff = (unsigned char *) malloc(80);
/*
*   If we ran out of memory, print a message.
*   The argument needs to go in A0: calla does this for us.
*/
   if (buff == NULL || serbuff == NULL) {
      xpru.xpru_updatemask = XPRU_ERRORMSG;
      xpru.xpru_errormsg   = "Ran out of memory!";
      calla(xupdate, &xpru);
      return(0L);
   }
/*
*   Read the send delay, if a XProtocolSetup() was done before.
*   If send delay is too large, cut it off at 10 seconds.
*   In this example, the xpr_data field contains a null terminated string
*   containing the number of ticks to delay each 80 characters.
*/
   if (IO->xpr_data) {
      sd = atol(IO->xpr_data);
      if (sd > 500L) sd = 500L;
   }
/*
*   Open the file. One could do wild card detection here.
*   xfopen requires two arguments, in a0 and a1 respectively.
*   Again, this must be done in assembler, and callaa does it.
*/
   fp = callaa(xfopen, IO->xpr_filename, "r");
   if (fp == NULL) {
      free(buff);
      free(serbuff);
      xpru.xpru_updatemask = XPRU_ERRORMSG | XPRU_FILENAME;
      xpru.xpru_errormsg   = "Failed to open input file";
      xpru.xpru_filename   = IO->xpr_filename;
      calla(xupdate, &xpru);
      return(0L);
   }
/*
*   Start the transfer. See 3.8 for a discussion on how to implement
*   xupdate.
*/
   xpru.xpru_updatemask = XPRU_MSG | XPRU_FILENAME;
   xpru.xpru_msg        = "Starting ASCII Send";
   xpru.xpru_filename   = IO->xpr_filename;
   calla(xupdate, &xpru);
/*
*   Now read 80 byte chunks from the file using xfread.
*   xfread requires four arguments, a0, d0, d1 and a1.
*/
   xpru.xpru_blocks = 0L;
   while (r = calladda(xfread, buff, 1L, 80L, fp)) {
/*
*   Convert line feeds to carriage returns before sending to host.
*   fl counts the characters. Display how many characters are sent.
*/
      for (i = 0L; i < r; i++) if (buff[i] == '\n') buff[i] = '\r';
      fl += r;
      xpru.xpru_updatemask = XPRU_BYTES | XPRU_BLOCKS | XPRU_BLOCKSIZE;
      xpru.xpru_bytes      = fl;
      xpru.xpru_blocks++;
      xpru.xpru_blocksize  = r;
      calla(xupdate, &xpru);
      callad(xswrite, buff, r);
/*
*   Every 80 bytes, put out a message and delay if requested.
*/
      xpru.xpru_updatemask  = XPRU_PACKETDELAY;
      xpru.xpru_packetdelay = sd * 20L;  /* msec! */
      calla(xupdate, &xpru);
/*
*   Can't use Delay() here, because Delay() is in dos.library!
*   However writing an equivalent function using the timer.device is
*   trivial.
*/
      TimeOut(sd);
/*
*   Eat any characters that might arrive from the serial port.
*   calladd stores arg1 in a0, arg2 in d0, arg3 in d1.
*   We're not really waiting for any characters: use a timeout of 0L.
*/
      while (calladd(xsread, serbuff, 80L, 0L) > 0L) ;
/*
*   Check for "abort" here. Perhaps should call chkmisc() as well.
*/
      if (brkflag = xchkabort()) break;
   }
/*
*   Close the file
*/
   calla(xfclose, fp);
   free(buff);
   free(serbuff);
/*
*   If we got here through chkabort() say Aborted.
*/
   xpru.xpru_updatemask       = XPRU_MSG;
   if (brkflag) xpru.xpru_msg = "Aborted";
   else         xpru.xpru_msg = "Done";
   calla(xupdate, &xpru);
   if (brkflag) return(0L);
   else         return(1L);
}


/**
*
*   Receive a file.
*
**/
long XProtocolReceive(IO)
struct XPR_IO *IO;
{
   long fp, r, i;
   long brkflag = 0, fl = 0L, sd = 0L;
   long (*xupdate)(), (*xswrite)(), (*xfopen)(), (*xfclose)(), (*xfwrite)(),
        (*xsread)(),  (*xchkabort)();
   unsigned char *serbuff = NULL;
   struct XPR_UPDATE xpru;

/*
*   These are the call-backs we need. If any of them isn't provided, quit.
*   Could do some error reporting if at least xupdate is there.
*/
   if ((xupdate    = IO->xpr_update)   == NULL) return(0L);
   if ((xswrite    = IO->xpr_swrite)   == NULL) return(0L);
   if ((xfopen     = IO->xpr_fopen)    == NULL) return(0L);
   if ((xfclose    = IO->xpr_fclose)   == NULL) return(0L);
   if ((xfwrite    = IO->xpr_fwrite)   == NULL) return(0L);
   if ((xsread     = IO->xpr_sread)    == NULL) return(0L);
   if ((xchkabort  = IO->xpr_chkabort) == NULL) return(0L);
/*
*   Allocate a buffer.
*/
   serbuff = (unsigned char *) malloc(80);
/*
*   If we ran out of memory, print a message.
*   The argument needs to go in A0: calla does this for us.
*/
   if (serbuff == NULL) {
      xpru.xpru_updatemask = XPRU_ERRORMSG;
      xpru.xpru_errormsg   = "Ran out of memory!";
      calla(xupdate, &xpru);
      return(0L);
   }
/*
*   Open the file.
*   xfopen requires two arguments, in a0 and a1 respectively.
*   Again, this must be done in assembler, and callaa does it.
*/
   fp = callaa(xfopen, IO->xpr_filename, "w");
   if (fp == NULL) {
      free(serbuff);
      xpru.xpru_updatemask = XPRU_ERRORMSG | XPRU_FILENAME;
      xpru.xpru_errormsg   = "Failed to open output file";
      xpru.xpru_filename   = IO->xpr_filename;
      calla(xupdate, &xpru);
      return(0L);
   }
/*
*   Start the transfer. See 3.8 for a discussion on how to implement
*   xupdate.
*/
   xpru.xpru_updatemask = XPRU_MSG | XPRU_FILENAME;
   xpru.xpru_msg        = "Starting ASCII Receive";
   xpru.xpru_filename   = IO->xpr_filename;
   calla(xupdate, &xpru);
/*
*   Now read 80 byte chunks from the serial port using xsread. Stop
*   when no characters arrive for 5 sec.
*/
   xpru.xpru_blocks = 0L;
   while ((r = calladd(xsread, serbuff, 80L, 5000000L)) > 0L)  {
/*
*   Strip high-bit before storing in file.
*   fl counts the characters. Display how many characters are received.
*/
      for (i = 0L; i < r; i++) serbuff[i] &= 0177;
      fl += r;
      xpru.xpru_updatemask = XPRU_BYTES | XPRU_BLOCKS | XPRU_BLOCKSIZE;
      xpru.xpru_bytes      = fl;
      xpru.xpru_blocks++;
      xpru.xpru_blocksize  = r;
      calla(xupdate, &xpru);
/*
*   Write 80 byte chunks to the file using xwrite
*/
      calladda(xfwrite, serbuff, 1L, r, fp);

