tree 860c80ddeaa7f333308677a13c458a832efa21fc
parent 720058cdcbd5285dc4e4a48216b10c9b96000141
author Willy Tarreau <w@1wt.eu> 1247594105 +0200
committer Willy Tarreau <w@1wt.eu> 1247594105 +0200
encoding latin1

[BUG] stream_sock: don't stop reading when the poller reports an error

As reported by Jean-Baptiste Quenot and Robbie Aelter, sometimes a
backend server error is converted to a 502 error if the backend stops
before reading all the request. The reason is that the remote system
sends a TCP RST packet because there are still unread data pending in
the socket buffer. This RST is translated as a socket error on the
local system, and this error is reported by the poller.

However, most of the time, it's a write error, but the system is
still able to read the remaining pending data, such as in the trace
below :

send(7, "GET /aaa HTTP/1.0\r\nUser-Agent: Mo"..., 1123, MSG_DONTWAIT|MSG_NOSIGNAL) = 1123
epoll_ctl(3, EPOLL_CTL_ADD, 7, {EPOLLIN, {u32=7, u64=7}}) = 0
epoll_wait(3, {{EPOLLIN|EPOLLERR|EPOLLHUP, {u32=7, u64=7}}}, 8, 1000) = 1
gettimeofday({1247593958, 643572}, NULL) = 0
recv(7, "HTTP/1.0 400 Bad request\r\nCache-C"..., 7000, MSG_NOSIGNAL) = 187
setsockopt(6, SOL_TCP, TCP_NODELAY, [0], 4) = 0
setsockopt(6, SOL_TCP, TCP_CORK, [1], 4) = 0
send(6, "HTTP/1.0 400 Bad request\r\nCache-C"..., 187, MSG_DONTWAIT|MSG_NOSIGNAL) = 187
shutdown(6, 1 /* send */)               = 0

The recv succeeded while epoll_wait() reported an error.

Note: This case is very hard to reproduce and requires that the backend
server is reached via the loopback in order to minimise latency and
reduce the risk of sent data being ACKed.