fix(iroh): Return error if disco send via relay fails

[flub]

Description

The signature of this function expects an error if the send fails, but
the relay part did not do this. The impact of this is that you might
silently drop a packet, which makes debugging a bit harder. Returning
an error should propagate this correctly and the failures will be
noticed and logged.

Breaking Changes

Notes & open questions

Change checklist

• Self-review.
• Documentation updates following the style guide, if relevant.
• Tests if relevant.
• All breaking changes documented.

[github-actions]

Documentation for this PR has been generated and is available at: https://n0-computer.github.io/iroh/pr/3130/docs/iroh/

Last updated: 2025-01-14T11:53:43Z

[github-actions]

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Last updated for commit: a01a141

[matheus23]

Looking through this part of the code I'm realizing some unrelated things that could be fixed:

• It looks like there exists MagicSock::handle_ping_actions and it's apparently unused (but... rustc doesn't realize apparently due to the #[instrument] macro)
• Instead of returning a bool from send_disco_message_relay we should probably just return the error we get from try_send_relay, and later .map_err, so we don't forget such stuff in the future. Even Result<(), ()> > bool.

[flub]

Looking through this part of the code I'm realizing some unrelated things that could be fixed:

* It looks like there exists `MagicSock::handle_ping_actions` and it's apparently unused (but... rustc doesn't realize apparently due to the `#[instrument]` macro)

* Instead of returning a bool from `send_disco_message_relay` we should probably just return the error we get from `try_send_relay`, and later `.map_err`, so we don't forget such stuff in the future. Even `Result<(), ()>` > `bool`.

Yeah... this code hasn't yet seen a proper cleanup.

Also, sad that #[instrument] does that, but I probably shouldn't be surprised.