Network programming allows programs to send or receive data through the network. In Python, network programming primarily uses the socket module.

1. Basics of Network Programming

Network programming enables programs to send data to other programs through a network or receive data from other programs. In Python, the socket module is mainly used for this purpose.

2. TCP Server Example

import socket

# Create a socket object
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Bind the port
host = 'localhost'
port = 12345
server_socket.bind((host, port))

# Listen for connections
server_socket.listen(5)
print('Server listening on port:', port)

while True:
    # Establish client connection
    client_socket, addr = server_socket.accept()
    print('Got connection from', addr)

    # Receive message from client
    msg = client_socket.recv(1024).decode()
    print('Message from client:', msg)

    # Send response
    response = 'Thank you for connecting'
    client_socket.send(response.encode())

    # Close connection
    client_socket.close()

This simple TCP server listens on port 12345. When a client connects, it prints the client's address, receives a message, sends a response, and then closes the connection.

3. TCP Client Example

import socket

# Create a socket object
client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Connect to server
host = 'localhost'
port = 12345
client_socket.connect((host, port))

# Send message
msg = 'Hello, server!'
client_socket.send(msg.encode())

# Receive response
response = client_socket.recv(1024).decode()
print('Response from server:', response)

# Close connection
client_socket.close()

This simple TCP client connects to the server, sends a message, receives the server’s response, and then closes the connection.

4. UDP Server Example

import socket

# Create a socket object
server_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

# Bind the port
host = 'localhost'
port = 12345
server_socket.bind((host, port))

print('Server listening on port:', port)

while True:
    # Receive message from client
    msg, addr = server_socket.recvfrom(1024)
    print('Message from client:', msg.decode(), 'at', addr)

    # Send response
    response = 'Thank you for your message'
    server_socket.sendto(response.encode(), addr)

This simple UDP server listens on port 12345, receives messages from clients, and sends a response.

5. UDP Client Example

import socket

# Create a socket object
client_socket = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)

# Send message
host = 'localhost'
port = 12345
msg = 'Hello, server!'
client_socket.sendto(msg.encode(), (host, port))

# Receive response
response, addr = client_socket.recvfrom(1024)
print('Response from server:', response.decode())

# Close connection
client_socket.close()

This simple UDP client sends a message to the server, receives a response, and closes the connection.

6. Multi-threaded TCP Server Example

import socket
import threading

def handle_client(client_socket, addr):
    print('Got connection from', addr)

    msg = client_socket.recv(1024).decode()
    print('Message from client:', msg)

    response = 'Thank you for connecting'
    client_socket.send(response.encode())

    client_socket.close()

# Create a socket object
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Bind the port
host = 'localhost'
port = 12345
server_socket.bind((host, port))

# Listen for connections
server_socket.listen(5)
print('Server listening on port:', port)

while True:
    # Establish client connection
    client_socket, addr = server_socket.accept()

    # Handle client connection in a new thread
    thread = threading.Thread(target=handle_client, args=(client_socket, addr))
    thread.start()

This server uses multi-threading to handle multiple client connections, with each client handled in a separate thread.

7. Non-blocking I/O TCP Server Example

import socket
import select

# Create a socket object
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)

# Set the socket to non-blocking mode
server_socket.setblocking(False)

# Bind the port
host = 'localhost'
port = 12345
server_socket.bind((host, port))

# Listen for connections
server_socket.listen(5)
print('Server listening on port:', port)

inputs = [server_socket]
outputs = []

while True:
    readable, writable, exceptional = select.select(inputs, outputs, inputs)

    for sock in readable:
        if sock == server_socket:
            # Establish client connection
            client_socket, addr = server_socket.accept()
            client_socket.setblocking(False)
            inputs.append(client_socket)
            print('Got connection from', addr)
        else:
            # Receive message from client
            data = sock.recv(1024)
            if data:
                print('Message from client:', data.decode())
                sock.send(data.upper())
            else:
                # Client disconnected
                print('Client disconnected')
                inputs.remove(sock)
                sock.close()

This non-blocking TCP server uses the select module to handle multiple client connections simultaneously, improving the program's responsiveness.

8. HTTP Protocol Example

from http.server import HTTPServer, BaseHTTPRequestHandler

class SimpleHTTPRequestHandler(BaseHTTPRequestHandler):
    def do_GET(self):
        self.send_response(200)
        self.end_headers()
        message = 'Hello, World!'
        self.wfile.write(message.encode())

# Create HTTP server
server_address = ('localhost', 8000)
httpd = HTTPServer(server_address, SimpleHTTPRequestHandler)

print('Starting simple HTTP server...')
httpd.serve_forever()

This simple HTTP server listens on port 8000 and responds with “Hello, World!” when it receives a GET request.

9. Sending HTTP Request Example

First, install the requests library:

pip install requests

Then, write the following code:

import requests

url = 'http://localhost:8000'
response = requests.get(url)

print('Response status code:', response.status_code)
print('Response content:', response.text)

This code sends a GET request to the local HTTP server and prints the status code and content of the response.

10. WebSocket Programming Example

First, install the websockets library:

pip install websockets

Then, write the following code:

import asyncio
import websockets

async def echo(websocket, path):
    async for message in websocket:
        print(f'Received message: {message}')
        await websocket.send(message)

# Create WebSocket server
start_server = websockets.serve(echo, 'localhost', 8765)

asyncio.get_event_loop().run_until_complete(start_server)
asyncio.get_event_loop().run_forever()

This simple WebSocket server listens on port 8765 and echoes any message it receives.

11. WebSocket Client Example

import asyncio
import websockets

async def send_message():
    uri = 'ws://localhost:8765'
    async with websockets.connect(uri) as websocket:
        message = 'Hello, WebSocket!'
        await websocket.send(message)
        print(f'Sent message: {message}')
        response = await websocket.recv()
        print(f'Received response: {response}')

asyncio.get_event_loop().run_until_complete(send_message())

This simple WebSocket client connects to the server, sends a message, and receives a response from the server.