gopkg.in/natefinch/lumberjack.v2 v2.2.1: Logger, Logger.Write, Logger.Rotate

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/gopkg.in/natefinch/lumberjack.v2@v2.2.1
Kind: HOW

Use EXACTLY these public packages and versions:
  - pkg:golang/gopkg.in/natefinch/lumberjack.v2@v2.2.1
Constraints:
  - executionContext: node
Required runtime conditions:
  - ecosystem: npm
  - language: javascript
  - moduleSystem: cjs
  - packageManager: npm@10.9.8
  - runtime: node@22.23.2

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:sha256:8f279615703df5c151c42ed9d02a0ae59409c56304a0fdb71905c5b68338d1e4","contract":["lumberjack.Logger implements io.WriteCloser","lumberjack.Logger.Write writes log content to the active log file","lumberjack.Logger.Rotate rotates the active log file to a timestamped backup","lumberjack.Logger.Close closes the active log file"],"goal":"verify pkg:golang/gopkg.in/natefinch/lumberjack.v2@v2.2.1","kind":"HOW","packages":["pkg:golang/gopkg.in/natefinch/lumberjack.v2@v2.2.1"],"schemaVersion":1,"symbols":["gopkg.in/natefinch/lumberjack.v2.Logger","gopkg.in/natefinch/lumberjack.v2.Logger.Write","gopkg.in/natefinch/lumberjack.v2.Logger.Rotate","gopkg.in/natefinch/lumberjack.v2.Logger.Close"]},"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/gopkg.in/natefinch/lumberjack.v2@v2.2.1"],"schemaVersion":1,"subject":"pkg:golang/gopkg.in/natefinch/lumberjack.v2@v2.2.1","symbols":["gopkg.in/natefinch/lumberjack.v2.Logger","gopkg.in/natefinch/lumberjack.v2.Logger.Write","gopkg.in/natefinch/lumberjack.v2.Logger.Rotate","gopkg.in/natefinch/lumberjack.v2.Logger.Close"],"verifierAdapter":"golang@1"}

module sample

go 1.22

require gopkg.in/natefinch/lumberjack.v2 v2.2.1

gopkg.in/natefinch/lumberjack.v2 v2.2.1 h1:bBRl1b0OH9s/DuPhuXpNl+VtCaJXFZ5/uEFST95x9zc=
gopkg.in/natefinch/lumberjack.v2 v2.2.1/go.mod h1:YD8tP3GAjkrDg1eZH7EGmyESg/lsYskCTPBJVb9jqSc=

package sample

import (
	"gopkg.in/natefinch/lumberjack.v2"
)

// NewLogger creates a new configured lumberjack.Logger.
func NewLogger(filename string, maxSizeMB int, maxBackups int) *lumberjack.Logger {
	return &lumberjack.Logger{
		Filename:   filename,
		MaxSize:    maxSizeMB,
		MaxBackups: maxBackups,
		LocalTime:  true,
		Compress:   false,
	}
}

// LogMessage writes a message to the logger.
func LogMessage(l *lumberjack.Logger, msg string) (int, error) {
	return l.Write([]byte(msg))
}

// RotateLog triggers a manual rotation of the log file.
func RotateLog(l *lumberjack.Logger) error {
	return l.Rotate()
}

// CloseLogger closes the active log file.
func CloseLogger(l *lumberjack.Logger) error {
	return l.Close()
}

{
  "schemaVersion": 1,
  "goal": "verify pkg:golang/gopkg.in/natefinch/lumberjack.v2@v2.2.1",
  "kind": "HOW",
  "packages": [
    "pkg:golang/gopkg.in/natefinch/lumberjack.v2@v2.2.1"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package main

import (
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"

	"gopkg.in/natefinch/lumberjack.v2"
	"sample"
)

func main() {
	tmpDir, err := os.MkdirTemp("", "lumberjack-test-*")
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to create temp dir: %v\n", err)
		os.Exit(1)
	}
	defer os.RemoveAll(tmpDir)

	logPath := filepath.Join(tmpDir, "app.log")

	// Assertion 1: lumberjack.Logger implements io.WriteCloser
	logger := sample.NewLogger(logPath, 1, 3)
	var _ io.WriteCloser = logger
	var _ *lumberjack.Logger = logger

	// Assertion 2: Writing to logger persists data to the target file
	msg1 := "first log line\n"
	n, err := sample.LogMessage(logger, msg1)
	if err != nil {
		fmt.Fprintf(os.Stderr, "LogMessage failed: %v\n", err)
		os.Exit(1)
	}
	if n != len(msg1) {
		fmt.Fprintf(os.Stderr, "expected %d bytes written, got %d\n", len(msg1), n)
		os.Exit(1)
	}

	content, err := os.ReadFile(logPath)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to read log file: %v\n", err)
		os.Exit(1)
	}
	if string(content) != msg1 {
		fmt.Fprintf(os.Stderr, "expected content %q, got %q\n", msg1, string(content))
		os.Exit(1)
	}

	// Assertion 3: Rotate creates a rotated archive and allows new writes
	if err := sample.RotateLog(logger); err != nil {
		fmt.Fprintf(os.Stderr, "RotateLog failed: %v\n", err)
		os.Exit(1)
	}

	msg2 := "second log line after rotation\n"
	if _, err := sample.LogMessage(logger, msg2); err != nil {
		fmt.Fprintf(os.Stderr, "LogMessage after rotate failed: %v\n", err)
		os.Exit(1)
	}

	// Active log file should now contain only msg2
	activeContent, err := os.ReadFile(logPath)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to read active log file: %v\n", err)
		os.Exit(1)
	}
	if string(activeContent) != msg2 {
		fmt.Fprintf(os.Stderr, "expected active log content %q, got %q\n", msg2, string(activeContent))
		os.Exit(1)
	}

	// Check that a rotated backup file exists containing msg1
	entries, err := os.ReadDir(tmpDir)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to list temp dir: %v\n", err)
		os.Exit(1)
	}
	var backupFound bool
	for _, e := range entries {
		if e.Name() != "app.log" && strings.HasPrefix(e.Name(), "app") {
			backupData, err := os.ReadFile(filepath.Join(tmpDir, e.Name()))
			if err == nil && string(backupData) == msg1 {
				backupFound = true
				break
			}
		}
	}
	if !backupFound {
		fmt.Fprintf(os.Stderr, "expected rotated backup file containing msg1 not found\n")
		os.Exit(1)
	}

	// Assertion 4: Close releases the file resource without error
	if err := sample.CloseLogger(logger); err != nil {
		fmt.Fprintf(os.Stderr, "CloseLogger failed: %v\n", err)
		os.Exit(1)
	}

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