github.com/go-kit/log v0.1.0: NewStdlibAdapter

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 pkg:golang/github.com/go-kit/log@v0.1.0
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/github.com/go-kit/log@v0.1.0

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:d3d8a4f98714919cc292e282125befe8abac3d8b6565c6093769209417579a1b","contract":["log.NewStdlibAdapter redirects standard library log events to a structured logger","log.NewStdlibAdapter extracts timestamp into the default ts field","log.NewStdlibAdapter extracts caller file and line into the default caller field","log.MessageKey, log.TimestampKey, and log.FileKey configure custom field names for extracted data","log.Prefix strips standard library prefixes or retains them when joinPrefixToMsg is true","log.NewStdlibAdapter supports thread-safe concurrent writes from multiple goroutines"],"goal":"verify pkg:golang/github.com/go-kit/log@v0.1.0","kind":"HOW","packages":["pkg:golang/github.com/go-kit/log@v0.1.0"],"schemaVersion":1,"symbols":["log.NewStdlibAdapter"]},"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/go-kit/log@v0.1.0"],"schemaVersion":1,"subject":"pkg:golang/github.com/go-kit/log@v0.1.0","symbols":["log.NewStdlibAdapter"],"verifierAdapter":"golang@1"}

module sample

go 1.26.6

require github.com/go-kit/log v0.1.0

require github.com/go-logfmt/logfmt v0.5.0 // indirect

github.com/go-kit/log v0.1.0 h1:DGJh0Sm43HbOeYDNnVZFl8BvcYVvjD5bqYJvp0REbwQ=
github.com/go-kit/log v0.1.0/go.mod h1:zbhenjAZHb184qTLMA9ZjW7ThYL0H2mk7Q6pNt4vbaY=
github.com/go-logfmt/logfmt v0.5.0 h1:TrB8swr/68K7m9CcGut2g3UOihhbcbiMAYiuTXdEih4=
github.com/go-logfmt/logfmt v0.5.0/go.mod h1:wCYkCAKZfumFQihp8CzCvQ3paCTfi41vtzG1KdI/P7A=
github.com/go-stack/stack v1.8.0 h1:5SgMzNM5HxrEjV0ww2lTmX6E2Izsfxas4+YHWRs3Lsk=
github.com/go-stack/stack v1.8.0/go.mod h1:v0f6uXyyMGvRgIKkXu+yp6POWl0qKG85gN/melR3HDY=

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/github.com/go-kit/log@v0.1.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/go-kit/log@v0.1.0"
  ]
}

package main

import (
	"bytes"
	"fmt"
	stdlog "log"
	"os"
	"regexp"
	"strings"
	"sync"

	"github.com/go-kit/log"
)

func main() {
	if err := runContractTests(); err != nil {
		fmt.Fprintf(os.Stderr, "Contract test failed: %v\n", err)
		os.Exit(1)
	}
	fmt.Println("All contract tests passed successfully.")
}

func runContractTests() error {
	var buf bytes.Buffer
	baseLogger := log.NewLogfmtLogger(&buf)

	// 1. log.NewStdlibAdapter redirects standard library log events to a structured logger
	{
		buf.Reset()
		adapter := log.NewStdlibAdapter(baseLogger)
		l := stdlog.New(adapter, "", 0)
		l.Print("service initialized successfully")

		out := strings.TrimSpace(buf.String())
		expected := `msg="service initialized successfully"`
		if out != expected {
			return fmt.Errorf("assertion 1 failed: expected %q, got %q", expected, out)
		}
	}

	// 2. log.NewStdlibAdapter extracts timestamp into the default ts field
	{
		buf.Reset()
		adapter := log.NewStdlibAdapter(baseLogger)
		l := stdlog.New(adapter, "", stdlog.Ldate|stdlog.Ltime)
		l.Print("timestamped event")

		out := strings.TrimSpace(buf.String())
		tsRegex := regexp.MustCompile(`^ts="[0-9]{4}/[0-9]{2}/[0-9]{2} [0-9]{2}:[0-9]{2}:[0-9]{2}" msg="timestamped event"$`)
		if !tsRegex.MatchString(out) {
			return fmt.Errorf("assertion 2 failed: output %q did not match timestamp pattern", out)
		}
	}

