Columbia Kermit/kermit.zip/archives/cku196.zip/ckcplm.txt

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CKCPLM.TXT                                                            Jan 2000

            C-KERMIT PROGRAM LOGIC MANUAL

As of C-Kermit version:  7.0.196
This file last updated:  Sun Dec  5 14:29:02 1999
Author: Frank da Cruz, Columbia University
E-Mail: [e-mail]

  Copyright (C) 1985, 2000,
    Trustees of Columbia University in the City of New York.
    All rights reserved.  See the C-Kermit COPYING.TXT file or the
    copyright text in the ckcmai.c module for disclaimer and permissions.


INTRODUCTION

The Kermit Protocol is specified in the book "Kermit, A File Transfer
Protocol" by Frank da Cruz, Digital Press / Butterworth Heinemann, Newton, MA,
USA (1987), 379 pages, ISBN 0-932376-88-6.  It is assumed the reader is
familiar with the Kermit protocol specification.

This file attempts to describe the relationship among the modules and
functions of C-Kermit 5A and later.  Before reading this file, please read the
file CKAAAA.TXT for an overview of C-Kermit file naming conventions.

C-Kermit is designed to be portable to any kind of computer that has a C
compiler.  The source code is broken into many files that are grouped
according to their function.  There are several major groups: 1 (the protocol
kernel), 2 (the user interface), 3 (system-dependent primitives), 4 (network
support), and 5 (formatted screen support).


CONTENTS:

  FILES
  SOURCE CODE PORTABILITY GUIDE

  GROUP 0    Library functions
  GROUP 1    System-independent file transfer protocol
  GROUP 1.5  Character set translation
  GROUP 2    User Interface
  GROUP 3    File & communications i/o and other system dependencies
  GROUP 4    Network support
  GROUP 5    Formatted screen support

  APPENDIX I File Permissions

WARNING: C-Kermit 6.1 is probably the last version preserving this
organization and naming.  The next major release after 6.1 will apply some
lessons we have learned about modularity and separation, and allow easier
integration of the code with other applications and/or user interfaces.


FILES

C-Kermit source files begin with the two letters CK (lowercase on UNIX
systems, uppercase on most others).  The third character denotes something
about the function group and the expected level of portability.  See the file
CKAAAA.TXT for details of file naming conventions and organization.

One hint before proceeding: functions are scattered all over the ckc*.c
and ckuu*.c modules, where function size has begun to take precedence over
the desirability of grouping related functions together, the aim being to
keep any particular module from growing disproportionately large.  The easiest
way (in UNIX) to find out what source file a given function is defined in is
like this (where the desired function is foo()...):

  grep ^foo ck*.c

This works because the coding convention has been to make function names
always start on the left margin with their contents indented, for example:

static char *
foo(x,y) int x, y; {
    ...
}

Also please note the style for bracket placement.  This allows
bracket-matching text editors (such as EMACS) to help you make sure you know
which opening bracket a closing bracket matches, particularly when it is no
longer visible on the screen, and it also makes it easy to find the end of a
function (search for '}' on the right margin).

Of course EMACS tags work nicely with this format too:

  $ cd <kermit-source-directory>
  $ etags ck[cu]*.[ch]
  $ emacs
  Esc-X Visit-Tags-Table<CR><CR>

(but remember that the source file for ckcpro.c is ckcpro.w!)


SOURCE CODE PORTABILITY GUIDE

When writing code for the system-indendent C-Kermit modules, please stick to
the following coding conventions to ensure portability to the widest possible
variety of C preprocessors, compilers, and linkers, as well as certain network
and/or email transports:

. Tabs should be set every 8 spaces, as on a VT100.
. All lines must no more than 79 characters wide after tab expansion.
. Note the distinction between physical tabs (ASCII 9) and the indentation
  conventions, which are: 4 for block contents, 2 for most other stuff.
. Try to keep variable and function names unique within 6 characters,
  especially if they are used across modules, since 6 is the maximum for
  some linkers.  (Actually, I think the last system that had this limitation
  was turned off in the 1980s -- remember SIXBIT? -- no now maybe it's 8?)
. Keep preprocessor symbols unique within 8 characters.
. Don't put #include directives inside functions or { blocks }.
. Don't use the #if preprocessor construction, only use #ifdef, #ifndef, #undef
. Put tokens after #endif in comment brackets, e.g. #endif /* FOO */.
. Don't indent preprocessor statements - # must always be first char on line.
. Don't put whitespace after # in preprocessor statements.
. Don't use #pragma, even within #ifdefs - it makes some preprocessors give up.
. Same goes for #module, #if, etc - #ifdefs do NOT protect them.
. Don't use logical operators in preprocessor constructions.
. Avoid #ifdefs inside argument list to function calls.
. Always cast strlen() in expressions to int: "if ((int)strlen(foo) < x)...".
. Any variable whose value might exceed 16383 should be declared as long,
  or if that is not possible, then as unsigned.
. Unsigned long is not portable.
. Don't use initializers with automatic arrays or structs.
. Don't assume that struct assignment performs a copy.
. Don't put prototypes for static functions into header files that are used
  by modules that don't contain that function.
. Avoid the construction *++p -- the order of evaluation varies.
. Reportedly, some compilers even mess up with *(++p).
. Don't use triple assignments, like a = b = c = 0; (or quadruple, etc).
  Some compilers generate bad code for these, or crash, etc.
. Structure members may not have the same names as other identifiers.
. Avoid huge switch() statements with many cases.
. Don't have a switch() statement with no cases (e.g. because of #ifdefs).
. Don't put anything between "switch() {" and case: --   switch blocks are not
  like other blocks.
. Don't make character-string constants longer than about 250.
. Don't write into character-string constants even when you know you are not
  writing past the end because the compiler or linker might have put them into
  read-only and/or shared memory, and/or coalesced multiple equal constants
  so if you change one you change them all.
. Don't depend on '\r' being carriage return.
. Don't depend on '\n' being linefeed or for that matter any SINGLE character.
. Don't depend on '\r' and '\n' being different (e.g. in switch() statements).
. In other words, don't use \n or \r to stand for specific characters;
  use \012 and \015 instead.
. Don't code for "buzzword 1.0 compliance", unless "buzzword" is K&R and
  "1.0" is the first edition.
. Don't use or depend on anything_t (size_t, time_t, etc).
. Don't use or depend on internationalization ("i18n") features, wchar_t,
  locales, etc, in portable code; they are not portable.  Anyway, locales are
  not the right model for Kermit's multi-character-set support.
. Don't make any assumption about signal handler type.  It can be void, int,
  long, or anything else.  Always declare signal handlers as SIGTYP (see
  definition in ckcdeb.h and augment it if necessary) and always use
  SIGRETURN at exit points from signal handlers.
. Signals should always be re-armed to be used again (this barely scratches
  the surface -- the difference between BSD/V7 and System V and POSIX signal
  handling are numerous, and some platforms do not even support signals,
  alarms, or longjmps correctly or at all -- avoid all of this stuff if you
  can).
. Don't call malloc() & friends from a signal handler.
. memset(), memmove(), and memcpy() are not portable, don't use them without
  protecting them in ifdefs.  bzero() too, except we're guaranteed to have
  bzero() when using the sockets library.  See examples in the source.
. Don't assume that strncpy() stops on the first null byte -- some versions
  always copy the number of bytes given in arg 3.  Probably also true of
  other strnblah() functions.
. DID YOU KNOW.. that some versions of inet_blah() routines return IP addresses
  in network byte order, while others return them local machine byte order?
  So passing them to htons(), etc, is not always the right thing to do.
. Don't use ANSI-format function declarations without #ifdef CK_ANSIC,
  and always provide an #else for the non-ANSI case.
. Don't depend on any other ANSI preprocessor features like "pasting" -- they
  are often missing or nonoperational.
. Don't assume any C++ syntax or semantics.
. Don't declare a string as "char foo[]" in one module and "extern char * foo"
  in another, or vice-versa.
. With compiler makers falling all over themselves trying to outdo each other
  in ANSI strictness, it has become increasingly necessary to cast EVERYTHING.
. a[x], where x is an unsigned char, can produce a wild memory reference if x,
  when promoted to an int, becomes negative.  Cast it to (unsigned), even
  though it ALREADY IS unsigned.
. Be careful how you declare functions that have char or long arguments;
  for ANSI compilers you MUST use ANSI declarations to avoid promotion
  problems, but you can't use ANSI declarations with non-ANSI compilers.
  Thus declarations of such functions must be hideously entwined in #ifdefs.
  Example of the latter:

  int                   /*  Put character in server command buffer  */
  #ifdef CK_ANSIC
  putsrv(char c)
  #else
  putsrv(c) char c;
  #endif /* CK_ANSIC */
  /* putsrv */ {
      *srvptr++ = c;
      *srvptr = '\0';        /* Make sure buffer is null-terminated */
      return(0);
  }

. Be careful how you return characters from functions that return int values --
  "getc-like functions" -- in the ANSI world.  Unless you explicitly cast the
  return value to (unsigned), it is likely to be "promoted" to an int and have
  its sign extended.

(many, many more...  This section needs massive filling in.)

C-Kermit needs constant adjustment to new OS and compiler releases.  Every
new release shuffles header files or their contents, or prototypes, or data
types, or levels of ANSI strictness, etc.  Every time you make an adjustment
to remove a new compilation error, BE VERY CAREFUL to #ifdef it on a symbol
unique to the new configuration so that the previous configuration (and all
other configurations on all other platforms) remain as before.

Assume nothing.  Don't assume header files are where they are supposed to be,
that they contain what you think they contain, that they define specific
symbols to have certain values -- or define them at all!  Don't assume system
header files protect themselves against multiple inclusion.  Don't assume that
particular system or library calls are available, or that the arguments are
what you think they are -- order, data type, passed by reference vs value,
etc.  Be very conservative when attempting to write portable code.  Avoid all
advanced features.  Stick with K&R First Edition, and even then you're on
shaky ground.

If you see something that does not make sense, don't assume it's a mistake --
it is probably there for a reason, and changing it or removing is very likely
to cause compilation, linking, or runtime failures sometime, somewhere.  Some
huge percentage of the code, especially in the system-dependent modules, is
workarounds for compiler, linker, or API bugs.

BUT... feel free to violate any or all of these rules in system-specific
modules for environments in which the rules are certain not to apply.  For
example, in VMS-specific code, it is OK to use #if.  But even then, allow for
different compilers or compiler versions used in that same environment,
e.g. VAX C vs DEC C vs GNU C.

