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From: Jean-Paul Calderone <calderone.jeanpaul@gmail.com>
Newsgroups: comp.lang.python
Subject: Re: Why doesn't this asyncore.dispatcher.handle_read() get called?
Date: Wed, 20 Apr 2011 13:01:08 -0700 (PDT)
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On Apr 20, 12:25=A0pm, Dun Peal <dunpea...@gmail.com> wrote:
> Hi,
>
> I'm writing and testing an asyncore-based server. Unfortunately, it
> doesn't seem to work. The code below is based on the official docs and
> examples, and starts a listening and sending dispatcher, where the
> sending dispatcher connects and sends a message to the listener - yet
> Handler.handle_read() never gets called, and I'm not sure why. Any
> ideas?
>
> Thanks, D.
>
> import asyncore, socket, sys
>
> COMM_PORT =3D 9345
>
> class Handler(asyncore.dispatcher):
> =A0 =A0 def handle_read(self):
> =A0 =A0 =A0 =A0 print 'This never prints'
>
> class Listener(asyncore.dispatcher):
> =A0 =A0 def __init__(self, port=3DCOMM_PORT):
> =A0 =A0 =A0 =A0 asyncore.dispatcher.__init__(self)
> =A0 =A0 =A0 =A0 self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
> =A0 =A0 =A0 =A0 self.set_reuse_addr()
> =A0 =A0 =A0 =A0 self.bind(('', port))
> =A0 =A0 =A0 =A0 self.listen(5)
>
> =A0 =A0 def handle_accept(self):
> =A0 =A0 =A0 =A0 client, addr =3D self.accept()
> =A0 =A0 =A0 =A0 print 'This prints.'
> =A0 =A0 =A0 =A0 return Handler(client)
>
> class Sender(asyncore.dispatcher):
> =A0 =A0 def __init__(self, host):
> =A0 =A0 =A0 =A0 asyncore.dispatcher.__init__(self)
> =A0 =A0 =A0 =A0 self.create_socket(socket.AF_INET, socket.SOCK_STREAM)
> =A0 =A0 =A0 =A0 self.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1=
)
> =A0 =A0 =A0 =A0 self.connect( (host, COMM_PORT) )
> =A0 =A0 =A0 =A0 self.buffer =3D 'Msg\r\n'
>
> =A0 =A0 def handle_connect(self):
> =A0 =A0 =A0 =A0 pass
>
> =A0 =A0 def writable(self):
> =A0 =A0 =A0 =A0 return len(self.buffer) > 0
>
> =A0 =A0 def handle_write(self):
> =A0 =A0 =A0 =A0 sent =3D self.send(self.buffer)
> =A0 =A0 =A0 =A0 self.buffer =3D self.buffer[sent:]
>
> def test_communication():
> =A0 =A0 from multiprocessing import Process
> =A0 =A0 def listener():
> =A0 =A0 =A0 =A0 l =3D Listener()
> =A0 =A0 =A0 =A0 asyncore.loop(timeout=3D10, count=3D1)
> =A0 =A0 lis =3D Process(target=3Dlistener)
> =A0 =A0 lis.start()
> =A0 =A0 def sender():
> =A0 =A0 =A0 =A0 s =3D Sender('localhost')
> =A0 =A0 =A0 =A0 asyncore.loop(timeout=3D10, count=3D1)
> =A0 =A0 sen =3D Process(target=3Dsender)
> =A0 =A0 sen.start()
> =A0 =A0 lis.join()
>
> test_communication()

You didn't let the program run long enough for the later events to
happen.  loop(count=3D1) basically means one I/O event will be processed
- in the case of your example, that's an accept().  Then asyncore is
done and it never gets to your custom handle_read.

So you can try passing a higher count to loop, or you can add your own
loop around the loop call.  Or you can switch to Twisted which
actually makes testing a lot easier than this - no need to spawn
multiple processes or call accept or recv yourself.  Here's a somewhat
equivalent Twisted-based version of your program:

    from twisted.internet.protocol import ServerFactory, Protocol
    from twisted.internet import reactor

    factory =3D ServerFactory()
    factory.protocol =3D Protocol

    reactor.listenTCP(0, factory)
    reactor.run()

It's hard to write the equivalent unit test, because the test you
wrote for the asyncore-based version is testing lots of low level
details which, as you can see, don't actually appear in the Twisted-
based version because Twisted does them for you already.  However,
once you get past all that low-level stuff and get to the part where
you actually implement some of your application logic, you might have
tests for your protocol implementation that look something like this:

    from twisted.trial.unittest import TestCase
    from twisted.test.proto_helpers import StringTransport

    from yourapp import Handler # Or a better name

    class HandlerTests(TestCase):
        def test_someMessage(self):
            """
            When the "X" message is received, the "Y" response is sent
back.
            """
            transport =3D StringTransport()
            protocol =3D Handler()
            protocol.makeConnection(transport)
            protocol.dataReceived("X")
            self.assertEqual(transport.value(), "Y")

Hope this helps,
Jean-Paul