[6.x] problem with AIO, non-blocking sockets on freebSD and IE7 on windows.
- From: Julian Elischer <julian@xxxxxxxxxxxx>
- Date: Fri, 22 Jun 2007 18:08:13 -0700
If one has an event-driven process that accepts tcp connections, one needs to set eh non-blocking socket option and use kqueue or similar to schedule work.
This is ok for data transfers, however when it comes to the close() call there is a problem. The problem in in the following code in so_close()
if (so->so_options & SO_LINGER) {
if ((so->so_state & SS_ISDISCONNECTING) &&
(so->so_state & SS_NBIO))
goto drop;
while (so->so_state & SS_ISCONNECTED) {
error = tsleep(&so->so_timeo,
PSOCK | PCATCH, "soclos", so->so_linger * hz);
if (error)
break;
}
}
}
drop:
[ continues on to destroy socket ]
because SS_NBIO is set, the socket acts as if SO_LINGER was set, with a timeout of 0.
the result of this, is the following behaviour:
========================================== The first + last packet output is below:
========================================== Source Destination Info
172.20.51.115 172.20.3.43 2597 > http [SYN] Seq=0 Len=0 172.20.3.43 172.20.51.115 http > 2597 [SYN, ACK] Seq=0 Ack=1 Len=0 172.20.51.115 172.20.3.43 2597 > http [ACK] Seq=1 Ack=1 Len=0
172.20.51.115 172.20.3.43 POST http://creative.gettyimages.com/source/<truncated>
HTTP/1.1
172.20.51.115 172.20.3.43 HTTP
172.20.3.43 172.20.51.115 http > 2597 [ACK] Seq=1 Ack=1261 Len=0
---------------
172.20.3.43 172.20.51.115 http > 2597 [ACK] Seq=1 Ack=13729 Len=0
172.20.51.115 172.20.3.43 HTTP
172.20.3.43 172.20.51.115 HTTP/1.0 407 Proxy Authentication Required
(text/html)
172.20.3.43 172.20.51.115 HTTP
172.20.3.43 172.20.51.115 http > 2597 [FIN, ACK] Seq=1858 Ack=13729 Len=0
172.20.51.115 172.20.3.43 2597 > http [ACK] Seq=13731 Ack=1859 Len=0
172.20.3.43 172.20.51.115 http > 2597 [RST] Seq=1 Len=0
172.20.3.43 172.20.51.115 http > 2597 [RST] Seq=1859 Len=0
The ACK that comes from the client is wquite legal and in fact a FIN should follow.
however we react to it by sending a reset.
This makes IE7 throw a "generic IE error page". Even though it has all the information it needs.
Less that a good result for the user.
The answer is to NOT destroy the socket immediately, but to schedule it for self destruction
in FIN_WAIT_1_TIME seconds (or so_linger secs) or when the FIN turns up, whichever occurs first.
however so_close is in the wrong layer to decide to do this I think... socket code in general
has no timer related stuff.. TCPhas timers, so I thin it would require a new call into TCP
to tell it to put the session in question onto a (new) timer..
thoughts anyone?
Julian
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