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<TITLE>Distinguishing TCP connections</TITLE>
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<P><FONT SIZE=2>Eric,</FONT>
</P>
<P><FONT SIZE=2>I came up with a nice way of managing connections on the last project I worked on:</FONT>
</P>
<P><FONT SIZE=2>The DataConnection is the protocol instance (in this case inheriting from Int32StringReceiver). Each time a protocol connects it calls the registerSource</FONT></P>
<P><FONT SIZE=2>class DataConnection(Int32StringReceiver):</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> def __init__(self, manager):</FONT>
<BR><FONT SIZE=2> self.manager = manager</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> def closeConnection(self):</FONT>
<BR><FONT SIZE=2> self.transport.loseConnection()</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> def connectionMade(self):</FONT>
<BR><FONT SIZE=2> print 'registering connection'</FONT>
<BR><FONT SIZE=2> self.registerConnection()</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> def connectionLost(self, reason):</FONT>
<BR><FONT SIZE=2> print 'connection lost, removing....'</FONT>
<BR><FONT SIZE=2> self.removeConnection()</FONT>
</P>
<P> <FONT SIZE=2>.</FONT>
<BR> <FONT SIZE=2>.</FONT>
<BR><FONT SIZE=2>[ code omitted for brevity ]</FONT>
<BR> <FONT SIZE=2>.</FONT>
<BR> <FONT SIZE=2>.</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> def registerConnection(self):</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> register data connection with connection manager.</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> self.manager.registerSource(self)</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> def removeConnection(self):</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> remove this connection from the connection manager.</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> self.manager.removeSource(self.id)</FONT>
</P>
<P><FONT SIZE=2> def setId(self, id):</FONT>
<BR><FONT SIZE=2> self.id = id</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2>And the ConnectionManager is the factory class (inherited from the generic Factory class).</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2>class ConnectionManager(Factory):</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> def __init__(self, eventhandler):</FONT>
<BR><FONT SIZE=2> self.ids = 0</FONT>
<BR><FONT SIZE=2> self.sources = {}</FONT>
<BR><FONT SIZE=2> self.eventhandler = eventhandler # -- see comments later</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> def buildProtocol(self, addr):</FONT>
<BR><FONT SIZE=2> return DataConnection(self)</FONT>
</P>
<P><FONT SIZE=2> def newId(self):</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> get an id that is unique for the life of the connection manager.</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> id = self.ids+1</FONT>
<BR><FONT SIZE=2> self.ids = id</FONT>
<BR><FONT SIZE=2> return id</FONT>
</P>
<P><FONT SIZE=2> def registerSource(self, source):</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> register a new source, this assigns the source an id and</FONT>
<BR><FONT SIZE=2> adds it to the sources dictionary.</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> id = self.newId()</FONT>
<BR><FONT SIZE=2> self.sources[id] = source</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> # set source id</FONT>
<BR><FONT SIZE=2> source.setId(id)</FONT>
</P>
<P><FONT SIZE=2> def removeSource(self, id):</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> remove the connection indicated by the source id from the current connection</FONT>
<BR><FONT SIZE=2> pool any subsequent behaviour must be handled in the event manager.</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> if self.sources.has_key(id):</FONT>
<BR><FONT SIZE=2> del self.sources[id]</FONT>
</P>
<P><FONT SIZE=2> def closeConnections(self):</FONT>
<BR><FONT SIZE=2> for source in self.sources.values():</FONT>
