atomicwritefile

atomicwritefile.go

// AtomicWriteFile atomically writes data to a file by first writing to a
// temp file and calling rename.
func AtomicWriteFile(filename string, data []byte, perm os.FileMode) error {
	buf := bytes.NewBuffer(data)
	return atomicWriteFile(filename, buf, int64(len(data)), perm)
}

// atomicWriteFile writes data to a file by first writing to a temp
// file and calling rename.
func atomicWriteFile(filename string, r io.Reader, dataSize int64, perm os.FileMode) error {
	f, err := ioutil.TempFile(filepath.Dir(filename), ".tmp-"+filepath.Base(filename))
	if err != nil {
		return err
	}
	err = os.Chmod(f.Name(), perm)
	if err != nil {
		f.Close()
		return err
	}
	n, err := io.Copy(f, r)
	if err == nil && n < dataSize {
		f.Close()
		return io.ErrShortWrite
	}
	if err != nil {
		f.Close()
		return err
	}
	if err := f.Sync(); err != nil {
		f.Close()
		return err
	}
	if err := f.Close(); err != nil {
		return err
	}
	return os.Rename(f.Name(), filename)
}