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

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/go-kit/log.FileKey in 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
Demonstrate these symbols/APIs:
  - github.com/go-kit/log.FileKey

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:sha256:30b87ec078f258dfb445639685e821c90c11050ac406c073fafffa3afcbab647","contract":["log.FileKey sets the key for caller file and line in NewStdlibAdapter","log.NewStdlibAdapter defaults to caller key when FileKey is omitted","log.FileKey is omitted when standard library logger output does not contain file information","log.FileKey custom key works alongside custom MessageKey and TimestampKey"],"goal":"verify github.com/go-kit/log.FileKey in 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":["github.com/go-kit/log.FileKey"]},"contractCommand":["go","run","./test"],"environment":{"arch":"x64","distro":"ubuntu","ecosystem":"golang","executionContext":"go","language":"go","libc":"glibc","libcVersion":"2.39","os":"linux","osVersionBucket":"24","packageManager":"go","runtime":"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":["github.com/go-kit/log.FileKey"],"verifierAdapter":"golang@1"}

module sample-log-filekey

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 github.com/go-kit/log.FileKey in pkg:golang/github.com/go-kit/log@v0.1.0",
  "kind": "HOW",
  "packages": [
    "pkg:golang/github.com/go-kit/log@v0.1.0"
  ],
  "symbols": [
    "github.com/go-kit/log.FileKey"
  ]
}

package main

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

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

func main() {
	// 1. log.FileKey sets the key for caller file and line in NewStdlibAdapter
	{
		var buf bytes.Buffer
		logger := log.NewLogfmtLogger(&buf)
		adapter := log.NewStdlibAdapter(logger, log.FileKey("file"))
		stdLogger := stdlog.New(adapter, "", stdlog.Lshortfile)
		stdLogger.Print("database connection initialized")

		out := buf.String()
		if !strings.Contains(out, "file=") {
			fmt.Fprintf(os.Stderr, "Contract 1 failed: expected custom file key in output %q\n", out)
			os.Exit(1)
		}
		if strings.Contains(out, "caller=") {
			fmt.Fprintf(os.Stderr, "Contract 1 failed: default caller key should not be present in output %q\n", out)
			os.Exit(1)
		}
		if !strings.Contains(out, "contract.go:") {
			fmt.Fprintf(os.Stderr, "Contract 1 failed: expected file name contract.go in output %q\n", out)
			os.Exit(1)
		}
		if !strings.Contains(out, "msg=\"database connection initialized\"") {
			fmt.Fprintf(os.Stderr, "Contract 1 failed: expected message in output %q\n", out)
			os.Exit(1)
		}
	}

	// 2. log.NewStdlibAdapter defaults to caller key when FileKey is omitted
	{
		var buf bytes.Buffer
		logger := log.NewLogfmtLogger(&buf)
		adapter := log.NewStdlibAdapter(logger)
		stdLogger := stdlog.New(adapter, "", stdlog.Lshortfile)
		stdLogger.Print("server worker starting")

		out := buf.String()
		if !strings.Contains(out, "caller=") {
			fmt.Fprintf(os.Stderr, "Contract 2 failed: expected default caller key in output %q\n", out)
			os.Exit(1)
		}
		if !strings.Contains(out, "contract.go:") {
			fmt.Fprintf(os.Stderr, "Contract 2 failed: expected file name contract.go in output %q\n", out)
			os.Exit(1)
		}
		if !strings.Contains(out, "msg=\"server worker starting\"") {
			fmt.Fprintf(os.Stderr, "Contract 2 failed: expected message in output %q\n", out)
			os.Exit(1)
		}
	}

	// 3. log.FileKey is omitted when standard library logger output does not contain file information
	{
		var buf bytes.Buffer
		logger := log.NewLogfmtLogger(&buf)
		adapter := log.NewStdlibAdapter(logger, log.FileKey("source_file"))
		stdLogger := stdlog.New(adapter, "", 0)
		stdLogger.Print("cache cleared")

		out := buf.String()
		if strings.Contains(out, "source_file=") || strings.Contains(out, "caller=") {
			fmt.Fprintf(os.Stderr, "Contract 3 failed: file key should be omitted when no file flag is set, got %q\n", out)
			os.Exit(1)
		}
		if !strings.Contains(out, "msg=\"cache cleared\"") {
			fmt.Fprintf(os.Stderr, "Contract 3 failed: expected message in output %q\n", out)
			os.Exit(1)
		}
	}

	// 4. log.FileKey custom key works alongside custom MessageKey and TimestampKey
	{
		var buf bytes.Buffer
		logger := log.NewLogfmtLogger(&buf)
		adapter := log.NewStdlibAdapter(
			logger,
			log.FileKey("src"),
			log.MessageKey("payload"),
			log.TimestampKey("ts"),
		)
		stdLogger := stdlog.New(adapter, "", stdlog.Ldate|stdlog.Lshortfile)
		stdLogger.Print("batch job completed")

		out := buf.String()
		if !strings.Contains(out, "src=") {
			fmt.Fprintf(os.Stderr, "Contract 4 failed: expected custom src key in output %q\n", out)
			os.Exit(1)
		}
		if !strings.Contains(out, "payload=\"batch job completed\"") {
			fmt.Fprintf(os.Stderr, "Contract 4 failed: expected payload key in output %q\n", out)
			os.Exit(1)
		}
		if !strings.Contains(out, "ts=") {
			fmt.Fprintf(os.Stderr, "Contract 4 failed: expected ts key in output %q\n", out)
			os.Exit(1)
		}
	}
}