Club Amiga de Montreal - CAM/CAM_CD_1.iso/files/550b.lha/Term_v1.8a/Libs.LZH/Libs/xprkermit.doc

Text File | 1991-07-26 | 11KB | 258 lines

                XPR Kermit
                Version 1.5 - RELEASE

                   Marco Papa - Felsina Software
           Stephen R. Walton, Cal State Northridge

This is a beta version of an External Protocol (XPR) library for the Kermit
file transfer protocol.  In keeping with the Kermit documents, here is a
list of the items supported and not supported.

XPR Kermit Capabilities At A Glance:

  Local operation:                   Yes
  Remote operation:                  No
  Login scripts:                     *
  Transfer text files:               Yes
  Transfer binary files:             Yes
  Wildcard send:                     Yes
  File transfer interruption:        Yes
  Filename collision avoidance:      No
  Can time out:                      Yes
  8th-bit prefixing:                 Yes
  Repeat count prefixing:            Yes
  Alternate block checks:            Yes
  Terminal emulation:                *
  Communication settings:            Yes
  Transmit BREAK:                    *
  Support for dialout modems:        *
  IBM mainframe communication:       *
  Transaction logging:               No
  Session logging (raw download):    No
  Debug logging:                     No
  Packet logging:                    No
  Act as server:                     No
  Talk to server:                    Yes
  Advanced server functions:         No
  Local file management:             *
  Command/Init files:                *
  UUCP and multiuser line locking:   *
  Long packets:                      Yes
  Sliding Windows:                   No
  File attributes packets:           No
  Command macros:                    *
  Raw file transmit:                 *

The items marked with a '*' above are those which are to be provided by the
calling terminal emulation program.

I. Introduction
---------------

XPR Kermit implements the Kermit file transfer protocol in the form of an
Amiga External Protocol (XPR) library.  This allows the addition of an
up-to-date version of the Kermit protocol to any communications program
which supports the XPR specification.  For further information on Kermit,
read the book "Kermit:  A File Transfer Protocol" by Frank da Cruz, 1986,
Digital Press.

To install XPR Kermit, simply copy the file "xprkermit.library" to your
LIBS: directory, and request your comm program to use XPRKERMIT as its
external file transfer protocol.

XPR Kermit supports Version 2.0 of the XPR Protocol specification.  For
more details on this, I recommend that you find a copy of the XPR Zmodem
library, version 2.0.  Its documentation contains a good deal of the
justification and philosophy of external protocol libraries, which I
won't repeat here.

II. Use
-------

XPR Kermit supports the parts of the Kermit protocol outlined in the table
above.  There are currently seven user-settable parameters in XPR Kermit,
which cover the parameters which are most often necessary to customize.
If your communications problem is especially severe--for example, your
method of connection to another system swallows characters which are special
to Kermit, such as '#' or '&'--you may need to get a copy of the stand-alone
Kermit program, C Kermit for the Amiga, distributed via many paths.

There are actually two sets of "setup" parameters in XPR Kermit.  The first
set are commands which XPR Kermit can send to a remote Kermit server. These
are not actually setups, but are in fact commands to XPR Kermit which cause it
to communicate with a remote Kermit server.  The fourth command in this group
is "Change Options," which causes no communication.  Instead, you are
requested for changes in the current values of the parameters which Kermit
will use for communication.

These items can be set in one of two ways.  One method is with a simple
character string which is sent to XPR Kermit by the comm program;  this string
will hereafter be referred to as the "init string."  This is generally done if
an environment variable named "xprkermit" exists and has a value, in which
case XPR Kermit is sent the value when you first select XPR Kermit as your
protocol.  Some comm programs also allow an initialization string to be sent
in other ways, such as from a script; VLT, for example, has an INITXPR script
command.  The format of this string is specified by the external protocol.

The second, more elegant method, is with some type of requester or set
of requesters.  In this case, you will be presented by your comm program
with a set of Intuition gadgets of some type which allow the choice of
XPR Kermit commands and the setting of the options.

However, the string method has the advantage of giving one the ability to
change external protocol settings non-interactively, such as from a script.
In the case of XPR Kermit, such a script can actually command XPR Kermit to
perform communication.  One obvious use of this is to transfer an entire
directory tree from your Amiga to a remote machine:  you can make the remote's
Kermit a server and command it to perform the appropriate CD commands, then
transfer files.

The currently supported XPR Kermit server commands are listed below.
The format of the init string is in parentheses, generally simply a
single letter.

    Kermit Finish (F):  Tells a Kermit server that you are done.  The
    remote server will stop being a server.

    Kermit Bye (B):  Tells a Kermit server that you are done;  the server
    will exit and log you off the remote machine.

    Kermit CD (C{dir}):  Change the default directory for files sent or
    received by the Kermit server.  Examples of the init string would
    be 'C/bin' or 'Cuser:[username.amiga]'.

For setting options via an init string, the first character of the init
string must be the letter O (for Options).  Following that letter can
be one or more of the option setting formats listed bellow;  these
can be separated by whitespace and/or commas.

