BitTorrent Client

Design

• design of this client is based on the BitTorrent v1.0 spec
• the client is written in Rust and only uses core stdlib for networking, i.e. no tokio or async
  • this was for a personal challenge to handle any asynchronous I/O using only stdlib
• custom http client from scratch to send GET requests to the tracker
• peer that performs the full BitTorrent peer wire protocol
• piece/block assembler and writer to disk
• central session orchestrator for concurrently handling downloads from multiple peers using a piece queue and handles validating pieces

Usage

cargo run --release -- \
  --torrent <path/to/file.torrent> \
  --output <path/to/output/file> \
  --compact 1 \
  --port 6881 \
  --verbose

Verifying a sample download

I got the torrent from Debian's official site which can be found here. Note that what lies in the current directory is the latest version of Debian, which at the time of writing is 12.10.0. Also note that the list of peers that the tracker returns for this torrent are mostly IPv6 addresses, so the client may not work as expected if you don't have IPv6 support on your network.

The page includes the following:

• SHA256SUMS
• SHA256SUMS.sign
• SHA512SUMS
• SHA512SUMS.sign
• debian-12.10.0-arm64-netinst.iso.torrent

To download all the files (you don't need to as you can eyeball the hash), you can use the following command:

wget https://cdimage.debian.org/debian-cd/current/arm64/bt-cd/SHA256SUMS \
     https://cdimage.debian.org/debian-cd/current/arm64/bt-cd/SHA256SUMS.sign \
     https://cdimage.debian.org/debian-cd/current/arm64/bt-cd/SHA512SUMS \
     https://cdimage.debian.org/debian-cd/current/arm64/bt-cd/SHA512SUMS.sign \
     https://cdimage.debian.org/debian-cd/current/arm64/bt-cd/debian-12.10.0-arm64-netinst.iso.torrent

If you downloaded a file (via the BT client), assuming it is named debian-12.10.0-arm64-netinst.iso, you can verify the hash of both the *.torrent and *.iso files (assuming they're all in the same directory) using the following command:

sha512sum -c SHA512SUMS # or sums256 -c SHA256SUMS

which should output something like:

debian-12.10.0-arm64-netinst.iso: OK
debian-12.10.0-arm64-netinst.iso.torrent: OK