C-Kermit Program Logic Manual

Frank da Cruz
The Kermit Project
Columbia University

As of: C-Kermit 8.0.211, 10 April 2004
This page last updated: Sat Apr 10 16:45:30 2004 (New York USA Time)

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CONTENTS

  1. INTRODUCTION
  2. FILES
  3. SOURCE CODE PORTABILITY AND STYLE
  4. MODULES
     4.A. Group A: Library Routines
     4.B. Group B: Kermit File Transfer
     4.C. Group C: Character-Set Conversion
     4.D. Group D: User Interface
     4.E. Group E: Platform-Dependent I/O
     4.F. Group F: Network Support
     4.G. Group G: Formatted Screen Support
     4.H. Group H: Pseudoterminal Support
     4.I. Group I: Security
  I. APPENDIX I: FILE PERMISSIONS

1. 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 describes the relationship among the modules and functions of C-Kermit 5A and later, and other programming considerations. 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, as shown in the Contents.

C-Kermit has seen constant development since 1985. Throughout its history, there has been a neverending tug-of-war among:

  1. Functionality: adding new features, fixing bugs, improving performance.
  2. Adding support for new platforms.
  3. "Buzzword 1.0 compliance".

The latter category is the most frustrating, since it generally involves massive changes just to keep the software doing what it did before in some new setting: e.g. the K&R-to-ANSIC conversion (which had to be done, of course, without breaking K&R); Y2K (not a big deal in our case); the many and varied UNIX and other API "standards"; IPv6.

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2. FILES

C-Kermit source files begin with the two letters "ck", for example ckutio.c. Filenames are kept short (6.3) for maximum portability and (obviously I hope) do not contain spaces or more than one period. The third character in the name denotes something about the function group and the expected level of portability:

a General descriptive material and documentation (text)
b BOO file encoders and decoders (obsolete)
c All platforms with C compilers (*)
d Data General AOS/VS
e Reserved for "ckermit" files, like ckermit.ini, ckermit2.txt
f (reserved)
g (reserved)
h (reserved)
i Commodore Amiga (Intuition)
j (unused)
k (unused)
l Stratus VOS
m Macintosh with Mac OS 1-9
n Microsoft Windows NT/2000/XP
o OS/2 and/or Microsoft Windows 9x/ME/NT/2000/XP
p Plan 9 from Bell Labs
q (reserved)
r DEC PDP-11 with RSTS/E (never used, open for reassigment)
s Atari ST GEMDOS (last supported in version 5A(189))
t DEC PDP-11 with RT-11 (never used, open for reassigment)
u Unix-based operating systems (*)
v VMS and OpenVMS
w Wart (Lex-like preprocessor, platform independent)
x (reserved)
y (reserved)
z (reserved)
0-3 (reserved)
4 IBM AS/400
5-8   (reserved)
9 Microware OS-9
_ Encryption modules

(*) In fact there is little distinction between the ckc*.* and cku*.* categories. It would make more sense for all cku*.* modules to be ckc*.* ones, except ckufio.c, ckutio.c, ckucon.c, ckucns.c, and ckupty.c, which truly are specific to Unix. The rest (ckuus*.c, ckucmd.c, etc) are quite portable.

One hint before proceeding: functions are scattered all over the ckc*.c and cku*.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 in what source file a given function is defined 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 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 the opening bracket is above the visible screen, and it also makes it easy to find the end of a function (search for '}' on the left margin).

Of course EMACS tags work nicely with this format too: 

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

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

Also:

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3. SOURCE CODE PORTABILITY AND STYLE

C-Kermit was designed in 1985 as a platform-independent replacement for the earlier Unix Kermit. c-Kermit's design was expected to promote portability, and judging from the number of platforms to which it has been adapted since then, the model is effective, if not ideal (obviously if we had it all to do over, we'd change a few things). To answer the oft-repeated question: "Why are there so many #ifdefs?", it's because:

And to answer the second-most-oft-repeated question: "Why don't you just use GNU autoconfig / automake / autowhatever instead of hard-coding all those #ifdefs?" Answers:

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. The same holds true for many of the "system dependent" modules too; particularly the Unix ones, since they must be buildable by a wide variety of compilers and linkers, new and old.

