Socket Programming

Learn network programming with sockets, client-server communication, and protocol implementation.

Socket Programming Concepts

Socket

Endpoint for communication between processes

Types:

• Stream Socket (TCP)
• Datagram Socket (UDP)
• Raw Socket

Key Characteristics:

• IP address + Port number
• Bidirectional communication
• Network abstraction

Client-Server Model

Communication pattern with server listening and client connecting

Types:

• One-to-One
• One-to-Many
• Many-to-One

Key Characteristics:

• Server binds to port
• Client connects to server
• Request-response pattern

TCP Socket

Connection-oriented, reliable stream socket

Types:

• Blocking I/O
• Non-blocking I/O
• Multiplexed I/O

Key Characteristics:

• Connection establishment
• Reliable delivery
• Flow control

UDP Socket

Connectionless, unreliable datagram socket

Types:

• Unicast
• Multicast
• Broadcast

Key Characteristics:

• No connection setup
• Fast transmission
• No delivery guarantee

Socket API Functions

socket()

Create a new socket

Parameters:

• domain (AF_INET, AF_INET6)
• type (SOCK_STREAM, SOCK_DGRAM)
• protocol

Usage:

Creates endpoint for communication

bind()

Bind socket to address

Parameters:

• socket descriptor
• address structure
• address length

Usage:

Associates socket with local address and port

listen()

Listen for connections

Parameters:

• socket descriptor
• backlog queue size

Usage:

Marks socket as passive, ready to accept connections

accept()

Accept incoming connection

Parameters:

• socket descriptor
• client address
• address length

Usage:

Blocks until client connects, returns new socket

connect()

Connect to remote socket

Parameters:

• socket descriptor
• server address
• address length

Usage:

Establishes connection to server

send()/recv()

Send/receive data

Parameters:

• socket descriptor
• buffer
• length
• flags

Usage:

Transfer data over established connection

Socket Communication Simulator

Socket Type:

Server Port:

disconnected

Communication Log

No communication yet

Code Examples

Language:

Protocol:

Server Code

import socket
import threading

def handle_client(client_socket, address):
    print(f"Connection from {address}")
    
    while True:
        try:
            message = client_socket.recv(1024).decode('utf-8')
            if not message:
                break
            
            print(f"Received: {message}")
            
            # Echo the message back
            client_socket.send(f"Echo: {message}".encode('utf-8'))
            
        except Exception as e:
            print(f"Error: {e}")
            break
    
    client_socket.close()

def start_server():
    server = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    server.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
    
    server.bind(('localhost', 8080))
    server.listen(5)
    
    print("Server listening on port 8080...")
    
    while True:
        client_socket, address = server.accept()
        client_thread = threading.Thread(
            target=handle_client, 
            args=(client_socket, address)
        )
        client_thread.start()

if __name__ == "__main__":
    start_server()

Client Code

import socket

def start_client():
    client = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
    
    try:
        client.connect(('localhost', 8080))
        print("Connected to server")
        
        while True:
            message = input("Enter message (or 'quit' to exit): ")
            
            if message.lower() == 'quit':
                break
                
            client.send(message.encode('utf-8'))
            
            response = client.recv(1024).decode('utf-8')
            print(f"Server response: {response}")
            
    except Exception as e:
        print(f"Error: {e}")
    finally:
        client.close()

if __name__ == "__main__":
    start_client()