feat(iroh): Retain stats for closed and abandoned paths in the path watcher

[Frando]

Description

Improves the path watcher for connections to reliably allow accessing the stats of abandoned paths.

• Abandoned paths are not removed from the value of the watchable for a connection's paths, as long as there are active watchers (subscribers)
• Only once all watchers are dropped, we drop the abandoned paths from the watchable's value on the next update
• This means that if you keep a PathWatcher alive for the duration of a connection, it will contain all paths the connection ever used.
• We use the changes from feat: Retain final path stats if a Path is alive, add WeakPathHandle quinn#386 and keep a WeakPathHandle for all paths in the watchable's value. This prevents the path stats to be dropped within a quinn connection even if the path is abandoned.
• We do no longer store path stats anywhere in iroh directly, but only ever access them from quinn. Due to keeping the WeakPathHandle, we can ensure that the stats are always available as long as the connection hasn't been dropped.

The combination of all this gives us a reliable way to access final path stats for all paths used in a connection, as long as you keep a reference to the connection around, which is quite straightforward to do and document.

Breaking Changes

• Connection::paths and ConnectionInfo::paths now return a PathWatcher (which still implements n0_watcher::Watcher but now also is a named struct)
• PathInfo::stats and PathInfo::rtt now return Option. They return None if the underlying connection has been droped.

Notes & open questions

I spend quite some time going back-and-forth over different approaches. Very open to other ideas, but I'm a bit out of further ideas currently and this is the best I could come up with so far.

Change checklist

• Self-review.
• Documentation updates following the style guide, if relevant.
• Tests if relevant.
• All breaking changes documented.
  • List all breaking changes in the above "Breaking Changes" section.
  • Open an issue or PR on any number0 repos that are affected by this breaking change. Give guidance on how the updates should be handled or do the actual updates themselves. The major ones are:
    • quic-rpc
    • iroh-gossip
    • iroh-blobs
    • dumbpipe
    • sendme

[github-actions]

Documentation for this PR has been generated and is available at: https://n0-computer.github.io/iroh/pr/3899/docs/iroh/

Last updated: 2026-02-09T14:52:23Z

[dignifiedquire]

could this be an impl of PartialEq instead?

[Frando]

Yes, why not. Changed it.