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BitTorrent Client

Build a BitTorrent Client with go to parse .torrent files

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🚀 Overview

This project is a fully functional BitTorrent client built from scratch using Go. Rather than using high-level libraries, I implemented the core protocol layers—from parsing bencoded data to managing peer-to-peer TCP connections and verifying file integrity.

🛠 Technical Details

  1. Bencode Parsing

BitTorrent metadata (the .torrent file) is stored in a format called Bencode. I built a parser to map these recursive structures (integers, strings, lists, and dictionaries) into Go structs. Used Go's interface and reflection principles to handle the dynamic nature of bencoded data.

  1. Concurrency with Goroutines and Channels

The "magic" of BitTorrent is downloading different pieces of a file from different peers simultaneously. The Worker Pool: I implemented a worker pattern where each peer connection runs in its own Goroutine. Work Queue: Pieces are distributed via a workQueue channel. If a peer drops or a piece fails a hash check, the piece is sent back to the channel to be retried by another worker.

  1. Bitfield and Piece Management

To keep track of which parts of the file I have versus what the peers have, I implemented a Bitfield data structure. This involves bitwise operations to efficiently check and set progress. Integrity: Every downloaded piece is hashed using SHA-1 and compared against the info-hash in the torrent file to prevent data corruption.

  1. TCP Peer Wire Protocol

I implemented the low-level handshake and messaging protocol: Message Types: Handshaking, Choking/Unchoking, Interested, and Requesting/Receiving blocks. Flow Control: Managed the state machine of each peer connection to ensure we only request data when "Unchoked."

🔧 Challenges & Lessons

Network Reliability: Dealing with flaky TCP connections taught me the importance of robust error handling and timeouts in Go. Binary Math: Working with big-endian integers and byte slices deepened my understanding of how data is actually transmitted over the wire. Resource Optimization: Balancing the number of active goroutines to maximize throughput without hitting system file descriptor limits.

📖 Usage

Only provides a CLI

torrent archlinux.iso.torrent

💻 Tech Stack

Language: Go
Concepts: TCP Networking, Binary Protocols, SHA-1 Hashing, Concurrency Patterns, Bencode.