TCP Chat App

Overview

A Python-based TCP chat application supporting multiple clients with broadcast (group chat) and unicast (private messages).
Designed to provide a reliable, real-time chat experience using socket programming and multithreading.

Features

Server

• Manages multiple clients with unique usernames.

• Handles client connections, disconnections, and username validation.

• Supports broadcast and unicast messaging.

• Sends join/leave notifications.

• Uses threading with locks to prevent race conditions.

• Implements error codes for reliable communication:

   0 – Client exit
   1 – Server requests readiness
   1RDY – Client ready acknowledgment
   2 – Valid username
   3 – Invalid username
   4 – Recipient not found
  

Client

• Connects to server with a unique username.
• Sends/receives broadcast and private messages.
• Handles real-time simultaneous input/output using msvcrt.
• Supports graceful exit with /quit command.
• Displays messages clearly using safe_print() with thread locks.
• Responds to server error codes.

Design Highlights

• Multithreading: Each client handled on a separate thread for concurrent communication.
• Publish–subscribe model: Ensures proper message broadcast without duplication.
• Username management: Dictionary-based storage for O(1) lookup and deletion.
• Error handling: Try-except blocks to prevent crashes during socket operations.
• Handshake system: Initial two-way handshake (1/1RDY) ensures proper message initiation.

User Experience

• Clear prompts and notifications (join/leave, invalid usernames, missing recipients).
• Real-time typing and message display without interruption.
• Interactive and responsive terminal-based interface.

Challenges & Solutions

• Simultaneous I/O : Terminal shared both input and output areas. Resolved using msvcrt and kbhit (input buffering).
• Race conditions: Managed with threading.Lock().
• Unique usernames: Dictionary for O(1) lookup.
• Initial handshake: Ensures correct transmission of initial server messages.

Conclusion

• Supports multiple clients, broadcast/unicast messaging, and robust communication.
• Learned socket programming, multithreading, live input logging, and error code design.
• Future improvements: GUI, authentication, server-side message storage.

Demonstration Link:

https://drive.google.com/drive/folders/1_lGV0ibQYmCn5O5JdvBZyk0Of9bB7j4u?usp=sharing