THE "CHAR" VS "UNSIGNED CHAR" DILEMMA

This is one of the most aggravating and vexing things about C.  By default,
chars (and char *'s) are SIGNED.  But in the modern era, we need to process
characters that can have 8-bit values, such as ISO Latin-1, IBM CP 850, and
other 8-bit (or 16-bit, etc) character sets, and so this data MUST be treated
as unsigned.  BUT...  Some C compilers (such as those based on the Bell UNIX
V7 compiler) do not support "unsigned char" as a data type.  Therefore we have
the macro or typedef CHAR, which we use when we need chars to be unsigned, but
which, unfortunately, resolves itself to "char" on those compilers that don't
support "unsigned char".  AND SO...  We have to do a lot of fiddling at
runtime to avoid sign extension and so forth.  BUT THAT'S NOT ALL...  Now some
modern compilers (e.g. IBM, DEC, Microsoft) have switches that say "make all
chars be unsigned" (e.g. GNU cc "-funsigned-char").  We use these switches
when they are available.  Other compilers don't have these, and at the same
time, are becoming increasingly strict about type mismatches, and spew out
torrents of warnings when we use a CHAR where a char is expected, or vice
versa.  We fix these one by one using casts, and the code becomes increasingly
ugly.  But there remains a serious problem, namely that certain library and
kernel functions have arguments that are declared as signed chars (or pointers
to them), whereas our character data is unsigned.  Fine, we can can use casts
here too -- but who knows what happens inside these routines.

MODES OF OPERATION

When C-Kermit is on the far end of a connection, it is said to be in
remote mode.  When C-Kermit has made a connection to another computer, it
is in local mode.  (If C-Kermit is "in the middle" of a multihop connection,
it is still in local mode.)

On another axis, C-Kermit has three major modes of operation:

Command Mode
  Reading and writing from the job's controlling terminal or "console".
  In this mode, all i/o is handled by the Group 3 conxxx() (console i/o)
  routines.

Protocol Mode
  Reading and writing from the communicatons device.  In this mode, all i/o is
  handled by the Group 3 ttxxx() (terminal i/o) routines.

Connect Mode
  Reading from the keyboard with conxxx() routines and writing to the
  communications device with ttxxx() routines AND vice-versa.

When in local mode, the console and communications device are distinct.
During file transfer, Kermit may put up a file-transfer display on the console
and sample the console for interruption signals.

When in remote mode, the console and communications device are the same, and
therefore there can be no file-transfer display on the console or
interruptions from it (except for "in-band" interruptions such as ^C^C^C).

GROUP 0:

Library functions, strictly portable, can be used by all modules on all
platforms.  CKCLIB.H, CKCLIB.C.

GROUP 1:

The Kermit protocol kernel.  The filenames start with CKC.  C means that these
files are supposed to be totally portable C, and are expected to compile
correctly on any platform with any C compiler.  "Portable" does not mean the
same as as "ANSI" -- these modules must compile on 10- and 20-year old
computers, with C preprocessors, compilers, and/or linkers that have all sorts
of restrictions.  The group 1 modules do not include any header files other
than those that come with Kermit itself.  They do not contain any library
calls (like printf) or any system calls (like open, close, read, write).
Files:

  CKCSYM.H - For use by C compilers that don't allow -D on the command line.
  CKCASC.H - ASCII character symbol definitions.
  CKCSIG.H - System-independent signal-handling definitions and prototypes.
  CKCDEB.H - Originally, debugging definitions.  Now this file also contains
         all definitions and prototypes that are shared by all modules in
             all groups.
  CKCKER.H - Kermit protocol symbol definitions.
  CKCXLA.H - Character-set-related symbol definitions (see next section).

  CKCMAI.C - The main program.  This module contains the declarations of all
  the protocol-related global variables that are shared among the other
  modules.

  CKCPRO.W - The protocol module itself, written in "wart", a lex-like
  preprocessor that is distributed with Kermit under the name CKWART.C.

  CKCFN*.C - The protocol support functions used by the protocol module.

Group 1 modules may call upon functions from Group 3 modules, but not from
Group 2 modules (with the single exception that the main program invokes the
user interface, which is in Group 2).  (This last assertion is really only a
conjecture.)

GROUP 1.5

Character set translation tables and functions.  Used by the Group I protocol
modules, but may be specific to different computers.  (So far, all character
character sets supported by C-Kermit are supported in CKUXLA.C and CKUXLA.H,
including Macintosh and IBM character sets).  These modules should be
completely portable, and not rely on any kind of system or library services.

  CKCXLA.H - Character-set definitions usable by all versions of C-Kermit.
  CK?XLA.H - Character-set definitions for computer "?", e.g. U for UNIX.

  CK?XLA.C - Character-set translation tables and functions for computer "?",
  For example, CKUXLA.C for UNIX, CKMXLA.C for Macintosh.  So far, these are
  the only two such modules.  The UNIX module is used for all versions of
  C-Kermit except the Macintosh version.

  CKCUNI.H - Unicode definitions
  CKCUNI.C - Unicode module

  Used for file transfer (SEND, RECEIVE, GET, REMOTE, etc), TRANSMIT,
  CONNECT, etc.

Here's how to add a new file character set.  Assuming it is based on the
Roman (Latin) alphabet.  Let's call it "Barbarian".  First, in CK?XLA.H,
add a definition for FC_BARBA (8 chars maximum length) and increase
MAXFCSETS by 1.  Then, in CK?XLA.C:

  . Add a barbarian entry into the fcsinfo array.
  . Add a "barbarian" entry to file character set keyword table, fcstab.
  . Add a "barbarian" entry to terminal character set keyword table, ttcstab.
  . Add a translation table from Latin-1 to barbarian: yl1ba[].
  . Add a translation table from barbarian to Latin-1: ybal1[].
  . Add a translation function from Barbarian to ASCII: xbaas().
  . Add a translation function from Barbarian to Latin-1: xbal1().
  . Add a translation function from Latin-1 to Barbarian: xl1ba().
  .  etc etc for each transfer character set...
  . Add translation function pointers to the xls and xlr tables.

Other translations involving Barbarian (e.g. from Barbarian to Latin-Cyrillic)
are performed through these tables and functions.  See CKUXLA.H and CKUXLA.C
for extensive examples.

To add a new Transfer Character Set, e.g. Latin Alphabet 9 (for the Euro
symbol)...

In ckcxla.h:
 . Add a TC_xxxx definition and increase MAXTCSETS accordingly.

In ck?xla.h (since any transfer charset is also a file charset):
 . Add an FC_xxxx definition and increase MAXFCSETS accordingly.

In ck?xla.c:
 . Add a tcsinfo[] entry.
 . Make a tcstab[] keyword table entry.
 . Make an fcsinfo[] table entry.
 . Make an fcstab[] keyword table entry.
 . Make a tcstab[] keyword table entry.
 . If necessary, make a langinfo[] table entry.
 . Make entries in the function pointer arrays.
 . Provide any needed functions.

In ckcuni.h:
 . (to be filled in)

In ckcuni.c:
 . (to be filled in)


GROUP 2:

The user interface.  This is the code that communicates with the user, gets
her commands, informs her of the results.  It may be command-line oriented,
interactive prompting dialog, menus and arrow keys, windows and mice, speech
recognition, telepathy, etc.  The user interface has three major functions:

1. Sets the parameters for the file transfer and then starts it.  This is done
by setting certain (many) global variables, such as the protocol machine start
state, the file specification, file type, communication parameters, packet
length, window size, character set, etc.

2. Displays messages on the user's screen during the file transfer, using the
screen() function, which is called by the group-1 modules.

3. Executes any commands directly that do not require Kermit protocol, such
as the CONNECT command, local file management commands, parameter-setting
commands, etc.

If you plan to imbed the Group 1 files into a program with a different user
interface, your interface must supply an appropriate screen() function, plus a
couple related ones like chkint() and intmsg() for handling keyboard (or
mouse, etc) interruptions during file transfer.  The best way to find out
about this is to link all the C-Kermit modules together except the CKUU*.O
and CKUCON.O modules, and see which missing symbols turn up.

C-Kermit's character-oriented user interface (as opposed to the Macintosh
version's graphical user interface) consists of the following modules.
C-Kermit can be built with an interactive command parser, a command-line-
option-only parser, a graphical user interface, or any combination, and it
can even be built with no user interface at all (in which case it runs as a
remote-mode Kermit server).

  CKUUSR.H - Definitions of symbols used in Kermit's commands.

  CKUUSR.H, CKUUSR.C, CKUUS2.C, CKUUS3.C, CKUUS4.C, CKUUS5.C, ... -
  Kermit's interactive command parser, including the script programming
  language.

  CKUUSY.C - The command-line-option parser.

  CKUUSX.C - Functions that are common to both the interactive and
  command-line parsers.

  CKUCMD.H, CKUCMD.C - The command parsing primitives used by the
  interactive command parser to parse keywords, numbers, filenames, etc,
  and to give help, complete fields, supply defaults, allow abbreviations
  and editing, etc.  This package is totally independent of Kermit, but
  does depend on the Group 3 functions.

  CKUVER.H - Version heralds for different implementations.

  CKUSCR.C - The (old, uucp-like) SCRIPT command.
  CKUDIA.C - The DIAL command.  Includes specific knowledge of many
             types of modems.

  CK?CON.C - The CONNECT command.  Terminal connection, and in some
             cases (Macintosh, OS/2, etc) also terminal emulation.
             NOTE: As of C-Kermit 6.1, there are two different CONNECT
             modules for UNIX: ckucon.c -- the regular, portable version
             -- and ckucns.c, a new version that uses select() rather
             than forks so it can handle encryption.  ckucns.c is the
             preferred version; ckucon.c is not likely to keep pace with
             it in terms of upgrades, etc.  However, since select() is
             not portable to every platform, ckucon.c will be kept
             indefinitely for those platforms that can't use ckucns.c.
             NOTE: SunLink X.25 support is available only in ckucon.c.

  CK_CRP.* - Modules having to do with authentication and encryption.
  CKUAT*.*   These are not part of the general distribution since they
             contain code and algorithms that are restricted by USA
             export law.

For other implementations, the files may, and probably do, have different
names.  For example, the Macintosh graphical user interface filenames start
with CKM.  OS/2 uses the CKUCMD and CKUUS* modules, but has its own CONNECT
command in CKOCON.C.  And so on.

Here is a brief description of C-Kermit's "user interface interface", from
CKUUSR.C.  It is nowhere near complete; in particular, hundreds of global
variables are shared among the many modules.  These should, some day, be
collected into classes or structures that can be passed around as needed;
not only for purity's sake, but also to allow for multiple simultaneous
communication sessions and or user interfaces.

The ckuus*.c modules depend on the existence of C library features like fopen,
fgets, feof, (f)printf, argv/argc, etc.  Other functions that are likely to
vary among operating systems -- like setting terminal modes or interrupts --
are invoked via calls to functions that are defined in the system-dependent
modules, ck?[ft]io.c.  The command line parser processes any arguments found
on the command line, as passed to main() via argv/argc.  The interactive
parser uses the facilities of the cmd package (developed for this program, but
usable by any program).  Any command parser may be substituted for this one.
The only requirements for the Kermit command parser are these:

1. Set parameters via global variables like duplex, speed, ttname, etc.  See
   ckcmai.c for the declarations and descriptions of these variables.

