gopkg.in/natefinch/lumberjack.v2 v2.2.1: lumberjack.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 lumberjack.Logger.Rotate 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.Rotate
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:sha256:77ddc187d1a54c629aa6b77f378105c63869ee3673a292e73ee1c2e32c16c5f8","contract":["lumberjack.Logger.Rotate() closes current log file and archives it as a timestamped backup","lumberjack.Logger opens a new active log file for subsequent writes after Rotate()","lumberjack.Logger.Rotate() returns nil error on successful rotation"],"goal":"verify lumberjack.Logger.Rotate 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.Rotate"]},"contractCommand":["go","test","./..."],"environment":{"arch":"amd64","distro":"ubuntu","ecosystem":"golang","language":"go","libc":"glibc","libcVersion":"2.39","moduleSystem":"go","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.Rotate"],"verifierAdapter":"golang@1"}

module example.com/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 main

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

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

func main() {
	tmpDir, err := os.MkdirTemp("", "lumberjack-demo-*")
	if err != nil {
		panic(err)
	}
	defer os.RemoveAll(tmpDir)

	logPath := filepath.Join(tmpDir, "app.log")
	logger := &lumberjack.Logger{
		Filename:   logPath,
		MaxSize:    1,
		MaxBackups: 3,
		MaxAge:     7,
		Compress:   false,
	}
	defer logger.Close()

	if _, err := logger.Write([]byte("initial log entry\n")); err != nil {
		panic(err)
	}

	if err := logger.Rotate(); err != nil {
		panic(err)
	}

	if _, err := logger.Write([]byte("post-rotation log entry\n")); err != nil {
		panic(err)
	}

	fmt.Println("lumberjack rotation complete")
}

{
  "schemaVersion": 1,
  "goal": "verify lumberjack.Logger.Rotate 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.Rotate"
  ],
  "constraints": {
    "executionContext": "node"
  },
  "runtimeConditions": {
    "ecosystem": "npm",
    "language": "javascript",
    "moduleSystem": "cjs",
    "packageManager": "npm@10.9.8",
    "runtime": "node@22.23.2"
  }
}

package test

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

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

func TestLumberjackLoggerRotate(t *testing.T) {
	tmpDir := t.TempDir()
	logFile := filepath.Join(tmpDir, "test.log")

	logger := &lumberjack.Logger{
		Filename:   logFile,
		MaxSize:    10,
		MaxBackups: 5,
		MaxAge:     30,
		Compress:   false,
	}
	defer logger.Close()

	// 1. Initial write
	firstContent := "line 1 before rotation\n"
	n, err := logger.Write([]byte(firstContent))
	if err != nil {
		t.Fatalf("unexpected write error: %v", err)
	}
	if n != len(firstContent) {
		t.Fatalf("expected write length %d, got %d", len(firstContent), n)
	}

	// 2. Perform rotation
	if err := logger.Rotate(); err != nil {
		t.Fatalf("unexpected rotate error: %v", err)
	}

	// Verify that backup file exists and has previous content
	entries, err := os.ReadDir(tmpDir)
	if err != nil {
		t.Fatalf("failed to read temp dir: %v", err)
	}

	var backupFound bool
	for _, entry := range entries {
		name := entry.Name()
		if name != "test.log" && strings.HasPrefix(name, "test-") && strings.HasSuffix(name, ".log") {
			backupFound = true
			data, err := os.ReadFile(filepath.Join(tmpDir, name))
			if err != nil {
				t.Fatalf("failed to read backup file: %v", err)
			}
			if string(data) != firstContent {
				t.Fatalf("backup file content mismatch: expected %q, got %q", firstContent, string(data))
			}
		}
	}
	if !backupFound {
		t.Fatalf("expected rotated backup file in directory %s, found files: %v", tmpDir, entries)
	}

	// 3. Write new content after rotation
	secondContent := "line 2 after rotation\n"
	n2, err := logger.Write([]byte(secondContent))
	if err != nil {
		t.Fatalf("unexpected write error after rotation: %v", err)
	}
	if n2 != len(secondContent) {
		t.Fatalf("expected write length %d, got %d", len(secondContent), n2)
	}

	// Verify active log file contains only the second content
	activeData, err := os.ReadFile(logFile)
	if err != nil {
		t.Fatalf("failed to read active log file: %v", err)
	}
	if string(activeData) != secondContent {
		t.Fatalf("active log content mismatch: expected %q, got %q", secondContent, string(activeData))
	}

	// 4. Close logger cleanly
	if err := logger.Close(); err != nil {
		t.Fatalf("unexpected close error: %v", err)
	}
}