docker-volume-backup/cmd/backup/archive.go

// Copyright 2022 - Offen Authors <hioffen@posteo.de>
// SPDX-License-Identifier: MPL-2.0

// Portions of this file are taken from package `targz`, Copyright (c) 2014 Fredrik Wallgren
// Licensed under the MIT License: https://github.com/walle/targz/blob/57fe4206da5abf7dd3901b4af3891ec2f08c7b08/LICENSE

package main

import (
	"archive/tar"
	"compress/gzip"
	"fmt"
	"io"
	"os"
	"path"
	"path/filepath"
	"strings"

	"github.com/klauspost/compress/zstd"
)

func createArchive(files []string, inputFilePath, outputFilePath string, compression string) error {
	inputFilePath = stripTrailingSlashes(inputFilePath)
	inputFilePath, outputFilePath, err := makeAbsolute(inputFilePath, outputFilePath)
	if err != nil {
		return fmt.Errorf("createArchive: error transposing given file paths: %w", err)
	}
	if err := os.MkdirAll(filepath.Dir(outputFilePath), 0755); err != nil {
		return fmt.Errorf("createArchive: error creating output file path: %w", err)
	}

	if err := compress(files, outputFilePath, filepath.Dir(inputFilePath), compression); err != nil {
		return fmt.Errorf("createArchive: error creating archive: %w", err)
	}

	return nil
}

func stripTrailingSlashes(path string) string {
	if len(path) > 0 && path[len(path)-1] == '/' {
		path = path[0 : len(path)-1]
	}

	return path
}

func makeAbsolute(inputFilePath, outputFilePath string) (string, string, error) {
	inputFilePath, err := filepath.Abs(inputFilePath)
	if err == nil {
		outputFilePath, err = filepath.Abs(outputFilePath)
	}

	return inputFilePath, outputFilePath, err
}

func compress(paths []string, outFilePath, subPath string, algo string) error {
	file, err := os.Create(outFilePath)
	var compressWriter io.WriteCloser
	if err != nil {
		return fmt.Errorf("compress: error creating out file: %w", err)
	}

	prefix := path.Dir(outFilePath)
	switch algo {
	case "gz":
		compressWriter = gzip.NewWriter(file)
	case "zst":
		compressWriter, err = zstd.NewWriter(file)
		if err != nil {
			return fmt.Errorf("compress: zstd error: %w", err)
		}
	default:
		return fmt.Errorf("compress: unsupported compression algorithm: %s", algo)
	}

	tarWriter := tar.NewWriter(compressWriter)

	for _, p := range paths {
		if err := writeTarball(p, tarWriter, prefix); err != nil {
			return fmt.Errorf("compress: error writing %s to archive: %w", p, err)
		}
	}

	err = tarWriter.Close()
	if err != nil {
		return fmt.Errorf("compress: error closing tar writer: %w", err)
	}

	err = compressWriter.Close()
	if err != nil {
		return fmt.Errorf("compress: error closing compression writer: %w", err)
	}

	err = file.Close()
	if err != nil {
		return fmt.Errorf("compress: error closing file: %w", err)
	}

	return nil
}

func writeTarball(path string, tarWriter *tar.Writer, prefix string) error {
	fileInfo, err := os.Lstat(path)
	if err != nil {
		return fmt.Errorf("writeTarball: error getting file infor for %s: %w", path, err)
	}

	if fileInfo.Mode()&os.ModeSocket == os.ModeSocket {
		return nil
	}

	var link string
	if fileInfo.Mode()&os.ModeSymlink == os.ModeSymlink {
		var err error
		if link, err = os.Readlink(path); err != nil {
			return fmt.Errorf("writeTarball: error resolving symlink %s: %w", path, err)
		}
	}

	header, err := tar.FileInfoHeader(fileInfo, link)
	if err != nil {
		return fmt.Errorf("writeTarball: error getting file info header: %w", err)
	}
	header.Name = strings.TrimPrefix(path, prefix)

	err = tarWriter.WriteHeader(header)
	if err != nil {
		return fmt.Errorf("writeTarball: error writing file info header: %w", err)
	}

	if !fileInfo.Mode().IsRegular() {
		return nil
	}

	file, err := os.Open(path)
	if err != nil {
		return fmt.Errorf("writeTarball: error opening %s: %w", path, err)
	}
	defer file.Close()

	_, err = io.Copy(tarWriter, file)
	if err != nil {
		return fmt.Errorf("writeTarball: error copying %s to tar writer: %w", path, err)
	}

	return nil
}