Twisted Network Programming Essentials, 2nd Edition

Chapter 2. Building Basic Clients and Servers

The best way to learn about the components of a Twisted application is to dive right into some examples. This chapter will introduce you to the reactor event loop, transports, and protocols through implementations of a few basic TCP servers and clients.

A TCP Echo Server and Client

Skim the code for the TCP echo server and client pair in Examples 2-1 and 2-2. The server’s job is to listen for TCP connections on a particular port and echo back anything it receives. The client’s job is to connect to the server, send it a message, receive a response, and terminate the connection.

Example 2-1. echoserver.py

from twisted.internet import protocol, reactor

class Echo(protocol.Protocol):
    def dataReceived(self, data):
        self.transport.write(data)

class EchoFactory(protocol.Factory):
    def buildProtocol(self, addr):
        return Echo()

reactor.listenTCP(8000, EchoFactory())
reactor.run()

Example 2-2. echoclient.py

from twisted.internet import reactor, protocol

class EchoClient(protocol.Protocol):
   def connectionMade(self):
       self.transport.write("Hello, world!")

   def dataReceived(self, data):
       print "Server said:", data
       self.transport.loseConnection()

class EchoFactory(protocol.ClientFactory):
   def buildProtocol(self, addr):
       return EchoClient()

   def clientConnectionFailed(self, connector, reason):
       print "Connection failed."
       reactor.stop()

   def clientConnectionLost(self, connector, reason):
       print "Connection lost."
       reactor.stop() 

reactor.connectTCP("localhost", 8000