Bug in xterm?

[Brian Candler]

On Sat, Nov 27, 2004 at 11:52:15AM +1100, Edwin Groothuis wrote:
>     [~] edwin at k7>perl -mDigest::MD5 -e 'print pack("H*",Digest::MD5::md5("test"))' | hexdump -C
>     00000000  9f 4d f1 3c ae 73 67 46                           |.M.<.sgF|
> 
> This shows that it outputs some high-ascii data, which causes the
> xterm to stop output. If you do "echo hi > /tmp/aaa" while in this
> state (be alert for typos), you see that it still accepts commands,
> but doesn't show them anymore.

Thanks. I got a nice analysis off-list:

--------------------------------------------------------------------------
>$ perl -mDigest::MD5 -e 'print pack("H*",Digest::MD5::md5("test"))' >ert
>$ wc ert
>      0       1       8 ert
>$ hexdump -C ert
>00000000  9f 4d f1 3c ae 73 67 46                           |.M.<.sgF|
>00000008
>$ cat ert
>
>At this point it hangs; sending ^Q doesn't help. But if you press cursor-up
>a few times it comes back to life.
>
>It must be a strange escape sequence if typing characters and hitting Return
>lots of times is not enough to bring it back to life. I suppose it's
>technically not an escape sequence, since it doesn't include 0x1B :-)

0x9f is APC - which begins a string.  Technically it's only terminated by
a ST (0x9c or ESC followed by backslash), but xterm also accepts a BEL,
which may be what's emitted when you do a few uparrows (getting an error
response from the shell).  There's also a resource setting to work around
some Linux junk (hardcoded applications with malformed sequences) that
can make it terminate on a carriage return.  But generally, it would look
as if it's hung.

(A soft-reset would fix the problem with less damage to your session).

Oddly, a real vt220 would do the same thing, but neither has any use for
the content of the string.
--------------------------------------------------------------------------

I guess I wasn't expecting any escape sequence which consumed an infinite
number of characters - and presumably also, Konsole implements a different
terminal emulation (or implements vt220 wrongly).

Cheers,

Brian.