Python Cookbook

Using Request/Reply in a Distributed Middleware Architecture

Credit: Graham Dumpleton

Problem

You need to allow some distributed services to supply methods, and other distributed services to access and use those methods, in a location-independent way by writing a suitable central exchange (middleware) server.

Solution

The OSE package also supports the request/reply architecture. First, we need a central middleware process to which all others connect:

# The central.py script -- needs the OSE package from http://ose.sourceforge.net

import netsvc
import signal

dispatcher = netsvc.Dispatcher(  )
dispatcher.monitor(signal.SIGINT)

exchange = netsvc.Exchange(netsvc.EXCHANGE_SERVER)
exchange.listen(11111)

dispatcher.run(  )

Next, we need a server that supplies methods through the middleware:

# The server.py script -- needs the OSE package from http://ose.sourceforge.net

import netsvc
import signal

class Service(netsvc.Service):

    def _ _init_ _(self):
        netsvc.Service._ _init_ _(self, "math")
        self.joinGroup("web-services")
        self.exportMethod(self.multiply)

    def multiply(self, x, y):
        return x*y

dispatcher = netsvc.Dispatcher(  )
dispatcher.monitor(signal.SIGINT)

exchange = netsvc.Exchange(netsvc.EXCHANGE_CLIENT)
exchange.connect("localhost",11111,5)

service = Service(  )

dispatcher.run(  )

Then, we need a client that consumes methods through the middleware:

# The client.py script -- needs the OSE package from http://ose.sourceforge.net import netsvc import signal import random class Client(netsvc.Service): ...