<BR><FONT SIZE=2> source.closeConnection()</FONT>
</P>
<P><FONT SIZE=2>[ code omitted for brevity ]</FONT>
</P>
<P><FONT SIZE=2>As you can see the when a connection is made it is registered with the factory instance. This uniquely identifies the connection, and allows you to identify when you get a message which connection it is from. This also simplifies sending a message back along the same channel:</FONT></P>
<P><FONT SIZE=2>To do this you can create an event handler that implements some form of event processing:</FONT>
</P>
<P><FONT SIZE=2>class EventHandler:</FONT>
</P>
<P><FONT SIZE=2> def __init__(self, manager):</FONT>
<BR><FONT SIZE=2> self.manager = manager</FONT>
</P>
<P><FONT SIZE=2> def messageReceived(self, id, message):</FONT>
<BR><FONT SIZE=2> # process message</FONT>
<BR><FONT SIZE=2> ...</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> # create new message</FONT>
<BR><FONT SIZE=2> newMessage = "this is a test"</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> # send new message back along same connection</FONT>
<BR><FONT SIZE=2> self.manager.sendMessage(id, newMessage)</FONT>
</P>
<P><FONT SIZE=2>And in the ConnectionManager add something like the following methods:</FONT>
</P>
<P><FONT SIZE=2> def propagateMessage(self, id, message):</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> This method simply passes the received message through to the</FONT>
<BR><FONT SIZE=2> EventHandler class instance along with the id of the connection</FONT>
<BR><FONT SIZE=2> the message was received from.</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> self.eventhandler.messageReceived(id, message)</FONT>
<BR><FONT SIZE=2> </FONT>
<BR><FONT SIZE=2> def sendMessage(self, id, message):</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> This method retrieves the correct connection and sends a message through it.</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> if self.sources.has_key(id):</FONT>
<BR><FONT SIZE=2> self.sources[id].emitMessage(message)</FONT>
</P>
<P><FONT SIZE=2>And the DataConnection:</FONT>
</P>
<P><FONT SIZE=2> def stringReceived(self, data):</FONT>
<BR><FONT SIZE=2> self.manager.propagateEvent(self.id, data)</FONT>
</P>
<P><FONT SIZE=2> def emitMessage(self, message):</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> send a message along the data connection.</FONT>
<BR><FONT SIZE=2> """</FONT>
<BR><FONT SIZE=2> self.sendString(message)</FONT>
</P>
<BR>
<P><FONT SIZE=2>If any of this is unclear please let me know.</FONT>
</P>
<P><FONT SIZE=2>Regards,</FONT>
</P>
<P><FONT SIZE=2>Grant McDonald</FONT>
</P>
<P><FONT SIZE=2>----Original Message-----</FONT>
<BR><FONT SIZE=2>From: twisted-python-bounces@twistedmatrix.com [<A HREF="mailto:twisted-python-bounces@twistedmatrix.com">mailto:twisted-python-bounces@twistedmatrix.com</A>]On Behalf Of Eric Hsu</FONT>
<BR><FONT SIZE=2>Sent: 21 June 2005 17:33</FONT>
<BR><FONT SIZE=2>To: radix@twistedmatrix.com</FONT>
<BR><FONT SIZE=2>Cc: Twisted general discussion</FONT>
<BR><FONT SIZE=2>Subject: Re: [Twisted-Python] How could I distinguish each TCP connection?</FONT>
</P>
<P><FONT SIZE=2>Thank you very much!</FONT>
<BR><FONT SIZE=2>You've been a GREAT help :D</FONT>
<BR><FONT SIZE=2>2005/6/21, Christopher Armstrong <radeex@gmail.com>:</FONT>
<BR><FONT SIZE=2>I suggest, instead of using the stock "Factory", making a subclass of</FONT>
<BR><FONT SIZE=2>it with buildProtocol implemented like so:</FONT>
</P>
<P><FONT SIZE=2>def buildProtocol(self, addr):</FONT>
<BR><FONT SIZE=2> p = Factory.buildProtocol(self, addr)</FONT>
<BR><FONT SIZE=2> self.connections.append (p)</FONT>
<BR><FONT SIZE=2> return p</FONT>
</P>
<P><FONT SIZE=2>Or similar (you'll have to define the 'connections' list yourself in</FONT>
<BR><FONT SIZE=2>__init__). In the protocol's connectionLost, you could then remove the</FONT>
<BR><FONT SIZE=2>protocol from that list.</FONT>
</P>
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