2. If a command can be executed without the use of Kermit protocol, then
   execute the command directly and set the variable sstate to 0.  Examples
   include 'set' commands, local directory listings, the 'connect' command.

3. If a command requires the Kermit protocol, set the following variables:

   sstate                             string data
     'x' (enter server mode)            (none)
     'r' (send a 'get' command)         cmarg, cmarg2
     'v' (enter receive mode)           cmarg2
     'g' (send a generic command)       cmarg
     's' (send files)                   nfils, cmarg & cmarg2 OR cmlist
     'c' (send a remote host command)   cmarg

   cmlist is an array of pointers to strings.
   cmarg, cmarg2 are pointers to strings.
   nfils is an integer.

   cmarg can be a filename string (possibly wild), or
      a pointer to a prefabricated generic command string, or
      a pointer to a host command string.
   cmarg2 is the name to send a single file under, or
      the name under which to store an incoming file; must not be wild.
      If it's the name for receiving, a null value means to store the
      file under the name it arrives with.
   cmlist is a list of nonwild filenames, such as passed via argv.
   nfils is an integer, interpreted as follows:
     -1: filespec (possibly wild) in cmarg, must be expanded internally.
      0: send from stdin (standard input).
     >0: number of files to send, from cmlist.

The screen() function is used to update the screen during file transfer.
The tlog() function writes to a transaction log (if TLOG is defined).
The debug() function writes to a debugging log (if DEBUG is defined).
The intmsg() and chkint() functions provide the user i/o for interrupting
file transfers.

GROUP 3:

System-dependent function definitions.  All the Kermit modules, including the
command package, call upon these functions, which are designed to provide
system-independent primitives for controlling and manipulating devices and
files.  For UNIX, these functions are defined in the files CKUFIO.C (files),
CKUTIO.C (communication devices), and CKUSIG.C (signal handling).

For VMS, the files are CKVFIO.C, CKVTIO.C, and CKUSIG.C (VMS can use the same
signal handling routines as UNIX).  For OS/2, CKOFIO.C, CKOTIO.C, CKOSIG.C
(OS/2 has its own signal handling).  It doesn't really matter what the files
are called, except for Kermit distribution purposes (grouping related files
together alphabetically), only that each function is provided with the name
indicated, observes the same calling and return conventions, and has the same
type.

The Group 3 modules contain both functions and global variables that are
accessed by modules in the other groups.  These are now described.

(By the way, I got this list by linking all the C-Kermit modules together
except CKUTIO and CKUFIO.  These are the symbols that ld reported as undefined)

A. Variables:

char *DELCMD;
  Pointer to string containing command for deleting files.
  Example: char *DELCMD = "rm -f ";  (UNIX)
  Example: char *DELCMD = "delete "; (VMS)
  Note trailing space.  Filename is concatenated to end of this string.
  NOTE: DELCMD is used only in versions that do not provide their own
  built-in DELETE command.

char *DIRCMD;
  Pointer to string containing command for listing files when a filespec
  is given.
  Example: char *DIRCMD = "/bin/ls -l "; (UNIX)
  Example: char *DIRCMD = "directory ";  (VMS)
  Note trailing space.  Filename is concatenated to end of this string.
  NOTE: DIRCMD is used only in versions that do not provide their own
  built-in DIRECTORY command.

char *DIRCM2;
  Pointer to string containing command for listing files when a filespec
  is not given.  (currently not used, handled in another way.)
  Example: char *DIRCMD2 = "/bin/ls -ld *";
  NOTE: DIRCMD2 is used only in versions that do not provide their own
  built-in DIRECTORY command.

char *PWDCMD;
  Pointer to string containing command to display current directory.
  Example: char *PWDCMD = "pwd ";
  NOTE: PWDCMD is used only in versions that do not provide their own
  built-in PWD command.

char *SPACMD;
  Pointer to command to display free disk space in current device/directory.
  Example: char *SPACMD = "df .";
  NOTE: SPACMD is used only in versions that do not provide their own
  built-in SPACE command.

char *SPACM2;
  Pointer to command to display free disk space in another device/directory.
  Example: char *SPACM2 = "df ";
  Note trailing space.  Device or directory name is added to this string.
  NOTE: SPACMD2 is used only in versions that do not provide their own
  built-in SPACE command.

char *TYPCMD;
  Pointer to command for displaying the contents of a file.
  Example: char *TYPCMD = "cat ";
  Note trailing space.  Device or directory name is added to this string.
  NOTE: TYPCMD is used only in versions that do not provide their own
  built-in TYPE command.

char *WHOCMD;
  Pointer to command for displaying logged-in users.
  Example: char *WHOCMD = "who ";
  Note trailing space.  Specific user name may be added to this string.

int backgrd = 0;
  Flag for whether program is running in foreground (0) or background
  (nonzero).  Background operation implies that screen output should not be
  done and that all errors should be fatal.

int ckxech;
  Flag for who is to echo console typein:
  1 - The program (system is not echoing).
  0 - The system, front end, terminal, etc (not this program)

char *ckxsys;
  Pointer to string that names the computer and operating system.
  Example: char *ckxsys = " NeXT Mach 1.0";
  Tells what computer system ckxv applies to.
  In UNIX Kermit, this variable is also used to print the program herald,
  and in the SHOW VERSION command.

char *ckxv;
  Pointer to version/edit info of ck?tio.c module.
  Example: char *ckxv = "UNIX Communications Support, 6.0.169, 6 Sep 96";
  Used by SHOW VERSION command.

char *ckzsys;
  Like ckxsys, but briefer.
  Example: char *ckzsys = " 4.3 BSD";
  Tells what platform ckzv applies to.
  Used by the SHOW VERSION command.

char *ckzv;
  Pointer to version/edit info of ck?fio.c module.
  Example: char *ckzv = "UNIX File support, 6.0.113, 6 Sep 96";
  Used by SHOW VERSION command.

int dfflow;
  Default flow control.
  0 = none, 1 = Xon/Xoff, ... (see FLO_xxx symbols in ckcdeb.h)
  Set to by group 3 module.
  Used by ckcmai.c to initialize flow control variable.

int dfloc;
  Default location.
  0 = remote, 1 = local.
  Set by group 3 module.
  Used by ckcmai.c to initialize local variable.  Used in various places in
  the user interface.

int dfprty;
  Default parity.
  0 = none, 'e' = even, 'o' = odd, 'm' = mark, 's' = space.
  Set by Group 3 module.  Used by ckcmai.c to initialize parity variable.

char *dftty;
  Default communication device.
  Set by group 3 module.  Used in many places.
  This variable should be initialized the the symbol CTTNAM, which is defined
  in ckcdeb.h, e.g. as "/dev/tty" for UNIX, "TT:" for VAX/VMS, etc.
  Example: char *dftty = CTTNAM;

char *mtchs[];
  Array of string pointers to filenames that matched the most recent
  wildcard match, i.e. the most recent call to zxpand().  Used (at least) by
  command parsing package for partial filename completion.

int tilde_expand;
  Flag for whether to attempt to expand leading tildes in directory names
  (used in UNIX only, and then only when the symbol DTILDE is defined.

int ttnproto;
  The protocol being used to communicate over a network device.  Values are
  defined in ckcnet.h.  Example: NP_TELNET is network protocol "telnet".

int maxnam;
  The maximum length for a filename, exclusive of any device or directory
  information, in the format of the host operating system.

int maxpath;
  The maximum length for a fully specified filename, including device
  designator, directory name, network node name, etc, in the format of
  the host operating system, and including all punctuation.

int ttyfd;
  File descriptor of the communication device.  -1 if there is no open
  or usable connection, including when C-Kermit is in remote mode.
  Since this is not implemented everywhere, references to it are in
  #ifdef CK_TTYFD..#endif.

B. Functions.

These are divided into three categories: file-related functions (B.1),
communication functions (B.2), and miscellaneous functions (B.3).

B.1.  File-related functions.

In most implementations, these are collected together into a module called
CK?FIO.c, where ? = U (UNIX), V (VMS), O (OS/2), etc (see CKAAAA.TXT).  To be
totally system-independent, C-Kermit maintains its own file numbers, and
provides the functions described in this section to deal with the files
associated with them.  The file numbers are referred to symbolically, and are
defined as follows in CKCKER.H:

#define ZCTERM      0            /* Console terminal */
#define ZSTDIO      1        /* Standard input/output */
#define ZIFILE        2        /* Current input file for SEND command */
#define ZOFILE      3            /* Current output file for RECEIVE command */
#define ZDFILE      4            /* Current debugging log file */
#define ZTFILE      5            /* Current transaction log file */
#define ZPFILE      6            /* Current packet log file */
#define ZSFILE      7        /* Current session log file */
#define ZSYSFN        8        /* Input from a system function (pipe) */
#define ZRFILE      9           /* Local file for READ command */  (NEW)
#define ZWFILE     10           /* Local file for WRITE command */ (NEW)
#define ZMFILE     11           /* Auxilliary file for internal use */ (NEW)
#define ZNFILS     12            /* How many defined file numbers */

In the descriptions below, fn refers to a filename, and n refers to one of
these file numbers.  Functions are of type int unless otherwise noted, and are
listed alphabetically.

int
chkfn(n) int n;
  Checks the file number n.  Returns:
  -1: File number n is out of range
   0: n is in range, but file is not open
   1: n in range and file is open

int
iswild(filspec) char *filespec;
  Checks if the file specification is "wild", i.e. contains metacharacters
  or other notations intended to match multiple filenames.  Returns:
   0: not wild
   1: wild

int
isdir(string) char *string;
  Checks if the string is the name of an existing directory.  Returns:
   0: not a directory (including any kind of error)
   1: it is an existing directory
  The idea is to check whether the string can be "cd'd" to, so in some cases
  (e.g. OS/2) it might also indicate any file structured device, such as a
  disk drive (like A:).  Other nonzero returns indicate system-dependent
  information; e.g. in VMS isdir("[.FOO]") returns 1 but isdir("FOO.DIR;1")
  returns 2 to indicate the directory-file name is in a format that needs
  conversion before it can be combined with a filename.

char *
zfcdat(name) char *name;
  Returns modification (preferably, otherwise creation) date/time of file
  whose name is given in the argument string.  Return value is a pointer to a
  string of the form yyyymmdd hh:mm:ss, for example 19931231 23:59:59, which
  represents the local time (no timezone or daylight savings time finagling
  required).  Returns the null string ("") on failure.  The text pointed to by
  the string pointer might be in a static buffer, and so should be copied to a
  safe place by the caller before any subsequent calls to this function.

struct zfnfp *
zfnqfp(fname, buflen, buf)  char * fname; int buflen; char * buf;
  Given the filename "fname", the corresponding fully qualified, absolute
  filename is placed into the buffer buf, with maximum length buflen.
  On failure returns a NULL pointer.  On success returns a pointer to
  a struct zfnfp (see ckcdeb.h) containing pointers to the full pathname
  and to just the filename.  All references to this function in mainline
  code must be protected by #ifdef ZFNQFP..#endif, because it is not present
  in all of the ck*fio.c modules.  So if you implement this function in a
  version that did not have it before, be sure to add #define ZFNQFP in the
  appropriate spot in ckcdeb.h.

