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  where * should be 127.0.0.1 for localhost.
 * Note: If the Source and Sink blocks are on two different computers on the same LAN, then the IP and port number of the Sink block must be specified on each end of that connection. For example, if the Sink is on IP 192.168.2.14:5678 and the Source is on IP 192.168.2.5, both Source and Sink blocks must specify the Sink IP and port (192.168.2.14:5678).


 * Timeout
 * Socket timeout in milliseconds, default is 100ms.

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.



The Python client code looks like this:


 * 1) !/usr/bin/python3
 * 2) -*- coding: utf-8 -*-


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

import datetime import time import signal import pmt import zmq

_debug = 1         # set to zero to turn off diagnostics

_PROTOCOL = "tcp://" _SERVER = "127.0.0.1"         # localhost _PORT = ":50123" _ADDR = _PROTOCOL + _SERVER + _PORT if (_debug): print ("zmqREP connecting to:", _ADDR) context = zmq.Context if (_debug): assert (context) sock = context.socket (zmq.REP) if (_debug): assert (sock) rc = sock.bind (_ADDR) if (_debug): assert (rc == None)
 * 1) create socket

while True: _tim = datetime.datetime.now _out = str (_tim) try: sock.recv                               # this is the non-standard "kludge" sock.send (pmt.serialize_str(pmt.to_pmt(_out)))      # send on the 'reply' socket time.sleep(5) except KeyboardInterrupt: if (_debug): print (" Interrupt received. shutting down.") # clean up       sock.close context.term exit

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. Note that two different ports are used.



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

from gnuradio import gr import pmt

class my_sync_block (gr.sync_block): 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)
 * 1)  accepts message string from input port
 * 2)  capitalizes the string
 * 3)  sends message to output port

def handle_msg(self, msg): 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)

The Python client code looks like this:


 * 1) !/usr/bin/python3
 * 2) -*- coding: utf-8 -*-


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

import datetime import time import signal import pmt import zmq

_debug = 1         # set to zero to turn off diagnostics

_PROTOCOL = "tcp://" _SERVER = "127.0.0.1"         # localhost _REQ_PORT = ":49202" _REQ_ADDR = _PROTOCOL + _SERVER + _REQ_PORT if (_debug): print ("'zmq_REQ_client' connecting to:", _REQ_ADDR) req_context = zmq.Context if (_debug): assert (req_context) req_sock = req_context.socket (zmq.REQ) if (_debug): assert (req_sock) rc = req_sock.connect (_REQ_ADDR) if (_debug): assert (rc == None)
 * 1) create a REQ socket

_PROTOCOL = "tcp://" _SERVER = "127.0.0.1"         # localhost _REP_PORT = ":49201" _REP_ADDR = _PROTOCOL + _SERVER + _REP_PORT if (_debug): print ("'zmq_REQ_client' binding to:", _REP_ADDR) rep_context = zmq.Context if (_debug): assert (rep_context) rep_sock = rep_context.socket (zmq.REP) if (_debug): assert (rep_sock) rc = rep_sock.bind (_REP_ADDR) if (_debug): assert (rc == None)
 * 1) create a REP socket

while True: # generate an outgoing message _tim = datetime.datetime.now _out = ("Local time is " + str (_tim)) try: print(_out) rep_sock.recv                                       # this is the non-standard "kludge" rep_sock.send (pmt.serialize_str(pmt.to_pmt(_out)))   # send on the 'reply' socket time.sleep(1) req_sock.send_string("\x01\x00\x00\x00")       # this is the non-standard "kludge" msg = req_sock.recv                          # receive on the 'request' socket print (pmt.to_python(pmt.deserialize_str(msg))) time.sleep(4) except KeyboardInterrupt: if (_debug): print (" Interrupt received. shutting down.") # clean up       req_sock.close req_context.term rep_sock.close rep_context.term exit

Source Files

 * C++ files
 * TODO


 * Header files
 * TODO


 * Public header files
 * TODO


 * Block definition
 * TODO