Rename a file with fallback when encountering "invalid cross-device link"

rename.go

package rename

// renameFile renames a file
// it can be used instead of os.Rename in cases where we attempt
// to move files between partitions (e.g when using Docker volumes)
func renameFile(src string, dst string) error {
	err := os.Rename(src, dst)
	if err == nil {
		return nil
	}

	if !isInvalidCrossDeviceLinkErr(err) {
		return errs.Append(err, "failed to rename file")
	}

	// fallback to manual copying of the file
	if err := copyFile(src, dst); err != nil {
		return errs.Append(err, "failed to copy file")
	}

	// remove src file
	if err := os.Remove(src); err != nil {
		return errs.Append(err, "failed to remove src file")
	}

	return nil
}

func copyFile(src string, dst string) error {
	// Open source file
	fSrc, err := os.Open(src)
	if err != nil {
		return err
	}
	defer fSrc.Close()

	// Create destination file
	fDst, err := os.Create(dst)
	if err != nil {
		return err
	}
	defer fDst.Close()

	// Copy from source to destination
	if _, err := io.Copy(fDst, fSrc); err != nil {
		return err
	}

	return nil
}

func isInvalidCrossDeviceLinkErr(err error) bool {
	lErr, ok := err.(*os.LinkError)
	if !ok {
		return false
	}

	uErr, ok := lErr.Err.(syscall.Errno)
	if !ok {
		return false
	}

	if int(uErr) != 18 {
		return false
	}

	return true
}