ZMQ REQ Message Source

The ZMQ REQ Message Source block receives messages from a ZMQ REQ socket and outputs async messages. This block will connect to a ZMQ REP Message Sink.
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 (send only)

An external Python program can send messages to a ZMQ REQ Message Source block. An example flowgraph and Python code follow.

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. An example flowgraph and Python code follow.

The Embedded Python block "Server demo" contains the following code:

from gnuradio import gr
import pmt

inputText = ""

class my_sync_block (gr.sync_block):
#  accepts message string from input port
#  capitalizes the string
#  sends message to output port
    def __init__(self):
        gr.sync_block.__init__(self,
            name = "Server demo",
            in_sig = None,
            out_sig = None)
        self.message_port_register_in(pmt.intern('msg_in'))
        self.message_port_register_out(pmt.intern('msg_out'))
        self.set_msg_handler(pmt.intern('msg_in'), self.handle_msg)

    def handle_msg(self, msg):
        global inputText
        inputText = pmt.symbol_to_string (msg)
        # print (inputText)
        if (len (inputText) > 0):
            #  capitalize the string
            outputText = inputText.upper()
            # print (outputText)
            #  Send reply back to client
            self.message_port_pub(pmt.intern('msg_out'), pmt.intern(outputText))

    def work(self, input_items, output_items):
        # with no data ports, there is nothing to do
        return (0)

Source Files

C++ files

TODO

Header files

TODO

Public header files

TODO

Block definition

TODO