ZeroMQ REQ/REP server error handling

Question

I am trying to use the ZeroMQ rep/req and cannot figure out how to handle server side errors. Look at the code from here:

socket.bind("tcp://*:%s" % port)
while True:
    #  Wait for next request from client
    message = socket.recv()
    print "Received request: ", message
    time.sleep (1)  
    socket.send("World from %s" % port)

My problem is what happens if the client calls socket.send() and then hangs or crashes. Wouldn't the server just get stuck on socket.send() or socket.recv() forever?

Note that it is not a problem with TCP sockets. With TCP sockets I can simply break the connection. With ZMQ, the connections are implicitly managed for me and I don't know if it is possible to break a 'session' or 'connection' and start over.

Answer 1

You can terminate ZMQ sockets much the same way you terminate TCP sockets.

socket.close()

If you need to wait on a message but only up for a finite amount of time you can pass a timeout flag to socket.recv(timeout=1024) and then handle the timeout error case the same way you would when a TCP socket timeouts or disconnects. If you need to manage several sockets all of which may be in an error state then the Poller class will let you accomplish this.

Answer 2

The ZMQ Z-guide offers lots of good hints on how to structure your services to handle different scenarios.

I think chapter 4 can be of interest to you, especially the Lazy Pirate Pattern.

Check out the examples of Lazy Pirate Server and Lazy Pirate Client.