There are three settings which are either "yes" or "no."  Your comm program
will give you some way of setting them interactively.  Simple button gadgets
will be labeled "yes" and "no;"  otherwise, you may see a string gadget,
into which you should type the word "yes" or "no" by hand.  This string is
case-insensitive.  In the init-string, "yes" is represented by the single
upper-case character Y.

    Convert FileName (C{Y|N}):  If "yes," then incoming file names are
    converted to a form acceptable to the Amiga.  Currently, this
    means simply translating them to lower case.  Default "yes."

    Host Server (G{Y|N}):  If "yes," then the host (remote) Kermit is
    assumed to be in server mode.  You will be prompted for file
    names when you request an XPR Kermit receive, and this file
    name will be sent to the server in the form of a Kermit GET
    command.  Default "no."

    Text File (T{Y|N}):  Flags whether the incoming file is text or binary.
    If "yes," then carriage-return/line-feed pairs in the incoming
    packets are converted to a single line-feed before writing the
    packet to a file, and the opposite conversion is made when a file
    is sent to a remote system.  Default "yes".

    If your communcations program supports its own text/binary flag
    (that is, if the xpr_finfo() function exists and can tell XPR
    Kermit whether a given file is text or binary), this option will
    not appear.

Numerical settings are as follows.  Here, the init string key letter should
be followed by a numerical value.

    Packet Length (P{length}):  The Long Packets extension to Kermit is
    fully supported. Setting a packet length larger than 94 (the
    default) enters long packet mode automatically.  If you use long
    packets, it is *strongly* recommended that you use block check 2
    or 3 (see below) if the host Kermit supports them. The current
    limit is 1024 for XPR Kermit;  the default value is 94, the
    longest standard Kermit packet.

    Block Check (B{type}):  This can have the value of 1, 2, or 3, and
    chooses successively more stringent types of error checking on
    the incoming data:  6-bit checksum, 12-bit checksum, and 16-bit
    CRC, respectively.  Default is 1 (6-bit checksum).

    Timeout (O{seconds}):  The length of time XPR Kermit will wait for a
    packet before assuming it isn't coming.  Default 5 seconds.  (The
    O is for Out, as in TimeOut;  T is already taken by the Text flag.)

     Retry Limit (R{number}):  The number of times XPR Kermit will attempt
    to send or receive the next packet of data before quitting.  Notice
    that if the remote end simply stops sending, a length of time equal
    to the retry limit times the timeout will elapse before XPR Kermit
    actually exits.  Default 10 retries.

These can be mixed and matched.  For instance, to talk to a Kermit server
with 750-byte packets, block check 2, binary files, and a 10-second timeout,
the init string could be "OP750,B2,TN,O10".  Cryptic, but usable.

III. Future Extensions
----------------------

There are several items to be added to this XPR.  In rough order of priority,
these are:

1.  Delete on error.  XPR Kermit does not delete a partial file if there
is an error on receive.

2.  A better display of the status of the file transfer.

3.  Re-entrancy.  If you are one of those lucky people with multiple serial
ports on your Amiga, then XPR Kermit will only run on one of those ports
at a time at present.

4. Speed. The book's code does a great deal of work which could be done
quite a bit more efficiently.  Many improvements are in the current
version of C Kermit, Columbia's version 4F(095).

5.  "Real" Kermit.  At some point, XPR Kermit will, I hope, become an
interface to Columbia University's C Kermit code.  This will allow
XPR Kermit to always contain the latest version of the Kermit protocol,
provided that I or someone writes the new machine-dependent functions,
if any.

Before embarking on any of the above improvements, I will be taking
a break from this code.  When I get started again, the first order of
business will be some code reorganization and a switch to version 5.0
of Manx Aztec C.

IV.  Other information
----------------------

The file "kermitproto.doc" describes the code contained in the file
"kermitproto.w," which actually implements the Kermit protocol.

V.  Credits
-----------

The following people had a hand in this code.  In chronological order,
they are:

-- Frank DaCruz of Columbia University, who wrote the original code and
   published it in his book.
-- Steve Walton of Cal State Northridge, who got Frank's code actually
   working in the form of the original "kermitproto.w" module.
-- Marco Papa of Felsina Software, for the first beta XPR version
-- Steve Walton, for second and subsequent XPR Kermit's.

Other acknowledgements go to Willy Langeveld for developing the XPR
spec, and to Rick Huebner, several of whose ideas in XPR Zmodem were
taken over into XPR Kermit by Steve Walton. Thank you all!

VI.  Gripes
-----------

The current author and babysitter of this code is:
    Stephen Walton
    Department of Physics and Astronomy
    Cal State Northridge
    18111 Nordhoff St.
    Northridge, CA 91330 USA
    [phone]

E-mail can go to:
    s_walton (BIX)
    WALTON (PeopleLink)
    [e-mail] or [e-mail] (Internet)

Thanks and congratulations gratefully accepted;  bug fixes and enhancements
even more so!