github.com/prometheus/client_model v0.6.1: go.Exemplar

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 github.com/prometheus/client_model/go.Exemplar in pkg:golang/github.com/prometheus/client_model@v0.6.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/prometheus/client_model@v0.6.1
Demonstrate these symbols/APIs:
  - github.com/prometheus/client_model/go.Exemplar

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.

{"case":{"caseId":"case:sha256:139dccff95099dbeaae7ff030c5161be920e92757a4b9b31bd79da8d5f198153","contract":["dto.Exemplar getter methods return default zero or nil values for nil and empty Exemplar instances.","dto.Exemplar stores and retrieves a float64 value via GetValue.","dto.Exemplar stores and retrieves a collection of LabelPair labels via GetLabel.","dto.Exemplar stores and retrieves an OpenMetrics-style timestamp via GetTimestamp.","dto.Exemplar serializes and deserializes via protobuf preserving all fields.","dto.Exemplar.Reset clears all fields back to zero or nil values."],"goal":"verify github.com/prometheus/client_model/go.Exemplar in pkg:golang/github.com/prometheus/client_model@v0.6.1","kind":"HOW","packages":["pkg:golang/github.com/prometheus/client_model@v0.6.1"],"schemaVersion":1,"symbols":["github.com/prometheus/client_model/go.Exemplar"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","schemaVersion":1},"license":"MIT-0","packages":["pkg:golang/github.com/prometheus/client_model@v0.6.1"],"schemaVersion":1,"subject":"pkg:golang/github.com/prometheus/client_model@v0.6.1","symbols":["github.com/prometheus/client_model/go.Exemplar"],"verifierAdapter":"golang@1"}

module example.com/exemplar

go 1.22

require (
	github.com/prometheus/client_model v0.6.1
	google.golang.org/protobuf v1.33.0
)

github.com/google/go-cmp v0.5.5 h1:Khx7svrCpmxxtHBq5j2mp/xVjsi8hQMfNLvJFAlrGgU=
github.com/google/go-cmp v0.5.5/go.mod h1:v8dTdLbMG2kIc/vJvl+f65V22dbkXbowE6jgT/gNBxE=
github.com/prometheus/client_model v0.6.1 h1:ZKSh/rekM+n3CeS952MLRAdFwIKqeY8b62p8ais2e9E=
github.com/prometheus/client_model v0.6.1/go.mod h1:OrxVMOVHjw3lKMa8+x6HeMGkHMQyHDk9E3jmP2AmGiY=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
google.golang.org/protobuf v1.33.0 h1:uNO2rsAINq/JlFpSdYEKIZ0uKD/R9cpdv0T+yoGwGmI=
google.golang.org/protobuf v1.33.0/go.mod h1:c6P6GXX6sHbq/GpV6MGZEdwhWPcYBgnhAHhKbcUYpos=

package main

import (
	"fmt"
	"time"

	dto "github.com/prometheus/client_model/go"
	"google.golang.org/protobuf/proto"
	"google.golang.org/protobuf/types/known/timestamppb"
)

func main() {
	now := time.Now()
	ts := timestamppb.New(now)

	exemplar := &dto.Exemplar{
		Label: []*dto.LabelPair{
			{
				Name:  proto.String("trace_id"),
				Value: proto.String("trace-12345"),
			},
		},
		Value:     proto.Float64(0.25),
		Timestamp: ts,
	}

	fmt.Printf("Exemplar value: %f\n", exemplar.GetValue())
	for _, l := range exemplar.GetLabel() {
		fmt.Printf("Label: %s=%s\n", l.GetName(), l.GetValue())
	}
	if t := exemplar.GetTimestamp(); t != nil {
		fmt.Printf("Timestamp: %s\n", t.AsTime().Format(time.RFC3339))
	}

	exemplar.Reset()
	fmt.Printf("After reset, value: %f\n", exemplar.GetValue())
}

{
  "schemaVersion": 1,
  "goal": "verify github.com/prometheus/client_model/go.Exemplar in pkg:golang/github.com/prometheus/client_model@v0.6.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/prometheus/client_model@v0.6.1"
  ],
  "symbols": [
    "github.com/prometheus/client_model/go.Exemplar"
  ]
}

package main

import (
	"fmt"
	"os"
	"time"

	dto "github.com/prometheus/client_model/go"
	"google.golang.org/protobuf/proto"
	"google.golang.org/protobuf/types/known/timestamppb"
)

func main() {
	// 1. dto.Exemplar getter methods return default zero or nil values for nil and empty Exemplar instances.
	var nilExemplar *dto.Exemplar
	if got := nilExemplar.GetValue(); got != 0.0 {
		fmt.Fprintf(os.Stderr, "nilExemplar.GetValue() expected 0, got %v\n", got)
		os.Exit(1)
	}
	if got := nilExemplar.GetLabel(); got != nil {
		fmt.Fprintf(os.Stderr, "nilExemplar.GetLabel() expected nil, got %v\n", got)
		os.Exit(1)
	}
	if got := nilExemplar.GetTimestamp(); got != nil {
		fmt.Fprintf(os.Stderr, "nilExemplar.GetTimestamp() expected nil, got %v\n", got)
		os.Exit(1)
	}