int
zfseek(pos) long pos;
  Positions the input pointer on the current input file to the given position.
  The pos argument is 0-based, the offset (distance in bytes) from beginning
  of the file.  Needed for RESEND, PSEND, and other recovery operations.  This
  function is not necessarily possible on all systems, e.g. record-oriented
  systems.  It should only be used on binary files (i.e. files we are sending
  in binary mode) and stream-oriented file systems.  Returns -1 on failure, 0
  on success.

int
zchdir(dirnam) char *dirnam;
  Change current or default directory to the one given in dirnam.
  Returns 1 on success, 0 on failure.

long
zchki(fn) char *fn;
  Check to see if file with name fn is a regular, readable, existing file,
  suitable for Kermit to send -- not a directory, not a symbolic link, etc.
  Returns:
  -3 if file exists but is not accessible (e.g. read-protected);
  -2 if file exists but is not of a readable type (e.g. a directory);
  -1 on error (e.g. file does not exist, or fn is garbage);
  >= 0 (length of file) if file exists and is readable.
  Also see isdir(), zgetfs().

int
zchkpid(pid) unsigned long pid;
  Returns 1 if the given process ID (e.g. pid in UNIX) is valid and active,
  0 otherwise.

long
zgetfs(fn) char *fn;
  Get the size of the given file, regardless of accessibility.  Used for
  directory listings.  Unlike zchki(), should return the size of any kind
  of file, even a directory.  zgetfs() also should serve as a mini "get
  file info" function that can be used until we design a better one, by
  also setting some global variables:
    int zgfs_link   = 1/0 = file is (not) a symbolic link.
    int zgfs_dir    = 1/0 = file is (not) a directory.
    char linkname[] = if zgfs_link != 0, name of file link points to.
  Returns:
    -1 on error (e.g. file does not exist, or fn is garbage);
    >= 0 (length of file) if file exists and is readable.

int
zchko(fn) char *fn;
  Checks to see if a file of the given name can be created.  Returns:
  -1 if file cannot be created, or on any kind of error.
   0 if file can be created.

int
zchkspa(fn,len) char *f; long len;
  Check to see if there is sufficient space to store the file named fn,
  which is len bytes long.  Returns:
  -1 on error.
   0 if there is not enough space.
   1 if there is enough space.
  If you can't write a function to do this, then just make a dummy that
  always returns 1.  Higher level code will recover from disk-full errors.
  The receiving Kermit uses this function to refuse an incoming file based
  on its size, via the attribute mechanism.

int
zchin(n,c) int n; int *c;
  Get a character from file number n, return it in c (call with &c).
  Returns:
  -1 on failure, including EOF.
   0 on success with character in c.

int
zchout(n,c) int n; char c;
  Write the character c to file number n.  Returns:
  -1 error
   0 OK

int
zclose(n) int n;
  Close file number n.  Returns:
  -1 error
   1 OK

int
zdelet(fn) char *name;
  Attempts to delete the named file.  Returns:
  -1 on error
   0 if file was deleted successfully

char *
zgperm(char * f)
  Returns a pointer to the system-dependent numeric permissions/protection
  string for file f, or NULL upon failure.  Used if CK_PERMS is defined.

char *
ziperm(char * f)
  Returns a pointer to the system-dependent symbolic permissions/protection
  string for file f, or NULL upon failure.  Used if CK_PERMS is defined.
  Example: In UNIX zgperm(f) might return "100770", but ziperm() might
  return "-rwxrwx---".  In VMS, zgperm() would return a hexadecimal string,
  but ziperm() would return something like "(RWED,RWED,RE,)".

char *
zgtdir()
  Returns a pointer to the name of the current directory, folder, etc, or a
  NULL pointer if the current directory cannot be determined.  If possible,
  the directory specification should be (a) fully specified, e.g. as a
  complete pathname, and (b) be suitable for appending a filename.  Thus, for
  example, UNIX directory names should end with '/'.  VMS directory names
  should look like DEV:[NAME] (rather than, say, NAME.DIR;1).

char *
zhome()
  Returns a pointer to a string containing the user's home directory, or NULL
  upon error.  Should be formatted like zgtdir() (q.v.).

int
zinfill()
  This function is used by the macro zminchar(), which is defined in ckcker.h.
  zminchar() manages its own buffer, and calls zinfill() to fill it whenever
  it becomes empty.  It is only used for sending files, and reads characters
  only from file number ZIFILE.  zinfill() returns -1 upon end of file,
  -2 upon fatal error, and -3 upon timeout (e.g. when reading from a pipe);
  otherwise it returns the first character from the buffer it just read.

int
zkself()
  Kills the current job, session, process, etc, logs out, disappears.  Used by
  the Kermit server when it receives a BYE command.  On failure, returns -1.
  On success, does not return at all!  This function should not be called
  until all other steps have been taken to close files, etc.

VOID
zstrip(fn,&fn2) char *fn1, **fn2;
  Strip device and directory, etc, from file specification, leaving only the
  filename.  For example DUA0:[PROGRAMS]OOFA.C;3 becomes OOFA.C, or
  /usr/fdc/oofa.c becomes oofa.c.  Returns pointer to result in fn2.

VOID
zltor(fn,fn2) char *fn1, *fn2;
  Local-To-Remote filename translation.  Translates the local filename fn into
  a format suitable for transmission to an arbitrary type of computer, and
  copies the result into the buffer pointed to by fn2.  Translation may involve
  (a) stripping the device and/or directory/path name, (b) converting
  lowercase to uppercase, (c) removing spaces and strange characters, or
  converting them to some innocuous alphabetic character like X, (d)
  discarding or converting extra periods (there should not be more than one).
  Does its best.  Returns no value.  name2 is a pointer to a buffer, furnished
  by the caller, into which zltor() writes the resulting name.  No length
  checking is done.

#ifdef NZLTOR
VOID
nzltor(fn,fn2,convert,pathnames,max) char *fn1,*fn2; int convert,pathnames,max;
  Replaces zltor.  This new version handles pathnames and checks length.  fn1
  and fn2 are as in zltor.  This version is called unconditionally for each
  file, rather than only when filename conversion is enabled.  Pathnames can
  have the following values:
    PATH_OFF: Pathname, if any, is to be stripped
    PATH_REL: The relative pathname is to be included
    PATH_ABS: The full pathname is to be included

  After handling pathnames, conversion is done to the result as in the zltor
  description if convert != 0; if relative or absolute pathnames are included,
  they are converted to UNIX format, i.e. with slash (/) as the directory
  separator.  The max parameter specifies the maximum size of fn2.
#endif /* NZLTOR */

int
nzxpand(fn,flags) char *fn; int flags;
  Replaces zxpand(), which is obsolete as of C-Kermit 7.0.
  Call with:
   s = pointer to filename or pattern.
   flags = option bits:

     flags & ZX_FILONLY   Match regular files
     flags & ZX_DIRONLY   Match directories
     flags & ZX_RECURSE   Descend through directory tree
     flags & ZX_MATCHDOT  Match "dot files"
     flags & ZX_NOBACKUP  Don't match "backup files"

  Returns the number of files that match s, with data structures set up
  so that first file (if any) will be returned by the next znext() call.
  If ZX_FILONLY and ZX_DIRONLY are both set, or neither one is set, files and
  directories are matched.

  NOTE: It is essential that the number returned by nzxpand() reflect the
  actual number of filenames that will be returned by znext calls().  In
  other words:

    for (n = nzxpand(string,flags); n > 0; n--) {
        znext(buf);
        printf("%s\n", buf);
    }

  should print all the file names; no more, no less.

  NOTE 2: In UNIX, DOS, OS-9, etc, where directories contain entries
  for themselves (.) and the superior directory (..), these should NOT be
  included in the list under any circumstances, including when ZX_MATCHDOT
  is set.

  NOTE 3: Additional option bits might be added in the future, e.g. for
  sorting (sort by date/name/size, reverse/ascending, etc).

int
zmail(addr,fn) char *addr, fn;
  Send the local, existing file fn as e-mail to the address addr.  Returns:
  Returns 0 on success
   2 if mail delivered but temp file can't be deleted
  -2 if mail can't be delivered

int
zmkdir(path) char *path;
  The path can be a file specification that might contain directory
  information, in which the filename is expected to be included, or an
  unambiguous directory specification (e.g. in UNIX it must end with "/").
  This routine attempts to create any directories in the given path
  that don't already exist.  Returns:
   0 or greater success: no directories needed creation,
     or else all directories that needed creation were created successfully;
     the return code is the number of directories that were created.
  -1 on failure to create any of the needed directories.

int
zrmdir(path) char *path;
  Attempts to remove the given directory.  Returns 0 on success, -1 on
  failure.  The detailed semantics are open -- should it fail if the directory
  contains any files or subdirectories, etc.  It is probably best for this
  routine to behave in whatever manner is customary on the underlying
  platform; e.g. in UNIX, VMS, DOS, etc, where directories can not be removed
  unless they are empty.

VOID
znewn(fn,s) char *fn, **s;
  Transforms the name fn into a filename which is guaranteed to be unique.
  If the file fn does not exist, then the new name will be the same as fn.
  Otherwise, it will be different.  Does its best, returns no value.  New
  name is created in caller's space.  Call like this: znewn(old,&new);.
  The second parameter is a pointer to the new name.  This pointer is set
  by znewn() to point to a static string in its own space.

int
znext(fn) char *fn;
  Copies the next file name from a file list created by zxpand() into the
  string pointed to by fn (see zxpand).  If no more files, then the null
  string is placed there.  Returns 0 if there are no more filenames, with
  0th element the array pointed to by fn set to NUL.  If there is a filename,
  it is stored in the array pointed to by fn, and a positive number is
  returned.  NOTE: This is a change from earlier definitions of this function
  (pre-1999), which returned the number of files remaining; thus 0 was the
  return value when returning the final file.  However, no mainline code
  ever depended on the return value, so this change should be safe.

int
zopeni(n,fn) int n; char *fn;
  Opens the file named fn for input as file number n.  Returns:
    0 on failure.
    1 on success.

