text: ###############################################################################
  ##
  ##  Copyright 2011 Tavendo GmbH
  ##
  ##  Licensed under the Apache License, Version 2.0 (the "License");
  ##  you may not use this file except in compliance with the License.
  ##  You may obtain a copy of the License at
  ##
  ##      http://www.apache.org/licenses/LICENSE-2.0
  ##
  ##  Unless required by applicable law or agreed to in writing, software
  ##  distributed under the License is distributed on an "AS IS" BASIS,
  ##  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  ##  See the License for the specific language governing permissions and
  ##  limitations under the License.
  ##
  ###############################################################################
  
  import hashlib
  from twisted.internet import reactor
  from autobahn.websocket import WebSocketServerFactory, WebSocketServerProtocol, listenWS
  
  
  class MessageBasedHashServerProtocol(WebSocketServerProtocol):
     """
     Message-based WebSockets server that computes a SHA-256 for every
     message it receives and sends back the computed digest.
     """
  
     def onMessage(self, message, binary):
        sha256 = hashlib.sha256()
        sha256.update(message)
        digest = sha256.hexdigest()
        self.sendMessage(digest)
        print "Sent digest for message: %s" % digest
  
  
  if __name__ == '__main__':
     factory = WebSocketServerFactory("ws://localhost:9000")
     factory.protocol = MessageBasedHashServerProtocol
     listenWS(factory)
     reactor.run()
  