TCP client/server with Python

Welcome to the next pikoTutorial !

The minimal TCP server

A TCP server listens for incoming connections on a specified port and communicates with clients over that connection.

Python

from socket import socket, AF_INET, SOCK_STREAM from argparse import ArgumentParser # define command line interface parser = ArgumentParser() parser.add_argument('-ip', help='IP') parser.add_argument('-server_port', type=int, help='Server port') # parse command line options args = parser.parse_args() # create a TCP socket with socket(AF_INET, SOCK_STREAM) as server_socket:  # bind server with a specific network address  # which consists of IP and port number  server_socket.bind((args.ip, args.server_port))  # start listening for requests  server_socket.listen()  print(f'TCP server up and listening on {args.ip}:{args.server_port}')  # accept an incoming connection  client_socket, client_address = server_socket.accept()  print(f'Connection established with {client_address[0]}:{client_address[1]}')  # receive data from the client  data: bytes = client_socket.recv(1024)  print(f'Received message: {data.decode()}')  # send response to client  client_socket.send('Message received'.encode())

The minimal TCP client

A TCP client establishes a connection with a server, sends data, and receives responses.

Python

from socket import socket, AF_INET, SOCK_STREAM from argparse import ArgumentParser # define command line interface parser = ArgumentParser() parser.add_argument('-ip', help='IP') parser.add_argument('-server_port', type=int, help='Server port') # parse command line options args = parser.parse_args() # create a TCP socket with socket(AF_INET, SOCK_STREAM) as client_socket:  # connect to the server  client_socket.connect((args.ip, args.server_port))  # send message to the server  print(f'Sending message to {args.ip}:{args.server_port}')  client_socket.send('Hello from TCP client!'.encode())  # receive response from server  data: bytes = client_socket.recv(1024)  print(f'Received response from server: {data.decode()}')

Bidirectional communication

You can now create the following setup:

Note for beginners: on the image above, I didn’t put any specific number of the client’s port because in the first example that number is assigned by operating system at random. If you want to know how to specify the client’s port as well, you’ll find it in the second example.

Run server with the command below:

Bash

python3 server.py -ip 127.0.0.1 -server_port 12345

And the client:

Bash

python3 client.py -ip 127.0.0.1 -server_port 12345

You’ll see the following output in the server console:

TCP server up and listening on 127.0.0.1:12345 Connection established with 127.0.0.1:36486 Received message: Hello from TCP client!

And on the client side, you’ll get:

Sending message to 127.0.0.1:12345 Received response from server: Message received

Specifying client’s port

In the previous example, although we defined the server port, the client’s port was randomly assigned by the operating system. If you need to specify the client’s port, you can bind it manually before connecting to the server:

Python

from socket import socket, AF_INET, SOCK_STREAM from argparse import ArgumentParser # define command line interface parser = ArgumentParser() parser.add_argument('-ip', help='IP') parser.add_argument('-server_port', type=int, help='Server port') parser.add_argument('-client_port', type=int, help='Client port') # parse command line options args = parser.parse_args() # create a TCP socket with socket(AF_INET, SOCK_STREAM) as client_socket:  # bind client to the specific address  client_socket.bind((args.ip, args.client_port))  # connect to the server  client_socket.connect((args.ip, args.server_port))  # send message to the server  print(f'Sending message to {args.ip}:{args.server_port}')  client_socket.send('Hello from TCP client!'.encode())  # receive response from server  data: bytes = client_socket.recv(1024)  print(f'Received response from server: {data.decode()}')

If you run the above script with the following command:

Bash

python3 client.py -ip 127.0.0.1 -server_port 12345 -client_port 56789

You’ll get the connection as presented on the image below:

You’ll also see the client’s port number in the server’s logs:

TCP server up and listening on 127.0.0.1:12345 Connection established with 127.0.0.1:56789 Received message: Hello from TCP client!