go.opentelemetry.io/otel/exporters/stdout/stdoutmetric v1.43.0: WithWriter

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 stdoutmetric.WithWriter in pkg:golang/go.opentelemetry.io/otel/exporters/stdout/stdoutmetric@v1.43.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/go.opentelemetry.io/otel/exporters/stdout/stdoutmetric@v1.43.0
Demonstrate these symbols/APIs:
  - stdoutmetric.WithWriter
Required runtime conditions:
  - ecosystem: golang
  - language: go
  - packageManager: go@1.26.6
  - runtime: go@1.26.6

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:c6473fe8f8d36ad77fce7f9a387a4e05cdc5bbdde0e91091aa3f7d91dfac6796","contract":["stdoutmetric.New with stdoutmetric.WithWriter initializes an Exporter directing output to the provided io.Writer","sdkmetric.MeterProvider flushes recorded metrics through stdoutmetric Exporter into the custom writer","Exported metric JSON in the writer contains recorded metric names and attributes"],"goal":"verify stdoutmetric.WithWriter in pkg:golang/go.opentelemetry.io/otel/exporters/stdout/stdoutmetric@v1.43.0","kind":"HOW","packages":["pkg:golang/go.opentelemetry.io/otel/exporters/stdout/stdoutmetric@v1.43.0"],"schemaVersion":1,"symbols":["stdoutmetric.WithWriter"]},"contractCommand":["go","run","./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/otel/exporters/stdout/stdoutmetric@v1.43.0"],"schemaVersion":1,"subject":"pkg:golang/go.opentelemetry.io/otel/exporters/stdout/stdoutmetric@v1.43.0","symbols":["stdoutmetric.WithWriter"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require (
	go.opentelemetry.io/otel v1.43.0
	go.opentelemetry.io/otel/exporters/stdout/stdoutmetric v1.43.0
	go.opentelemetry.io/otel/metric v1.43.0
	go.opentelemetry.io/otel/sdk/metric v1.43.0
)

require (
	github.com/cespare/xxhash/v2 v2.3.0 // indirect
	github.com/go-logr/logr v1.4.3 // indirect
	github.com/go-logr/stdr v1.2.2 // indirect
	github.com/google/uuid v1.6.0 // indirect
	go.opentelemetry.io/auto/sdk v1.2.1 // indirect
	go.opentelemetry.io/otel/sdk v1.43.0 // indirect
	go.opentelemetry.io/otel/trace v1.43.0 // indirect
	golang.org/x/sys v0.42.0 // 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/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/otel v1.43.0 h1:mYIM03dnh5zfN7HautFE4ieIig9amkNANT+xcVxAj9I=
go.opentelemetry.io/otel v1.43.0/go.mod h1:JuG+u74mvjvcm8vj8pI5XiHy1zDeoCS2LB1spIq7Ay0=
go.opentelemetry.io/otel/exporters/stdout/stdoutmetric v1.43.0 h1:TC+BewnDpeiAmcscXbGMfxkO+mwYUwE/VySwvw88PfA=
go.opentelemetry.io/otel/exporters/stdout/stdoutmetric v1.43.0/go.mod h1:J/ZyF4vfPwsSr9xJSPyQ4LqtcTPULFR64KwTikGLe+A=
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 main

import (
	"context"
	"fmt"
	"io"
	"log"
	"os"

	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/exporters/stdout/stdoutmetric"
	"go.opentelemetry.io/otel/metric"
	sdkmetric "go.opentelemetry.io/otel/sdk/metric"
)

// SetupMeterProvider initializes an OpenTelemetry MeterProvider writing metric exports to the specified io.Writer.
func SetupMeterProvider(w io.Writer) (*sdkmetric.MeterProvider, error) {
	exp, err := stdoutmetric.New(
		stdoutmetric.WithWriter(w),
	)
	if err != nil {
		return nil, fmt.Errorf("failed to create stdoutmetric exporter: %w", err)
	}

	mp := sdkmetric.NewMeterProvider(
		sdkmetric.WithReader(sdkmetric.NewPeriodicReader(exp)),
	)
	return mp, nil
}

func main() {
	ctx := context.Background()

