After testing with basic socket APIs in Python, let us create a socket server and client now. Here, you will have the chance to utilize your basic knowledge gained in the previous recipes.
In this example, a server will echo whatever it receives from the client. We will use the Python argparse module to specify the TCP port from a command line. Both the server and client script will take this argument.
First, we create the server. We start by creating a TCP socket object. Then, we set the reuse address so that we can run the server as many times as we need. We bind the socket to the given port on our local machine. In the listening stage, we make sure we listen to multiple clients in a queue using the backlog argument to the listen() method. Finally, we wait for the client to be connected and send some data to the server. When the data is received, the server echoes back the data to the client.
Listing 1.13a shows how to write a simple echo client/server application as follows:
#!/usr/bin/env python
# Python Network Programming Cookbook -- Chapter – 1
# This program is optimized for Python 2.7. It may run on any
# other Python version with/without modifications.
import socket
import sys
import argparse
host = 'localhost'
data_payload = 2048
backlog = 5
def echo_server(port):
""" A simple echo server """
# Create a TCP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# Enable reuse address/port
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
# 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)
# Listen to clients, backlog argument specifies the max no. of queued connections
sock.listen(backlog)
while True:
print "Waiting to receive message from client"
client, address = sock.accept()
data = client.recv(data_payload)
if data:
print "Data: %s" %data
client.send(data)
print "sent %s bytes back to %s" % (data, address)
# end connection
client.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_server(port)On the client-side code, we create a client socket using the port argument and connect to the server. Then, the client sends the message, Test message. This will be echoed to the server, and the client immediately receives the message back in a few segments. Here, two try-except blocks are constructed to catch any exception during this interactive session.
Listing 1-13b shows the echo client as follows:
#!/usr/bin/env python
# Python Network Programming Cookbook -- Chapter – 1
# This program is optimized for Python 2.7. It may run on any
# other Python version with/without modifications.
import socket
import sys
import argparse
host = 'localhost'
def echo_client(port):
""" A simple echo client """
# Create a TCP/IP socket
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# Connect the socket to the server
server_address = (host, port)
print "Connecting to %s port %s" % server_address
sock.connect(server_address)
# Send data
try:
# Send data
message = "Test message. This will be echoed"
print "Sending %s" % message
sock.sendall(message)
# Look for the response
amount_received = 0
amount_expected = len(message)
while amount_received < amount_expected:
data = sock.recv(16)
amount_received += len(data)
print "Received: %s" % data
except socket.errno, e:
print "Socket error: %s" %str(e)
except Exception, e:
print "Other exception: %s" %str(e)
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_13a_echo_server.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_13b_echo_client.py --port=9900 Connecting to localhost port 9900 Sending Test message. This will be echoed Received: Test message. Th Received: is will be echoe Received: d Closing connection to the server
Upon connecting to the localhost, the client server will also print the following message:
Data: Test message. This will be echoed sent Test message. This will be echoed bytes back to ('127.0.0.1', 42961) Waiting to receive message from client