[Turnserver-devel] Bug in TCP transport

[Alexander P. <pz...@pz...>]

Hi,

I'm trying to use the turnserver as a solution for NAT traversal for a 
very restricted network environment with only TCP traffic allowed by 
firewall.

If TCP is being used as a transport between client and server, the 
following problem occurs. If client sends more that one TURN message to 
the server, only the first message is handled by server normally, all 
other messages cause server to print "Bad STUN / TURN message" diagnostics.

Looking to a server code I came to conclusion that this is due to a way 
how TCP reception is implemented in the server.

Server calls recv() for a TCP socket and assumes that the returned data 
is a TURN message.

This assumption is not correct. TCP is a stream rather that message 
protocol, it doesn't preserve message boundaries. It means that recv() 
may return more that one message at once, or message may be split 
between consecutive recv()s and so on.

The only correct way to deal with TCP is to reconstruct message 
boundaries based on a message size transmitted in a message headers.

Data from TCP socket should go to some temporary buffer, and only when 
entire message is available it needs to be processed.

--
Hope it helps,
Wishes, Alexander Pevzner (pz...@pz...)