go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.68.0: LabelerFromContext

Clean-room public code sample — generation instructions

Write a brand-new, minimal, self-contained code sample in this clean-room directory.
Do not copy, paraphrase, or reference any existing project source. Work only from this spec.

A csx.json manifest scaffold already exists. Do not recreate it from memory. Preserve its case.goal, packages and symbols; fill its empty case.contract with exact assertions and correct its environment, commands and verifierAdapter for the files you generate.

Goal: verify otelhttp.LabelerFromContext in pkg:golang/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp@v0.68.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp@v0.68.0
Demonstrate these symbols/APIs:
  - otelhttp.LabelerFromContext

Rules:
  - One focused purpose; the smallest project that proves the goal.
  - Include a contract test (test/contract.*) that runs OFFLINE and exits 0 exactly when the goal behavior works.
  - Pin every dependency with a lockfile so resolution is reproducible.
  - No secrets, credentials, or tokens. No real URLs (only example.com or localhost). No absolute paths.
  - No personal names, emails, company names, or project identifiers of any kind.
  - No binaries and no generated output (node_modules, dist, target, venv, .git, .env).
  - Keep it under 200 files and 256KB packed.

{"buildCommand":["go","test","-c","-o","test/contract.test","./test"],"case":{"caseId":"case:sha256:e2c60a3c09df3c9b6c491737e7fb39de323b323e1640ca0f8546d729b3332010","contract":["otelhttp.LabelerFromContext retrieves (*otelhttp.Labeler, true) from request context in an instrumented handler","otelhttp.Labeler.Add appends custom metric attributes to the labeler","otelhttp.Labeler.Get returns the slice of added attribute.KeyValue attributes","otelhttp.LabelerFromContext returns (*otelhttp.Labeler, false) when called on an uninstrumented context without panicking"],"goal":"verify otelhttp.LabelerFromContext in pkg:golang/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp@v0.68.0","kind":"HOW","packages":["pkg:golang/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp@v0.68.0"],"schemaVersion":1,"symbols":["otelhttp.LabelerFromContext"]},"contractCommand":["./test/contract.test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","packageManagerVersion":"1.26.6","runtime":"go","runtimeVersion":"1.26.6","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp@v0.68.0"],"schemaVersion":1,"subject":"pkg:golang/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp@v0.68.0","symbols":["otelhttp.LabelerFromContext"],"verifierAdapter":"golang@1"}

module example.com/otelhttp-labeler

go 1.26.6

require (
	go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.68.0
	go.opentelemetry.io/otel v1.43.0
)

require (
	github.com/cespare/xxhash/v2 v2.3.0 // indirect
	github.com/felixge/httpsnoop v1.0.4 // indirect
	github.com/go-logr/logr v1.4.3 // indirect
	github.com/go-logr/stdr v1.2.2 // indirect
	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
	go.opentelemetry.io/otel/metric v1.43.0 // indirect
	go.opentelemetry.io/otel/trace v1.43.0 // indirect
)

github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
github.com/felixge/httpsnoop v1.0.4 h1:NFTV2Zj1bL4mc9sqWACXbQFVBBg2W3GPvqp8/ESS2Wg=
github.com/felixge/httpsnoop v1.0.4/go.mod h1:m8KPJKqk1gH5J9DgRY2ASl2lWCfGKXixSwevea8zH2U=
github.com/go-logr/logr v1.2.2/go.mod h1:jdQByPbusPIv2/zmleS9BjJVeZ6kBagPoEUsqbVz/1A=
github.com/go-logr/logr v1.4.3 h1:CjnDlHq8ikf6E492q6eKboGOC0T8CDaOvkHCIg8idEI=
github.com/go-logr/logr v1.4.3/go.mod h1:9T104GzyrTigFIr8wt5mBrctHMim0Nb2HLGrmQ40KvY=
github.com/go-logr/stdr v1.2.2 h1:hSWxHoqTgW2S2qGc0LTAI563KZ5YKYRhT3MFKZMbjag=
github.com/go-logr/stdr v1.2.2/go.mod h1:mMo/vtBO5dYbehREoey6XUKy/eSumjCCveDpRre4VKE=
github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
github.com/google/uuid v1.6.0 h1:NIvaJDMOsjHA8n1jAhLSgzrAzy1Hgr+hNrb57e+94F0=
github.com/google/uuid v1.6.0/go.mod h1:TIyPZe4MgqvfeYDBFedMoGGpEw/LqOeaOT+nhxU+yHo=
github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
go.opentelemetry.io/auto/sdk v1.2.1 h1:jXsnJ4Lmnqd11kwkBV2LgLoFMZKizbCi5fNZ/ipaZ64=
go.opentelemetry.io/auto/sdk v1.2.1/go.mod h1:KRTj+aOaElaLi+wW1kO/DZRXwkF4C5xPbEe3ZiIhN7Y=
go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.68.0 h1:CqXxU8VOmDefoh0+ztfGaymYbhdB/tT3zs79QaZTNGY=
go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp v0.68.0/go.mod h1:BuhAPThV8PBHBvg8ZzZ/Ok3idOdhWIodywz2xEcRbJo=
go.opentelemetry.io/otel v1.43.0 h1:mYIM03dnh5zfN7HautFE4ieIig9amkNANT+xcVxAj9I=
go.opentelemetry.io/otel v1.43.0/go.mod h1:JuG+u74mvjvcm8vj8pI5XiHy1zDeoCS2LB1spIq7Ay0=
go.opentelemetry.io/otel/metric v1.43.0 h1:d7638QeInOnuwOONPp4JAOGfbCEpYb+K6DVWvdxGzgM=
go.opentelemetry.io/otel/metric v1.43.0/go.mod h1:RDnPtIxvqlgO8GRW18W6Z/4P462ldprJtfxHxyKd2PY=
go.opentelemetry.io/otel/sdk v1.43.0 h1:pi5mE86i5rTeLXqoF/hhiBtUNcrAGHLKQdhg4h4V9Dg=
go.opentelemetry.io/otel/sdk v1.43.0/go.mod h1:P+IkVU3iWukmiit/Yf9AWvpyRDlUeBaRg6Y+C58QHzg=
go.opentelemetry.io/otel/sdk/metric v1.43.0 h1:S88dyqXjJkuBNLeMcVPRFXpRw2fuwdvfCGLEo89fDkw=
go.opentelemetry.io/otel/sdk/metric v1.43.0/go.mod h1:C/RJtwSEJ5hzTiUz5pXF1kILHStzb9zFlIEe85bhj6A=
go.opentelemetry.io/otel/trace v1.43.0 h1:BkNrHpup+4k4w+ZZ86CZoHHEkohws8AY+WTX09nk+3A=
go.opentelemetry.io/otel/trace v1.43.0/go.mod h1:/QJhyVBUUswCphDVxq+8mld+AvhXZLhe+8WVFxiFff0=
golang.org/x/sys v0.42.0 h1:omrd2nAlyT5ESRdCLYdm3+fMfNFE/+Rf4bDIQImRJeo=
golang.org/x/sys v0.42.0/go.mod h1:4GL1E5IUh+htKOUEOaiffhrAeqysfVGipDYzABqnCmw=
gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

