As we have developed a simple TCP server and client in the previous recipe, we will now look at how to develop the same with UDP.

This recipe is similar to the previous one, except this one is with UDP. The method recvfrom() reads the messages from the socket and returns the data and the client address.

Listing 1.14a shows how to write a simple UDP echo client/server application as follows:

#!/usr/bin/env python 
# Python Network Programming Cookbook,
   Second Edition -- Chapter - 1 
# This program is optimized for Python 2.7.12
   and Python 3.5.2. 
# It may run on any other version with/without 
  modifications. 
 
import socket 
import sys 
import argparse 
 
host = 'localhost' 
data_payload = 2048 
 
def echo_server(port): 
    """ A simple echo server """ 
    # Create a UDP socket 
    sock = socket.socket(socket.AF_INET, 
                         socket.SOCK_DGRAM) 
 
    # Bind the socket to the port 
    server_address = (host, port) 
    print ("Starting up echo server 
            on %s port %s" % server_address) 
 
    sock.bind(server_address) 
 
    while True: 
        print ("Waiting to receive message
                 from client") 
        data, address = sock.
                        recvfrom(data_payload) 
     
        print ("received %s bytes 
                from %s" % (len(data), address)) 
        print ("Data: %s" %data) 
     
        if data: 
            sent = sock.sendto(data, address) 
            print ("sent %s bytes back
                    to %s" % (sent, address)) 
 
 
if __name__ == '__main__': 
    parser = argparse.ArgumentParser
             (description='Socket Server Example') 
    parser.add_argument('--port', action="store", dest="port", type=int, required=True) 
    given_args = parser.parse_args()  
    port = given_args.port 
    echo_server(port) 
 

On the client side code, we create a client socket using the port argument and connect to the server, as we did in the previous recipe. Then, the client sends the message, Test message. This will be echoed, and the client immediately receives the message back in a few segments.

Listing 1-14b shows the echo client as follows:

#!/usr/bin/env python 
# Python Network Programming Cookbook, Second Edition -- Chapter - 1 
# This program is optimized for Python 2.7.12 and Python 3.5.2. 
# It may run on any other version with/without modifications. 
 
import socket 
import sys 
import argparse 
 
host = 'localhost' 
data_payload = 2048 
 
def echo_client(port): 
    """ A simple echo client """ 
    # Create a UDP socket 
    sock = socket.socket(socket.AF_INET, 
                         socket.SOCK_DGRAM) 
 
    server_address = (host, port) 
    print ("Connecting to %s port %s" % server_address) 
    message = 'This is the message.  It will be 
               repeated.' 
 
    try: 
 
        # Send data 
        message = "Test message. This will be 
                   echoed" 
        print ("Sending %s" % message) 
        sent = sock.sendto(message.encode
               ('utf-8'), server_address) 
 
        # Receive response 
        data, server = sock.recvfrom(data_payload) 
        print ("received %s" % data) 
 
    finally: 
        print ("Closing connection to the server") 
        sock.close() 
 
if __name__ == '__main__': 
    parser = argparse.ArgumentParser
             (description='Socket Server Example') 
    parser.add_argument('--port', action="store", dest="port", type=int, required=True) 
    given_args = parser.parse_args()  
    port = given_args.port 
    echo_client(port) 

In order to see the client/server interactions, launch the following server script in one console:

$ python 1_14a_echo_server_udp.py --port=9900 
Starting up echo server on localhost port 9900
Waiting to receive message from client
  

Now, run the client from another terminal as follows:

$ python 1_14b_echo_client_udp.py --port=9900 
Connecting to localhost port 9900
Sending Test message. This will be echoed
received Test message. This will be echoed
Closing connection to the server
    
  

Upon receiving the message from the client, the server will also print something similar to the following message:

received 33 bytes from ('127.0.0.1', 43542)
Data: Test message. This will be echoed
sent 33 bytes back to ('127.0.0.1', 43542)
Waiting to receive message from client