PeerLinker is an experimental BitTorrent implementation for .NET

Demo

PeerLinker downloading a debian image:
https://github.com/user-attachments/assets/c302e353-bfc0-41a8-a179-e2c5c3b01f0c

Checksums match

Features

• Truly concurrent piece fetching with 30 active connections
• Peer discovery, handshake, etc.
• Support for all message types (the Peer Wire protocol)
• All messages are implemented as unsafe structs. This makes marshaling to and from byte arrays a trivial operation.
• Distribution of requests to peers depending on how useful they are to us, with a weighted random roll to pick them. obviously weighted towards the faster ones
• The architecture of the message recv system is sort of interesting. It's essentially handled with one channel. The incoming messages are dispatched to a set of 10 channels, one for each message type, so there's a dispatcher class that encompasses Piece messages, Choke messages, Interest messages etc. Using channels allows us to lazily process messages whenever we actually need to. A consumer could just await the next Unchoke, or the next Piece. it's more flexible
• Request pipelining. 32 requests at any given moment for every connection
• Choke handling. If a peer chokes us mid-transfer, its unfinished requests just go back into the pool and get redistributed to everyone else
• Blocks can arrive in any order from any peer. Everything is written at its exact offset into one preallocated scratch file, so there's no reassembly buffering in memory
• Single and multi-file torrents, split into the final file layout at the end
• .torrent file parsing to fetch metadata
• Bencode pretty printer
• Tracker server connectivity (Announce mechanism)
• BEP20 Azureus peer ID (-PL0001-)
• Dead peer detection
• Pretty logs
• SHA1 verification of pieces, with bad ones automatically re-downloaded
• Writing file to the disk

Wishlist

• Implement uploading / seeding
• Library API improvements
• PeX Peer Exchange protocol
• DHT Distrubed Hash Tables
• Rarest pieces first strategy
• Desktop application

How to set it up

• Take a sample .torrent file under /testfiles
• Place it under the build output directory (so under peerlinker/bin/Release/net10.0/ for example)
• peerlinker/Program.cs has a variable that allows you to set the torrent file name that peerlinker is configured to use at runtime.

State of the project

PeerLinker is my attempt at a BitTorrent library. I work on it when I have free time / when i'm interested. hopefully that explains the 5 month gaps between a surge of commits. I just remember that this repository exists sometimes
My goal is to have a class library of BitTorrent like the C++ library "libtorrent" but in C#, plus a desktop application using eto.forms

At this point in time, peerlinker can download entire files. I tested it with a few linux distro ISOs. It maxed out my available bandwidth, downloading at an average of 25mb/s.

Around ~1500 loc