chore(metrics): make Identify allowlist configurable

[torrpriius]

Make the Identify allowlist configurable instead of hard-coding protocol IDs.

• Add identify::Metrics::new_with_allowed_protocols(...) to accept extra StreamProtocols.
• Add libp2p_metrics::Metrics::new_with_identify_allowed_protocols(...) to forward user-provided protocols.
• Defaults remain unchanged; apps can pass custom IDs when using ConfigBuilder::protocol_id.

Usage

use libp2p_metrics::{Metrics, Registry};
use libp2p_swarm::StreamProtocol;

let extra = [StreamProtocol::new("/myappsub/1.2.3")];

let mut registry = Registry::default();
let metrics = Metrics::new_with_identify_allowed_protocols(&mut registry, extra);

Notes & open questions

• Happy to adjust naming or expose a builder if maintainers prefer a different API.

Change checklist

• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• A changelog entry has been made in the appropriate crates

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[torrpriius]

@elenaf9

Thanks for the feedback!

• I addressed the Identify allowlist note by making it configurable rather than hardcoding protocol IDs. This keeps defaults intact while allowing applications to opt-in their custom protocol IDs (e.g., when using ConfigBuilder::protocol_id).

• To keep this PR focused and reduce surface area, I dropped the Debug implementation for OneShotHandler. If there is interest, I can follow up with a small change (or guard behind cfg(test)/a feature) to aid test-only usage.

What changed concretely

• Identify metrics allowlist:
  • Kept a stable base set of protocols and added a simple API to pass additional protocol IDs.
  • No behavior changes by default. Applications that customize protocol IDs can now pass theirs.
• OneShotHandler:
  • Removed the Debug impl to align with the handler’s typical usage within the swarm and to keep the PR scoped.
• Docs:
  • TransportTimeout example now uses ListenerId::next() and is marked no_run; doctest passes.

How to pass custom protocols (example)

use libp2p_metrics::{Metrics, Registry};
use libp2p_swarm::StreamProtocol;

// e.g., when an app uses a custom pubsub protocol ID via ConfigBuilder::protocol_id
let custom_gossipsub = StreamProtocol::new("/myappsub/1.2.3");

// You can pass multiple protocols (meshsub/floodsub/customs) as needed.
let extra = [
    custom_gossipsub,
    // StreamProtocol::new("/meshsub/1.2.0"),
    // StreamProtocol::new("/floodsub/1.0.0"),
];

let mut registry = Registry::default();
let metrics = Metrics::new_with_identify_allowed_protocols(&mut registry, extra);

Defaults remain unchanged when using:

let metrics = Metrics::new(&mut registry);

If anything else would make this more useful for users (naming, docs, or making a builder), happy to adjust.

[elenaf9]

• I addressed the Identify allowlist note by making it configurable rather than hardcoding protocol IDs. This keeps defaults intact while allowing applications to opt-in their custom protocol IDs (e.g., when using ConfigBuilder::protocol_id).

This is not pushed yet, I think? I can't see it in the diff.

[torrpriius]

@elenaf9
Thanks for pointing it out — I hadn’t included the Identify parameterization earlier. It’s now pushed.

• Identify allowlist is configurable (no hard-coded Gossipsub IDs).
• Added identify::Metrics::new_with_allowed_protocols(...).
• Added libp2p_metrics::Metrics::new_with_identify_allowed_protocols(...).
• Defaults remain unchanged; applications can pass custom StreamProtocol when using ConfigBuilder::protocol_id.

[torrpriius]

@dariusc93
Thanks for the suggestion — done.

I moved the TransportTimeout doc example into a separate PR as requested: #6152. This PR (#6147) now contains only the Identify allowlist parameterization.