[Pan-users] Bug 117496 : 502 Error (Socket problems)

[Christopher S Horler]

I was going to submit a new bug report, but I noticed this one (117496).
However it doesn't like the idea of me changing a number of fields I'd
like to.

I'd be grateful if someone with a greater knowledge of socket
programming could please comment on this.


I have seen 502's (max num connections exceeded) 

I did a fair amount of investigation to find the cause of this. 
Using netstat I get things like the following (tidied foreign 
addresses for clarity). 
 
Active Internet connections (w/o servers) 
Proto Recv-Q Send-Q Local Address     Foreign Address   State 
tcp        0      0 192.168.0.2:32973 uk.clara.net:nntp ESTABLISHED 
tcp        0     18 192.168.0.2:32971 uk.clara.net:nntp FIN_WAIT1 
 
Watching the connection, what appears to happen is this.  The 
connection stops receiving data mid transmission (unknown why), at 
this point pan calls close on the socket.  The socket enters 
FIN_WAIT1 but still has data in the send-q.  The socket remains in 
this state until the server sends FIN to the client or the socket 
times out on the server (or the client end - 60 secs on Linux) 
 
http://www.derkeiler.com/Mailing-Lists/securityfocus/focus-linux/2001-08/0215.html
 
 
Pan then opens a new connection because it believes the old one is 
down.  However this is a problem if the news server doesn't agree (as 
we've not seen the socket enter FIN_WAIT2 this end) and you already 
have your connections used up because you'll open another and then 
get a 502 at which point Pan closes all connections.

Thanks,

Chris.