Intercepting system messages (Was Re: talk and talkd)

[Michael I. Bushnell]

Sheesh.  Everyone wants a means of intercepting system messages 
intended for your terminal, so that emacs can deal with them
nicely.  Here is a PAINFUL but workable scheme.

Set up the following:

                                mas         sla
  +-------+     +---------+       +---------+         +----------+
  |       | A   |         |   A   |         |    A    |          |
  | Real  |---->|   filt  |------>|         |-------->|          |
  |login  |     |         |       |   PTY   |         |   emacs  |
  | tty   |<----|         |<------| (login) |<--------|          |
  |       |  B  |         |   B   |         |    B    |          |
  +-------+     +---------+       +---------+         +----------+
                       |		^		  ^
                       |		|		  |
                       +----------------)------------------+
			C		|
					|C
				  +---------+
				  |         |
				  |  talkd  |
				  |         |
				  |         |
				  +---------+




The PTY is put in USER IOCTL mode (remember?).  That means that
every read on the master side has an extra byte prepended.  0
means it was written normally on the slave side, anything else
is from an ioctl call the slave made.  Change emacs to do this
ioctl call before every write to the terminal.  Then, filt
watches for this byte.  If it's zero, then the write came from a stupid
system process, and is sent to emacs on a pipe.  the filt 
program is started by emacs, which then changes its tty (to the pty)
and mugs utmp to fool talkd into using the new pty, and then
goes into "ioctl before each write" mode.

Channel A:  Your keystrokes
Channel B: Emacs's writes, identified by the ioctl
Channel C: Stupid system program's writes, identified by the lack of ioctl 



UGH!  But I think it would work....
                N u m q u a m   G l o r i a   D e o 

			Michael I. Bushnell
			HASA - "A" division
14308 Skyline Rd NE				Computer Science Dept.
Albuquerque, NM  87123		OR		Farris Engineering Ctr.
	OR					University of New Mexico
mike at turing.unm.edu				Albuquerque, NM  87131
{ucbvax,gatech}!unmvax!turing.unm.edu!mike