This list does not purport to be comprehensive, and although some items on it might seem far-fetched, they would not be listed unless I had encountered them somewhere, some time. I wish I had kept better records so I could cite specific platforms and compilers.

This overflows the CPP output buffer of more than a few C preprocessors (this happened, for example, with SunOS 4.1 cc, which evidently has a 1K macro expansion buffer).

C-Kermit needs constant adjustment to new OS and compiler releases. Every new OS 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 conservative when attempting to write portable code. Avoid all advanced features.

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

But finally... feel free to violate any or all of these rules in platform-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, because VAX C, DEC C, and VMS GCC all support it.

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3.1. Memory Leaks

The C language and standard C library are notoriously inadequate and unsafe. Strings are arrays of characters, usually referenced through pointers. There is no native string datatype. Buffers are fixed size, and C provides no runtime bounds checking, thus allowing overwriting of other data or even program code. With the popularization of the Internet, the "buffer exploit" has become a preferred method for hackers to hijack privileged programs; long data strings are fed to a program in hopes that it uses unsafe C library calls such as strcpy() or sprintf() to copy strings into automatic arrays, thus overwriting the call stack, and therefore the routine's return address. When such a hole is discovered, a "string" can be constructed that contains machine code to hijack the program's privileges and penetrate the system.

This problem is partially addressed by the strn...() routines, which should always be used in preference to their str...() equivalents (except when the copy operation has already been prechecked, or there is a good reason for not using them, e.g. the sometimes undesirable side effect of strncpy() zeroing the remainder of the buffer). The most gaping whole, however, is sprintf(), which performs no length checking on its destination buffer, and is not easy to replace. Although snprintf() routines are starting to appear, they are not yet widespread, and certainly not universal, nor are they especially portable, or even full-featured.

For these reasons, we have started to build up our own little library of C Library replacements, ckclib.[ch]. These are safe and highly portable primitives for memory management and string manipulation, such as:

ckstrncpy()
Like strncpy but returns a useful value, doesn't zero buffer.

ckitoa()
Opposite of atoi()

ckltoa()
Opposite of atol()

ckctoa()
Returns character as string

ckmakmsg()
Used with ck?to?() as a safe sprintf() replacement for up to 4 items

ckmakxmsg()
Like ckmakmsg() but accepts up to 12 items

More about library functions in Section 4.A.

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3.2. The "char" vs "unsigned char" Dilemma

This is one of the most aggravating and vexing characteristics of the C language. By design, chars (and char *'s) are SIGNED. But in the modern era, however, we need to process characters that can have (or include) 8-bit values, as in the ISO Latin-1, IBM CP 850, or UTF-8 character sets, 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.

Some modern compilers (e.g. IBM, DEC, Microsoft) have options that say "make all chars be unsigned" (e.g. GCC "-funsigned-char") and we use them when they are available. Other compilers don't have this option, 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.

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4. MODULES

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 can be in any of several major states:

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

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

Terminal State
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).

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4.A. Group A: Library Functions

Library functions, strictly portable, can be used by all modules on all platforms: ckclib.h, ckclib.c.

(To be filled in... For now, see Section 3.1 and the comments in ckclib.c.)

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4.B. Group B: Kermit File Transfer

The Kermit protocol kernel. These files, whose names start with "ckc 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 B modules do not include any header files other than those that come with Kermit itself. They do not contain any library calls except from the standard C library (e.g. printf()). They most certainly do not contain any system calls. 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.

ckcfns.c, ckcfn2.c, ckcfn3.c
The protocol support functions used by the protocol module.