(zopeno - the second two parameters are new to C-Kermit 5A)
int
zopeno(n,fn,zz,fcb) int n; char *name; struct zattr *zz; struct filinfo *fcb;
  Attempts to open the named file for output as file number n.  zz is a Kermit
  file attribute structure as defined in ckcdeb.h, containing various
  information about the file, including its size, creation date, and so forth.
  This function should attempt to honor as many of these as possible.  fcb is
  a "file control block" in the traditional sense, defined in ckcdeb.h,
  containing information of interest to complicated file systems like VAX/VMS,
  IBM MVS, etc, like blocksize, record length, organization, record format,
  carriage control, disposition (like create vs append), etc.  Returns:
    0 on failure.
    1 on success.

int
zoutdump()
  Dumps an output buffer.  Used with the macro zmchout() defined in ckcker.h.
  Used only with file number ZOFILE, i.e. the file that is being received by
  Kermit during file transfer.  Returns:
   -1 on failure.
    0 on success.

int
zprint(p,fn) char *p, *f;
  Prints the file with name fn on a local printer, with options p.  Returns:
  Returns 0 on success
    3 if file sent to printer but can't be deleted
   -3 if file can't be printed

int
zrename(fn,fn2) char *fn, *fn2;
  Changes the name of file fn to fn2.  If fn2 is the name of an existing
  directory, or a file-structured device, then file fn1 is moved to that
  directory or device, keeping its original name.  If fn2 lacks a directory
  separator when passed to this function, an appropriate one is supplied.
  Returns:
   -1 on failure.
    0 on success.

int
zcopy(source,dest) char * source, * dest;
  Copies the source file to the destination.  One file only.
  No wildcards.  The destination string may be a filename or a directory
  name.  Returns:
   0 on success.
  <0 on failure:
  -2 = source file is not a regular file.
  -3 = source file not found.
  -4 = permission denied.
  -5 = source and destination are the same file.
  -6 = i/o error.
  -1 = other error.

VOID
zrtol(fn,fn2) char *fn, *fn2;
  Remote-To-Local filename translation.  Translates a "standard" filename
  (see zrtol) to a local filename.  For example, in Unix this function might
  convert an all-uppercase name to lowercase, but leave lower- or mix-case
  names alone.  Does its best, returns no value.  New name is in string
  pointed to by fn2.  No length checking is done.

#ifdef NZLTOR
nzrtol(fn,fn2,convert,pathnames,max) char *fn1,*fn2; int convert,pathnames,max;
  Replaces zrtol.  Like zrtol but handles pathnames and checks length.  See
  nzltor for detailed description of parameters.
#endif /* NZLTOR */

int
zsattr(xx) struct zattr *xx; {
  Fills in a Kermit file attribute structure for the file which is to be sent,
  namely the currently open ZIFILE.
  Returns:
  -1 on failure.
   0 on success with the structure filled in.
  If any string member is null, then it should be ignored by the caller.
  If any numeric member is -1, then it should be ignored by the caller.

int
zshcmd(s) char *s;
  s contains to pointer to a command to be executed by the host computer's
  shell, command parser, or operating system.  If the system allows the user
  to choose from a variety of command processors (shells), then this function
  should employ the user's preferred shell.  If possible, the user's job
  (environment, process, etc) should be set up to catch keyboard interruption
  signals to allow the user to halt the system command and return to Kermit.
  The command must run in ordinary, unprivileged user mode.
  If possible, this function should return -1 on failure to start the command,
  or else it should return 1 if the command succeeded and 0 if it failed.

int
pexitstatus
  zshcmd() and zsyscmd() should set this to the command's actual exit status
  code if possible.

int
zsyscmd(s) char *s;
  s contains to pointer to a command to be executed by the host computer's
  shell, command parser, or operating system.  If the system allows the user
  to choose from a variety of command processors (shells), then this function
  should employ the system standard shell (e.g. /bin/sh for Unix), so that the
  results will always be the same for everybody.  If possible, the user's job
  (environment, process, etc) should be set up to catch keyboard interruption
  signals to allow the user to halt the system command and return to Kermit.
  The command must run in ordinary, unprivileged user mode.
  If possible, this function should return -1 on failure to start the command,
  or else it should return 1 if the command succeeded and 0 if it failed.

VOID
z_exec(s,args) char * s; char * args[];
  This one executes the command s (which is searched for using the system's
  normal searching mechanism, such as PATH in UNIX), with the given argument
  vector, which follows the conventions of UNIX argv[]: the name of the
  command pointed to by element 0, the first arg by element 1, and so on.
  A null args[] pointer indicates the end of the arugment list.  All open
  files must remain open so the exec'd process can use them.  Returns only
  if unsuccessful.

int
zsinl(n,s,x) int n, x; char *s;
  Reads a line from file number n.
  Writes the line into the address s provided by the caller.
  Writing terminates when newline is read, but with newline discarded.
  Writing also terminates upon EOF or if length x is exhausted.
  Returns:
  -1 on EOF or error.
   0 on success.

int
zsout(n,s) int n; char *s;
  Writes the string s out to file number n.  Returns:
  -1 on failure.
   0 on success.

int
zsoutl(n,s) int n; char *s;
  Writes the string s out to file number n and adds a line (record) terminator
  (boundary) appropriate for the system and the file format.
  Returns:
  -1 on failure.
   0 on success.

int
zsoutx(n,s,x) int n, x; char *s;
  Writes exactly x characters from string s to file number n.  If s has
  fewer than x characters, then the entire string s is written.  Returns:
  -1 on error.
  >= 0 on success, the number of characters actually written.

int
zstime(f,yy,x) char *f; struct zattr *yy; int x;
  Sets the creation date (and other attributes) of an existing file, or
  compares a file's creation date with a given date.  Call with:
  f  = pointer to name of existing file.
  yy = pointer to a Kermit file attribute structure in which yy->date.val
       is a date of the form yyyymmdd hh:mm:ss, e.g. 19900208 13:00:00, which
       is to be used for setting or comparing the date.  Other attributes
       in the struct can also be set, such as the protection/permission
       (See Appendix I), when it makes sense (e.g. "yy->lprotect.val" can be
       set if the remote system ID matches the local one).
  x  = is a function code: 0 means to set the file's creation date as given.
       1 means compare the date from the yy struct with the file's date.
  Returns:
  -1 on any kind of error.
   0 if x is 0 and the file date was set successfully.
   0 if x is 1 and date from attribute structure > file creation date.
   1 if x is 1 and date from attribute structure <= file creation date.

VOID
zstrip(name,name2) char *name, **name2;
  Strips pathname from filename "name".  Constructs the resulting string
  in a static buffer in its own space and returns a pointer to it in name2.
  Also strips device name, file version numbers, and other "non-name" material.

(zxcmd - arguments are new, writing to a command is new)

int
zxcmd(n,s) char *s;
  Runs a system command so its output can be accessed as if it were file n.
  The command is run in ordinary, unprivileged user mode.
  If n is ZSTDIO or ZCTERM, returns -1.
  If n is ZIFILE or ZRFILE, then Kermit reads from the command, otherwise
  Kermit writes to the command.  Returns 0 on error, 1 on success.

int
zxpand(fn) char *fn;
  OBSOLETE!  Replaced by nzxpand(), q.v.

int
zxrewind()
  Returns the number of files returned by the most recent zxpand call,
  and resets the list to the beginning so the next znext() call returns the
  first file.  Returns -1 if zxpand has not yet been called.  If this function
  is available, ZXREWIND should be defined; otherwise it should not be
  referenced.

int
xsystem(cmd) char *cmd;
  Executes the system command without redirecting any of its i/o, similar
  (well, identical) to system() in Unix.  But before passing the command to
  the system, xsystem() ensures that all privileges are turned off, so that
  the system command will execute in ordinary unprivileged user mode.

B.1.2 IKSD Functions

These must be implemented in any C-Kermit version that is to be installed as
an Internet Kermit Service Daemon (IKSD).  IKSD is expected to be started by
the Internet Daemon (e.g. inetd) with its standard i/o redirected to the
incoming connection.

int ckxanon;
  Nonzero if anonymous logins allowed.

extern int inserver;
  Nonzero if started in IKSD mode.

extern int isguest;
  Nonzero if IKSD and user logged in anonymously.

extern char * homdir;
  Pointer to user's home directory.

extern char * anonroot;
  Pointer to file-system root for anonymous users.

Existing functions must make "if (inserver && isguest)" checks for actions
that would not be legal for guests: zdelete(), zrmdir(), zprint(), zmail(),
etc.

int
zvuser(name) char * name;
  Verifies that user "name" exists and is allowed to log in.  If the name is
  "ftp" or "anonymous" and ckxanon != 0, a guest login is set up.  Returns 0
  if user not allowed to log in, nonzero if user may log in.

zvpass(string) char * string;
  Verifies password of the user from the most recent zvuser() call.  Returns
  nonzero if password is valid for user, 0 if it isn't.  Makes any appropriate
  system log entries (IKSD logins, failed login attempts, etc).  If password
  is valid, logs the user in as herself (if real user), or sets up restricted
  anonymous access if user is guest (e.g. changes file-system root to
  anonroot and sets isguest = 1).

void
zsyslog()
  Begins any desired system logging of an IKSD session.

void
zvlogout()
  Terminates an IKSD session.  In most cases this is simply a wrapper for
  exit() or doexit(), with some system logging added.

B.1.3 Security/Privilege Functions (all)

These functions are used by C-Kermit to adapt itself to operating systems
where the program can be made to run in a "privileged" mode.  C-Kermit
should NOT read and write files or start subprocesses as a privileged program.
This would present a serious threat to system security.  The security package
has been installed to prevent such security breaches by turning off the
program's special privileges at all times except when they are needed.

In UNIX, the only need Kermit has for privileged status is access to the UUCP
lockfile directory, in order to read, create, and destroy lockfiles, and to
open communication devices that are normally protected against the user.
Therefore, privileges should only be enabled for these operations and disabled
at all other times.  This relieves the programmer of the responsibility of
putting expensive and unreliable access checks around every file access and
subprocess creation.

Strictly speaking, these functions are not required in all C-Kermit
implementations, because their use (so far, at least) is internal to the group
3 modules.  However, they should be included in all C-Kermit implementations
for operating systems that support the notion of a privileged program (UNIX,
RSTS/E, what else?).

int
priv_ini()
  Determine whether the program is running in privileged status.  If so,
  turn off the privileges, in such a way that they can be turned on again
  when needed.  Called from sysinit() at program startup time.  Returns:
    0 on success
    nonzero on failure, in which case the program should halt immediately.

int
priv_on()
  If the program is not privileged, this function does nothing.  If the
  program is privileged, this function returns it to privileged status.
  priv_ini() must have been called first.  Returns:
    0 on success
    nonzero on failure

int
priv_off()
  Turns privileges off (if they are on) in such a way that they can be
  turned back on again.  Returns:
    0 on success
    nonzero on failure

int
priv_can()
  Turns privileges off in such a way that they cannot be turned back on.
  Returns:
    0 on success
    nonzero on failure

int
priv_chk()
  Attempts to turns privileges off in such a way that they can be turned on
  again later.  Then checks to make sure that they were really turned off.
  If they were not really turned off, then they are cancelled permanently.
  Returns:
    0 on success
    nonzero on failure

B.2.  Console-Related Functions.