	emptyExemplar := &dto.Exemplar{}
	if got := emptyExemplar.GetValue(); got != 0.0 {
		fmt.Fprintf(os.Stderr, "emptyExemplar.GetValue() expected 0, got %v\n", got)
		os.Exit(1)
	}
	if got := emptyExemplar.GetLabel(); got != nil {
		fmt.Fprintf(os.Stderr, "emptyExemplar.GetLabel() expected nil, got %v\n", got)
		os.Exit(1)
	}
	if got := emptyExemplar.GetTimestamp(); got != nil {
		fmt.Fprintf(os.Stderr, "emptyExemplar.GetTimestamp() expected nil, got %v\n", got)
		os.Exit(1)
	}

	// 2. dto.Exemplar stores and retrieves a float64 value via GetValue.
	val := 42.75
	exemplarWithVal := &dto.Exemplar{
		Value: proto.Float64(val),
	}
	if got := exemplarWithVal.GetValue(); got != val {
		fmt.Fprintf(os.Stderr, "exemplarWithVal.GetValue() expected %v, got %v\n", val, got)
		os.Exit(1)
	}

	// 3. dto.Exemplar stores and retrieves a collection of LabelPair labels via GetLabel.
	labels := []*dto.LabelPair{
		{
			Name:  proto.String("trace_id"),
			Value: proto.String("req-12345"),
		},
		{
			Name:  proto.String("span_id"),
			Value: proto.String("span-67890"),
		},
	}
	exemplarWithLabels := &dto.Exemplar{
		Label: labels,
	}
	gotLabels := exemplarWithLabels.GetLabel()
	if len(gotLabels) != 2 {
		fmt.Fprintf(os.Stderr, "expected 2 labels, got %d\n", len(gotLabels))
		os.Exit(1)
	}
	if gotLabels[0].GetName() != "trace_id" || gotLabels[0].GetValue() != "req-12345" {
		fmt.Fprintf(os.Stderr, "first label mismatch: %v=%v\n", gotLabels[0].GetName(), gotLabels[0].GetValue())
		os.Exit(1)
	}
	if gotLabels[1].GetName() != "span_id" || gotLabels[1].GetValue() != "span-67890" {
		fmt.Fprintf(os.Stderr, "second label mismatch: %v=%v\n", gotLabels[1].GetName(), gotLabels[1].GetValue())
		os.Exit(1)
	}

	// 4. dto.Exemplar stores and retrieves an OpenMetrics-style timestamp via GetTimestamp.
	now := time.Unix(1700000000, 500000000)
	ts := timestamppb.New(now)
	exemplarWithTs := &dto.Exemplar{
		Timestamp: ts,
	}
	gotTs := exemplarWithTs.GetTimestamp()
	if gotTs == nil {
		fmt.Fprintf(os.Stderr, "expected non-nil timestamp\n")
		os.Exit(1)
	}
	if gotTs.GetSeconds() != 1700000000 || gotTs.GetNanos() != 500000000 {
		fmt.Fprintf(os.Stderr, "timestamp mismatch: seconds=%v nanos=%v\n", gotTs.GetSeconds(), gotTs.GetNanos())
		os.Exit(1)
	}

	// 5. dto.Exemplar serializes and deserializes via protobuf preserving all fields.
	fullExemplar := &dto.Exemplar{
		Value:     proto.Float64(99.5),
		Label:     labels,
		Timestamp: ts,
	}
	data, err := proto.Marshal(fullExemplar)
	if err != nil {
		fmt.Fprintf(os.Stderr, "proto.Marshal failed: %v\n", err)
		os.Exit(1)
	}
	decodedExemplar := &dto.Exemplar{}
	if err := proto.Unmarshal(data, decodedExemplar); err != nil {
		fmt.Fprintf(os.Stderr, "proto.Unmarshal failed: %v\n", err)
		os.Exit(1)
	}
	if !proto.Equal(fullExemplar, decodedExemplar) {
		fmt.Fprintf(os.Stderr, "proto.Equal failed after marshal/unmarshal\n")
		os.Exit(1)
	}

	// 6. dto.Exemplar.Reset clears all fields back to zero or nil values.
	fullExemplar.Reset()
	if got := fullExemplar.GetValue(); got != 0.0 {
		fmt.Fprintf(os.Stderr, "after Reset(), GetValue() expected 0, got %v\n", got)
		os.Exit(1)
	}
	if got := fullExemplar.GetLabel(); got != nil {
		fmt.Fprintf(os.Stderr, "after Reset(), GetLabel() expected nil, got %v\n", got)
		os.Exit(1)
	}
	if got := fullExemplar.GetTimestamp(); got != nil {
		fmt.Fprintf(os.Stderr, "after Reset(), GetTimestamp() expected nil, got %v\n", got)
		os.Exit(1)
	}

	fmt.Println("All contract assertions passed.")
}