/*
*   Check for "abort" here. Perhaps should call chkmisc() as well.
*/
      if (brkflag = xchkabort()) break;
   }
/*
*   Close the file
*/
   calla(xfclose, fp);
   free(serbuff);
/*
*   If we got here through chkabort() say Aborted.
*/
   xpru.xpru_updatemask       = XPRU_MSG;
   if (brkflag) xpru.xpru_msg = "Aborted";
   else         xpru.xpru_msg = "Done";
   calla(xupdate, &xpru);
   if (brkflag) return(0L);
   else         return(1L);
}


/**
*
*   Setup
*
**/
long XProtocolSetup(IO)
struct XPR_IO *IO;
{
   long (*xupdate)(), (*xgets)();
   struct XPR_UPDATE xpru;

   if ((xupdate = IO->xpr_update) == NULL) return(0L);
   if ((xgets   = IO->xpr_gets)   == NULL) return(0L);
/*
*   Allocate a bit of memory for a data buffer
*/
   if (IO->xpr_data == NULL) {
      if ((IO->xpr_data = (long *) malloc(256)) == NULL) {
         xpru.xpru_updatemask = XPRU_ERRORMSG;
         xpru.xpru_errormsg   = "ASCII - Out of memory!";
         calla(xupdate, &xpru);
         return(0L);
      }
   }
/*
*   If setup string isn't handed to us, ask questions
*/
   if (IO->xpr_filename == NULL) {
/*
*   Get the value for the send delay
*/
      callaa(xgets, "Enter ASCII send delay (ticks, 1 tick = 20 msec)",
                  IO->xpr_data);
   }
   else {
      strcpy(IO->xpr_data, IO->xpr_filename);
   }

   return(1L);
}

/**
*
*   Cleanup
*
**/
long XProtocolCleanup(IO)
struct XPR_IO *IO;
{
   if (IO->xpr_data) free(IO->xpr_data);
   IO->xpr_data = NULL;

   return(1L);
}

/**
*
*   The following functions setup the proper registers for the call-back
*   functions.
*
**/
#asm
        public _callad
_callad:
        movea.l 8(sp),a0                ; Second argument goes in a0
        move.l  12(sp),d0               ; Third  argument goes in d0
/*
*   Now this is a trick to avoid using another register.
*   Charlie taught me this...
*/
        move.l  4(sp),-(sp)             ; First  argument is function
        rts

        public  _calladda
_calladda:
        movea.l 8(sp),a0                ; Second argument goes in a0
        move.l  12(sp),d0               ; Third  argument goes in d0
        move.l  16(sp),d1               ; Fourth argument goes in d1
        movea.l 20(sp),a1               ; Fifth  argument goes in a1
        move.l  4(sp),-(sp)             ; First  argument is function
        rts

        public  _calla
_calla:
        movea.l 8(sp),a0                ; Second argument goes in a0
        move.l  4(sp),-(sp)             ; First  argument is function
        rts

        public  _callaa
_callaa:
        movea.l 8(sp),a0                ; Second argument goes in a0
        movea.l 12(sp),a1               ; Third  argument goes in a1
        move.l  4(sp),-(sp)             ; First  argument is function
        rts

        public  _calladd
_calladd:
        move.l  8(sp),a0                ; Second argument goes in a0
        move.l  12(sp),d0               ; Third  argument goes in d0
        move.l  16(sp),d1               ; Fourth argument goes in d1
        move.l  4(sp),-(sp)             ; First  argument is function
        rts

#endasm
/*
*   Could have added any other functions needed for other call-backs.
*   Could have written a fancier single one... Could've...
*/
                              __
                             /  \ o    /
                       -----/----\----/-----
                           /    o \__/

        Clearly it isn't very hard to implement a simple protocol. More
elaborate protocols are straightforward extensions to the above example. Of
course, there are a few more standard files needed to make the above example
into a complete library (like Open, Close and Expunge functions and a ROM-Tag
structure) but those parts are the same for any library and aren't given here.



5. The interface to the communications program.
===============================================

        The following is an annotated listing of a few call-back functions as
they are implemented in VLT. Also, it is shown how to initialize the XPR_IO
structure. Notice that the files supplied in this archive are likely more up to
date and more extensive than the minimal example given here.

/** xprfuncs.c
*
*   Call-back functions for eXternal PRotocol support
*
**/
#include <functions.h>
#include <exec/exec.h>
#include <stdio.h>
/*
*   xproto.h is given in Appendix B
*/
#include "xproto.h"
/*
*   xfer.h is a VLT private header file containing some information for
*   file transfer protocols
*/
#include "xfer.h"

/*
*   These are the C versions of the interface
*/
long        vlt_update(),  vlt_swrite(),  vlt_fread(),  vlt_fopen(),
            vlt_fclose(),  vlt_gets(),    vlt_sread(),  vlt_chkabort();
/*
*   These are the assembly level glue functions, see vltface.asm
*/
extern long avlt_update(), avlt_swrite(), avlt_fread(), avlt_fopen(),
            avlt_fclose(), avlt_gets(),   avlt_sread(), avlt_chkabort();

