🧾 Real-Time Chat System (C++ with Winsock & JSON)

🔷 Overview

This is a real-time, multi-client chat system implemented in C++ using Winsock for networking and nlohmann::json for structured message handling. It supports:

• Encrypted messaging using a MessageHandler
• Multi-threaded client/server communication
• Auto-reconnection and per-client messaging
• Modular and maintainable codebase

The system consists of two core components:

• Client Module – connects to the server, sends/receives messages
• Server Module – accepts multiple clients, routes messages, and handles communication

---

🔹 Client Module

📁 Structure

client/

 ├── include/

 │ ├── ChatClient.h

 │ └── MessageHandler.h

 ├── src/

 │ ├── ChatClient.cpp

 │ ├── MessageHandler.cpp

 │ └── main.cpp

🧠 Responsibilities

• Connects to the server using provided IP and port
• Receives a JSON-based welcome message with an assigned clientId
• Sends and receives encrypted messages in JSON format
• Automatically reconnects if the connection is lost
• Handles message reception asynchronously via thread
• Uses MessageHandler for encryption and decryption

🛠️ Key Class: ChatClient

Method	Description
connectToServer()	Initiates socket connection and receives welcome JSON
sendMessage(msg)	Sends a message (formatted internally as JSON)
startReceiving()	Starts a thread to listen for incoming messages
setOnMessageReceived(callback)	Registers a callback for received messages
disconnect()	Closes the socket connection
enableAutoReconnect(flag)	Enables retry mechanism on disconnection

---

📤 Outgoing Message Format

json { "type": "message", "message": "Hello!" }

📥 Incoming Message Format

json { "type": "message", "message": "Welcome to the server!" }

📬 Welcome Message Example

json { "type": "welcome", "clientId": 1 }

🔹 Server Module

📁 Structure

server/

 ├── include/

 │ ├── ChatServer.h # Core server logic

 │ └── MessageHandler.h # JSON-based message encoding/decoding

 ├── src/

 │ ├── ChatServer.cpp # Server implementation

 │ ├── MessageHandler.cpp # Message utilities

 │ └── main.cpp # Entry point to start the server

---

🧠 Responsibilities

• Accepts multiple TCP clients via Winsock.
• Assigns unique client IDs upon connection.
• Sends JSON welcome message to each new client.
• Parses incoming client messages (JSON format).
• Forwards messages to all clients or a specific one.
• Uses MessageHandler for JSON and optional obfuscation.
• Supports clean socket management and multithreading.

---

🛠️ Key Class: ChatServer

Method	Description
start(uint16_t port)	Initializes and binds socket, begins accepting clients
acceptClients()	Listens for and handles new client connections
sendMessageToClient(id)	Sends a JSON message to a specific client
broadcastMessage(json)	Sends message to all connected clients
receiveFromClient(id)	Receives JSON messages from a client
disconnectClient(id)	Gracefully removes a client

---

📤 Welcome Message Format (Sent to Clients)

json { "type": "welcome", "clientId": 1 }

📥 Expected Incoming Message Format json { "type": "message", "message": "Hello from client" }

🔐 MessageHandler The MessageHandler class handles:

🔄 Conversion between strings and JSON

🔒 Optional XOR-style obfuscation (easy to replace with AES/RSA)

📦 Clean formatting of messages for network transmission

🔧 Dependencies 🖥️ Platform: Windows (Winsock2)

🧾 JSON Library: nlohmann/json.hpp

🔧 Language: C++17

📤 Threads: , for concurrency

📌 Notes

-Make sure to call WSAStartup() and WSACleanup() appropriately in main.cpp.

-Supports full-duplex messaging with client-side multithreaded listener.

-Use console input to send messages to specific clients by ID.

🖼️ Architecture Diagrams

Client Workflow: flowchart TD

A[Client Start] --> B[Connect to Server]

B --> C{Connected?}

C -- Yes --> D[Receive Welcome Message]

D --> E[Start Receiving Thread]

C -- No --> F[Retry Connection if Enabled]

E --> G[Send/Receive JSON Messages]

Server Workflow:
 flowchart TD

 A[Server Start] --> B[Listen on Port]

 B --> C[Accept Client Connection]

 C --> D[Assign clientId]

 D --> E[Send Welcome JSON]

 E --> F[Start Client Thread]
 
 F --> G[Receive JSON / Route Message]

🚀 How to Compile & Run from Console

✅ Recommended (With C++17 Support — Required for Structure Binding)

Make sure your compiler supports C++17. You can compile and run using:

🔹 Windows (MinGW or g++):

g++ -std=c++17 -I./include -I../libs ./src/*.cpp -o ChatServer -lws2_32
./ChatServer

🔹 Visual Studio Developer Command Prompt:

cl /std:c++17 /I include /I ..\libs src\*.cpp /Fe:ChatServer.exe ws2_32.lib
ChatServer.exe