Ejabberd hooks with twisted

Few days ago I’ve found on Launchpad an interesting project by Thomas Hervé, the twisted interface to OTP, which allows to connect to erlang nodes using Twisted Matrix. The idea is incredibily powerful because it allows to easily build mixed-distributed applications using both erlang and python/twisted where they are best. So I gave it a try with ejabberd which has hooks for adding callbacks to its internal components (i.e. it’s possible to intercept and modify packets). Unfortunately I’ve discovered that the present implementation of ejabberd hooks allows to connect only callbacks from the same node of ejabberd, i.e. as an extension module, but ejabberd folks have been incredibily quick in releasing a patch which allows distributed hooks, by adding the “CallNode” atom as parameter. The patch may be not stable yet, but it works perfectly with the last release of ejabberd (2.0.2), and here is an example of a twisted node which intercepts and logs all packets sent and received by any user (here is the full code, change the node names accordingly to your setup).

It works very simply. The hooks are written as methods of a regular python class with the “remote_” prefix:

class UserMonitor(object):
    
    def remote_receive_packet(self, jid, frm, to, packet):
        print ">>",  to_domish(packet).toXml()
    
    def remote_send_packet(self, frm, to, packet):
        print "<<",  to_domish(packet).toXml()

which is published by using a PersistentPortMapper:

nodeName = buildNodeName("uccaro@olindo.bluendo.priv")
epmd = PersistentPortMapperFactory(nodeName, cookie, "olindo.bluendo.priv")
epmd.publish(proxy = UserMonitor()) 

After this it’s possible to call the methods proxy:receive_packtes and proxy:send_packet from any erlang node.

Then we register with ejabberd using a second node which calls the register methods, using the ejabberd api:

And bingo, after this ejabberd happily starts calling our hooks!

As bonus in the code you find also a function which translates from the ejabberd xml representation to twisted domish nodes, which is far more usable.

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