feat(middleware): record HTTP server request duration metrics

[gandalf-at-lerian]

Summary

• Adds native OpenTelemetry http.server.request.duration metrics to the Fiber WithTelemetry middleware.
• Records a Float64 histogram in seconds with http.request.method, http.route, http.response.status_code, and error.type for handler errors / 5xx responses.
• Keeps excluded routes and nil telemetry / meter / metrics factory paths as no-op paths.

Context

Originally requested through LerianStudio/lib-commons#462, but the middleware now lives in lib-observability after the lib-commons v5 split, so the implementation lands here.

Tests

• go test -tags=unit ./middleware/ -count=1
• go test -tags=unit ./...
• golangci-lint run ./...

Requested by: @gauchito91

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

Review profile: ASSERTIVE

Plan: Pro

Run ID: 30e493f7-1d10-42ec-aec8-3545f7db64b5

📥 Commits

Reviewing files that changed from the base of the PR and between 972c752 and b57e0cf.

📒 Files selected for processing (2)

• middleware/telemetry.go
• middleware/telemetry_metrics_test.go

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Walkthrough

The PR adds OpenTelemetry HTTP server request duration metrics to the telemetry middleware. A Float64 histogram named http.server.request.duration (in seconds) is precomputed when telemetry provides both a MeterProvider and MetricsFactory. For each request, the middleware captures the start time before execution and records the duration upon completion, including HTTP semantic attributes and error type classification from handler errors or status codes.

Changes

HTTP Request Duration Metrics

Layer / File(s)	Summary
Histogram metric definition and initialization middleware/telemetry.go	Imports time and strconv; adds a histogram construction helper with explicit second-based bucket boundaries; precomputes the http.server.request.duration histogram at handler construction time when effective telemetry has both MeterProvider and MetricsFactory.
Request timing and duration recording middleware/telemetry.go	Captures request start time before handler execution; records duration histogram upon completion with HTTP semantic attributes (http.request.method, http.route, http.response.status_code) and conditional error.type; includes helpers recordHTTPServerDuration and classifyHTTPErrorType that handle typed-nil checks and derive error type from handler errors or server status codes.
Metric recording test suite middleware/telemetry_metrics_test.go	Adds an OTel ManualReader-based test harness and tests asserting histogram recording and attributes for success (2xx), 4xx, 5xx (status-derived error.type), handler errors (Go concrete type), Fiber errors, excluded routes (no recording), and no-op behavior when telemetry, MeterProvider, or MetricsFactory are absent.

Sequence Diagram

sequenceDiagram
    participant Request
    participant Middleware
    participant Handler
    participant OTelMeter
    Request->>Middleware: HTTP request arrives
    Middleware->>Middleware: requestStart ← current time
    Middleware->>Handler: c.Next()
    Handler-->>Middleware: status code + optional error
    Middleware->>OTelMeter: recordHTTPServerDuration(duration, attributes)
    OTelMeter->>OTelMeter: record histogram sample
    OTelMeter->>OTelMeter: attach http.request.method
    OTelMeter->>OTelMeter: attach http.route
    OTelMeter->>OTelMeter: attach http.response.status_code
    OTelMeter->>OTelMeter: conditionally attach error.type
    OTelMeter-->>Request: response sent

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Possibly related issues

• Emit native HTTP server request metrics from Fiber telemetry middleware lib-commons#462: Implements native HTTP server request duration histogram recording (http.server.request.duration) with route-based http.route, http.request.method, http.response.status_code, and error.type classification logic directly matching the objectives in the linked issue.

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[lerian-studio]

⚠️ Invalid Source Branch

Pull requests to main can only come from:

• develop
• release-candidate
• hotfix/*

Your source branch: feat/http-server-request-metrics

Please change the base branch or create a PR from an allowed branch.

[lerian-studio]

🔍 PR Validation Summary

✅ PR Mergeable — no blocking failures

Check	Status	Blocking
Source Branch	✅ success	yes
PR Title	✅ success	yes
PR Description	✅ success	yes
PR Size	✅ success	no
Auto Labels	✅ success	no
PR Metadata	✅ success	no

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[lerian-studio]

🔒 Security Scan Results — lib-observability

✅ PR Mergeable — no blocking findings

Stage	Status	Blocking?
Filesystem Scan	✅ Clean	—
Docker Image Scan	➖ Skipped	—
Docker Hub Health Score	➖ Skipped	—
Pre-release Version Check	✅ Clean	—

Trivy

Filesystem Scan

✅ No vulnerabilities or secrets found.

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Pre-release Version Check

✅ No unstable version pins found.

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[lerian-studio]

📊 Unit Test Coverage Report: lib-observability

Metric	Value
Overall Coverage	84.5% ✅ PASS
Threshold	80%

Coverage by Package

Package	Coverage
github.com/LerianStudio/lib-observability/assert	97.9%
github.com/LerianStudio/lib-observability/constants	83.3%
github.com/LerianStudio/lib-observability/log	94.9%
github.com/LerianStudio/lib-observability/metrics	91.4%
github.com/LerianStudio/lib-observability/middleware	68.6%
github.com/LerianStudio/lib-observability/redaction	95.8%
github.com/LerianStudio/lib-observability/runtime	80.4%
github.com/LerianStudio/lib-observability/tracing	84.9%
github.com/LerianStudio/lib-observability/zap	96.0%
github.com/LerianStudio/lib-observability	91.1%

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Generated by Go PR Analysis workflow

[blacksmith-sh]

Found 1 test failure on Blacksmith runners:

Failure

Test	View Logs
github.com/LerianStudio/lib-observability/middleware/ TestWithTelemetry_RecordsDurationOnSuccess	View Logs