Day 02: Socket Programming - Book Shop System 📚

Overview 🎯

A simple client-server application using Python sockets to simulate an online bookshop where customers can view and purchase books.

Files 📁

• shopowner.py - Server program (Shop Owner)
• customer.py - Client program (Customer)

How It Works 🔄

Server Side (shopowner.py) 🏪

• Creates a socket and binds to host and port 8080
• Maintains a book inventory with name, price, and stock quantity
• Listens for client connections
• Handles three types of requests:
  • View Available Books: Sends formatted list of all books
  • Buy: Processes purchase requests, checks stock, calculates total price
  • Exit: Closes connection gracefully

Client Side (customer.py) 🛒

• Connects to the server using hostname and port
• Provides interactive menu:
  1. View Available Books
  2. Buy a Book (enter book name and quantity)
  3. Exit
• Sends requests to server and displays responses

How to Run 🚀

Terminal 1 - Start Server:

python shopowner.py

Terminal 2 - Start Client:

python customer.py

Enter the hostname shown by the server (or use localhost)

Key Concepts 💡

• Socket Programming: Network communication between client and server
• TCP Connection: Reliable connection-oriented protocol
• Request-Response Pattern: Client sends requests, server processes and responds
• Encoding/Decoding: Convert strings to bytes for network transmission

Sample Books 📖

• Harry Potter 1 - $2000.00 (5 in stock)
• Harry Potter 2 - $4000.00 (10 in stock)
• Abc - $400.00 (2 in stock)

Quick Code Reference 📝

Server Template (4 Steps) 🏪

# 1. Create & Bind
s = socket.socket()
s.bind((host, port))
s.listen(1)

# 2. Accept Connection
conn, addr = s.accept()

# 3. Receive & Send
msg = conn.recv(1024).decode()
conn.send(response.encode())

# 4. Close
conn.close()

Client Template (3 Steps) 🛒

# 1. Connect
s = socket.socket()
s.connect((host, port))

# 2. Send & Receive
s.send(message.encode())
response = s.recv(1024).decode()

# 3. Close
s.close()

Remember 🧠

• Server: Create → Bind → Listen → Accept → Recv/Send
• Client: Create → Connect → Send/Recv
• Always encode() before sending, decode() after receiving

Complete Code Snippets 💻

Full Server Code (Minimal Version) 🏪

import socket

# Setup
s = socket.socket()
host = socket.gethostname()
port = 8080
s.bind((host, port))
s.listen(1)

# Accept connection
conn, addr = s.accept()
print(f"{addr} connected")

# Communication loop
while True:
    msg = conn.recv(1024).decode()

    if msg == "Exit":
        conn.send("Goodbye!".encode())
        break

    # Process and respond
    response = f"Received: {msg}"
    conn.send(response.encode())

conn.close()

Full Client Code (Minimal Version) 🛒

import socket

# Connect to server
s = socket.socket()
host = input("Enter server hostname: ")
port = 8080
s.connect((host, port))

# Communication loop
while True:
    msg = input("Enter message (or 'Exit'): ")
    s.send(msg.encode())

    response = s.recv(1024).decode()
    print("Server:", response)

    if msg == "Exit":
        break

s.close()

Important Code Patterns 🔑

Handling Multiple Messages:

# Server receives multiple inputs
msg1 = conn.recv(1024).decode()
msg2 = conn.recv(1024).decode()
msg3 = conn.recv(1024).decode()

Working with Lists/Data:

# Send formatted data
for item in book_list:
    response += f"{item[0]} - ${item[1]}\n"
conn.send(response.encode())

Error Handling:

try:
    s.connect((host, port))
except:
    print("Connection failed!")

Common Functions 📚

socket.socket()         # Create socket
s.bind((host, port))   # Bind to address (server only)
s.listen(1)            # Start listening (server only)
conn, addr = s.accept() # Accept connection (server only)
s.connect((host, port)) # Connect to server (client only)
s.send(data.encode())  # Send data (bytes)
s.recv(1024).decode()  # Receive data (convert to string)
s.close()              # Close connection

• Client: Create → Connect → Send/Recv
• Always encode() before sending, decode() after receiving