These relate to the program's "console", or controlling terminal, i.e. the
terminal that the user is logged in on and types commands at, or on a PC or
workstation, the actual keyboard and screen.

int
conbin(esc) char esc;
  Puts the console into "binary" mode, so that Kermit's command parser can
  control echoing and other treatment of characters that the user types.
  esc is the character that will be used to get Kermit's attention during
  packet mode; puts this in a global place.  Sets the ckxech variable.
  Returns:
  -1 on error.
   0 on success.

int
concb(esc) char esc;
  Put console in "cbreak" (single-character wakeup) mode.  That is, ensure
  that each console character is available to the program immediately when the
  user types it.  Otherwise just like conbin().  Returns:
  -1 on error.
   0 on success.

int
conchk()
  Returns a number, 0 or greater, the number of characters waiting to be read
  from the console, i.e. the number of characters that the user has typed that
  have not been read yet.

long
congspd();
  Returns the speed ("baud rate") of the controlling terminal, if known,
  otherwise -1L.

int
congks(timo) int timo;
  Get Keyboard Scancode.  Reads a keyboard scan code from the physical console
  keyboard.  If the timo parameter is greater than zero, then times out and
  returns -2 if no character appears within the given number of seconds.  Upon
  any other kind of error, returns -1.  Upon success returns a scan code,
  which may be any positive integer.  For situations where scan codes cannot
  be read (for example, when an ASCII terminal is used as the job's
  controlling terminal), this function is identical to coninc(), i.e. it
  returns an 8-bit character value.  congks() is for use with workstations
  whose keyboards have Alternate, Command, Option, and similar modifier keys,
  and Function keys that generate codes greater than 255.

int
congm()
  Console get modes.  Gets the current console terminal modes and saves them
  so that conres() can restore them later.  Returns 1 if it got the modes OK,
  0 if it did nothing (e.g. because Kermit is not connected with any terminal),
  -1 on error.

int
coninc(timo) int timo;
  Console Input Character.  Reads a character from the console.  If the timo
  parameter is greater than zero, then coninc() times out and returns -2 if no
  character appears within the given number of seconds.  Upon any other kind
  of error, returns -1.  Upon success, returns the character itself, with a
  value in the range 0-255 decimal.

VOID
conint(f,s) SIGTYP (*f)(), (*s)();
  Sets the console to generate an interrupt if the user types a keyboard
  interrupt character, and to transfer control the signal-handling function f.
  For systems with job control, s is the address of the function that suspends
  the job.  Sets the global variable "backgrd" to zero if Kermit is running in
  the foreground, and to nonzero if Kermit is running in the background.
  See ckcdeb.h for the definition of SIGTYP.  No return value.

VOID
connoi()
  Console no interrupts.  Disable keyboard interrupts on the console.
  No return value.

int
conoc(c) char c;
  Write character c to the console terminal.  Returns:
  0 on failure, 1 on success.

int
conol(s) char *s;
  Write string s to the console.  Returns -1 on error, 0 or greater on
  success.

int
conola(s) char *s[]; {
  Write an array of strings to the console.  Returns -1 on error, 0 or greater
  on success.

int
conoll(s) char *s;
  Write string s to the console, followed by the necessary line termination
  characters to put the console cursor at the beginning of the next line.
  Returns -1 on error, 0 or greater on success.

int
conres()
  Restore the console terminal to the modes obtained by congm().  Returns:
  -1 on error, 0 on success.

int
conxo(x,s) int x; char *s;
  Write x characters from string s to the console.  Returns 0 or greater on
  success, -1 on error.

char *
conkbg();
  Returns a pointer to the designator of the console keyboard type.
  For example, on a PC, this function would return "88", "101", etc.
  Upon failure, returns a pointer to the empty string.


B.3 - Communication Device Functions

The communication device is the device used for terminal emulation and file
transfer.  It may or may not be the same device as the console, and it may
or may not be a terminal device (it could also be a network device).  For
brevity, the communication device is referred to here as the "tty".  When the
communication device is the same as the console device, Kermit is said to be
in remote mode.  When the two devices are different, Kermit is in local mode.

int
ttchk()
  Returns the number of characters that have arrived at the communication
  device but have not yet been read by ttinc(), ttinl(), and friends.  If
  communication input is buffered (and it should be), this is the sum of the
  number of unread characters in Kermit's buffer PLUS the number of unread
  characters in the operating system's internal buffer.  The call must be
  nondestructive and nonblocking, and as inexpensive as possible.
  Returns:
   0 or greater on success,
   0 in case of internal error,
  -1 or less when it determines the  connection has been broken,
     or there is no connection.
  That is, a negative return from ttchk() should reliably indicate that there
  is no usable connection.  Furthermore, ttchk() should be callable at any
  time to see if the connection is open.  When the connection is open, every
  effort must be made to ensure that ttchk returns an accurate number of
  characters waiting to be read, rather than just 0 (no characters) or 1
  (1 or more characters), as would be the case when we use select().  This
  aspect of ttchk's operation is critical to successful operation of sliding
  windows and streaming, but "nondestructive buffer peeking" is an obscure
  operating system feature, and so when it is not available, we have to do it
  ourselves by managing our own internal buffer at a level below ttinc(),
  ttinl(), etc, as in the UNIX version (non-FIONREAD case).

  An external global variable, clsondisc, if nonzero, means that if a serial
  connection drops (carrier on-to-off transition detected by ttchk()), the
  device should be closed and released automatically.


int
ttclos()
  Closes the communication device (tty or network).  If there were any kind of
  exclusive access locks connected with the tty, these are released.  If the
  tty has a modem connection, it is hung up.  For true tty devices, the
  original tty device modes are restored.  Returns:
  -1 on failure.
   0 on success.

int
ttflui()
  Flush communications input buffer.  If any characters have arrived but have
  not yet been read, discard these characters.  If communications input is
  buffered by Kermit (and it should be), this function flushes Kermit's buffer
  as well as the operating system's internal input buffer.
  Returns:
  -1 on failure.
   0 on success.

int
ttfluo()
  Flush tty output buffer.  If any characters have been written but not
  actually transmitted (e.g. because the system has been flow-controlled),
  remove them from the system's output buffer.  (Note, this function is
  not actually used, but it is recommended that all C-Kermit programmers
  add it for future use, even if it is only a dummy function that returns 0
  always.)

int
ttgmdm()
  Looks for the modem signals CTS, DSR, and CTS, and returns those that are
  on in as its return value, in a bit mask as described for ttwmdm,
  in which a bit is on (1) or off (0) according to whether the corresponding
  signal is on (asserted) or off (not asserted).  Return values:
  -3 Not implemented
  -2 if the line does not have modem control
  -1 on error
  >= 0 on success, with bit mask containing the modem signals.

long
ttgspd()
  Returns the current tty speed in BITS (not CHARACTERS) per second, or -1
  if it is not known or if the tty is really a network, or upon any kind of
  error.  On success, the speed returned is the actual number of bits per
  second, like 1200, 9600, 19200, etc.

int
ttgwsiz()
  Get terminal window size.  Returns -1 on error, 0 if the window size can't
  be obtained, 1 if the window size has been successfully obtained.  Upon
  success, the external global variables tt_rows and tt_cols are set to the
  number of screen rows and number of screen columns, respectively.
  As this function is not implemented in all ck*tio.c modules, calls to it
  must be wrapped in #ifdef CK_TTGWSIZ..#endif.  NOTE: This function must
  be available to use the TELNET NAWS feature (Negotiate About Window Size)
  as well as Rlogin.

int
tthang()
  Hang up the current tty device.  For real tty devices, turn off DTR for
  about 1/3-1/2 second (or other length of time, depending on the system).
  If the tty is really a network connection, close it.  Returns:
  -1 on failure.
   0 if it does not even try to hang up.
   1 if it believes it hung up successfully.

VOID
ttimoff()
  Turns off all pending timer interrupts.

int
ttinc(timo) int timo; (function is old, return codes are new)
  Reads one character from the communication device.  If timo is greater than
  zero, wait the given number of seconds and then time out if no character
  arrives, otherwise wait forever for a character.  Returns:
  -3 internal error (e.g. tty modes set wrong)
  -2 communications disconnect
  -1 timeout or other error
  >= 0 the character that was read.
  It is HIGHLY RECOMMENDED that ttinc() be internally buffered so that calls
  to it are relatively inexpensive.  If it is possible to to implement ttinc()
  as a macro, all the better, for example something like:

  #define ttinc(t) ( (--txbufn >= 0) ? txbuf[ttbufp++] : txbufr(t) )

  (see description of txbufr() below)

(ttinl - 5th arg, requirement not to destroy read-ahead characters)
int
ttinl(dest,max,timo,eol,start,turn)
 int max,timo,turn; CHAR *dest, eol, start;

  ttinl() is Kermit's packet reader.  Reads a packet from the communications
  device, or up to max characters, whichever occurs first.  A line is a string
  of characters starting with the start character up to and including the
  character given in eol or until the length is exhausted, or, if turn != 0,
  until the line turnaround character (turn) is read.  If turn is 0, ttinl()
  *should* use the packet length field to detect the end, to allow for the
  possibility that the eol character appears unprefixed in the packet data.
  (The turnaround character is for half-duplex linemode connections.)

  If timo is greater than zero, ttinl() times out if the eol character is not
  encountered within the given number of seconds and returns -1.

  The characters that were input are copied into "dest" with their parity bits
  stripped if parity is not none.  The first character copied into dest should
  be the start character, and the last should be the final character of the
  packet (the last block check character).  ttinl() should also absorb and
  discard the eol and turn characters, and any other characters that are
  waiting to be read, up until the next start character, so that subsequent
  calls to ttchk() will not succeed simply because there are some terminators
  still sitting in the buffer that ttinl() didn't read.  This operation, if
  performed, MUST NOT BLOCK (so if it can't be performed in a guaranteed
  nonblocking way, don't do it).

  On success, ttinl() returns the number of characters read.  Optionally,
  ttinl() can sense the parity of incoming packets.  If it does this, then it
  should set the global variable ttprty accordingly.  ttinl() should be coded
  to be as efficient as possible, since it is at the "inner loop" of packet
  reception.  ttinl() returns:

   -1 Timeout or other possibly correctable error.
   -2 Interrupted from keyboard.
   -3 Uncorrectable i/o error -- connection lost, configuration problem, etc.
   >= 0 on success, the number of characters that were actually read
        and placed in the dest buffer, not counting the trailing null.

int
ttoc(c) char c;
  Outputs the character c to the communication line.  If the operation fails
  to complete within two seconds, this function returns -1.  Otherwise it
  returns the number of characters actually written to the tty (0 or 1).  This
  function should only be used for interactive, character-mode operations, like
  terminal connection, script execution, dialer i/o, where the overhead of the
  signals and alarms does not create a bottleneck.  (THIS DESCRIPTION NEEDS
  IMPROVEMENT -- If the operation fails within a "certain amount of time"...
  which might be dependent on the communication method, speed, etc.  In
  particular, flow-control deadlocks must be accounted for and broken out of
  to prevent the program from hanging indefinitely, etc.)

int
ttol(s,n) int n; char *s;
  Kermit's packet writer.  Writes the n characters of the string pointed to
  to by s.  NOTE: It is ttol's responsibility to write ALL of the characters,
  not just some of them.  Returns:
  -1 on a possibly correctable error (so it can be retried).
  -3 on a fatal error, e.g. connection lost.
  >= 0 on success, the actual number of characters written (the specific
     number is not actually used for anything).

