CODEWITHSUNDEEP
pythonsocketsnetwork-programmingtcpconnection
FaultException
FaultException

Reputation: 149

sockets - only receiving errors after attempting send

I have a TCP server with code that looks like this (in a loop):

r, w, e = select([self.sock], [self.sock], [self.sock], 0)
if r or e:
    try:
        data = self.sock.recv(2048)
    except:
        debug("%s: .recv() crashed!"%self.id)
        debug(traceback.format_exc())
        break

For some reason, my connection from the client to this server randomly breaks, but I only see that it broke once I try to send data, then I get the error from recv(), is there any way to detect the error without trying to send data?

Upvotes: 0

Views: 90

Answers (1)

xaxxon
xaxxon

Reputation: 19761

Depending on how the connection was closed, you may not know it's closed until you attempt a send. By default, TCP won't automatically detect if the remote machine disappears without sending a disconnect.

What you're seeing is the correct behavior and something you need to handle. Make sure you don't assume that all exceptions from recv are "crashes", though. I don't know python, but there are likely different exceptions (including disconnects) that you need to handle but the code you posted doesn't deal with properly.

You should either enable TCP keepalive or send application-layer no-op packets to determine if your connection is still open.

Upvotes: 1

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