	// Direct metric exports to stdout using stdoutmetric.WithWriter
	mp, err := SetupMeterProvider(os.Stdout)
	if err != nil {
		log.Fatalf("failed to initialize meter provider: %v", err)
	}
	defer func() {
		if err := mp.Shutdown(ctx); err != nil {
			log.Printf("error shutting down meter provider: %v", err)
		}
	}()

	meter := mp.Meter("example-writer-meter")
	counter, err := meter.Int64Counter(
		"app.custom_writer.operations",
		metric.WithDescription("Operations exported via custom writer"),
		metric.WithUnit("{operation}"),
	)
	if err != nil {
		log.Fatalf("failed to create counter: %v", err)
	}

	counter.Add(ctx, 1, metric.WithAttributes(
		attribute.String("status", "success"),
	))

	if err := mp.ForceFlush(ctx); err != nil {
		log.Fatalf("failed to flush meter provider: %v", err)
	}
}

{
  "schemaVersion": 1,
  "goal": "verify stdoutmetric.WithWriter in pkg:golang/go.opentelemetry.io/otel/exporters/stdout/stdoutmetric@v1.43.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/go.opentelemetry.io/otel/exporters/stdout/stdoutmetric@v1.43.0"
  ],
  "symbols": [
    "stdoutmetric.WithWriter"
  ],
  "runtimeConditions": {
    "ecosystem": "golang",
    "language": "go",
    "packageManager": "go@1.26.6",
    "runtime": "go@1.26.6"
  }
}

package main

import (
	"bytes"
	"context"
	"fmt"
	"os"
	"strings"

	"go.opentelemetry.io/otel/attribute"
	"go.opentelemetry.io/otel/exporters/stdout/stdoutmetric"
	"go.opentelemetry.io/otel/metric"
	sdkmetric "go.opentelemetry.io/otel/sdk/metric"
)

func main() {
	ctx := context.Background()
	var buf bytes.Buffer

	// Assertion 1: stdoutmetric.New with stdoutmetric.WithWriter initializes an Exporter directing output to the provided io.Writer
	exp, err := stdoutmetric.New(
		stdoutmetric.WithWriter(&buf),
	)
	if err != nil {
		fmt.Fprintf(os.Stderr, "CONTRACT FAIL: stdoutmetric.New failed: %v\n", err)
		os.Exit(1)
	}
	if exp == nil {
		fmt.Fprintf(os.Stderr, "CONTRACT FAIL: stdoutmetric.New returned nil exporter\n")
		os.Exit(1)
	}

	// Assertion 2: sdkmetric.MeterProvider flushes recorded metrics through stdoutmetric Exporter into the custom writer
	reader := sdkmetric.NewPeriodicReader(exp)
	mp := sdkmetric.NewMeterProvider(
		sdkmetric.WithReader(reader),
	)
	if mp == nil {
		fmt.Fprintf(os.Stderr, "CONTRACT FAIL: NewMeterProvider returned nil\n")
		os.Exit(1)
	}

	meter := mp.Meter("test-writer-meter")
	counter, err := meter.Int64Counter("test.writer.counter", metric.WithDescription("contract test counter"))
	if err != nil {
		fmt.Fprintf(os.Stderr, "CONTRACT FAIL: Int64Counter creation failed: %v\n", err)
		os.Exit(1)
	}

	counter.Add(ctx, 42, metric.WithAttributes(attribute.String("env", "contract-test")))

	if err := mp.ForceFlush(ctx); err != nil {
		fmt.Fprintf(os.Stderr, "CONTRACT FAIL: ForceFlush failed: %v\n", err)
		os.Exit(1)
	}

	if err := mp.Shutdown(ctx); err != nil {
		fmt.Fprintf(os.Stderr, "CONTRACT FAIL: Shutdown failed: %v\n", err)
		os.Exit(1)
	}

	// Assertion 3: Exported metric JSON in the writer contains recorded metric names and attributes
	output := buf.String()
	if !strings.Contains(output, "test.writer.counter") {
		fmt.Fprintf(os.Stderr, "CONTRACT FAIL: expected metric name in output buffer, got: %s\n", output)
		os.Exit(1)
	}
	if !strings.Contains(output, "contract-test") {
		fmt.Fprintf(os.Stderr, "CONTRACT FAIL: expected attribute value in output buffer, got: %s\n", output)
		os.Exit(1)
	}

	fmt.Println("Contract tests passed successfully.")
}