/**
*
*   This function initializes an XPR_IO structure.
*
**/
xpr_setup(IO)
struct XPR_IO *IO;
{
/*
*   NULL out all the functions we don't do yet.
*   Fill the other ones with the addresses to the assembler glue version
*   of the interface routines. See vltface.asm
*/
   IO->xpr_filename  = NULL;
   IO->xpr_fopen     = avlt_fopen;
   IO->xpr_fclose    = avlt_fclose;
   IO->xpr_fread     = avlt_fread;
   IO->xpr_fwrite    = NULL;
   IO->xpr_sread     = avlt_sread;
   IO->xpr_swrite    = avlt_swrite;
   IO->xpr_sflush    = NULL;
   IO->xpr_update    = avlt_update;
   IO->xpr_chkabort  = avlt_chkabort;
   IO->xpr_chkmisc   = NULL;
   IO->xpr_gets      = avlt_gets;
   IO->xpr_setserial = NULL;
   IO->xpr_ffirst    = NULL;
   IO->xpr_fnext     = NULL;
   IO->xpr_finfo     = NULL;
   IO->xpr_fseek     = NULL;
/*
*   Support the 1 defined extension
*/
   IO->xpr_extension = 1L;
/*
*   But don't actually implement it yet.
*/
   IO->xpr_options   = NULL
/*
*   Especially, NULL out the XPR private data field.
*/
   IO->xpr_data      = NULL;

   return;
}

/**
*
*   Interface to VLT's MsgDisplay() function.
*
**/
/*
*   These are formats for VLT's requester
*/
static char *xprnamfmt = "%s\n%s\n\n\n\n";
static char *filnamfmt = "\n\n%s\n\n\n";
static char *blksizfmt = "\n\n\n\nBlock:  %6ld  --  Block Size:  %6ld\n";
static char *errtimfmt = "\n\n\n\n\nErrors: %6ld  --  Timeouts:    %6ld";
static char *delayfmt  = "\n\n\n\n\nPacket delay %ld";
/*
*   Below are some VLT globals to orchestrate the display
*/
long xpr_blocks = 0L, xpr_blocksize = 0L, xpr_errors = 0L, xpr_timeouts = 0L;
/*
*   The function
*/
long vlt_update(x)
struct XPR_UPDATE *x;
{
   extern struct Window *mywindow;
   extern char *XPR_Name;
/*
*   First time, determine the window size (50 chars wide, 5 lines tall).
*/
   SetMsgWindow(mywindow, 50, 6);
/*
*   Use VLT's PostMsg function to display all the information.
*/
   if (x->xpru_updatemask & XPRU_PROTOCOL) {
      PostMsg(mywindow, xprnamfmt, XPR_Name, x->xpru_protocol);
   }
   if (x->xpru_updatemask & XPRU_MSG) {
      PostMsg(mywindow, xprnamfmt, XPR_Name, x->xpru_msg);
   }
   if (x->xpru_updatemask & XPRU_ERRORMSG) {
      PostMsg(mywindow, xprnamfmt, XPR_Name, x->xpru_errormsg);
   }
   if (x->xpru_updatemask & XPRU_FILENAME) {
      PostMsg(mywindow, filnamfmt, x->xpru_filename);
   }
   if (x->xpru_updatemask & XPRU_PACKETDELAY) {
      PostMsg(mywindow, delayfmt, x->xpru_packetdelay);
   }
   if (x->xpru_updatemask & (XPRU_BLOCKS | XPRU_BLOCKSIZE)) {
      if (x->xpru_updatemask & XPRU_BLOCKS)    xpr_blocks    = x->xpru_blocks;
      if (x->xpru_updatemask & XPRU_BLOCKSIZE) xpr_blocksize = x->xpru_blocksize;
      PostMsg(mywindow, blksizfmt, xpr_blocks, xpr_blocksize);
   }
   if (x->xpru_updatemask & (XPRU_ERRORS | XPRU_TIMEOUTS)) {
      if (x->xpru_updatemask & XPRU_ERRORS)   xpr_errors   = x->xpru_errors;
      if (x->xpru_updatemask & XPRU_TIMEOUTS) xpr_timeouts = x->xpru_timeouts;
      PostMsg(mywindow, errtimfmt, xpr_errors, xpr_timeouts);
   }
   return(0L);
}

/**
*
*   Prompt the user for input
*
**/
long vlt_gets(s, t)
char *s, *t;
{
/*
*   Use VLT's DoRequest() function
*/
   return((long) DoRequest(mywindow, t, s, NULL, " Cancel "));
}

/**
*
*   Write a string to the serial port
*
**/
long vlt_swrite(s, n)
char *s;
long n;
{
/*
*   Use VLT's SendString() function
*/
   SendString(s, (int) n);
   return(0L);
}

/**
*
*   Read characters from the serial port
*
**/
long vlt_sread(buff, length, micros)
unsigned char *buff;
long length, micros;
{
   extern int timeout;
   long secs = 0L;

   if (buff == NULL) return(-1L);
/*
*   Convert timeout to seconds and micros if necessary
*/
   if (micros) {
      if (micros > 1000000L) {
         secs   = micros / 1000000L;
         micros = micros % 1000000L;
      }
   }
/*
*   What follows is pseudo code. VLT's implementation is at this point
*   different.
*/
   StartTimer(secs, micros);
/*
*   VLT has a global called timeout. This comes in xfer.h.
*   If the read was successful, add character to buffer.
*/
   for (i = 0; (timeout == GOODREAD) && (i < size); i++)
      buff[i] = (unsigned char) readchar();
/*
*   Either timed out or buffer is full.
*/
   if (timeout != TIMEOUT) AbortTimer();
/*
*   If carrier dropped, return error condition
*/
   if (timeout == CARRIER_DROPPED) return(-1L);
/*
*   Else return the number of characters read.
*/
   return(i);
}

/**
*
*   Interfaces to stdio
*
**/
long vlt_fopen(s, t)
char *s, *t;
{
   return((long) fopen(s, t));
}

long vlt_fclose(fp)
FILE *fp;
{
   return((long) fclose(fp));
}

long vlt_fread(buff, size, count, fp)
char *buff;
long size, count;
FILE *fp;
{
   int res;
   res = fread(buff, (int) size, (int) count, fp);
   return((long) res);
}

