def begin(self, transaction=None, headers={}, **keyword_headers):
     headers = utils.merge_headers([headers, keyword_headers])
     if not transaction:
         transaction = str(uuid.uuid4())
     headers[HDR_TRANSACTION] = transaction
     self.send_frame(CMD_BEGIN, headers)
     return transaction

 def subscribe(self, destination, id=None, ack='auto', headers={}, **keyword_headers):
     assert destination is not None, "'destination' is required"
     headers = utils.merge_headers([headers, keyword_headers])
     headers[HDR_DESTINATION] = destination
     if id:
         headers[HDR_ID] = id
     headers[HDR_ACK] = ack
     self.send_frame(CMD_SUBSCRIBE, headers)

 def unsubscribe(self, destination=None, id=None, headers={}, **keyword_headers):
     assert id is not None or destination is not None, "'id' or 'destination' is required"
     headers = utils.merge_headers([headers, keyword_headers])
     if id:
         headers[HDR_ID] = id
     if destination:
         headers[HDR_DESTINATION] = destination
     self.send_frame(CMD_UNSUBSCRIBE, headers)

 def unsubscribe(self, id, headers={}, **keyword_headers):
     """
     Unsubscribe from a destination by its unique identifier
     
     :param id: the unique identifier to unsubscribe from
     :param headers: additional headers to send with the unsubscribe
     """
     assert id is not None, "'id' is required"
     headers = utils.merge_headers([headers, keyword_headers])
     headers[HDR_ID] = id
     self.send_frame(CMD_UNSUBSCRIBE, headers)

 def send(self, destination, body, content_type=None, headers={}, **keyword_headers):
     assert destination is not None, "'destination' is required"
     assert body is not None, "'body' is required"
     headers = utils.merge_headers([headers, keyword_headers])
     headers[HDR_DESTINATION] = destination
     if content_type:
         headers[HDR_CONTENT_TYPE] = content_type
     body = encode(body)
     #if HDR_CONTENT_LENGTH not in headers:
     #    headers[HDR_CONTENT_LENGTH] = len(body)
     self.send_frame(CMD_SEND, headers, body)

    def abort(self, transaction, headers={}, **keyword_headers):
        """
        Abort a transaction.

        :param transaction: the identifier of the transaction
        :param headers: a map of any additional headers the broker requires
        :param keyword_headers: any additional headers the broker requires
        """
        assert transaction is not None, "'transaction' is required"
        headers = utils.merge_headers([headers, keyword_headers])
        headers[HDR_TRANSACTION] = transaction
        self.send_frame(CMD_ABORT, headers)

    def disconnect(self, receipt=str(uuid.uuid4()), headers={}, **keyword_headers):
        """
        Disconnect from the server.

        :param receipt: the receipt to use (once the server acknowledges that receipt, we're
            officially disconnected)
        :param headers: a map of any additional headers the broker requires
        :param keyword_headers: any additional headers the broker requires
        """
        headers = utils.merge_headers([headers, keyword_headers])
        if receipt:
            headers[HDR_RECEIPT] = receipt
        self.send_frame(CMD_DISCONNECT, headers)

 def subscribe(self, destination, id, ack='auto', headers={}, **keyword_headers):
     """
     Subscribe to a destination
     
     :param destination: the topic or queue to subscribe to
     :param id: the identifier to uniquely identify the subscription
     :param ack: either auto, client or client-individual (see https://stomp.github.io/stomp-specification-1.2.html#SUBSCRIBE for more info)
     :param headers: any additional headers to send with the subscription
     """
     assert destination is not None, "'destination' is required"
     assert id is not None, "'id' is required"
     headers = utils.merge_headers([headers, keyword_headers])
     headers[HDR_DESTINATION] = destination
     headers[HDR_ID] = id
     headers[HDR_ACK] = ack
     self.send_frame(CMD_SUBSCRIBE, headers)

    def begin(self, transaction=None, headers={}, **keyword_headers):
        """
        Begin a transaction.

