[anacrolix]

I found the trickiest parts to be DHT concurrency (finally solved this adequately after 5-6 years of experimenting), and efficient block requesting (I've rewritten this every few years, but my latest implementation seems to be solid since 2020 or so). The major thing I've not solved, but also been too lazy to tackle is a peer cache. I just reaannounce when all peers are exhausted and start over.

[ikatson]

Concurrency and the shared state nature of torrents are definitely what makes it all hard and tricky. I've rewritten this part of DHT completely recently, but according to your experience looks like this time won't be the last.

For block requesting, rqbit has a pretty simple algorithm https://github.com/ikatson/rqbit/blob/main/crates/librqbit/s..., and I didn't notice it in benchmarks, thanks to Rust being fast by default I guess. I admit though, never looked how other clients do it, maybe the rqbit algorithm is too naive.