logrotate

A concurrent io.WriteCloser for size- and time-based log rotation. The active path stays stable; compression and retention run on one maintenance goroutine. Requires Go 1.27.

go get github.com/libtnb/logrotate

Usage

w, err := logrotate.New(
	"/var/log/myapp/app.log",
	logrotate.WithMaxSize(64*logrotate.MB),
	logrotate.WithRotateEvery(24*time.Hour),
	logrotate.WithMaxBackups(14),
	logrotate.WithMaxAge(14*logrotate.Day),
	logrotate.WithCompress(),
)
if err != nil {
	log.Fatal(err)
}
defer func() {
	if err := w.Close(); err != nil {
		log.Printf("log maintenance: %v", err)
	}
}()

log.SetOutput(w)

New validates the complete configuration, creates the parent directory, and opens the file before returning.

Option	Effect
WithMaxSize	Size limit; default 100 MB, zero disables
WithRotateEvery / WithRotateAt	Wall-clock rotation schedule
WithMaxBackups	Backup count limit
WithMaxAge	Backup age limit
WithMaxTotalSize	Total compressed/on-disk backup limit
WithCompress / WithCompressor	Background compression
WithLocation	Schedule and backup-name timezone; default UTC
WithErrorHandler	Prompt advisory maintenance notifications

Time boundaries are checked on writes, so idle periods create no empty backup. Oversized records are written in full and rotated afterward. Timestamp collisions use a sequence suffix; an existing backup is never overwritten. Files outside this writer's backup naming pattern are never removed.

Shutdown and errors

Close waits for maintenance and returns a bounded aggregate of retained compression/cleanup errors. Shutdown adds a deadline:

ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
defer cancel()
if err := w.Shutdown(ctx); err != nil {
	log.Printf("log shutdown: %v", err)
}

The shutdown context reaches the active Compressor; custom implementations should honor cancellation. WithErrorHandler is notification-only: handlers run serially outside Writer locks, and a slow handler cannot block writes or maintenance. Close and Shutdown remain the authoritative error result.

After shutdown begins, Write, Sync, Rotate, and Reopen return ErrClosed. Reopen is intended for an external rotator that moved or truncated the active file.

Writer is safe for concurrent goroutines but assumes one process owns the active path. It works directly with log, slog, and zap-style Sync users.

API details and signal examples are on pkg.go.dev.