netcat strange behaviour

[shibbsd at spymac.com]

Hi,

I recently came across a very stupid behaviour of netcat - the one in base system
(/usr/bin/nc in my FreeBSD 5.4-RC3).

I just wanted to connect to a POP3 server, authenticate and grab the STAT
information, so
I issued the following command:

printf "USER XXX\nPASS XXX\nSTAT\nQUIT\n" | nc -i 1 <mypopserver> 110

And what I got on stdout was:

+OK <greeting string>
+OK
+OK

...and nothing more, the command just exited without any error (FIN_WAIT in
netstat). The
server had interpreted USER and PASS commands, but ignored anything that came
later... The
error is 100% reproductible, has been observed on a few different FreeBSD 5
machines, and
- what is more - does not depend on a POP3 server! I tried a couple of public
ISPs. I have
also used a range of -i delays without success.

I investigated more and ran tcpdump -xx -v dst host <mypopserver>, and what I got
was:

[...omitted...]
08:55:23.196753 IP (tos 0x0, ttl  64, id 145, offset 0, flags [DF], length: 80)
mypc.63175
>
mypopserver.pop3: P [bad tcp cksum 2f41 (->71d2)!] 0:40(40) ack 36 win 65535
        0x0000:  0050 da74 56b1 0011 11c1 fa55 0800 4500  .P.tV......U..E.
        0x0010:  0050 0091 4000 4006 0b19 0a01 0ac7 d94a  .P.. at .@........J
        0x0020:  40ec f6c7 006e f760 36fd f3cd 8805 5018  @....n.`6.....P.
        0x0030:  ffff 2f41 0000 5553 4552 20XX XXXX XXXX  ../A..USER.XXXXX
        0x0040:  XXXX XXXX 0a50 4153 5320 XXXX XXXX XXXX  XXXX.PASS.XXXXXX
        0x0050:  XXXX XX0a 5354 4154 0a51 5549 540a       XXX.STAT.QUIT.
[...omitted...]

And my BIG question is:
should netcat send all these POP3 commands in one packet? I thought that separate
lines
ought to be separated in TCP/IP terms too - and what is more, I wanted a 1 second
delay
between lines! (-i option).

Any suggestions, bug anticipations or maybe networking lectures for me? ;) I just
wanted
to check mail :P Thanks

Kuba <shibbsd at spymac.com>