gopkg.in/natefinch/lumberjack.v2 v2.2.1: lumberjack.Logger

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 lumberjack.Logger in 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
Demonstrate these symbols/APIs:
  - lumberjack.Logger
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.

package sample

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

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

func TestContractLogger(t *testing.T) {
	tempDir, err := os.MkdirTemp("", "csx-lumberjack-*")
	if err != nil {
		t.Fatalf("failed to create temp dir: %v", err)
	}
	defer os.RemoveAll(tempDir)

	logFilePath := filepath.Join(tempDir, "app.log")

	// 1. Verify io.WriteCloser interface compliance
	var _ io.WriteCloser = (*lumberjack.Logger)(nil)

	logger := NewLogger(logFilePath, 1, 3, 7, false)
	defer logger.Close()

	// 2. Verify writing log messages
	msg := "test log entry line 1"
	if err := LogMessage(logger, msg); err != nil {
		t.Fatalf("failed to write log message: %v", err)
	}

	content, err := os.ReadFile(logFilePath)
	if err != nil {
		t.Fatalf("failed to read log file: %v", err)
	}
	if !strings.Contains(string(content), msg) {
		t.Fatalf("expected log file to contain %q, got %q", msg, string(content))
	}

	// 3. Verify Rotate creates a backup and opens a fresh file
	if err := RotateLogger(logger); err != nil {
		t.Fatalf("failed to rotate logger: %v", err)
	}

	msg2 := "test log entry line 2 after rotation"
	if err := LogMessage(logger, msg2); err != nil {
		t.Fatalf("failed to write log message after rotation: %v", err)
	}

	entries, err := os.ReadDir(tempDir)
	if err != nil {
		t.Fatalf("failed to read temp dir: %v", err)
	}
	if len(entries) < 2 {
		t.Fatalf("expected at least 2 files after rotation, found %d", len(entries))
	}

	// 4. Verify Close
	if err := CloseLogger(logger); err != nil {
		t.Fatalf("failed to close logger: %v", err)
	}
}

{"case":{"caseId":"case:sha256:a336ed80cfc02e6a54dd66ca9233e9eb384509c30cdb4c7c61039ff80087f3eb","contract":["lumberjack.Logger implements io.WriteCloser","lumberjack.Logger writes log data to the configured file path","lumberjack.Logger.Rotate rotates the log file","lumberjack.Logger.Close closes the active log file"],"goal":"verify lumberjack.Logger in 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":["lumberjack.Logger"]},"contractCommand":["go","test","./..."],"environment":{"arch":"amd64","compiler":"go","compilerVersion":"1.26.6","distro":"ubuntu","ecosystem":"golang","language":"go","languageVersion":"1.26.6","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/gopkg.in/natefinch/lumberjack.v2@v2.2.1"],"schemaVersion":1,"subject":"pkg:golang/gopkg.in/natefinch/lumberjack.v2@v2.2.1","symbols":["lumberjack.Logger"],"verifierAdapter":"golang@1"}

module example.com/sample

go 1.26.6

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 (
	"fmt"

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

// NewLogger creates and configures a lumberjack.Logger instance.
func NewLogger(filename string, maxSizeMB int, maxBackups int, maxAgeDays int, compress bool) *lumberjack.Logger {
	return &lumberjack.Logger{
		Filename:   filename,
		MaxSize:    maxSizeMB,
		MaxBackups: maxBackups,
		MaxAge:     maxAgeDays,
		Compress:   compress,
		LocalTime:  true,
	}
}

// LogMessage writes a log message with newline using lumberjack.Logger.
func LogMessage(logger *lumberjack.Logger, message string) error {
	_, err := fmt.Fprintln(logger, message)
	return err
}

// RotateLogger forces the logger to rotate its log file.
func RotateLogger(logger *lumberjack.Logger) error {
	return logger.Rotate()
}

// CloseLogger closes the logger, releasing resources.
func CloseLogger(logger *lumberjack.Logger) error {
	return logger.Close()
}

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