Debug technique for comint, need stdin/stdout logger.

[Oleksandr Gavenko <gavenko@bifit.com.ua>]

When work with Emacs comint I need logger for stdin/stdout process
interaction.

So I change name of calling program in Emacs
and that logger/script call original command and log
stdin and stdout to files.

I try write expect script:

#!/usr/bin/env expect

set in [open in.log w]
set out [open out.log w]

log_user 0

spawn sort
set proc_id $spawn_id

stty -echo

expect {
     -i $user_spawn_id -re . {
         puts -nonewline $in $expect_out(buffer)
         send -i $proc_id $expect_out(buffer)
         exp_continue
     } eof { }
     -i $proc_id -re . {
         puts -nonewline $out $expect_out(buffer)
         send_user $expect_out(buffer)
         exp_continue
     } eof { }
}

expect -i $proc_id -re . {
     puts -nonewline $out $expect_out(buffer)
     send_user $expect_out(buffer)
     exp_continue
} eof { }

close $in
close $out

but this is my first serious Expect script and it works bad:

   $ printf 'b\nquit\na\n' | ./logger.exp; \
     printf '\n===in===\n'; cat in.log; \
     printf '\n===out===\n'; cat out.log
b
quit
a
   C-c C-c   # I type C-c

===in===
b
quit
a

===out===
b
quit         # Why not sorted???
a

Are there any program that do this job or please help fix this script.