From 9eda23e512d29252b778c3cdc9c732eb5add032a Mon Sep 17 00:00:00 2001
From: Frederik Ring <frederik.ring@gmail.com>
Date: Tue, 19 Apr 2022 21:08:53 +0200
Subject: [PATCH] Make header format for created tar archive configurable

---
 cmd/backup/archive.go | 18 +++++++++++++-----
 cmd/backup/config.go  | 32 +++++++++++++++++++++++++++++++-
 cmd/backup/script.go  |  4 +++-
 3 files changed, 47 insertions(+), 7 deletions(-)

diff --git a/cmd/backup/archive.go b/cmd/backup/archive.go
index d419eac..a3f7604 100644
--- a/cmd/backup/archive.go
+++ b/cmd/backup/archive.go
@@ -18,7 +18,7 @@ import (
 	"strings"
 )
 
-func createArchive(inputFilePath, outputFilePath string) error {
+func createArchive(inputFilePath, outputFilePath string, options createArchiveOptions) error {
 	inputFilePath = stripTrailingSlashes(inputFilePath)
 	inputFilePath, outputFilePath, err := makeAbsolute(inputFilePath, outputFilePath)
 	if err != nil {
@@ -28,7 +28,7 @@ func createArchive(inputFilePath, outputFilePath string) error {
 		return fmt.Errorf("createArchive: error creating output file path: %w", err)
 	}
 
-	if err := compress(inputFilePath, outputFilePath, filepath.Dir(inputFilePath)); err != nil {
+	if err := compress(inputFilePath, outputFilePath, filepath.Dir(inputFilePath), options); err != nil {
 		return fmt.Errorf("createArchive: error creating archive: %w", err)
 	}
 
@@ -52,7 +52,7 @@ func makeAbsolute(inputFilePath, outputFilePath string) (string, string, error)
 	return inputFilePath, outputFilePath, err
 }
 
-func compress(inPath, outFilePath, subPath string) error {
+func compress(inPath, outFilePath, subPath string, options createArchiveOptions) error {
 	file, err := os.Create(outFilePath)
 	if err != nil {
 		return fmt.Errorf("compress: error creating out file: %w", err)
@@ -71,7 +71,7 @@ func compress(inPath, outFilePath, subPath string) error {
 	}
 
 	for _, p := range paths {
-		if err := writeTarGz(p, tarWriter, prefix); err != nil {
+		if err := writeTarGz(p, tarWriter, prefix, options.format); err != nil {
 			return fmt.Errorf("compress error writing %s to archive: %w", p, err)
 		}
 	}
@@ -94,7 +94,7 @@ func compress(inPath, outFilePath, subPath string) error {
 	return nil
 }
 
-func writeTarGz(path string, tarWriter *tar.Writer, prefix string) error {
+func writeTarGz(path string, tarWriter *tar.Writer, prefix string, format tar.Format) error {
 	fileInfo, err := os.Lstat(path)
 	if err != nil {
 		return fmt.Errorf("writeTarGz: error getting file infor for %s: %w", path, err)
@@ -113,6 +113,10 @@ func writeTarGz(path string, tarWriter *tar.Writer, prefix string) error {
 	}
 
 	header, err := tar.FileInfoHeader(fileInfo, link)
+	if format >= 0 {
+		header.Format = format
+	}
+
 	if err != nil {
 		return fmt.Errorf("writeTarGz: error getting file info header: %w", err)
 	}
@@ -140,3 +144,7 @@ func writeTarGz(path string, tarWriter *tar.Writer, prefix string) error {
 
 	return nil
 }
+
+type createArchiveOptions struct {
+	format tar.Format
+}
diff --git a/cmd/backup/config.go b/cmd/backup/config.go
index 06c8c3a..954e1e5 100644
--- a/cmd/backup/config.go
+++ b/cmd/backup/config.go
@@ -3,7 +3,11 @@
 
 package main
 
-import "time"
+import (
+	"archive/tar"
+	"fmt"
+	"time"
+)
 
 // Config holds all configuration values that are expected to be set
 // by users.
@@ -42,4 +46,30 @@ type Config struct {
 	ExecLabel                  string        `split_words:"true"`
 	ExecForwardOutput          bool          `split_words:"true"`
 	LockTimeout                time.Duration `split_words:"true" default:"60m"`
+	TarArchiveHeaderFormat     TarFormat     `split_words:"true"`
+}
+
+type TarFormat tar.Format
+
+func (t *TarFormat) Decode(value string) error {
+	switch value {
+	case "PAX":
+		*t = TarFormat(tar.FormatPAX)
+		return nil
+	case "USTAR":
+		*t = TarFormat(tar.FormatUSTAR)
+		return nil
+	case "GNU":
+		*t = TarFormat(tar.FormatGNU)
+		return nil
+	case "":
+		*t = TarFormat(-1)
+		return nil
+	default:
+		return fmt.Errorf("tarFormat: unknown format %s", value)
+	}
+}
+
+func (t *TarFormat) Format() tar.Format {
+	return tar.Format(*t)
 }
diff --git a/cmd/backup/script.go b/cmd/backup/script.go
index 8bc6074..d7dfdca 100644
--- a/cmd/backup/script.go
+++ b/cmd/backup/script.go
@@ -388,7 +388,9 @@ func (s *script) takeBackup() error {
 		s.logger.Infof("Removed tar file `%s`.", tarFile)
 		return nil
 	})
-	if err := createArchive(backupSources, tarFile); err != nil {
+	if err := createArchive(backupSources, tarFile, createArchiveOptions{
+		format: s.c.TarArchiveHeaderFormat.Format(),
+	}); err != nil {
 		return fmt.Errorf("takeBackup: error compressing backup folder: %w", err)
 	}