text: ###############################################################################
  #
  # The MIT License (MIT)
  #
  # Copyright (c) Tavendo GmbH
  #
  # Permission is hereby granted, free of charge, to any person obtaining a copy
  # of this software and associated documentation files (the "Software"), to deal
  # in the Software without restriction, including without limitation the rights
  # to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  # copies of the Software, and to permit persons to whom the Software is
  # furnished to do so, subject to the following conditions:
  #
  # The above copyright notice and this permission notice shall be included in
  # all copies or substantial portions of the Software.
  #
  # THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  # IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  # FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  # AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  # LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  # OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
  # THE SOFTWARE.
  #
  ###############################################################################
  
  from autobahn.asyncio.websocket import WebSocketServerProtocol, \
      WebSocketServerFactory
  
  import json
  import trollius
  
  
  class SlowSquareServerProtocol(WebSocketServerProtocol):
  
      @trollius.coroutine
      def slowsquare(self, x):
          if x > 5:
              raise Exception("number too large")
          else:
              yield trollius.sleep(1)
              raise trollius.Return(x * x)
  
      @trollius.coroutine
      def onMessage(self, payload, isBinary):
          if not isBinary:
              x = json.loads(payload.decode('utf8'))
              try:
                  res = yield self.slowsquare(x)
              except Exception as e:
                  self.sendClose(1000, "Exception raised: {0}".format(e))
              else:
                  self.sendMessage(json.dumps(res).encode('utf8'))
  
  
  if __name__ == '__main__':
  
      factory = WebSocketServerFactory(u"ws://127.0.0.1:9000")
      factory.protocol = SlowSquareServerProtocol
  
      loop = trollius.get_event_loop()
      coro = loop.create_server(factory, '127.0.0.1', 9000)
      server = loop.run_until_complete(coro)
  
      try:
          loop.run_forever()
      except KeyboardInterrupt:
          pass
      finally:
          server.close()
          loop.close()
  