Gopher-FS: Secure Distributed File Transfer System

A robust, concurrent, and secure file transfer system built in Go. This tool allows for decentralized server discovery, secure file uploads/downloads, and automatic data integrity verification.

🚀 Key Features

• Zero-Config Discovery: Servers are automatically discovered on the local network using UDP broadcasting. No IP configuration needed.
• Secure Transport: All file transfers are encrypted using TLS 1.3 (Self-Signed Certificates generated on-the-fly for this demo).
• Data Integrity: Every file transfer is verified with SHA-256 checksums to ensure zero corruption.
• High Performance: Uses io.Copy and Go's streaming interfaces to handle large files with minimal memory footprint.
• Concurrency: Capable of handling multiple client requests simultaneously using lightweight Goroutines.

🛠 Architecture

The project is structured following standard Golang layout patterns:

• cmd/server: The server application entry point. Handles TCP/TLS listening and concurrent client dispatch.
• cmd/client: The client CLI tool. Handles discovery, connection, and file operations.
• internal/discovery: UDP Multicast/Broadcast logic for service discovery.
• internal/protocol: Defined binary protocol for efficient framing (Size, Name, Checksum, Data) and Operation Codes.
• internal/security: Logic for ephemeral TLS certificate generation.

📦 Installation & Usage

Prerequisites: Go 1.21+

1. Clone the repository:

   git clone https://github.com/yourusername/gopher-fs.git
   cd gopher-fs

2. Start the Server (Terminal 1):

   go run cmd/server/main.go

   Output: Secure File Server listening on :9000 (TLS enabled)

3. Run the Client (Terminal 2):

   • Download a File:

     go run cmd/client/main.go -file my_document.txt

   • Upload a File:

     go run cmd/client/main.go -file my_upload.png -upload

🔒 Security & Protocol Detail

Binary Protocol

Size (Bytes)	Field	Description
1	OpCode	0x01 (Download) or 0x02 (Upload)
4	NameLen	Length of the filename
8	FileSize	Size of the file in bytes
32	Checksum	SHA-256 Hash of the file
N	Name	The filename string
M	Data	Raw file content stream

Encryption

All TCP connections are upgraded to TLS automatically using ephemeral keys. This prevents passive network sniffing from reading your files.

📝 License

MIT License