`wss://tracker.webtorrent.dev` unexpected announce response

[Jhonfunk]

[2024-09-27 14:03:01 +0800 WRN websocketTrackers github.com/anacrolix/torrent/webtorrent tracker-client.go:342]
  tracker client for "wss://tracker.webtorrent.dev": unexpected announce response "{\"failure reason\":\"Invalid request\"}" <*torrent.Client 0xc000191408>

[anacrolix]

Interesting thanks. Do you use other wss trackers and do they do it too?

[Jhonfunk]

@anacrolix
Other wss trackers don't have this problem. But it's a bit strange, so I'm bringing it up. Maybe webtorrent updated its tracker protocol?

[anacrolix]

Thanks for following up. If anyone else comes across this behaviour we can start investigating. I think there a few other trackers that work in the meanwhile.

[SilentBot1]

Hi @anacrolix and @Jhonfunk,

To comment on this issue, the tracker software I run on wss://tracker.webtorrent.dev is aquatic-ws. The Invalid request response is caused by the default value of AnnounceRequest's Left being -1.

In WebTorrent, when metadata has not been determined, a left of null is sent as the default value.

Aquatic handles parsing the left field as an Option<usize>, effectively allowing either null, a uint32 or uint64 depending on the architecture, and can't be negative, which is why the request fails to be deserialized.

Note: The -1 value does not break bittorrent-tracker, as no validation is performed on left, and OpenWebTorrent parses this as an int64_t from what I can see.

When testing this locally, making Left an *int64 and correcting -1 to nil causes the request to be marshalled as null, fixing the issue and allowing communication with the tracker.

I'm not proficient enough in Go to submit this as a PR, but ensuring an unknown left is null and not -1 fixes this and matches WebTorrent's behaviour.

[anacrolix]

Thanks very much!