TCP Chat - NetCat

A Go implementation of a TCP-based group chat server inspired by NetCat, supporting multiple concurrent clients with real-time messaging, connection management, and comprehensive logging.

Overview

This project recreates the NetCat functionality in a Server-Client architecture, allowing multiple clients to connect to a TCP server and participate in a group chat. The server manages connections, broadcasts messages, and maintains chat history for new joining clients.

Features

Core Functionality

• TCP Server-Client Architecture: One server handling multiple concurrent clients
• Real-time Group Chat: Instant message broadcasting to all connected clients
• Connection Management: Maximum 10 concurrent connections with graceful handling
• Message History: New clients receive all previous chat messages
• User Authentication: Name requirement and validation for all clients
• Timestamped Messages: All messages include timestamp and sender identification

Advanced Features

• Name Change Support: Clients can change their names using --name command
• Join/Leave Notifications: Server announces when clients join or leave
• Input Validation: Comprehensive text validation and error handling
• Logging System: Server logs all activities to file with optional log clearing
• Connection Limits: Prevents server overload with maximum connection enforcement

Technical Implementation

• Go Routines: Concurrent handling of multiple client connections
• Mutexes: Thread-safe access to shared resources
• Channels: Efficient communication between goroutines
• Error Handling: Robust error management for network operations

Usage

Starting the Server

Default port (8989):

go run server/main.go

Custom port:

go run server/main.go 2525

Clear logs:

go run server/main.go --clear
go run server/main.go 2525 --clear

Connecting Clients

Using netcat:

nc localhost 8989

Using telnet:

telnet localhost 8989

Client Interaction Flow

1. Connection: Client connects and receives welcome message with Linux logo
2. Name Entry: Client enters a unique name (1-9 characters, no spaces)
3. Chat History: Client receives all previous messages
4. Real-time Chat: Client can send/receive messages in real-time
5. Name Change: Client can change name using --name newname
6. Disconnection: Clean exit with notification to other clients

Example Session

Welcome to TCP-Chat!
         _nnnn_
        dGGGGMMb
       @p~qp~~qMb
       M|@||@) M|
       @,----.JM|
      JS^\__/  qKL
     dZP        qKRb
    dZP          qKKb
   fZP            SMMb
   HZM            MMMM
   FqM            MMMM
 __| ".        |\dS"qML
 |    `.       | `' \Zq
_)      \.___.,|     .'
\____   )MMMMMP|   .'
     `-'       `--'

[ENTER YOUR NAME]: Alice
[2024-01-20 15:48:41][Alice]: Hello everyone!

Bob has joined the chat.
[2024-01-20 15:49:15][Bob]: Hi Alice!
[2024-01-20 15:49:20][Alice]: Welcome Bob!

Message Format

All messages follow the format:

[YYYY-MM-DD HH:MM:SS][username]: message

System notifications:

username has joined the chat.
username has left the chat.
username has changed their name to newname.

Project Structure

tcp-chat/
├── server/
│   ├── main.go              # Server entry point and connection handling
│   └── server.log           # Server activity logs
├── client/
│   └── clients.go           # Client connection and message handling
├── utils/
│   ├── globalvariables.go   # Shared variables and data structures
│   ├── Validation.go        # Input validation functions
│   ├── change.go            # Client management (add/remove/exit)
│   ├── send.go              # Message broadcasting and history
│   ├── welcome.go           # Welcome message and Linux logo
│   └── logging.go           # Logging setup and management
├── go.mod                   # Go module definition
└── README.md

Validation Rules

Name Validation

• Length: 1-9 characters maximum
• Characters: No spaces or control characters (ASCII < 32)
• Uniqueness: Names must be unique across all connected clients
• Required: Empty names are not allowed

Message Validation

• Content: No control characters (ASCII < 32) except spaces
• Empty Messages: Cannot send empty messages
• Special Commands: --name newname for name changes

Error Handling

The server handles various error conditions:

• Connection Limit: "There are too many connections, try to log in later."
• Invalid Characters: "Invalid characters in your input"
• Empty Input: "Can't send empty name/messages"
• Name Conflicts: "Name have been taken, try another name"
• Network Errors: Graceful disconnection and cleanup

Logging

Server maintains comprehensive logs in server.log:

• Client connections and disconnections
• Name changes and validations
• Error conditions and network issues
• Server start/stop events

Log management:

# Clear logs on startup
go run server/main.go --clear

# View logs
tail -f server.log

Technical Details

Concurrency

• Go Routines: Each client connection runs in a separate goroutine
• Mutexes: Protect shared data structures (client map, message history)
• Thread Safety: All operations on shared resources are mutex-protected

Network Programming

• TCP Sockets: Reliable connection-oriented communication
• Connection Pooling: Efficient management of multiple connections
• Graceful Shutdown: Clean disconnection handling

Data Structures

var Clients = make(map[net.Conn]string)  // Connection to name mapping
var Messages []string                     // Chat history storage
var Mutex sync.Mutex                     // Thread synchronization