/**
*
*   Check for Abort
*
**/
long vlt_chkabort()
{
/*
*   VLT aborts its protocols when the escape key is pressed.
*   CheckForKey loops over the UserPort messages looking for an escape.
*/
   return((long) CheckForKey(69));
}
                              __
                             /  \ o    /
                       -----/----\----/-----
                           /    o \__/

        Clearly, this part of the implementation isn't hard either. The only
thing left is the assembly level glue on the communications program side. You
may wonder at this point why all this assembly level stuff is necessary. It is
necessary because many programs and libraries are written in small code/small
data. This means that both the communications program and the library address
their code/data off of some register, in the case of Manx usually A4. The
problem is that the communications program and the library are loaded in
different parts of memory, while startup code takes care of setting up the
proper value for A4. And the values of A4 are different for the the
communications program and the library! Now, if you just call a library
function, the assembly level glue does a few things, among which are: (1) saving
the caller's A4 somewhere safe and (2) retrieving the A4 it stored somewhere
when the library was loaded. Then the library function is executed, and the
function returns to the glue. The glue then restores A4 to the state it was in
before the library call.
        In the case of these call-back functions, we have to do the reverse.
After all, when a function like xpr_update is called, the current value of A4 is
the one that goes with the library's code. If the call-back function tries to
access any data back in the communications program, we're in big trouble.
        So what the assembly part of the call-backs has to do is (1) save the
library's A4 (on the stack) and (2) get the value of A4 appropriate for the
communications program. Then we can push the various registers onto the stack,
call the C version of the call-back and then restore the value of A4 to what the
library wants.
        For the above call-backs, the assembly level glue is listed below.

;;; vltface.asm
;
;   DESCRIPTION:
;   ===========
;
;        This is an interface to VLT callback functions from
;        external protocol libraries.
;
;   AUTHOR/DATE:  W.G.J. Langeveld, March 1989.
;   ============
;
;;;

        public  _geta4

setup   macro
        movem.l d2/d3/d4-d7/a2-a6,-(sp)
        jsr     _geta4                        ; Get a4.
        endm

push    macro
        move.l  \1,-(sp)
        endm

fix     macro
        ifc     '\1',''
                mexit
        endc
        ifle    \1-8
                addq.l  #\1,sp
        endc
        ifgt    \1-8
                lea     \1(sp),sp
        endc
        endm

restore macro
        fix     \1
        movem.l (sp)+,d2/d3/d4-d7/a2-a6
        rts
        endm

        public  _avlt_fopen
        public  _vlt_fopen
        public  _avlt_fclose
        public  _vlt_fclose
        public  _avlt_fread
        public  _vlt_fread
        public  _avlt_sread
        public  _vlt_sread
        public  _avlt_swrite
        public  _vlt_swrite
        public  _avlt_update
        public  _vlt_update
        public  _avlt_chkabort
        public  _vlt_chkabort
        public  _avlt_gets
        public  _vlt_gets

_avlt_fopen:
        setup
        push    a1
        push    a0
        jsr     _vlt_fopen
        restore 8

_avlt_fclose:
        setup
        push    a0
        jsr     _vlt_fclose
        restore 4

_avlt_fread:
        setup
        push    a1
        push    d1
        push    d0
        push    a0
        jsr     _vlt_fread
        restore 16

_avlt_sread:
        setup
        push    d1
        push    d0
        push    a0
        jsr     _vlt_sread
        restore 12

_avlt_swrite:
        setup
        push    d0
        push    a0
        jsr     _vlt_swrite
        restore 8

_avlt_update:
        setup
        push    a0
        jsr     _vlt_update
        restore 4

_avlt_chkabort:
        setup
        jsr     _vlt_chkabort
        restore

_avlt_gets:
        setup
        push    a1
        push    a0
        jsr     _vlt_gets
        restore 8

                              __
                             /  \ o    /
                       -----/----\----/-----
                           /    o \__/







6. XPR Extensions
=================

        While simple protocols can usually get by with the functionality  given
in sections 2 through 5 above, some more elaborate protocols may need additional
functionality. Also, one may want to present the user with a more polished
interface in certain situations. This is accomplished under the XPR
specification in a number of ways.
        It has become clear that in many cases the communications program needs
to know a few details about the XPR that it is currently running. Some of these
relate to simple yes/no decisions on the part of the communications program, and
can be represented as bits that are either set or not. A number of bits in the
return codes of the XProtocolSetup() function have been defined in this way, and
they are listed in section 6.1.
        The straightforward way to extend the XPR capabilities is through the
use of more call-back functions. The first such function, xpr_options(), was
already described in a previous release of this document. This document will
describe and standardize this and a few more such functions in section 6.2.
        Finally, there is a need in certain file transfer protocols to monitor
what host and/or user are doing even while not in the process of sending or
receiving files by protocol transfer. For that purpose, a few XPR library
functions have been added. The mechanics of this is described in section 6.3.


6.1 Library function calling conventions and return codes.
----------------------------------------------------------

        This section defines more precisely what the return codes of the four
standard XPR library functions mean. Also, in some cases calling conventions
are more clearly specified.

6.1.1 XProtocolSetup()
----------------------

        The library function XProtocolSetup() is called with as the single
argument a pointer to a previously initialized XPR_IO structure. The calling
sequence is:

        long setup_flags = XProtocolSetup(struct XPR_IO *IO);
        D0                                A0

where struct XPR_IO is defined as in section 3 and appendix B.
        When this function is called by the communications program with a NULL
value in the xpr_filename field, the function is expected to prompt the user for
setup information. When the xpr_filename field points to a null terminated
string, this string is expected to be interpreted as a direct command or
initialization sequence, and the function is in general NOT expected to prompt
the user for input. An exception to this latter rule occurs, when the command or
initialization string directly or indirectly instructs the XPR to prompt the
user for input. In particular, the empty string "", should always be interpreted
as a void command (a NOP), and should never cause XProtocolSetup() to prompt for
input.
        This is particularly useful when the communications program only wants
to retrieve the value of setup_flags, which is the return code of
XProtocolSetup(), without going through the protocol setup sequence.
        With this extension of the specification, it now becomes natural to
always call XProtocolSetup() right after opening the XPR library, either with an
empty string or with an initialization string if one can be found. In all cases,
the XPR should return a proper value for the return code, as defined below. The
communications program still should have a menu option or other way to allow the
user to go through an XPR setup sequence, by calling XProtocolSetup() with a
NULL pointer in the xpr_filename field.