package sample

import (
	"context"
	"net/http"

	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
	"go.opentelemetry.io/otel/attribute"
)

// AddLabelToContextRequest adds the specified metric attributes to the active otelhttp.Labeler if present.
// Returns true if a Labeler was found in the context, or false otherwise.
func AddLabelToContextRequest(ctx context.Context, attrs ...attribute.KeyValue) (*otelhttp.Labeler, bool) {
	labeler, ok := otelhttp.LabelerFromContext(ctx)
	if labeler != nil && len(attrs) > 0 {
		labeler.Add(attrs...)
	}
	return labeler, ok
}

// NewInstrumentedHandler wraps an http.Handler with otelhttp instrumentation,
// which injects an otelhttp.Labeler into the request context for downstream handlers.
func NewInstrumentedHandler(operation string, handler http.Handler) http.Handler {
	return otelhttp.NewHandler(handler, operation)
}

{
  "schemaVersion": 1,
  "goal": "verify otelhttp.LabelerFromContext in pkg:golang/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp@v0.68.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp@v0.68.0"
  ],
  "symbols": [
    "otelhttp.LabelerFromContext"
  ]
}

package test

import (
	"context"
	"net/http"
	"net/http/httptest"
	"testing"

	sample "example.com/otelhttp-labeler"
	"go.opentelemetry.io/contrib/instrumentation/net/http/otelhttp"
	"go.opentelemetry.io/otel/attribute"
)

func TestLabelerFromContextContract(t *testing.T) {
	// 1. Inside an otelhttp-instrumented handler, LabelerFromContext retrieves the active *otelhttp.Labeler with ok=true
	var capturedLabeler *otelhttp.Labeler
	var capturedOk bool

	innerHandler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		capturedLabeler, capturedOk = sample.AddLabelToContextRequest(
			r.Context(),
			attribute.String("http.route", "/api/items"),
			attribute.Int("item.count", 42),
		)
		w.WriteHeader(http.StatusOK)
	})

	instrumented := sample.NewInstrumentedHandler("test-operation", innerHandler)

	req := httptest.NewRequest(http.MethodGet, "/api/items", nil)
	rec := httptest.NewRecorder()

	instrumented.ServeHTTP(rec, req)

	if !capturedOk {
		t.Fatalf("expected LabelerFromContext to return ok=true inside instrumented handler")
	}
	if capturedLabeler == nil {
		t.Fatalf("expected non-nil Labeler inside instrumented handler")
	}

	// 2. Added attributes are stored in the labeler and retrievable via Get()
	attrs := capturedLabeler.Get()
	if len(attrs) != 2 {
		t.Fatalf("expected 2 attributes on Labeler, got %d", len(attrs))
	}
	if attrs[0].Key != "http.route" || attrs[0].Value.AsString() != "/api/items" {
		t.Fatalf("unexpected first attribute: %v", attrs[0])
	}
	if attrs[1].Key != "item.count" || attrs[1].Value.AsInt64() != 42 {
		t.Fatalf("unexpected second attribute: %v", attrs[1])
	}

	// 3. In an uninstrumented context, LabelerFromContext returns ok=false and an empty non-nil *otelhttp.Labeler
	plainCtx := context.Background()
	emptyLabeler, ok := sample.AddLabelToContextRequest(
		plainCtx,
		attribute.String("sample.key", "sample.val"),
	)
	if ok {
		t.Fatalf("expected ok=false for plain uninstrumented context")
	}
	if emptyLabeler == nil {
		t.Fatalf("expected non-nil Labeler even when ok=false")
	}
	emptyAttrs := emptyLabeler.Get()
	if len(emptyAttrs) != 1 || emptyAttrs[0].Key != "sample.key" {
		t.Fatalf("unexpected attributes on empty labeler: %v", emptyAttrs)
	}
}