[Twisted-Python] client connecting to 2 servers (nonsimultaneously)

[benjamin.bertrand at lfv.se]

One small question about the following code:
Why did you use reactor.callWhenRunning in the __init__ method?
Why not calling directly reactor.connectTCP?

Cheers,

Benjamin

Från: twisted-python-bounces at twistedmatrix.com [mailto:twisted-python-bounces at twistedmatrix.com] För Jason Rennie
Skickat: den 11 januari 2011 14:11
Till: Twisted general discussion
Ämne: Re: [Twisted-Python] client connecting to 2 servers (nonsimultaneously)

You could probably generalize and simplify by using a collections.deque of hosts/ports and using the rotate() method before each reactor.connectTCP.  Also, no need for multiple reactor imports---one at the top of the code is fine.  Note that if the connection is "lost" in a non-clean fashion, you may also want to reconnect.  IIUC, "fail" only handles the case that no connection is made (protocol is never created).

import collections
from twisted.internet import reactor

class MyClientFactory(object):
    protocol = MyClientProtocol
    def __init__(self, hosts):
        self.hosts = collections.deque(hosts)
        reactor.callWhenRunning(reactor.connectTCP, self.hosts[0][0], self.hosts[0][1], self)
        self.hosts.rotate(1)
    def clientConnectionFailed(self, connector, reason):
        reactor.callLater(2.0, connectTCP, self.hosts[0][0], self.hosts[0][1], self)
        self.hosts.rotate(1)

factory = MyClientFactory([('host1', port1), ('host2', port2), ...])
reactor.run()

Cheers,

Jason

On Tue, Jan 11, 2011 at 5:17 AM, <benjamin.bertrand at lfv.se> wrote:
Hi,

I'm new to twisted and I have started to write a new protocol with a TCP
client and server.
In my protocol, a client should be able to connect to 2 servers
(master/slave node - only the master accepts connection).
The client should try to connect to server1. If it fails, try to connect
to server2 (after a specific timeout). If that fails, try server1...
I came up with a solution (see below).
As I'm new to twisted and I haven't seen anything like that in the
examples, I'd like to check if that's a proper way to do it.
Any comments is welcome.

Thanks

Benjamin

***********************************************
class MyClientFactory(ClientFactory):

   protocol = MyClientProtocol

   def __init__(self, host2=None):
       self.host1 = None
       self.host2 = host2

   def clientConnectionFailed(self, connector, reason):
       from twisted.internet import reactor
       if self.host2 is None:
           # host2 is not defined, reconnect to host1
           reactor.callLater(2.0, connector.connect)
       else:
           destination = connector.getDestination()
           if self.host1 is None:
               # First connection failed, initialize host1, and try
host2
               self.host1 = destination.host
               host = self.host2
           elif destination.host == self.host1:
               # Connection to host1 failed, try host2
               host = self.host2
           else:
               # Connection to host2 failed, try host1
               host = self.host1
           reactor.callLater(2.0, reactor.connectTCP, host,
destination.port, self)


factory = MyClientFactory(server2)
from twisted.internet import reactor
reactor.connectTCP(server1, 8010, factory)
reactor.run()
***********************************************


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-- 
Jason Rennie
Research Scientist, ITA Software
617-714-2645
http://www.itasoftware.com/