        The return code, setup_flags, is a bit mask. The currently defined bits,
when turned on, have the following meaning:

        Bit 0:   Successful completion.
        Bit 1:   Protocol requires no communications program supplied file
                 requester for receive: either the XPR supplies the file
                 requester or the protocol is capable of receiving file name
                 information through other means (e.g., from the host).
        Bit 2:   Protocol requires no communications program supplied file
                 requester for send: either the XPR supplies the file requester
                 or the protocol is capable of receiving file name information
                 through other means.
        Bit 3:   Communications program is requested to call XProtocolHostMon()
                 for all serial port input (see section 6.3).
        Bit 4:   Communications program is requested to call XProtocolUserMon()
                 for all user input (see section 6.3).
        Bit 5:   Communications program is requested to call XProtocolHostMon()
                 without waiting for serial input (see section 6.3).

        The value 0L is returned to indicate failure.


6.1.2 XProtocolSend()
---------------------

The calling sequence is:

        long status = XProtocolSend(struct XPR_IO *IO);
        D0                          A0

where struct XPR_IO is defined as in section 3 and appendix B.
        The value 0L is returned to indicate failure, 1L to indicate success.
Other non-zero return codes are also to be interpreted as successful, but the
meaning of the other bits is not currently specified.


6.1.3 XProtocolReceive()
------------------------

The calling sequence is:

        long status = XProtocolReceive(struct XPR_IO *IO);
        D0                             A0

where struct XPR_IO is defined as in section 3 and appendix B.
        The value 0L is returned to indicate failure, 1L to indicate success.
Other non-zero return codes are also to be interpreted as successful, but the
meaning of the other bits is not currently specified.


6.1.4 XProtocolCleanup()
------------------------

The calling sequence is:

        long status = XProtocolCleanup(struct XPR_IO *IO);
        D0                             A0

where struct XPR_IO is defined as in section 3 and appendix B.
        The value 0L is returned to indicate failure, 1L to indicate success.
Other non-zero return codes are also to be interpreted as successful, but the
meaning of the other bits is not currently specified.




6.2 XPR_IO extension functions.
-------------------------------

        The following functions are now part of the XPR_IO extended structure
definition:

        xpr_options()     Prompts user for commands or options.
        xpr_unlink()      Deletes files by name.
        xpr_squery()      Returns actual size of current serial buffer contents.
        xpr_getptr()      Gets various pointers from user.

        The following sections will discuss each of these functions in detail.


6.2.1    long  *xpr_options();
------------------------------

        This function is in the first extension field of the XPR_IO structure.
Only use this function if the value of the xpr_extension field is 1L or larger.
The calling sequence is:

        long status = (*xpr_options)(long n, struct xpr_option *opt[])
        D0                           D0      A0

The function passes to the comm program a pointer to an array of n pointers to
xpr_option structures, where n is limited to 31. The xpr_option structures are
defined as follows:

struct xpr_option {
   char *xpro_description;      /* description of the option                  */
   long  xpro_type;             /* type of option                             */
   char *xpro_value;            /* pointer to a buffer with the current value */
   long  xpro_length;           /* buffer size                                */
}

Valid values for xpro_type are:

#define XPRO_BOOLEAN 1L         /* xpro_value is "yes", "no", "on" or "off"   */
#define XPRO_LONG    2L         /* xpro_value is string representing a number */
#define XPRO_STRING  3L         /* xpro_value is a string                     */
#define XPRO_HEADER  4L         /* xpro_value is ignored                      */
#define XPRO_COMMAND 5L         /* xpro_value is ignored                      */
#define XPRO_COMMPAR 6L         /* xpro_value contains command parameters     */

        The array is allocated and initialized by the XPR to default values. If
the comm program implements this function, it should display the description of
the option and its current value to the user and allow him/her to change them.
This could be accomplished either by dynamically building a requester or by
displaying each line one at a time and allow the user to enter new values or
accept the default. Options that have boolean values could be implemented by the
comm program as boolean gadgets, but the new value must be returned as "yes" or
"on" for logical 1 or "no" or "off" for logical 0 in the xpro_value buffer.
Note, that the XPR, if it uses this function must recognize both "yes" and "on"
for logical 1 and "no" and "off" for logical 0. Long values must if necessary be
converted to a string and copied to the xpro_value buffer.  For options that
have string values, the comm program must ensure that the new string selected by
the user fits in the value buffer as determined by the xpro_length field. The
buffer is supplied by the XPR, and must be large enough to be able to hold the
'\0' termination.
        The option of type XPRO_HEADER contains a pointer to an explanatory
message in its xpro_description field. It is to be interpreted as a header
string for the options that follow. It has no other function, any bits
corresponding to this option in the return value should be ignored, and the
xpr_value string is meaningless, but should be initialized to either NULL or a
valid pointer to a buffer. The message should have a length of 50 characters or
less.
        The options of type XPRO_COMMAND and XPRO_COMMPAR are used for such
functions as Kermit Bye or Finish. Simple commands (XPRO_COMMAND) could be
displayed as boolean gadgets in a requester, while commands needing parameters
could have an associated string gadget. The difference between commands like
this and other options is that when one of these commands is selected, the
requester should disappear and xpr_options() should return immediately, with
only the bit coresponding to the command set. Therefore, ideally, the XPR should
not mix XPRO_COMMAND/XPRO_COMMPAR options with other options (except of type
XPRO_HEADER). Rather, the XPR should first call xpr_options() with only
XPRO_COMMAND/XPRO_COMMPAR/XPRO_HEADER options, one of which would be a "Change
Defaults" command (type XPRO_COMMAND). This command, when selected, would cause
the XPR to call xpr_options() with a list of other xpr_option structures for
non-commands and their headers. This way, the communications program would
automatically list the XPR commands first, and one of the commands would be a
"Change Defaults" command, which when selected by the user would bring up a
second requester with the various other options supported by the XPR. For simple
commands, the xpr_value string is meaningless and should either be set to NULL
or contain a valid pointer to a buffer anyway. For commands needing parameters,
the xpr_value string should contain the current default value of the parameter.
There is a compatibility issue: communications programs written with earlier
versions of the XPR spec may not know about XPRO_COMMAND etc. It is therefore
advisable to bring up the second requester anyway if no command is selected
from the first requester. In that case, it would be a good idea to include a
"CANCEL" command in the first requester, which does nothing but provide a means
to prevent the second requester from appearing.

