SOCKS5 Proxy Server - Delphi Implementation

A lightweight and efficient SOCKS5 proxy server implementation in Delphi using the Netcom7 socket library. This implementation focuses on simplicity and reliability while maintaining good performance characteristics.

Features

• SOCKS5 Protocol Support: Implements RFC 1928 specification
• Thread-Safe Design: Proper synchronization for multi-threaded operation
• Performance Optimized:
  • Uses non-blocking I/O
  • Configurable read buffer size (default: 8KB for proxy operations)
  • TCP optimization with NoDelay and KeepAlive options
• Error Handling: Comprehensive error detection and graceful connection termination
• Connection Monitoring: Built-in connection tracking and logging capabilities

Technical Details

Core Components

• TProxyServer: Main server class handling the SOCKS5 protocol implementation
• TClientContext: Context management for client connections
• TncTCPServer: Underlying TCP server from Netcom7 library
• TncTCPClient: Client implementation for target connections

Supported SOCKS5 Features

• Version: SOCKS5 (version 5)
• Authentication Methods:
  • NO_AUTH (0x00)
• Commands:
  • CONNECT (0x01)
• Address Types:
  • IPv4 (0x01)
  • Domain Name (0x03)
• Reply Codes:
  • Succeeded (0x00)
  • General SOCKS server failure (0x01)
  • Host unreachable (0x04)
  • Command not supported (0x07)
  • Address type not supported (0x08)

Architecture

• Event-Driven Design: Uses callbacks for connection and data events
• State Machine: Clean state transitions (None → AuthMethod → Command → Forwarding)
• Thread Pool: Leverages Netcom7's thread pool for handling connections
• Context Management: Thread-safe context tracking with proper cleanup

Limitations

1. Authentication:

   • Only supports NO_AUTH method
   • No username/password authentication
   • No GSSAPI support

2. Command Support:

   • Only CONNECT command implemented
   • No support for BIND command
   • No support for UDP ASSOCIATE

3. Address Types:

   • No IPv6 support
   • Limited to IPv4 and domain names

4. Protocol Features:

   • No support for SOCKS5 protocol extensions
   • No support for custom authentication methods

Performance Considerations

• Default read buffer size: 8KB (configurable)
• TCP optimizations enabled by default:
  • TCP_NODELAY enabled
  • TCP KeepAlive supported
• Connection timeout: 5 seconds for target connections
• No automatic reconnection for target connections

Requirements

• Delphi (Compatible with recent versions)
• Netcom7 socket library ⚠️
  • You must replace the original ncSockets.pas with the one provided in the Netcom7 folder.
  • I made changes in :
    • TncCustomTCPServer.DataSocketDisconnected
    • Created a new property to allow customizing the read buffer size

Optional: You can also replace the ncLines.pas (corrected version allowing compilation on Linux)

Usage

For any application/browsers that supports SOCKS5 proxies, configure with :

• Proxy Type: SOCKS5
• Server: Your proxy server IP address
• Port: 1080 (default) or your configured port
• No authentication required

Error Handling

The implementation includes comprehensive error handling for:

• Invalid protocol versions
• Unsupported commands
• Connection failures
• Network errors
• Resource cleanup

Logging and Monitoring

• Connection tracking with unique connection IDs (based on socket handles)
• Error logging for connection failures and protocol violations
• Basic connection event logging (connect, disconnect)
• Visual connection monitoring through the UI

⚠️ Known bug

Sometimes web browsing no longer works. I still haven't found a solution. OS-level socket connections work but nothing reaches the code. If anyone would like to help find a solution it would really be appreciated 🙏

Contributing

Contributions are welcome! If you have suggestions or bug fixes, please fork the repository and submit a pull request.

Made with ❤️ using Delphi RAD Studio