Copas weirdness

[David Given <dg@...>]

I'm trying to write a proxy that tunnels TCP connections over a sequence
of HTTP POST requests. (Yes, this is evil.) I'm using Lua and Copas for
this as being the easiest way to do this kind of server. It's mostly
working well except for... well, this.

What I'm finding is that I can establish the tunnel, and pass data back
and forth, and then eventually something will go wrong. This can
manifest in various ways: either the proxy will block on a Copas read or
write and stop responding to any other connections, or else one of the
sockets will mysteriously close itself.

I managed to persuade it to fail in the second mode often enough to do
some debugging. Looking at the system call trace, I can see it do this:

send(5, "\0\0\0\214\6
\0\0\0\200\37U\22I\21k\"!\260\302\317\17\307\352&\220\33\327\2Eu\213"..., 144,
0) = 144

...as it sends some stuff to the upstream server; then I can see this:

send(4, "HTTP/1.1 200 OK\r\nX-SessionId: 84"..., 40, 0) = 40
fcntl64(4, F_GETFL) = 0x802 (flags O_RDWR|O_NONBLOCK)
fcntl64(4, F_SETFL, O_RDWR) = 0
close(4)

...as it tells the downstream server it's done it. This happens over and
over again as data goes through. Then, eventually, this happens:

send(5, "\0\0\0\f\n\25\0\0\0\0\0\0\0\0\0\0", 16, 0) = 16

send(4, "HTTP/1.1 200 OK\r\nX-SessionId: 84"..., 40, 0) = 40
fcntl64(5, F_GETFL) = 0x802 (flags O_RDWR|O_NONBLOCK)
fcntl64(5, F_SETFL, O_RDWR) = 0
close(5) = 0

It seems to have just closed the wrong socket!

My program, such as it is, is here: http://pastebin.com/yTXGh6xB (183
lines, too antisocial to post). Am I going insane, or am I just making a
stupid mistake somewhere?

I'm on Debian, using stock Lua 5.1.4-5, copas 1.1.5-2, coxpcall
1.13.0-2, luasocket 2.0.2-4 respectively.

-- 
┌─── ｄｇ＠ｃｏｗｌａｒｋ．ｃｏｍ ───── http://www.cowlark.com ─────
│
│ "I have a mind like a steel trap. It's rusty and full of dead mice."
│ --- Anonymous, on rasfc

Attachment: signature.asc
Description: OpenPGP digital signature