feat: allow RPC metrics disable + less locks

[LesnyRumcajs]

Summary of changes

Changes introduced in this pull request:

• allow disabling RPC metrics
• made metrics layer less needy, i.e., less locks and allocations, relying more on static data.

Reference issue to close (if applicable)

Closes

Other information and links

Change checklist

• I have performed a self-review of my own code,
• I have made corresponding changes to the documentation. All new code adheres to the team's documentation standards,
• I have added tests that prove my fix is effective or that my feature works (if possible),
• I have made sure the CHANGELOG is up-to-date. All user-facing changes should be reflected in this document.

Outside contributions

• I have read and agree to the CONTRIBUTING document.
• I have read and agree to the AI Policy document. I understand that failure to comply with the guidelines will lead to rejection of the pull request.

Summary by CodeRabbit

• New Features

  • Added an environment variable to disable per-method JSON-RPC metrics while leaving the metrics endpoint and other metrics active; runtime now honors this setting.

• Documentation

  • Updated changelog and environment variables reference to document the new setting and how to fully disable metrics.

• Tests

  • Added tests to validate per-method metrics behavior and the disable flag.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 2da9e21a-78cf-4e54-ae85-0b60a6ab6871

📥 Commits

Reviewing files that changed from the base of the PR and between b657e95 and 64cf1d7.

📒 Files selected for processing (7)

• CHANGELOG.md
• docs/docs/users/reference/env_variables.md
• src/daemon/mod.rs
• src/metrics/mod.rs
• src/rpc/metrics_layer.rs
• src/rpc/mod.rs
• src/tool/offline_server/server.rs

🔗 Linked repositories identified

CodeRabbit considers these linked repositories for cross-repo context during reviews:

• filecoin-project/lotus (manual)

✅ Files skipped from review due to trivial changes (3)

• docs/docs/users/reference/env_variables.md
• src/daemon/mod.rs
• CHANGELOG.md

🚧 Files skipped from review as they are similar to previous changes (4)

• src/tool/offline_server/server.rs
• src/metrics/mod.rs
• src/rpc/metrics_layer.rs
• src/rpc/mod.rs

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Walkthrough

Adds a mode-aware RPC metrics layer with a pre-resolved per-method metrics registry and a MetricsMode toggle (honoring FOREST_RPC_METRICS_DISABLED), threads metrics_mode through RPC startup call sites, updates the RPC method label type, and documents the new environment variable.

Changes

RPC Metrics Conditional Control

Layer / File(s)	Summary
Metrics Layer with MetricsMode and Pre-Resolved Handles src/rpc/metrics_layer.rs	Defines MetricsMode, implements MetricsLayer::new(mode) that respects FOREST_RPC_METRICS_DISABLED, builds a static METHOD_METRICS registry of pre-resolved Prometheus Histogram/Counter handles (including aliases and "unknown"), and conditionally wraps call/notification to record metrics when enabled; includes tests.
Metrics Label Type: String to Static Str src/metrics/mod.rs	Changes RpcMethodLabel.method from String to &'static str to match static registry keys.
RPC Module: MetricsMode Threading src/rpc/mod.rs	Re-exports MetricsMode, adds metrics_mode: MetricsMode parameter to start_rpc, and constructs per-connection middleware with MetricsLayer::new(metrics_mode); updates test to pass MetricsMode::Enabled.
Configuration Propagation: Daemon and Offline Server src/daemon/mod.rs, src/tool/offline_server/server.rs	Daemon computes metrics_mode from config.client.enable_metrics_endpoint and passes it to start_rpc; offline server calls start_rpc with MetricsMode::Enabled.
Documentation: Changelog and Environment Variable Reference CHANGELOG.md, docs/docs/users/reference/env_variables.md	Adds changelog entry and docs table row for FOREST_RPC_METRICS_DISABLED, documenting that it disables per-method JSON-RPC metrics while preserving the metrics endpoint and other metrics; notes --no-metrics disables metrics entirely.

Estimated code review effort

🎯 3 (Moderate) | ⏱️ ~25 minutes

Possibly related PRs

• ChainSafe/forest#7113: Also touches RPC metrics middleware and metric counting for RPC calls.

Suggested labels

RPC

Suggested reviewers

• akaladarshi
• hanabi1224
• sudo-shashank

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 40.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title 'feat: allow RPC metrics disable + less locks' directly and clearly summarizes the two main changes: adding RPC metrics disable functionality and optimizing locks/allocations in the metrics layer.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[coderabbitai]

Actionable comments posted: 1

🤖 Prompt for all review comments with AI agents

Verify each finding against current code. Fix only still-valid issues, skip the
rest with a brief reason, keep changes minimal, and validate.

Inline comments:
In `@CHANGELOG.md`:
- Line 32: Replace the incorrect issue link in the CHANGELOG entry that
currently reads "[`#7168`](https://github.com/ChainSafe/forest/issues/7168)" with
the PR link format "[`#7168`](https://github.com/ChainSafe/forest/pull/7168)" so
the changelog references PR `#7168` instead of an issue; update the single line
containing "Added the `FOREST_RPC_METRICS_DISABLED` environment variable..."
accordingly.

🪄 Autofix (Beta)

Fix all unresolved CodeRabbit comments on this PR:

• Push a commit to this branch (recommended)
• Create a new PR with the fixes

---

ℹ️ Review info

⚙️ Run configuration

Configuration used: Repository UI

Review profile: CHILL

Plan: Pro

Run ID: 32e8a073-0a00-4c6a-bcac-5ff52ace4831

📥 Commits

Reviewing files that changed from the base of the PR and between be7fba3 and fdc6ff4.

📒 Files selected for processing (7)

• CHANGELOG.md
• docs/docs/users/reference/env_variables.md
• src/daemon/mod.rs
• src/metrics/mod.rs
• src/rpc/metrics_layer.rs
• src/rpc/mod.rs
• src/tool/offline_server/server.rs

🔗 Linked repositories identified

CodeRabbit considers these linked repositories for cross-repo context during reviews:

• filecoin-project/lotus (manual)

[codecov]

Codecov Report

❌ Patch coverage is 78.20513% with 17 lines in your changes missing coverage. Please review.
✅ Project coverage is 64.37%. Comparing base (aff42c3) to head (64cf1d7).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/rpc/metrics_layer.rs	79.10%	14 Missing ⚠️
src/daemon/mod.rs	0.00%	2 Missing ⚠️
src/tool/offline_server/server.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

Files with missing lines	Coverage Δ
src/metrics/mod.rs	39.83% <ø> (+7.62%)	⬆️
src/rpc/mod.rs	89.68% <100.00%> (+0.19%)	⬆️
src/tool/offline_server/server.rs	27.23% <0.00%> (ø)
src/daemon/mod.rs	24.81% <0.00%> (-0.08%)	⬇️
src/rpc/metrics_layer.rs	74.72% <79.10%> (+10.01%)	⬆️

... and 6 files with indirect coverage changes

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