(ttopen - negative value for modem = network, new timeout feature)
int
ttopen(ttname,lcl,modem,timo) char *ttname; int *lcl, modem, timo;
  Opens a tty device, if it is not already open.  ttopen must check to make
  sure the SAME device is not already open; if it is, ttopen returns
  successfully without doing anything.  If a DIFFERENT device is currently
  open, ttopen() must call ttclos() to close it before opening the new one.
Parameters:
    ttname: character string - device name or network host name.
    lcl:   If called with lcl < 0, sets value of lcl as follows:
      0: the terminal named by ttname is the job's controlling terminal.
      1: the terminal named by ttname is not the job's controlling terminal.
      If the line is already open, or if the requested line can't
      be opened, then lcl remains (and is returned as) -1.
    modem:
      Less than zero: this is the negative of the network type,
      and ttname is a network host name.  Network types (from ckcnet.h):
        NET_TCPB 1   TCP/IP Berkeley (socket)  (implemented in ckutio.c)
        NET_TCPA 2   TCP/IP AT&T (streams)     (not yet implemented)
        NET_DEC  3   DECnet                    (not yet implemented)
      Zero or greater: ttname is a terminal device name.
      Zero means a direct connection (don't use modem signals).
      Positive means use modem signals depending on the current setting
      of ttcarr ( see ttscarr() ).
    timo:
      > 0: number of seconds to wait for open() to return before timing out.
      <=0: no timer, wait forever (e.g. for incoming call).
    For real tty devices, ttopen() attempts to gain exclusive access to the
    tty device, for example in UNIX by creating a "lockfile" (in other
    operating systems, like VMS, exclusive access probably requires no special
    action).
  Side effects:
    Copies its arguments and the tty file descriptor to global variables that
    are available to the other tty-related functions, with the lcl value
    altered as described above.   Gets all parameters and settings associated
    with the line and puts them in a global area, so that they can be restored
    by ttres(), e.g. when the device is closed.
  Returns:
    0 on success
   -5 if device is in use
   -4 if access to device is denied
   -3 if access to lock mechanism denied
   -2 upon timeout waiting for device to open
   -1 on other error

int
ttpkt(speed,flow,parity) long speed; int flow, parity;
  Puts the currently open tty device into the appropriate modes for
  transmitting Kermit packets.  The arguments are interpreted as follows:
  speed: if speed > -1, and the device is a true tty device, and Kermit is in
         local mode, ttpkt also sets the speed.
  flow:  if in the range 0-3, ttpkt selects the corresponding type of flow
         control.  Currently 0 is defined as no flow control, 1 is Xon/Xoff,
         and no other types are defined.  If (and this is a horrible hack, but
         it goes back many years and will be hard to eradicate) flow is 4,
         then the appropriate tty modes are set for modem dialing, a special
         case in which we talk to a modem-controlled line without requiring
         carrier.  If flow is 5, then we require carrier.
  parity:  This is simply copied into a global variable so that other
         functions (like ttinl, ttinc, etc) can use it.
  Side effects: Copies its arguments to global variables, flushes the terminal
         device input buffer.
  Returns:
   -1 on error.
    0 on success.

int
ttsetflow(int)
  Enables the given type of flow control on the open serial communications
  device immediately.  Arguments are the FLO_xxx values from ckcdeb.h, except
  FLO_DIAL, FLO_DIAX, or FLO_AUTO, which are not actual flow-control types.
  Returns 0 on success, -1 on failure.  This definition added 6 Sep 96.

long *
ttspdlist() 6 Sep 1997
  Returns a pointer to an array of longs, or NULL on failure.  On success,
  element 0 of the array contains number, n, indicating how many follow.
  Elements 1-n are serial speeds, expressed in bits per second, that are legal
  on this platform.  The user interface may use this list to construct a menu,
  keyword table, etc.  As this is a new function, its use is protected by
  #ifdef TTSPDLIST..#endif.

int
ttres()
  Restores the tty device to the modes and settings that were in effect at
  the time it was opened (see ttopen).  Returns:
  -1 on error.
   0 on success.

int
ttruncmd(string) char * string;
  Runs the given command on the local system, but redirects its input and
  output to the communication (SET LINE, SET PORT, or SET HOST) device.
  Returns 1 on success, 0 on failure.

int
ttscarr(carrier) int carrier;
  Copies its argument to a variable that is global to the other tty-related
  functions, and then returns it.  The values for carrier are defined in
  ckcdeb.h: CAR_ON, CAR_OFF, CAR_AUTO.  ttopen(), ttpkt(), and ttvt() use this
  variable when deciding how to open the tty device and what modes to select.
  The meanings are these:
  CAR_OFF:  Ignore carrier at all times.
  CAR_ON:   Require carrier at all times, except when dialing.
            This means, for example, that ttopen() could hang forever waiting
            for carrier if it is not present.
  CAR_AUTO: If the modem type is zero (i.e. the connection is direct), this
            is the same as CAR_OFF.  If the modem type is positive, then heed
            carrier during CONNECT (ttvt mode), but ignore it at other times
            (packet mode, during SET LINE, etc).  Compatible with pre-5A
            versions of C-Kermit.  This should be the default carrier mode.
  Kermit's DIAL command ignores the carrier setting, but ttopen(), ttvt(), and
  ttpkt() all honor the carrier option in effect at the time they are called.
  None of this applies to remote mode (the tty device is the job's controlling
  terminal) or to network host connections (modem type is negative).

int
ttsndb()
  Send a BREAK signal on the tty device.  On a real tty device, send a real
  BREAK lasting approximately 275 milliseconds.  If this is not possible,
  simulate a BREAK by (for example) dropping down some very low baud rate,
  like 50, and sending a bunch of null characters.  On a network connection,
  do the appropriate network protocol for BREAK.  Returns:
  -1 on error.
   0 on success.

int
ttsndlb()
  Like ttsndb(), but sends a "Long BREAK" (approx 1.5 seconds).
  For network connections, it is identical to ttsndb().
  Currently, this function is used only if CK_LBRK is defined (as it is
  for UNIX and VAX/VMS).

int
ttsspd(cps) int cps; (argument is now cps instead of bps)
  For real tty devices only, set the device transmission speed to (note
  carefully) TEN TIMES the argument.  The argument is in characters per
  second, but transmission speeds are in bits per second.  cps are used rather
  than bps because high speeds like 38400 are not expressible in a 16-bit int
  but longs cannot be used because keyword-table values are ints and not longs.
  If the argument is 7, then the bps is 75, not 70.  If the argument is 888,
  this is a special code for 75/1200 split-speed operation (75 bps out, 1200
  bps in).  Returns:
  -1 on error, meaning the requested speed is not valid or available.
  >= 0 on success (don't try to use this value for anything).

int
ttvt(speed,flow) long speed; int flow;
  Puts the currently open tty device into the appropriate modes for terminal
  emulation.  The arguments are interpreted as in ttpkt().  Side effects:
  ttvt() stores its arguments in global variables, and sets a flag that it has
  been called so that subsequent calls can be ignored so long as the arguments
  are the same as in the last effective call.  Other functions, such as
  ttopen(), ttclose(), ttres(), ttvt(), etc, that change the tty device in any
  way must unset this flag.  In UNIX Kermit, this flag is called tvtflg.

int
ttwmdm(mdmsig,timo) int mdmsig, timo;
  Waits up to timo seconds for all of the given modem signals to appear.
  mdmsig is a bit mask, in which a bit is on (1) or off (0) according to
  whether the corresponding signal is to be waited for.  These symbols are
  defined in ckcdeb.h:
     BM_CTS (bit 0) means wait for Clear To Send
     BM_DSR (bit 1) means wait for Data Set Ready
     BM_DCD (bit 2) means wait for Carrier Detect
  Returns:
    -3 Not implemented.
    -2 This line does not have modem control.
    -1 Timeout: time limit exceeded before all signals were detected.
     1 Success.

int
ttxin(n,buf) int n; CHAR *buf;
  (note: CHAR is used throughout this program, and should be typedef'd to
  unsigned char if your C compiler supports it.  See ckcdeb.h.)
  Read x characters from the tty device into the specified buf, stripping
  parity if parity is not none.  This call waits forever, there is no timeout.
  This function is designed to be called only when you know that at least x
  characters are waiting to be read (as determined, for example, by ttchk()).
  This function should use the same buffer as ttinc().

int
txbufr(timo) int timo;
  Read characters into the interal communications input buffer.  timo is a
  timeout interval, in seconds.  0 means no timeout, wait forever.  Called by
  ttinc() (and possibly ttxin() and ttinl()) when the communications input
  buffer is empty.  The buffer should be called ttxbuf[], its length is
  defined by the symbol TXBUFL.  The global variable txbufn is the number of
  characters available to be read from ttxbuf[], and txbufp is the index of
  the next character to be read.  Should not be called if txbufn > 0, in which
  case the buffer does not need refilling.  This routine returns:
   -2    Communications disconnect
   -1    Timeout
   >= 0  A character (0 - 255), the first character that was read, with
         the variables txbufn and txbufp set appropriately for any remaining
         characters.
  NOTE: Currently this routine is used internally only by the UNIX and VMS
  versions.  The aim is to make it available to all versions so there is one
  single coherent and efficient way of reading from the communications device
  or network.

B.4 - Miscellaneous system-dependent functions.

VOID
ztime(s) char **s;
  Returns a pointer, s, to the current date-and-time string in s.  This string
  must be in the fixed-field format associated with the C runtime asctime()
  function, like: "Sun Sep 16 13:23:45 1973\n" so that callers of this
  function can extract the different fields.  The pointer value is filled in
  by ztime, and the data it points to is not safe, so should be copied to a
  safe place before use.  ztime() has no return value.  As a side effect,
  this routine can also fill in the following two external variables (which
  must be defined in the system-dependendent modules for each platform):
    long ztusec:  Fraction of seconds of clock time, microseconds.
    long ztmsec:  Fraction of seconds of clock time, milliseconds.
  If these variables are not set by zstime(), they remain at their initial
  value of -1L.

int
gtimer()
  Returns the current value of the elapsed time counter in seconds (see
  rtimer), or 0 on any kind of error.

#ifdef GFTIMER
float
gtimer()
  Returns the current value of the elapsed time counter in seconds, as
  a floating point number, capable of representing not only whole seconds,
  but also the fractional part, to the millisecond or microsecond level,
  whatever precision is available.  Requires a function to get times at
  subsecond precision, as well as floating-point support.  That's why it's
  #ifdef'd.
#endif /* GFTIMER */

int
msleep(m) int m;
  Sleeps (pauses, does nothing) for m milliseconds (a millisecond is one
  thousandth of a second).  Returns:
  -1 on failure.
   0 on success.

