Expand Prometheus metrics with request counters and latency histogram

[mikewheeleer]

Implement richer Prometheus metrics for requests and latency

Description

GET /api/v1/metrics in src/index.ts only exposes two gauges (stableroute_pairs_total, stableroute_paused). The request-timing middleware already measures per-request duration but discards it after logging. This issue records request counts and latency so operators can graph traffic and tail latency from the existing /metrics endpoint.

Requirements and context

• Repository scope: StableRoute-Org/Stableroute-backend only.
• Add stableroute_http_requests_total{method,status} counter and stableroute_http_request_duration_seconds histogram (or summary) populated by the existing res.on("finish") timing hook.
• Add counters for rate-limited (429) and paused (503) responses.
• Keep the Prometheus text exposition format (text/plain; version=0.0.4).
• Avoid unbounded label cardinality — bucket path to route templates, not raw paths.

Suggested execution

• Fork the repo and create a branch
• git checkout -b feature/observability-11-metrics-expansion
• Implement changes
  • Write code in: src/index.ts — extend the timing middleware to update in-memory metric registries and the /metrics serializer.
  • Write comprehensive tests in: src/__tests__/index.test.ts — make requests, then assert the counters/histogram lines appear with correct labels.
  • Add documentation: list metric names in README.md.
  • Add TSDoc on the metric helpers.
  • Validate security: ensure metrics expose no secrets or raw IPs.
• Test and commit

Test and commit

• Run npm run build, npm run lint, and npm test.
• Cover edge cases: 2xx, 4xx, 429, 503 increments; histogram bucket presence.
• Paste full npm test output in the PR.

Example commit message

feat(observability): expose request counters and latency histogram

Guidelines

• Minimum 95 percent test coverage for impacted code.
• Clear, reviewer-focused documentation.
• Timeframe: 96 hours.

Community & contribution rewards

• 💬 Join the StableRoute community on Discord for questions, reviews, and faster merges: https://discord.gg/37aCpusvx
• ⭐ This is a GrantFox OSS / Official Campaign task and may be rewarded. When your PR is merged you'll be prompted to rate the project — if this issue and the maintainers helped you ship, we'd be grateful for a 5-star rating. Clear questions in Discord and tidy, well-tested PRs are the fastest path to a merge and a reward.

[GBOYEE]

Hi maintainers! I'd like to pick this up — Prometheus metrics expansion is right in my wheelhouse.

My plan: extend the existing timing middleware to populate a Counter for requests (method/status labels) and a Histogram for latency, with route template bucketing to keep cardinality bounded. Will add 429/503-specific counters and full test coverage asserting metric labels in the /metrics output.

PR incoming within 24 hours. Cheers!

[YfengJ]

Hi maintainers, I would like to work on this issue if it is still available. I can keep the scope focused on bounded Prometheus request/latency metrics, tests, and docs without touching billing, auth, wallet, or payment behavior. I will wait for maintainer or GrantFox assignment/confirmation before opening a PR.