docs: def _readable(self, watcher, events):
          """Called by the pyev watcher (self.read_watcher) whenever the socket
          is readable.
     
          This means either the socket has been closed or there is a new
          client connection waiting.
  
          """
          protocol = self.factory.build(self.loop)
          try:
              sock, address = self.sock.accept()
              connection = Connection(self.loop, sock, address, protocol, self)
              self.connections.add(connection)
              connection.make_connection()
              logger.debug("added connection")
          except IOError as e:
              self.shutdown(e)