        As an example, when selecting a ZMODEM based XPR the following array of
xpr_option structures could be passed to the comm program:

xpro_description                xpro_value    xpro_type
--------------------------------------------------------------
Convert NL to NL/CR             no            XPRO_BOOLEAN
Escape only CTRL chars          yes           XPRO_BOOLEAN
Escape ALL chars                no            XPRO_BOOLEAN
Send full pathname              yes           XPRO_BOOLEAN
Send 1K blocks                  no            XPRO_BOOLEAN
Subpacket length                512           XPRO_LONG
Disable 32-bit CRC              no            XPRO_BOOLEAN
Protect destination file        no            XPRO_BOOLEAN
Timeout value (sec)             10            XPRO_LONG
Delete after transmission       no            XPRO_BOOLEAN
Overwrite existing file         no            XPRO_BOOLEAN

Notice again, that the COMM program still knows little about the individual
option items (and in fact there is no way for it to find out, in keeping with
the philosophy of XPR). Also notice that a cheap way to implement this function
is to loop over the n supplied xpr_option's and to call the likely already
implemented xpr_gets function with the option description and the value buffer
(but remember that some options may not have valid value buffers!).
        It is important to follow a few rules when calling this function: the
description strings should be 25 characters or less (except for XPRO_HEADER's).
The value strings can be any length up to 255 characters, but be aware that in a
typical situation only about 10 to 15 of them will be displayed in a string
gadget.
        The return value, status, reflects which options have changed by having
the corresponding bit set. The first option in the xpr_option array corresponds
to  bit 0 (low-order), etc. If the options are all of the types boolean, long,
string or header, the comm program may decide to not detect whether the options
changed or not, and 0x07FFFFFFL may be returned, in effect specifying that all
options have changed. On the other hand, if the communications program returns
a value with multiple bits set even though some or all of the options are of
type command, the XPR should be careful to cause minimal damage, or display
an error message.
        If nothing changed or no command was selected, 0L is returned. If an
error occurred, the function returns -1L.


6.2.2    long  *xpr_unlink();
-----------------------------

        This function is in the second extension field of the XPR_IO structure.
Only use this function if the value of the xpr_extension field is 2L or larger.
The calling sequence is:

        long status = (*xpr_unlink)(char *filename)
        D0                          A0

This function returns 0L on success, -1L on failure. It attempts to delete the
file who's name is contained in the character array pointed to bye the only
argument. The file cannot be locked at the time by any process.


6.2.3    long  *xpr_squery();
------------------------------

        This function is in the third extension field of the XPR_IO structure.
Only use this function if the value of the xpr_extension field is 3L or larger.
The calling sequence is:

        long size = (*xpr_squery)()
        D0

        This function returns the number of characters currently available
in the serial device. It returns -1L on error. When no characters are available
the function returns 0L.


6.2.4    long  *xpr_getptr();
-----------------------------

        This function is in the fourth extension field of the XPR_IO structure.
Only use this function if the value of the xpr_extension field is 4L or larger.
The calling sequence is:

        long *ptr = (*xpr_getptr)(type)
        D0                        D0

This function returns selected pointers to structures or buffers defined in
the communications program.
        Currently the only allowed pointer type is

        type:                   resulting pointer:
        ...................................................

        1L                      pointer to custom Screen
                                or 0L for Workbench.

        (other values)          (to be determined)

This function can be used to open windows on the communications program's
custom screen, and together with the library functions XProtocolHostMon() and
XProtocolUserMon() such protocols as DoubleTalk should be feasible. Indeed,
entire external terminal emulations might be written in this way.

The function returns -1L on failure. Note that the failure can be due to
various causes: the communications program may not want to return a particular
pointer, the version may not know about some allowed types, or the type may for
other reasons not be valid. Also: if 0L is returned, it is up to the XPR to
determine whether this is a legal return value. With type 1, this is fine, but
in general a NULL pointer may of course not be valid. The XPR is responsible
for closing any windows or other resources on a call to XProtocolCleanup().


6.3 New library functions.
--------------------------

        We now discuss the two library functions XProtocolHostMon and
XProtocolUserMon(). These two functions are provided by the XPR as additional
library entries and their presence is made known to the communications program
by setting certain bits in the return value of XProtocolSetup(). They are called
by the communcations program whenever data is received from (HostMon) or sent to
(UserMon) the serial port, except that care has to be taken that these functions
are not called directly or indirectly by the xpr_sread() and xpr_swrite()
functions.


6.3.1 XProtocolHostMon()
------------------------

        This function should be called by the communications program only when
bit 3 of the flags returned by XProtocolSetup() is set. Calling this function
when bit 3 is not set will probably cause a system failure. The function should
be called just after any input from the serial device is received, and just
before anything else is done with the received data. The calling sequence is

        long newactual = XProtocolHostMon(struct XPR_IO *IO, char *serbuff,
        D0                                A0                 A1
                                          long actual, long maxsize)
                                          D0           D1

