Introduction to Sockets in Python

What are Sockets?

A socket is an endpoint for sending and receiving data across a network. Sockets enable communication between devices, applications, or servers over the TCP/IP protocol. Python provides the socket module to create and manage sockets for networking.

Types of Sockets

Stream Sockets (TCP) – Reliable, connection-oriented communication.
Datagram Sockets (UDP) – Unreliable, connectionless communication.
Raw Sockets – Direct packet-level communication (used in security & network analysis).

Creating a Simple TCP Server and Client in Python

Step 1: Import the Socket Module

The socket module provides the necessary functions for working with sockets.

import socket

TCP Server Example

A TCP server listens for incoming client connections and responds to their requests.

Step 2: Create a TCP Server

import socket

server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)  # TCP socket
server_socket.bind(("127.0.0.1", 8080))  # Bind to localhost and port 8080
server_socket.listen(5)  # Allow up to 5 connections
print("Server is listening...")

while True:
    client_socket, client_address = server_socket.accept()  # Accept connection
    print(f"Connection established with {client_address}")
    
    client_socket.send(b"Hello from Server!")  # Send a message
    data = client_socket.recv(1024)  # Receive data
    print("Received:", data.decode())

    client_socket.close()  # Close client connection

The server listens for connections and communicates with the client.

TCP Client Example

A TCP client connects to the server and sends data.

Step 3: Create a TCP Client

import socket

client_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
client_socket.connect(("127.0.0.1", 8080))  # Connect to the server

message = client_socket.recv(1024)  # Receive data from the server
print("Server says:", message.decode())

client_socket.send(b"Hello from Client!")  # Send a message
client_socket.close()  # Close the connection

The client connects to the server and exchanges messages.

UDP Server and Client Example

UDP is faster but does not guarantee message delivery.

UDP Server

import socket

udp_server = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
udp_server.bind(("127.0.0.1", 8081))  # Bind to port 8081
print("UDP Server is listening...")

while True:
    data, addr = udp_server.recvfrom(1024)  # Receive message
    print(f"Received from {addr}: {data.decode()}")
    udp_server.sendto(b"Hello from UDP Server!", addr)  # Send response

UDP Client

import socket

udp_client = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
udp_client.sendto(b"Hello from UDP Client!", ("127.0.0.1", 8081))  # Send message

response, _ = udp_client.recvfrom(1024)  # Receive response
print("Server says:", response.decode())

udp_client.close()

UDP is useful for real-time applications like gaming and video streaming.

Handling Multiple Clients with Threads

A server can handle multiple clients using multithreading.

Multi-Client TCP Server

import socket
import threading

def handle_client(client_socket, client_address):
    print(f"Connection from {client_address}")
    client_socket.send(b"Hello from Multi-Threaded Server!")
    data = client_socket.recv(1024)
    print(f"Received from {client_address}: {data.decode()}")
    client_socket.close()

server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.bind(("127.0.0.1", 8082))
server_socket.listen(5)
print("Server is listening for multiple clients...")

while True:
    client_socket, client_address = server_socket.accept()
    thread = threading.Thread(target=handle_client, args=(client_socket, client_address))
    thread.start()

This allows handling multiple clients simultaneously.

Sending Large Data using Sockets

When sending large amounts of data, it is best to split data into chunks.

def send_large_data(sock, data):
    chunk_size = 1024
    for i in range(0, len(data), chunk_size):
        sock.send(data[i:i+chunk_size])

Ensures efficient transmission of large files or messages.

Applications of Sockets

✔ Web servers – Handle HTTP requests
✔ Chat applications – Real-time messaging
✔ File transfer – Sending & receiving files over networks
✔ IoT – Communication between smart devices
✔ Cybersecurity – Penetration testing & network scanning