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

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4.C. Group C: Character-Set Conversion

Character set translation tables and functions. Used by the Group B, 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. ckuxla.h for UNIX, ckmxla.h for Macintosh.

ck?xla
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

Here's how to add a new file character set in the original (non-Unicode modules). 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:

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), again in the "old" character-set modules:

In ckcxla.h:

In ck?xla.h (since any transfer charset is also a file charset):

In ck?xla.c:

As of C-Kermit 7.0, character sets are also handled in parallel by the new (and very large) Unicode module, ckcuni.[ch]. Eventually we should phase out the old way, described just above, and operate entirely in (and through) Unicode. The advantages are many. The disadvantages are size and performance. To add a character to the Unicode modules:

In ckcuni.h:

In ckcuni.c:

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4.D. Group D: 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 one provided is command-and prompt, with the ability to read commands from various sources: the console keyboard, a file, or a macro definition. 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, FTP client commands, etc.

If you plan to imbed the Group B, 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).

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 E functions.

ckuusr.h
Definitions of symbols used in Kermit's commands.

ckuus*.c
Kermit's interactive command parser, including the script programming language: ckuusr.c (includes top-level keyword tables); ckuus2.c (HELP command text); ckuus3.c (most of the SET command); ckuus4.c (includes variables and functions); ckuus[567].c (miscellaneous);

ckuusy.c
The command-line-option parser.

ckuusx.c
User interface functions common to both the interactive and command-line parsers.

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.

Note that none of the above files is actually Unix-specific. Over time they have proven to be portable among all platforms where C-Kermit is built: Unix, VMS, AOS/VS, Amiga, OS-9, VOS, etc etc. Thus the third letter should more properly be "c", but changing it would be too confusing.

ck?con.c, ckucns.c
The CONNECT command. Terminal connection, and in some cases (Macintosh, Windows) also terminal emulation. NOTE: As of C-Kermit 7.0, there are two different CONNECT modules for UNIX: ckucon.c -- the traditional, portable, fork()-based version -- and ckucns.c, a new version that uses select() rather than forks so it can handle encryption. ckucns.c is the preferred version for Unix; 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_*.*, ckuat*.*
Modules having to do with authentication and encryption. Since the relaxation of USA export laws, they are included with the general source-code distribution. Secure C-Kermit binaries can be built using special targets in the standard makefile. However, secure prebuilt binaries may not be distributed.

For other implementations, the files may, and probably do, have different names. For example, the Macintosh graphical user interface filenames start with "ckm". Kermit 95 uses the ckucmd and ckuus* modules, but has its own CONNECT command modules. 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. Our list of things to do is endless, and reorganizing the source is almost always at the bottom.

The ckuus*.c modules (like many of the ckc*.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 Group E platform-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, in theory, 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 sstate (start state) variable 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 (hmmm, probably should be an unsigned long).

    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.

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4.E. Group E: Platform-Dependent I/O

Platform-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 (communications), 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). 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 E 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. But that was a long time ago, probably circa Version 6.)

4.E.1. Global 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 OS, 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 by Group E module. Used by ckcmai.c to initialize flow control variable.

int dfloc;
Default location. 0 = remote, 1 = local. Set by Group E 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 E module. Used by ckcmai.c to initialize parity variable.

char *dftty;
Default communication device. Set by Group E 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 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.

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4.E.2. Functions

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

4.E.2.1. File-Related Functions

In most implementations, these are collected together into a module called ck?fio.c, where ? = "u" (ckutio.c for Unix), "v" (ckvtio.c for VMS), etc. To be totally platform-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 mostly 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. The idea is to check whether the string can be "cd'd" to, so in some cases (e.g. DOS) 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. Returns:
  0: not a directory (including any kind of error)
  1: it is an existing directory

