'Asks the proxy to open a tunnel.'

def requestTunnel(self, protocol):

    tunnelReq = tunnel_request_data(self._tunneledHost, self._tunneledPort, self._proxyAuthHeader)
    protocol.transport.write(tunnelReq)
    self._protocolDataReceived = protocol.dataReceived
    protocol.dataReceived = self.processProxyResponse
    self._protocol = protocol
    return protocol
