issue with server-client example

[epifanio]

@ashishrv thanks for this documentation.
I was trying to run the client-server example, but after I run the two scripts pairserver.py and pairclient.py I can't see the messages printed in the shell. Nothing is printed. The scripts are:

• pairserver.py

import zmq
import random
import sys
import time

port = "5556"

if len(sys.argv) > 1:
    port =  sys.argv[1]
    int(port)

context = zmq.Context()
socket = context.socket(zmq.PAIR)
socket.bind("tcp://*:%s" % port)

while True:
    socket.send_string("Server message to client3")
    msg = socket.recv()
    print(msg)
    time.sleep(1)

• pairclient.py

import zmq
import random
import sys
import time

port = "5556"

if len(sys.argv) > 1:
    port =  sys.argv[1]
    int(port)

context = zmq.Context()
socket = context.socket(zmq.PAIR)
socket.connect("tcp://localhost:%s" % port)

while True:
    msg = socket.recv()
    print(msg)
    socket.send_string("client message to server1")
    socket.send_string("client message to server2")
    time.sleep(1)

My python and pyzmq versions are:

Python 3.6.1 (default, Apr  4 2017, 09:40:21) 
[GCC 4.2.1 Compatible Apple LLVM 8.1.0 (clang-802.0.38)] on darwin
>>> import zmq
>>> zmq.__version__
'16.0.2'

[MrYsLab]

@epifanio I just ran the code you posted above and it works both on a Raspberry Pi and on Ubuntu 17.04. I am using the same versions of python and zmq as you on the raspberry pi. On Ubuntu I am using python 3.5.3.

[epifanio]

Hi @MrYsLab, thanks for confirming it does for you.
I tried on an other machine:
laptop runnin osx as client and a remote debian as server. I allowed the firewall on the server and used its real IP and it works just fine.

Now I wander way is not working on my other laptop (same osx version) , I'll check if has something to do with the fireall .. any clue on how to debug "a denied connection" ?

[epifanio]

I just tried on a different machine here in the office and it works fine! I'll investigate why on my laptop is not working .. Thanks for confirming that it should work. I

[epifanio]

Oh! seems I found the problem. This I guess has to do with my lack of knowledge about zmq and tcp /socket connection I guess...

To reproduce the problem:

• run the server script
• run the client script

• it should work, then:

• stop the client (ctr+c)
• restart the client -> doesn't work anymore. I need to restart the server and re-run the client to have it working again.

If I stop/restart the server (and leave the client running) I can see it still work fine.
If I stop/restart the client .. it doesn't, the server doesn't receive the pessage anymore.
i need to stop/restart the server to see the new messages coming.

I think the code needs to be changed to handle "N" client to connect/disconnect .. I'll try to go through the documents to find a solution. Thanks for any pointer, a help will be great!

[MrYsLab]

I don't have much experience with pairs. I use pub/sub with a forwarder . The Python Banyan library makes extensive use of this pattern.

[epifanio]

Thanks for your help @MrYsLab.
Of course, it was my fault in implementing the code using the wrong socket type.
I changed the code to use: zmq.REQ and zmq.REP for the client and server.

• client.py

import zmq
import random
import sys
import time

port = "5556"

if len(sys.argv) > 1:
    port =  sys.argv[1]
    int(port)

context = zmq.Context()
socket = context.socket(zmq.REQ)
socket.connect("tcp://0.0.0.0:%s" % port)

messaggio='ls -la'
socket.send_string(messaggio)
msg = socket.recv()
print(msg)

• server.py

import os
import sys
import subprocess
import zmq
import random
import time

port = "5556"

if len(sys.argv) > 1:
    port =  sys.argv[1]
    int(port)

context = zmq.Context()
socket = context.socket(zmq.REP)
socket.bind("tcp://*:%s" % port)

while True:
    msg = socket.recv()
    print('client meesage: ', msg)
    gmsg=msg.split()
    try:
        proc = subprocess.Popen(gmsg, stdout=subprocess.PIPE)
        output = proc.stdout.read()
        socket.send_string(output)
    except:
        pass
    time.sleep(0.5)

Now it works as expected.