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Show HN: I wrote a BitTorrent Client from scratch

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I picked up programming in late 2023 and been enjoying it now. Wanted to challenge myself and set a stretch goal, so set out to build a bittorrent client.

Great work! Just an FYI, you might want to limit the dynamic allocation size in the bencode decoder: since it's untrusted input (either from torrent or announce), a malicious input could DoS the client by requesting extremely large allocations during string parsing. A good upper bound could be the remaining length of the input, as a well formed torrent can't contain a string longer than the rest of the file.

7 months agoby jorkingit

Excellent, looks clean and simple.

Suggestion: Add a simple usage one liner in the README on how to actually download a .torrent file with it.

  ./go-torrent My-Linux-Distro-Wink-ISO.torrent

Suggestion: Bonus points if you add torrent.ParseFromUrl

Everyone should do this for their own spiritual journey.

7 months agoby vkaku

Neat! There is this challenge on codecrafters that guides you through the process a little, provides tests and such, I've played around with it a bit during a free month they had, was fun:

https://app.codecrafters.io/courses/bittorrent/overview

7 months agoby __jonas

This is cool! I’ve been thinking about something like this as well. How hard was it, and do you have a sense for how “complete” it is? Does it handle DHT and Magnet and all the crazy NAT traversal stuff?

I’m guessing the main obstacle for me has always been that I’m not sure what the complete list of features is to have a client that will just work for the majority of torrents in the wild. It seems like there are dozens of protocols associated with torrenting and I don’t even know what the full list is much less what each does.

7 months agoby throwaway894345

As a non go developer, may I ask why you're using older go version 1.21? Is there a reason to stay with older releases?

EDIT: It seems like it was deprecated 10 months ago

7 months agoby ashirviskas

Very cool!

This brings me back to college. We did this as our final project for our networking class at Georgia Tech.

I've long lost the code for this, but the lessons learned have lived on :)

Projects like these are great ways to learn new languages too!

7 months agoby agiron123

It's a great kind of project to try! I did something similar and I was humbled when looking at other people's bencode encoders/decoders. It's also a great way to check out language features! Of course it is quite futile to try to match all the features of large libraries, and I believe the compatibility between clients is already lacking...

7 months agoby mikeponders

Do you plan to release docs about the process? personally I'd be more interested in that than the code itself, as few people really go in-depth about the process, the approaches to implementing different aspects of the protocol, etc.