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."
- ZMQ socket address specifier. The format of the address is
tcp://*:portwhere * should be 127.0.0.1 for localhost.
- Socket timeout in milliseconds, default is 100ms.
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.
- C++ files
- Header files
- Public header files
- Block definition