Here, IO is a previously initialized XPR_IO structure, serbuff is a pointer to a
buffer containing the data from the serial device, actual is the number of bytes
received from the serial device, and maxsize is the actual allocated size of
serbuff. The XPR is entitled to make any modifications to the data in serbuff it
wants, as long as the amount of modified data does not overflow the buffer as
indicated by maxsize. When the XPR is done looking at or changing the data, it
returns the new actual number of bytes of data in serbuff in newactual. Note,
that some actions of the XPR may cause the buffer to become invalid: for
efficiency, the communications program will usually hand a pointer to its one
and only serial port read buffer in "serbuff" rather than making a copy every
time. Whenever the XPR, based on the information found in the buffer, decides to
call any of the callbacks that deal with the serial device (xpr_sread(),
xpr_sflush(), xpr_squery()), the communications program may reuse the buffer,
erasing the previous contents. Consequently, if the XPR needs to preserve the
contents of the buffer, it must first make a local copy. Whenever there is a
chance that the data in serbuff was invalidated, the XPR should return
newactual = 0L.
    Note to the communications program author: when this function is called
after serial input was received, the state of the communications program is
usually such that no serial read request is outstanding. Still, the XPR may
start a file transfer from inside XProtocolHostMon. This situation is different
from the case where the user requests an upload or download by selecting e.g. a
menu item: at such a time, the communications program typically does have an
outstanding serial read request. Moreover, upon return from the
XProtocolHostMon() call, a previous call by the XPR to xpr_sread() may have
caused a serial read request to be queued. It is therefore important that the
communications program ensure that read requests are queued when appropriate,
including from inside xpr_sread(), and that read requests are not queued more
than once.
    Some XPR's may require control even when there is no outstanding
serial input or user input. In order to prevent the communications program
from going into a Wait() state, there is another bit returned by
XProtocolSetup(). When bit 5 is set, the communications program should not
wait, but call XProtocolHostMon() instead. If XProtocolHostMon() returns a
non-zero newactual, the data in serbuff should be treated just as if new
serial input was received. The XPR should never set this bit unless there is
a good reason: bypassing the communications program's Wait is very multitasking
unfriendly.

        This function, together with XProtocolUserMon(), can be used to modify
the behavior of communications programs dramatically. Especially, the entire data
handling of the communications program could be bypassed by returning newactual
= 0L, and processing all data inside of XProtocolHostMon(), effectively allowing
external terminal emulations if the XPR were to open appropriate windows for
displaying the data. It is in fact possible to have both an external protocol
(XPR) and an external emulation (XEM) running at the same time: the best way
to do this is to have duplicate copies of the xpr.lib glue routines, one for
XPR's and one for XEM's. It is recommended that names of external emulation
libraries follow the prescription: xem<emulation>.library, e.g. xemvt100.library
or xemtek4014.library.
        Another use for these functions would be to decode and encode and
perhaps compress the data after, resp. before transmission, for example for use
with hosts supporting error correction/detection protocols such as MNP.
        A more mundane purpose of this function is to watch the data stream
for incoming escape or control sequences otherwise not supported by the
communications program. Most notably, those sequences used to automatically
start file transfers as in ZMODEM or CompuServe B+, etc. When such a sequence
is detected, the XPR should directly call the appropriate XPR function to
handle the transfer from inside XProtocolHostMon(), and return newactual = 0L
to the communications program after the transfer has finished.
    Note to the XPR implementer: if the protocol the XPR implements is able
to autostart using XProtocolHostMon(), but als needs user input, it can use
xpr_gets() or xpr_options(). If those functions do not satisfy the need, the XPR
must use other means. One should be aware that for example the ARP file
requester can be called from inside an XPR library, in the same manner as it
can be called from any other program. The function xpr_getptr() can be used to
retrieve the pointer to the communications program's screen.


6.3.2 XProtocolUserMon()
------------------------

        This function should be called by the communications program only when
bit 4 of the flags returned by XProtocolSetup() is set. Calling this function
when bit 4 is not set will probably cause a system failure. The function should
be called just before any output is sent to the serial device. The calling
sequence is

        long newactual = XProtocolUserMon(struct XPR_IO *IO, char *serbuff,
        D0                                A0                 A1
                                          long actual, long maxsize)
                                          D0           D1

Here, IO is a previously initialized XPR_IO structure, serbuff is a pointer to a
buffer containing the data to be sent to the host, actual is the number of bytes
to be sent, and maxsize is the actual allocated size of serbuff. The XPR is
entitled to make any modifications to the data in serbuff it wants, as long as
the amount of modified data does not overflow the buffer as indicated by
maxsize. When the XPR is done looking at or changing the data, it returns the
new actual number of bytes of data in serbuff in newactual.
        This function, together with XProtocolHostMon(), can be used to modify
the behavior of communications programs dramatically. Especially, the entire data
handling of the communications program could be bypassed by returning newactual
= 0L, and processing all data inside of XProtocolUserMon(), effectively allowing
external terminal emulations, if the XPR were to open appropriate windows for
displaying the data. To get RAW KEY user input etc., the XPR would however have
to also open its own windows for IDCMP input. To that end, the function
xpr_getptr can be used to obtain the pointer to the screen of the communications
program where the window(s) should open.
        Another use for these functions would be to decode and encode and
perhaps compress the data after, resp. before transmission, for example for use
with hosts supporting error correction/detection protocols such as MNP.

                              __
                             /  \ o    /
                       -----/----\----/-----
                           /    o \__/


This concludes the documentation on external protocols using Amiga shared
libraries. If you have any questions, comments or suggestions, contact me on
BIX.
        Meanwhile, have fun!








Appendix A: XPR library skeleton.
=================================

;;; libface.c
;
;   DESCRIPTION:
;   ===========
;
;       This is the skeleton for an Amiga Exec library.
;       This version is written for Aztec C. It is based on the example
;       library by Jim Mackraz who got some stuff from Neil Katin.
;       This library implements a protocol transfer library.
;       All changes and additions by me.
;
;   AUTHOR/DATE:  W.G.J. Langeveld, February 1989.
;   ============
;
;;;

        include 'exec/types.i'

setup   macro
        movem.l d2/d3/d4-d7/a2-a6,-(sp)
        jsr     _geta4                  ;set up a4 for small model
        endm

push    macro
        move.l  \1,-(sp)
        endm

fix     macro
        ifc     '\1',''
                mexit
        endc
        ifle    \1-8
                addq.l  #\1,sp
        endc
        ifgt    \1-8
                lea     \1(sp),sp
        endc
        endm

restore macro
        fix     \1
        movem.l (sp)+,d2/d3/d4-d7/a2-a6
        rts
        endm

        dseg

        public  _libfunctab
_libfunctab:
        dc.l    XPRopen
        dc.l    XPRclose
        dc.l    XPRexpunge
        dc.l    $0000
        dc.l    XPRXProtocolCleanup
        dc.l    XPRXProtocolSetup
        dc.l    XPRXProtocolSend
        dc.l    XPRXProtocolReceive
        dc.l    XPRXProtocolHostMon
        dc.l    XPRXProtocolUserMon
        dc.l    $ffffffff

        cseg

        ;--- library functions
        public  _XPROpen
        public  _XPRClose
        public  _XPRExpunge
        public  _XProtocolCleanup
        public  _XProtocolSetup
        public  _XProtocolSend
        public  _XProtocolReceive
        public  _XProtocolHostMon
        public  _XProtocolUserMon

        public  _geta4

XPRopen:
        setup
        push a6
        jsr     _XPROpen
        restore 4

