Telnetd rewrite

[Sergey Poznyakoff]

Hi,

The first working version of the rewritten telnetd is finally in
repository. The version has been tested on GNU/Hurd, GNU/Linux and
Solaris. Please give it a try on whatever platforms you have access
to. Issues of special interest for testing are: correct handling of
terminal capabilities and utmp/wtmp issues (correct operation of who,
last, etc.) The kerberos authentication/encryption has not been tested
yet.

Below is a list of user-visible changes:

1. Long options are supported. Run telnetd --help for a list.
2. New option --exec-login (-E) allows to specify the command line for
   invocation of login or equivalent program. The macro-notations,
   currently understood by this option are:

      %h     --         Hostname or IP of the remote (client) host
      %l     --         Hostname or IP of the local (server) host
      %t     --         TTY (without the "/dev/" prefix)
      %T     --         Name of the terminal
      %u     --         User name (only when using Kerberos
                        authentication)
      %d     --         Local time

   The notation %?N (where N is any of the symbols described above, 
   allows to check if variable N is set. It is used to build
   if-else-endif sequences, e.g.:

                 %?u{%u}{--}

   is expanded to the username, if it is not-null and to double dash
   otherwise.

   The default login invocation for GNU/Linux and GNU/Hurd systems is:

      /bin/login -p -h %h %?u{-f %u}

   For Solaris systems it defaults to:

      /bin/login -h %h %?T{TERM=%T}{-} %?u{%?a{-f }-- %u}

3. BSDish -B option is not supported (yet). It should be easily
   implemented using

      telnetd -E '/bin/login -h %h -p -e /usr/ucb/bftp %?u{-f %u}'

4. The argument to -D (--debug) switch can be a comma-separated list
   of debug levels to be enabled.

5. Debugging output goes to file "/tmp/telnet.debug" instead of being
   sent over the network.

6. -l (--linemode) switch takes an optional argument. If it is used
   without argument it does the same as usual telnet option, i.e.
   tries to enable line-at-a-time mode. Specifying -lnoklugde
   (--linemode=nokludge) will disable `kludge line mode' unless the
   remote party requires it. It is roughly equivalent to old '-k',
   therefore -k is not supported.

7. All options related to UNICOS (CRAY) have been removed.


Regards,
Sergey