	// 3. log.NewStdlibAdapter extracts caller file and line into the default caller field
	{
		buf.Reset()
		adapter := log.NewStdlibAdapter(baseLogger)
		l := stdlog.New(adapter, "", stdlog.Lshortfile)
		l.Print("caller tracked event")

		out := strings.TrimSpace(buf.String())
		callerRegex := regexp.MustCompile(`^caller=.+?:[0-9]+ msg="caller tracked event"$`)
		if !callerRegex.MatchString(out) {
			return fmt.Errorf("assertion 3 failed: output %q did not match caller pattern", out)
		}
	}

	// 4. log.MessageKey, log.TimestampKey, and log.FileKey configure custom field names for extracted data
	{
		buf.Reset()
		adapter := log.NewStdlibAdapter(baseLogger,
			log.MessageKey("log_message"),
			log.TimestampKey("log_time"),
			log.FileKey("log_source"),
		)
		l := stdlog.New(adapter, "", stdlog.Ldate|stdlog.Ltime|stdlog.Lshortfile)
		l.Print("customized key event")

		out := strings.TrimSpace(buf.String())
		customRegex := regexp.MustCompile(`^log_time="[0-9]{4}/[0-9]{2}/[0-9]{2} [0-9]{2}:[0-9]{2}:[0-9]{2}" log_source=.+?:[0-9]+ log_message="customized key event"$`)
		if !customRegex.MatchString(out) {
			return fmt.Errorf("assertion 4 failed: output %q did not match custom keys pattern", out)
		}
	}

	// 5. log.Prefix strips standard library prefixes or retains them when joinPrefixToMsg is true
	{
		// 5a. joinPrefixToMsg = false (prefix stripped)
		buf.Reset()
		adapterStrip := log.NewStdlibAdapter(baseLogger, log.Prefix("WORKER: ", false))
		lStrip := stdlog.New(adapterStrip, "WORKER: ", 0)
		lStrip.Print("task finished")

		out := strings.TrimSpace(buf.String())
		expected := `msg="task finished"`
		if out != expected {
			return fmt.Errorf("assertion 5a failed: expected %q, got %q", expected, out)
		}

		// 5b. joinPrefixToMsg = true (prefix joined)
		buf.Reset()
		adapterJoin := log.NewStdlibAdapter(baseLogger, log.Prefix("WORKER: ", true))
		lJoin := stdlog.New(adapterJoin, "WORKER: ", 0)
		lJoin.Print("task finished")

		out = strings.TrimSpace(buf.String())
		expectedJoin := `msg="WORKER: task finished"`
		if out != expectedJoin {
			return fmt.Errorf("assertion 5b failed: expected %q, got %q", expectedJoin, out)
		}
	}

	// 6. log.NewStdlibAdapter supports thread-safe concurrent writes from multiple goroutines
	{
		buf.Reset()
		syncLogger := log.NewSyncLogger(baseLogger)
		adapter := log.NewStdlibAdapter(syncLogger)
		l := stdlog.New(adapter, "", 0)

		const workerCount = 20
		var wg sync.WaitGroup
		for i := 0; i < workerCount; i++ {
			wg.Add(1)
			go func(id int) {
				defer wg.Done()
				l.Printf("worker %d completed", id)
			}(i)
		}
		wg.Wait()

		lines := strings.Split(strings.TrimSpace(buf.String()), "\n")
		if len(lines) != workerCount {
			return fmt.Errorf("assertion 6 failed: expected %d lines, got %d", workerCount, len(lines))
		}
		for _, line := range lines {
			if !strings.HasPrefix(line, `msg="worker `) || !strings.HasSuffix(line, ` completed"`) {
				return fmt.Errorf("assertion 6 failed: unexpected line content %q", line)
			}
		}
	}

	return nil
}