VOID
rtimer()
  Sets the elapsed time counter to zero.  If you want to time how long an
  operation takes, call rtimer() when it starts and gtimer when it ends.
  rtimer() has no return value.

#ifdef GFTIMER
VOID
rftimer()
  Sets the elapsed time counter to zero.  If you want to time how long an
  operation takes, call rftimer() when it starts and gftimer when it ends.
  rftimer() has no return value.  Note: rftimer() is to be used with gftimer()
  and rtimer() is to be used with gtimer().  See rftimer() description.
#endif /* GFTIMER */

int
sysinit()
  Does whatever needs doing upon program start.  In particular, if the
  program is running in any kind of privileged mode, turns off the privileges
  (see priv_ini()).  Returns:
  -1 on error.
   0 on success.

int
syscleanup()
  Does whatever needs doing upon program exit.  Returns:
  -1 on error.
   0 on success.

int
psuspend()
  Suspends the Kermit process, puts it in the background so it can be
  continued ("foregrounded") later.  Returns:
  -1 if this function is not supported.
   0 on success.

GROUP 4 - Network Support.

As of version 5A, C-Kermit includes support for several networks.  Originally,
this was just worked into the ttopen(), ttclos(), ttinc(), ttinl(), and
similar routines in CKUTIO.C.  However, this made it impossible to share this
code with non-UNIX versions, like VMS.

As of edit 168, this support has been separated out into its own module and
header file, CKCNET.C and CKCNET.H.

As of edit 195, Telnet protocol is split out into its own files, since it
can be implemented in remote mode, which does not have a network connection:

  CKCNET.H - Network-related symbol definitions.
  CKCNET.C - Network i/o (TCP/IP, X.25, etc), shared by most platforms.
  CKLNET.C - Network i/o (TCP/IP, X.25, etc) specific to Stratus VOS.
  CKCTEL.H - Telnet protocol symbol definitions.
  CKCTEL.C - Telnet protocol.

The routines and variables in these modules fall into two categories: (1)
support for specific network packages like SunLink X.25 and TGV MultiNet, and
(2) support for specific network virtual terminal protocols like CCITT X.3 and
TCP/IP telnet.  Category (1) functions are analogs to the tt*() functions, and
have names like netopen, netclos, nettinc, etc.  Group I and II modules do not
(and must not) know anything about these functions -- they continue to call
the old Group III functions (ttopen, ttinc, etc).  Category (2) functions are
protocol specific and have names prefixed by a protocol identifier, like tn
for telnet x25 for X.25.

CKCNET.H contains prototypes for all these functions, as well as symbol
definitions for network types, protocols, and network- and protocol- specific
symbols, as well as #includes for the header files necessary for each network
and protocol.

The following functions are to be provided for networks that do not use normal
system i/o (open, read, write, close):

int
netopen()
  To be called from within ttopen() when a network connection is requested.
  Calling conventions and purpose same as Group III ttopen().

int
netclos()
  To be called from within ttclos() when a network connection is being closed.
  Calling conventions and purpose same as Group III ttclos().

int
nettchk()
  To be called from within ttchk().
  Calling conventions and purpose same as Group III ttchk().

int
netflui()
  To be called from within ttflui().
  Calling conventions and purpose same as Group III ttflui().

int
netbreak()
  To send a network break (attention) signal.
  Calling conventions and purpose same as Group III ttsndbrk().

int
netinc()
  To get a character from the network.
  Calling conventions same as Group III ttsndbrk().

int
nettoc()
  Send a "character" (byte) to the network.
  Calling conventions same as Group III ttoc().

int
nettol()
  Send a "line" (sequence of bytes) to the network.
  Calling conventions same as Group III ttol().

Conceivably, some systems support network connections simply by letting
you open a device of a certain name and letting you do i/o to it.  Others
(like the Berkeley sockets TCP/IP library on UNIX) require you to open the
connection in a special way, but then do normal i/o (read, write).  In such
a case, you would use netopen(), but you would not use nettinc, nettoc, etc.

TGV MultiNET on VAX/VMS has its own set of functions for all network
operations, so in that case the full range of netxxx() functions is used.

The technique is to put a test in each corresponding ttxxx() function to
see if a network connection is active (or is being requested), test for which
kind of network it is, and if necessary route the call to the corresponding
netxxx() function.  The netxxx() function must also contain code to test for
the network type, which is available via the global variable ttnet.

TELNET SUPPORT:

The telnet protocol is supported by the following variables and routines:

(global) int tn_init: nonzero if telnet protocol initialized, zero otherwise.

int
tn_init()
  Initialize the telnet protocol (send initial options).

int
tn_sopt()
  Send a telnet option.

int
tn_doop()
  Receive and act on a telnet option from the remote.

int
tn_sttyp()
  Send terminal type using telnet protocol.

X.25 SUPPORT:

These are presently specific to SunLink X.25, but it is hoped that they can
be integrated better with the functions above, and made more general so they
could be used, for instance, with VAX PSI.

x25diag()
  Read and print X.25 diagnostic

x25oobh()
  X.25 out of band signal handler

x25intr()
  Send X.25 interrupt packet

x25reset()
  Reset X.25 virtual circuit

x25clear()
  Clear X.25 virtual circuit

x25stat()
  X.25 status

setqbit()
  Set X.25 Q-bit

resetqbit()
  Reset X.25 Q-bit

x25xin()
  Read n characters from X.25 circuit.

x25inl()
  Read a Kermit packet from X.25 circuit.

ADDING SUPPORT FOR A NEW NETWORK TYPE

Example: Adding support for IBM X.25 and Hewlett Packard X.25.
First, add new network type symbols for each one.  There are already
some network types defined for other X.25 packages:

  NET_SX25 is the network-type ID for SunLink X.25.
  NET_VX25 is the network-type ID for VOS X.25.

So first you should new symbols for the new network types, giving them
the next numbers in the sequence, e.g.:

#define NET_HX25 11            /* Hewlett-Packard X.25 */
#define NET_IX25 12            /* IBM X.25 */

This is in ckcnet.h.

Then we need symbols to say that we are actually compiling in the code
for these platforms.  These would be defined on the cc command line:

  -DIBMX25  (for IBM)
  -DHPX25   (for HP)

So we can build C-Kermit versions for AIX and HP-UX both with and without
X.25 support (since not all AIX and IBM systems have the needed libraries,
and so an executable that was linked with them might no load).

Then in ckcnet.h:

#ifdef IBMX25
#define ANYX25
#endif /* IBMX25 */

#ifdef HPX25
#define ANYX25
#endif /* HPX25 */

And then use ANYX25 for code that is common to all of them,
and IBMX25 or HPX25 for code specific to IBM or HP.

It might also happen that some code can be shared between two or more of
these, but not the others.  Suppose, for example, that you write code that
applies to both IBM and HP, but not Sun or VOS X.25.  Then you add the
following definition to ckcnet.h:

#ifndef HPORIBMX25
#ifdef HPX25
#define HPORIBMX25
#else
#ifdef IBMX25
#define HPORIBMX25
#endif /* IBMX25 */
#endif /* HPX25 */
#endif /* HPORIBMX25 */

You can NOT use constructions like "#if defined (HPX25 || IBMX25)"; they
are not portable (see ckcplm.txt).

GROUP 5 - Formatted Screen Support

So far, this is used only for the fullscreen local-mode file transfer display.
In the future, it might be extended to other uses.  The fullscreen display
code is in and around the routine screenc() in ckuusx.c.

In the UNIX version, we use the curses library, plus one call from the termcap
library.  In other versions (OS/2, VMS, etc) we insert dummy routines that
have the same names as curses routines.  So far, there are two methods for
simulating curses routines:

 1. In VMS, we use the Screen Management Library (SMG), and insert stubs
    to convert curses calls into SMG calls.

 2. In OS/2, we use the MYCURSES code, in which the stub routines
    actually emit the appropriate escape sequences themselves.

Here are the stub routines:

tgetent(char *buf, char *term)
  Arguments are ignored.  Returns 1 if the user has a supported terminal
  type, 0 otherwise.  Sets a global variable (for example, "isvt52" or
  "isdasher") to indicate the terminal type.

move(int row, int col)
  Sends the escape sequence to position the cursor at the indicated row
  and column.  The numbers are 0-based, e.g. the home position is 0,0.

clear()
  Sends the escape sequence to clear the screen.

clrtoeol()
  Sends the escape sequence to clear from the current cursor position to
  the end of the line.

In the MYCURSES case, code must be added to each of the last three routines
to emit the appropriate escape sequences for a new terminal type.

clearok(curscr), wrefresh()
  In real curses, these two calls are required to refresh the screen, for
  example after it was fractured by a broadcast message.  These are useful
  only if the underlying screen management service keeps a copy of the entire
  screen, as curses and SMG do.  C-Kermit does not do this itself.

APPENDIX I - File Permissions

I.1. Format of System-Dependent File Permissions in A-Packets

The format of this field (the "," attribute) is interpreted according to the
System ID ("." Attribute).

For UNIX (System ID = U1), it's the familiar 3-digit octal number, the
low-order 9 bits of the filemode: Owner, Group, World, e.g. 660 = read/write
access for owner and group, none for world, recorded as a 3-digit octal string.
High-order UNIX permission bits are not transmitted.

For VMS (System ID = D7), it's a 4-digit hex string, representing the 16-bit
file protection WGOS fields (World,Group,Owner,System), in that order (which
is the reverse of how they're shown in a directory listing); in each field,
Bit 0 = Read, 1 = Write, 2 = Execute, 3 = Delete.  A bit value of 0 means
permission is granted, 1 means permission is denied.  Sample:

  r-01-00-^A/!FWERMIT.EXE'"
  s-01-00-^AE!Y/amd/watsun/w/fdc/new/wermit.exe.DV
  r-02-01-^A]"A."D7""B8#119980101 18:14:05!#8531&872960,$A20B-!7(#512@ #.Y
  s-02-01-^A%"Y.5!                                     ^^^^^^

A VMS directory listing shows the file's protection as (E,RWED,RED,RE) which
really means (S=E,O=RWED,G=RED,W=RE), which is reverse order from the internal
storage, so (RE,RED,RWED,E).  Now translate each letter to its corresponding
bit:

  RE=0101, RED=1101, RWED=1111, E=0010

Now reverse the bits:

  RE=1010, RED=0010, RWED=0000, E=1101

This gives the 16-bit quantity:

  1010001000001101

This is the internal representation of the VMS file permission; in hex:

  A20B

as shown in the sample packet above.

The VMS format probably would also apply to RSX or any other FILES-11 system.

I.2. Handling of Generic Protection

To be used when the two systems are different (and/or do not recognize or
understand each other's local protection codes).

First of all, the book is wrong.  This should not be the World protection,
but the Owner protection.  The other fields should be set according to system
defaults (e.g. UNIX umask, VMS default protection, etc), except that no
non-Owner field should give more permissions than the Owner field.

(End of CKCPLM.TXT)