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POpython socket server/client protocol with unstable client connection
 

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  1. POpython socket server/client protocol with unstable client connection
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    <p>I have a threaded python socket server that opens a new thread for each connection.</p> <p>The thread is a very simple communication based on question and answer. Basically client sends initial data transmission, server takes it run an external app that does stuff to the transmission and returns a reply that the server will send back and the loop will begin again until client disconnects.</p> <p>Now because the client will be on a mobile phone thus an unstable connection I get left with open threads no longer connected and because the loop starts with recv it is rather difficult to break on lost connectivity this way.</p> <p>I was thinking on adding a send before the recv to test if connection is still alive but this might not help at all if the client disconnects after my failsafe send as the client sends a data stream every 5 seconds only.</p> <p>I noticed the recv will break sometimes but not always and in those cases I am left with zombie threads using resources.</p> <p>Also this could be a solid vulnerability for my system to be DOSed. I have looked through the python manual and Googled since thursday trying to find something for this but most things I find are related to client and non blocking mode.</p> <p>Can anyone point me in the right direction towards a good way on fixing this issue?</p> <p><strong>Code samples:</strong></p> <p>Listener:</p> <pre><code>serversocket = socket(AF_INET, SOCK_STREAM) serversocket.setsockopt(SOL_SOCKET, SO_REUSEADDR, 1) serversocket.bind(addr) serversocket.listen(2) logg("Binded to port: " + str(port)) # Listening Loop while 1: clientsocket, clientaddr = serversocket.accept() threading.Thread(target=handler, args=(clientsocket, clientaddr,port,)).start() # This is useless as it will never get here serversocket.close() </code></pre> <p>Handler:</p> <pre><code> # Socket connection handler (Threaded) def handler(clientsocket, clientaddr, port): clientsocket.settimeout(15) # Loop till client closes connection or connection drops while 1: stream = '' while 1: ending = stream[-6:] # get stream ending if ending == '.$$$$.': break try: data = clientsocket.recv(1) except: sys.exit() if not data: sys.exit() # this is the usual point where thread is closed when a client closes connection normally stream += data # Clear the line ending stream = base64.b64encode(stream[:-6]) # Send data to be processed re = getreply(stream) # Send response to client try: clientsocket.send(re + str('.$$$$.')) except: sys.exit() </code></pre> <p>As you can see there are three conditions that at least one should trigger exit if connection fails but sometimes they do not.</p>
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    1. COCould you post the relevant parts of the code? Are you using a Queue.queue? Using a Queue.queue enables you to see if you have jobs waiting for your threads, you can then set a timeout on the threads and if they don't get anything - they finish.
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    2. COI am not using twisted or anything else. Will ad the relevant code.
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    3. COTwo things come to my mind - you could try the .timeout() function of a socket object to close clientsocket after a few seconds of inactivity on the socket (http://docs.python.org/library/socket.html#socket.socket.settimeout). Or I also believe that slightly rewriting the multithreading part of you program to use a Queue. Using a Queue has the benefits of setting the number of threads you want to allow as well handling the jobs passed to those threads. I just found out about it recently and it blew my mind.
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