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(fn, buflen, buf) char * fn; int buflen; char * buf;
Given the filename fn, the corresponding fully qualified, absolute filename is placed into the buffer buf, whose length is buflen. On failure returns a NULL pointer. On success returns a pointer to a struct zfnfp containing pointers to the full pathname and to just the filename, and an int giving the length of the full pathname. 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 or in the build-procedure CFLAGS.

int
zcmpfn(s1,s2) char * s2, * s2;
Compares two filenames to see if they refer to the same. Internally, the arguments can be converted to fully qualified pathnames, e.g. with zfnqfp(), realpath(), or somesuch. In Unix or other systems where symbolic links exist, the link should be resolved before making the comparison or looking at the inodes. Returns:
  0: Files are not identical.
  1: Files are identical.

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;
Changes current or default directory to the one given in dirnam. Returns:
  0: On failure.
  1: on success.

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;
Gets 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;
Checks to see if there is sufficient space to store the file named fn, which is len bytes long. 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. Returns:
 -1: on error.
  0: if there is not enough space.
  1: if there is enough space.

int
zchin(n,c) int n; int *c;
Gets 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;
Writes the character c to file number n. Returns:
 -1: on error.
  0: on success.

int
zclose(n) int n;
Closes file number n. Returns:
 -1: on error.
  1: on success.

int
zdelet(fn) char *name;
Attempts to delete (remove, erase) the named file. Returns:
 -1: on error.
  1: 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()
Fill buffer from input file. 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 used only 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;
Strips device and directory, etc, from file specification fn, leaving only the filename (including "extension" or "filetype" -- the part after the dot). For example DUA0:[PROGRAMS]OOFA.C;3 becomes OOFA.C, or /usr/fdc/oofa.c becomes oofa.c. Returns a pointer to result in fn2.

int
zsetperm(char * file, unsigned int code)
Set permissions of file to given system-dependent code.   0: On failure.
  1: on success.

int
zsetroot(char * dir)
Sets the root for the user's file access, like Unix chroot(), but does not require privilege. In Unix, this must be implemented entirely by Kermit's own file access routines. Returns:
  1: Success
 -1: Invalid argument
 -2:
 -3: Internal error
 -4: Access to given directory denied
 -5: New root not within old root

int
zinroot(char * file)
If no root is set (zsetroot()), returns 1.
Otherwise, if given file is in the root, returns 1.
Otherwise, returns 0.

VOID
zltor(fn,fn2) char *fn1, *fn2;
Local-To-Remote filename translation. OBSOLETE: replaced by nzltor() (q.v.). 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. If convert > 0, the regular conversions are done; if convert < 0, minimal conversions are done (we skip uppercasing the letters, we allow more than one period, etc; this can be used when we know our partner is UNIX or similar).

#endif /* NZLTOR */

int
nzxpand(fn,flags) char *fn; int flags;
Replaces zxpand(), which is obsolete as of C-Kermit 7.0.
Call with:
  fn = 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"
    flags & ZX_NOLINKS  Don't follow symlinks.

Returns the number of files that match fn, with data structures set up so the 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. Notes:

  1. 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.

  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.

  3. Additional option bits might be added in the future, e.g. for sorting (sort by date/name/size, reverse/ascending, etc). Currently this is done only in higher level code (through a hack in which the nzxpand() exports its filename array, which is not portable because not all OS's can use this mechanism).

int
zmail(addr,fn) char *addr, fn;
Send the local, existing file fn as e-mail to the address addr. 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. Returns -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 that is guaranteed to be unique. If the file fn does not exist, then the new name is the same as fn; Otherwise, it's different. this function 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, so be sure to the result to a safe place before calling this function again.

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.

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 relevant to complicated file systems like VMS (RMS), IBM MVS, etc, like blocksize, record length, organization, record format, carriage control, etc. Returns:
  0: on failure.
  1: on success.

int
zoutdump()
Dumps a file 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:
  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 fn 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.

char *
zlocaltime(char *)
Call with: "yyyymmdd hh:mm:ss" GMT/UTC date-time. Returns pointer to local date-time string "yyyymmdd hh:mm:ss" on success, NULL on failure.