        :param transaction: the identifier for the transaction (optional - if not specified
            a unique transaction id will be generated)
        :param headers: a map of any additional headers the broker requires
        :param keyword_headers: any additional headers the broker requires

        :return: the transaction id
        """
        headers = utils.merge_headers([headers, keyword_headers])
        if not transaction:
            transaction = str(uuid.uuid4())
        headers[HDR_TRANSACTION] = transaction
        self.send_frame(CMD_BEGIN, headers)
        return transaction

    def connect(self, username=None, passcode=None, wait=False, headers={}, **keyword_headers):
        cmd = CMD_CONNECT
        headers = utils.merge_headers([headers, keyword_headers])
        headers[HDR_ACCEPT_VERSION] = self.version

        if username is not None:
            headers[HDR_LOGIN] = username

        if passcode is not None:
            headers[HDR_PASSCODE] = passcode

        self.send_frame(cmd, headers)

        if wait:
            self.transport.wait_for_connection()
            if self.transport.connection_error:
                raise ConnectFailedException()

    def disconnect(self, receipt=None, headers=None, **keyword_headers):
        """
        Disconnect from the server.

        :param str receipt: the receipt to use (once the server acknowledges that receipt, we're
            officially disconnected; optional - if not specified a unique receipt id will
            be generated)
        :param dict headers: a map of any additional headers the broker requires
        :param keyword_headers: any additional headers the broker requires
        """
        if not self.transport.is_connected():
            log.debug('Not sending disconnect, already disconnected')
            return
        headers = utils.merge_headers([headers, keyword_headers])
        rec = receipt or utils.get_uuid()
        headers[HDR_RECEIPT] = rec
        self.set_receipt(rec, CMD_DISCONNECT)
        self.send_frame(CMD_DISCONNECT, headers)

    def send(self, destination, body, content_type=None, headers=None, **keyword_headers):
        """
        Send a message to a destination.

        :param str destination: the destination of the message (e.g. queue or topic name)
        :param body: the content of the message
        :param str content_type: the content type of the message
        :param dict headers: a map of any additional headers the broker requires
        :param keyword_headers: any additional headers the broker requires
        """
        assert destination is not None, "'destination' is required"
        assert body is not None, "'body' is required"
        headers = utils.merge_headers([headers, keyword_headers])
        headers[HDR_DESTINATION] = destination
        if content_type:
            headers[HDR_CONTENT_TYPE] = content_type
        if self.auto_content_length and body and HDR_CONTENT_LENGTH not in headers:
            headers[HDR_CONTENT_LENGTH] = len(body)
        self.send_frame(CMD_SEND, headers, body)

 def send(self, destination, body, content_type=None, headers={}, **keyword_headers):
     """
     Send a message to a destination in the messaging system (as per https://stomp.github.io/stomp-specification-1.2.html#SEND)
     
     :param destination: the destination (such as a message queue - for example '/queue/test' - or a message topic)
     :param body: the content of the message
     :param content_type: the MIME type of message 
     :param headers: additional headers to send in the message frame
     """
     assert destination is not None, "'destination' is required"
     assert body is not None, "'body' is required"
     headers = utils.merge_headers([headers, keyword_headers])
     headers[HDR_DESTINATION] = destination
     if content_type:
         headers[HDR_CONTENT_TYPE] = content_type
     body = encode(body)
     if body and HDR_CONTENT_LENGTH not in headers:
         headers[HDR_CONTENT_LENGTH] = len(body)
     self.send_frame(CMD_SEND, headers, body)

 def disconnect(self, receipt=str(uuid.uuid4()), headers={}, **keyword_headers):
     headers = utils.merge_headers([headers, keyword_headers])
     if receipt:
         headers[HDR_RECEIPT] = receipt
     self.send_frame(CMD_DISCONNECT, headers)

 def commit(self, transaction=None, headers={}, **keyword_headers):
     assert transaction is not None, "'transaction' is required"
     headers = utils.merge_headers([headers, keyword_headers])
     headers[HDR_TRANSACTION] = transaction
     self.send_frame('COMMIT', headers)

 def abort(self, transaction, headers={}, **keyword_headers):
     assert transaction is not None, "'transaction' is required"
     headers = utils.merge_headers([headers, keyword_headers])
     headers[HDR_TRANSACTION] = transaction
     self.send_frame(CMD_ABORT, headers)