Comment by throwaway894345

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.

piyushgupta53 4 days ago

it was challenging for sure. Took me almost a month to get acquainted with the protocol, how bencoding works etc, build a mental model and then eventually writing code.

Magnet and DHT are yet to be added.

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Charon77 4 days ago

In my experience, magnet is pretty straightforward. Dht is quite the rabbit hole, and it might be difficult finding clients that support dht (not everyone does)

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CactusRocket 3 days ago

How hard it is depends a lot on your experience, how comfortable you are with the programming language, and if you have an experimentation mindset. To offer a perspective, I also decided to build a Bittorrent client in Go last week, and I'm about 80% of the way of the posted project in a week. But then again I have a lot of experience with Go, extensive knowledge about protocols and networking, and experimentation has become a kind of second nature for me.

If you're interested, the main Bittorrent spec is actually quite small, you can easily read and understand it in an hour or so: https://www.bittorrent.org/beps/bep_0003.html

There's a lot of stuff "around" Bittorrent, like protocol extensions. But in my experience so far, many clients have different levels of support. E.g. they would try communicating using Protocol Encryption (obfuscation, actually) and if it doesn't work fall back to the regular protocol (if configured in the settings).

If you just want to download a Linux distribution (e.g. Debian) using the .torrent file on their website, it's relatively straight forward. It has just one file, there's a tracker, plenty of peers using the regular protocol, and you could get away not listening for connections when you're behind a NAT.

Naturally when you get into the grey area of content, then you'd need to parse magnet links, use DHT to discover peers, and perhaps you'd want to implement UPnP to try and automatically map a port on your modem. But that is also an iterative process, you can just build out one by one. The more features, the more peers you'll be able to discover and have successful exchanges with.

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