telnetd binary mode

[Alison Winters <alison at sdf dot lonestar dot org>]

Hi,

We have a piece of software that opens a telnet connection then
initializes binary communication between server and client.  It works
happily on SCO OpenServer 5 and Red Hat Linux (5.2+).  It doesn't on the
latest Cygwin build.  Essentially it sends a bit of information back and
forth, then (seeming randomly) things hang.  At first i thought it may
be a telnetd version problem, but on SCO the daemon is built from
90/91/92 source files; the Cygwin build uses 93/95 source files.

My suspicion is that this has something to do with binary vs text i/o.
I know calling open(2) in Cygwin you need to explicitly add the O_BINARY
flag; is something like this also the case when opening a socket?  The
other (related) possibility is that the telnet daemon should be set
explicitly into binary mode (IAC WILL TRANSMIT-BINARY and IAC DO
TRANSMIT-BINARY).  This doesn't need to be done on UNIX, so i would find
it odd if it had to be explicit in Cygwin, but is it possible that that
is the problem?

The final possibility is that there's a byte under 0x20 that is causing
some kind of lockup.  I've already escaped ^Q, ^S, ^], \r and \n to have
it work correctly under UNIX; are there any that might be doing strange
things in Cygwin specifically?  I have set TERM to vt100 and done a tset
before initializing the binary flow.

Any help would be great appreciated.  Thanks,
Alison


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