def request(self, request):
    """
    Issue C{request} over C{self.transport} and return a L{Deferred} which
    will fire with a L{Response} instance or an error.

    @param request: The object defining the parameters of the request to
       issue.
    @type request: L{Request}

    @rtype: L{Deferred}
    @return: The deferred may errback with L{RequestGenerationFailed} if
        the request was not fully written to the transport due to a local
        error.  It may errback with L{RequestTransmissionFailed} if it was
        not fully written to the transport due to a network error.  It may
        errback with L{ResponseFailed} if the request was sent (not
        necessarily received) but some or all of the response was lost.  It
        may errback with L{RequestNotSent} if it is not possible to send
        any more requests using this L{HTTP11ClientProtocol}.
    """
    if self._state != 'QUIESCENT':
        return fail(RequestNotSent())

    self._state = 'TRANSMITTING'
    _requestDeferred = maybeDeferred(request.writeTo, self.transport)

    def cancelRequest(ign):
        # Explicitly cancel the request's deferred if it's still trying to
        # write when this request is cancelled.
        if self._state in (
                'TRANSMITTING', 'TRANSMITTING_AFTER_RECEIVING_RESPONSE'):
            _requestDeferred.cancel()
        else:
            self.transport.abortConnection()
            self._disconnectParser(Failure(CancelledError()))
    self._finishedRequest = Deferred(cancelRequest)