XPRclose:
        setup
        push a6
        jsr     _XPRClose
        restore 4

XPRexpunge:
        setup
        push a6
        jsr     _XPRExpunge
        restore 4

XPRXProtocolCleanup:
        setup
        push a0
        jsr     _XProtocolCleanup
        restore 4

XPRXProtocolSetup:
        setup
        push a0
        jsr     _XProtocolSetup
        restore 4

XPRXProtocolSend:
        setup
        push a0
        jsr     _XProtocolSend
        restore 4

XPRXProtocolReceive:
        setup
        push a0
        jsr     _XProtocolReceive
        restore 4

XPRXProtocolHostMon:
        setup
        push d1
        push d0
        push a1
        push a0
        jsr     _XProtocolHostMon
        restore 16

XPRXProtocolUserMon:
        setup
        push d1
        push d0
        push a1
        push a0
        jsr     _XProtocolUserMon
        restore 16


        end





Appendix B: The xproto.h include file
=====================================

/** xproto.h
*
*   Include file for External Protocol Handling
*
**/
/*
*   The structure
*/
struct XPR_IO {
                  char  *xpr_filename;      /* File name(s)             */
                  long (*xpr_fopen)();      /* Open file                */
                  long (*xpr_fclose)();     /* Close file               */
                  long (*xpr_fread)();      /* Get char from file       */
                  long (*xpr_fwrite)();     /* Put string to file       */
                  long (*xpr_sread)();      /* Get char from serial     */
                  long (*xpr_swrite)();     /* Put string to serial     */
                  long (*xpr_sflush)();     /* Flush serial input buffer*/
                  long (*xpr_update)();     /* Print stuff              */
                  long (*xpr_chkabort)();   /* Check for abort          */
                  long (*xpr_chkmisc)();    /* Check misc. stuff        */
                  long (*xpr_gets)();       /* Get string interactively */
                  long (*xpr_setserial)();  /* Set and Get serial info  */
                  long (*xpr_ffirst)();     /* Find first file name     */
                  long (*xpr_fnext)();      /* Find next file name      */
                  long (*xpr_finfo)();      /* Return file info         */
                  long (*xpr_fseek)();      /* Seek in a file           */
                  long   xpr_extension;     /* Number of extensions     */
                  long  *xpr_data;          /* Initialized by Setup.    */
                  long (*xpr_options)();    /* Multiple XPR options.    */
                  long (*xpr_unlink)();     /* Delete a file.           */
                  long (*xpr_squery)();     /* Query serial device      */
                  long (*xpr_getptr)();     /* Get various host ptrs    */
              };
/*
*   Number of defined extensions
*/
#define XPR_EXTENSION 4L

/*
*   The functions
*/
extern long XProtocolSend(),  XProtocolReceive(),
            XProtocolSetup(), XProtocolCleanup();
/*
*   Flags returned by XProtocolSetup()
*/
#define XPRS_FAILURE    0x00000000L
#define XPRS_SUCCESS    0x00000001L
#define XPRS_NORECREQ   0x00000002L
#define XPRS_NOSNDREQ   0x00000004L
#define XPRS_HOSTMON    0x00000008L
#define XPRS_USERMON    0x00000010L
#define XPRS_HOSTNOWAIT 0x00000020L
/*
*   The update structure
*/
struct XPR_UPDATE {     long  xpru_updatemask;
                        char *xpru_protocol;
                        char *xpru_filename;
                        long  xpru_filesize;
                        char *xpru_msg;
                        char *xpru_errormsg;
                        long  xpru_blocks;
                        long  xpru_blocksize;
                        long  xpru_bytes;
                        long  xpru_errors;
                        long  xpru_timeouts;
                        long  xpru_packettype;
                        long  xpru_packetdelay;
                        long  xpru_chardelay;
                        char *xpru_blockcheck;
                        char *xpru_expecttime;
                        char *xpru_elapsedtime;
                        long  xpru_datarate;
                        long  xpru_reserved1;
                        long  xpru_reserved2;
                        long  xpru_reserved3;
                        long  xpru_reserved4;
                        long  xpru_reserved5;
                   };
/*
*   The possible bit values for the xpru_updatemask are:
*/
#define XPRU_PROTOCOL           0x00000001L
#define XPRU_FILENAME           0x00000002L
#define XPRU_FILESIZE           0x00000004L
#define XPRU_MSG                0x00000008L
#define XPRU_ERRORMSG           0x00000010L
#define XPRU_BLOCKS             0x00000020L
#define XPRU_BLOCKSIZE          0x00000040L
#define XPRU_BYTES              0x00000080L
#define XPRU_ERRORS             0x00000100L
#define XPRU_TIMEOUTS           0x00000200L
#define XPRU_PACKETTYPE         0x00000400L
#define XPRU_PACKETDELAY        0x00000800L
#define XPRU_CHARDELAY          0x00001000L
#define XPRU_BLOCKCHECK         0x00002000L
#define XPRU_EXPECTTIME         0x00004000L
#define XPRU_ELAPSEDTIME        0x00008000L
#define XPRU_DATARATE           0x00010000L
/*
*   The xpro_option structure
*/
struct xpr_option {
   char *xpro_description;      /* description of the option                  */
   long  xpro_type;             /* type of option                             */
   char *xpro_value;            /* pointer to a buffer with the current value */
   long  xpro_length;           /* buffer size                                */
};
/*
*   Valid values for xpro_type are:
*/
#define XPRO_BOOLEAN 1L         /* xpro_value is "yes", "no", "on" or "off"   */
#define XPRO_LONG    2L         /* xpro_value is string representing a number */
#define XPRO_STRING  3L         /* xpro_value is a string                     */
#define XPRO_HEADER  4L         /* xpro_value is ignored                      */
#define XPRO_COMMAND 5L         /* xpro_value is ignored                      */
#define XPRO_COMMPAR 6L         /* xpro_value contains command parameters     */