ZMQ REP Message Sink

The ZMQ REP Message Sink block receives async messages and sends them to a ZMQ REP socket. This block will connect to a ZMQ REQ Message Source.
The zeromq.org website says:
"The REQ-REP socket pair is in lockstep. The client issues zmq_send() and then zmq_recv(), in a loop (or once if that's all it needs). Doing any other sequence (e.g., sending two messages in a row) will result in a return code of -1 from the send or recv call." Likewise, the server "issues zmq_recv() and then zmq_send() in that order, as often as it needs to."

Parameters

(R): Run-time adjustable

Address

ZMQ socket address specifier. The format of the address is tcp://*:port where * should be 127.0.0.1 for localhost.

Timeout

Socket timeout in milliseconds, default is 100ms.

Example Flowgraph

Inter-flowgraph

Request/Reply pairs can be used on one, or two separate, flowgraphs to exchange messages.

External Python client (receive only)

An external Python program can receive messages from a ZMQ REP Message Sink block. An example flowgraph and Python code follow.

The Python client code looks like this:

#!/usr/bin/env python3
# -*- coding: utf-8 -*-

#   The REQest / REPly nomenclature of the GNU Radio message blocks is from
#   the perspective of the flowgraph. So, to send a 'request' to GNU Radio, the message
#   must be sent as a 'reply' from the Python client, Likewise, a 'reply' from GNU Radio
#   must be received as a 'request' to the Python client! Therefore, send on the reply socket
#   and receive on the request socket.
#
#   The zeromq.org website says:
#   "The REQ-REP socket pair is in lockstep. The client issues zmq_send() and then zmq_recv(),
#   in a loop (or once if that's all it needs). Doing any other sequence (e.g., sending two messages in a row)
#   will result in a return code of -1 from the send or recv call." Likewise, the server "issues zmq_recv() 
#   and then zmq_send() in that order, as often as it needs to."
#
#   To conform to that requirement, a non-standard "kludge" is used (see below).

import zmq
import pmt

def main():
    zmq_context = zmq.Context()
    zmq_sock = zmq_context.socket(zmq.REQ)
    zmq_sock.connect("tcp://127.0.0.1:50247")
    while(True):
         zmq_sock.send_string("\x01\x00\x00\x00")    # this is the non-standard "kludge"
         msg = zmq_sock.recv()
         print (pmt.to_python(pmt.deserialize_str(msg)))
if __name__ == '__main__':
    main()

GNU Radio as a server

If the GNU Radio flowgraph(s) is configured as a server, the REQ message is processed by the flowgraph and a message is sent back in a REP message as the response. See ZMQ_REQ_Message_Source#GNU_Radio_as_a_server for details.

Source Files

C++ files

TODO

Header files

TODO

Public header files

TODO

Block definition

TODO