VOID
zrtol(fn,fn2) char *fn, *fn2;
Remote-To-Local filename translation. OBSOLETE: replaced by nzrtol(). Translates a "standard" filename 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
int
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. Note that this is not a very good design, but we're stuck with it. Callers must ensure that zsattr() is called only on real files, not on pipes, internally generated file-like objects such as server REMOTE command responses, etc. Returns:
 -1: on failure.
  0: on success with the structure filled in.
If any string member is null, it should be ignored by the caller.
If any numeric member is -1, 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 failure.
>= 0: on success, the number of characters actually written.

int
zstime(fn,yy,x) char *fn; 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:
fn: 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 file 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: 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.

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.

#ifdef ZXREWIND
int
zxrewind()
Returns the number of files returned by the most recent nzxpand() 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.
#endif /* ZXREWIND */

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 executes in ordinary unprivileged user mode. If possible, xsystem() returns the return code of the command that was executed.

4.E.2.2. IKSD Variables and 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.

int
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.

4.E.2.3. Privilege Functions

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, e.g. setuid or setgid in Unix. 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 (see the Unix C-Kermit Installation Instructions for discussion). 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 E 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 others?).

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

4.E.2.4. 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 by Kermit.

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;
Writes character c to the console terminal. Returns:
0 on failure, 1 on success.

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

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

int
conoll(s) char *s;
Writes 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()
Restores 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.

4.E.2.5. Communications 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 (serial-port) device; it could also be a network connection. 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)

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).

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 device is already open, or if the requested device 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 and receiving Kermit packets.

Arguments:
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.

#ifdef TTSPDLIST
long *
ttspdlist()
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.
#endif /* TTSPDLIST */

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:
  0: on failure.
  1: on success.

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()
Sends 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 VMS).

int
ttsspd(cps) int cps;
For serial 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;
Reads 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;
Reads characters into the internal 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) On success, 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.

4.E.2.6. 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
CKFLOAT
gftimer()
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 the 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.

[ Contents ] [ C-Kermit ] [ Kermit Home ]

4.F. Group F: 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. But this made it impossible to share this code with non-UNIX versions, like VMS, AOS/VS, OS/2, etc. So as of edit 168, network code has been separated out into its own module and header file, ckcnet.c and ckcnet.h:

  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.

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 A-D modules do not (and must not) know anything about these functions -- they continue to call the old Group E 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 E ttopen().

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

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

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

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

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

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

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

VMS TCP/IP products have their 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.

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4.F.1. Telnet Protocol

(This section needs a great deal of updating...)

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:

   ckctel.h: Telnet protocol symbol definitions.
   ckctel.c: Telnet protocol.

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

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.

4.F.2. FTP Protocol

(To be filled in...)

4.F.3. HTTP Protocol

(To be filled in...)

4.F.4. X.25 Networks

These routines were written SunLink X.25 and have since been adapted to at least on one other: IBM AIXLink/X.25.

int
x25diag()
Reads and prints X.25 diagnostics

int
x25oobh()
X.25 out of band signal handler

int
x25intr()
Sends X.25 interrupt packet

int
x25reset()
Resets X.25 virtual circuit

int
x25clear()
Clear X.25 virtual circuit

int
x25stat()
X.25 status

int
setqbit()
Sets X.25 Q-bit

int
resetqbit()
Resets X.25 Q-bit

int
x25xin()
Reads n characters from X.25 circuit.

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

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4.F.5. Adding New Network Types

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.

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4.G. Group G: 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:

int
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.

VOID
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.

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

int
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.

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4.H. Group H: Pseudoterminal Support

(To be filled in...)

4.I. Group I: Security

(To be filled in...)

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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.

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C-Kermit Program Logic Manual / The Kermit Project / Columbia University / kermit@columbia.edu / 10 April 2004