Implemented tar+xz compression + unit tests for it.

internal/backer/loadConfig.go

@@ -142,8 +142,8 @@ func LoadConfig(path string) error {
 		log.Warnf("Config option compression_algorithm is not set, fallback to %s", C.CompressionAlgorithm)
 	}
 
-	if C.CompressionAlgorithm != "gzip" && C.CompressionAlgorithm != "bzip2" && C.CompressionAlgorithm != "zstd" && C.CompressionAlgorithm != "lz4" {
-		return fmt.Errorf("Compression_algorithm must be gzip, bzip2, zstd or lz4, got %s", C.CompressionAlgorithm)
+	if C.CompressionAlgorithm != "gzip" && C.CompressionAlgorithm != "bzip2" && C.CompressionAlgorithm != "zstd" && C.CompressionAlgorithm != "lz4" && C.CompressionAlgorithm != "xz" {
+		return fmt.Errorf("Compression_algorithm must be gzip, bzip2, zstd, lz4 or xz, got %s", C.CompressionAlgorithm)
 	}
 
 	// Compile exclude patterns.

internal/backer/loadConfig_test.go

@@ -295,6 +295,27 @@ func TestLoadConfigCompressionAlgorithmLz4(t *testing.T) {
 	}
 }
 
+// TestLoadConfigCompressionAlgorithmXz tests xz compression algorithm.
+func TestLoadConfigCompressionAlgorithmXz(t *testing.T) {
+	config := `{
+		"user": "test",
+		"password": "test",
+		"directories": ["../../test_data/test1/foo"],
+		"nohttps": true,
+		"compression_algorithm": "xz"
+	}`
+	tmpFile := writeTempConfig(t, config)
+
+	err := LoadConfig(tmpFile)
+	if err != nil {
+		t.Errorf("Expected no error, got %v", err)
+	}
+
+	if C.CompressionAlgorithm != "xz" {
+		t.Errorf("C.CompressionAlgorithm should be xz, got %s", C.CompressionAlgorithm)
+	}
+}
+
 // TestLoadConfigCompressionAlgorithmInvalid tests invalid compression algorithm.
 func TestLoadConfigCompressionAlgorithmInvalid(t *testing.T) {
 	config := `{

internal/backer/newServer.go

@@ -91,6 +91,10 @@ func NewServer(configPath string) (*http.Server, error) {
 			archive = CreateTarLz4Stream(ctx, files)
 			extension = "tar.lz4"
 
+		case "xz":
+			archive = CreateTarXzStream(ctx, files)
+			extension = "tar.xz"
+
 		default:
 			archive = CreateTarGzStream(ctx, files)
 			extension = "tar.gz"

internal/backer/utils.go

@@ -15,6 +15,7 @@ import (
 	"github.com/dsnet/compress/bzip2"
 	"github.com/klauspost/compress/zstd"
 	"github.com/pierrec/lz4"
+	"github.com/ulikunitz/xz"
 )
 
 // CreateTarGzStream takes a list of files and returns a reader that reads from a tar archive containing these files.
@@ -590,6 +591,145 @@ func CreateTarLz4Stream(ctx context.Context, filepaths []string) io.ReadCloser {
 	return pr
 }
 
+// CreateTarXzStream takes a list of files and returns a reader that reads from an xz-compressed tar archive.
+func CreateTarXzStream(ctx context.Context, filepaths []string) io.ReadCloser {
+	pr, pw := io.Pipe()
+
+	go func() {
+		var pipeErr error
+
+		closePipeWithError := func(err error) {
+			if pipeErr != nil {
+				return
+			}
+
+			pipeErr = err
+			pw.CloseWithError(err)
+		}
+
+		defer func() {
+			if pipeErr == nil {
+				pw.Close()
+			}
+		}()
+
+		xw, err := xz.NewWriter(pw)
+		if err != nil {
+			closePipeWithError(fmt.Errorf("xz writer error: %w", err))
+
+			return
+		}
+
+		defer func() {
+			if pipeErr == nil {
+				if err := xw.Close(); err != nil {
+					if !isPipeClosedError(err) {
+						log.Errorf("Failed to close xz writer: %v", err)
+					}
+				}
+			}
+		}()
+
+		tw := tar.NewWriter(xw)
+
+		defer func() {
+			if pipeErr == nil {
+				if err := tw.Close(); err != nil {
+					if !isPipeClosedError(err) {
+						log.Errorf("Failed to close tar writer: %v", err)
+					}
+				}
+			}
+		}()
+
+		for _, fpath := range filepaths {
+			var (
+				err        error
+				linkTarget string
+			)
+
+			select {
+			case <-ctx.Done():
+				closePipeWithError(ctx.Err())
+
+				return
+
+			default:
+			}
+
+			log.Debugf("Adding file: %s", fpath)
+
+			st, err := os.Lstat(fpath)
+
+			if err != nil {
+				log.Warnf("Skipping %s: %v", fpath, err)
+
+				continue
+			}
+
+			if st.Mode()&os.ModeSymlink != 0 {
+				linkTarget, err = os.Readlink(fpath)
+
+				if err != nil {
+					log.Warnf("Skipping %s: readlink failed: %v", fpath, err)
+
+					continue
+				}
+			}
+
+			if st.Mode()&os.ModeSocket != 0 {
+				log.Debugf("Skipping socket: %s", fpath)
+
+				continue
+			}
+
+			header, err := tar.FileInfoHeader(st, linkTarget)
+
+			if err != nil {
+				log.Warnf("Skipping %s: tar header failed: %v", fpath, err)
+
+				continue
+			}
+
+			header.Format = tar.FormatGNU
+			header.Name = strings.TrimPrefix(filepath.ToSlash(filepath.Clean(fpath)), "/")
+
+			mode := st.Mode()
+
+			if err := writeWithContext(ctx, func() error {
+				return tw.WriteHeader(header)
+			}); err != nil {
+				closePipeWithError(err)
+
+				return
+			}
+
+			if mode.IsRegular() {
+				f, err := os.Open(fpath)
+				if err != nil {
+					log.Warnf("Skipping %s: open failed: %v", fpath, err)
+
+					continue
+				}
+
+				err = copyWithContext(ctx, tw, f)
+
+				if e := f.Close(); e != nil {
+					log.Warnf("Failed to close file %s: %v", fpath, e)
+				}
+
+				if err != nil {
+					log.Warnf("Skipping %s: copy failed: %v", fpath, err)
+
+					continue
+				}
+			}
+		}
+	}()
+
+	return pr
+}
+
 // isPipeClosedError checks if the error is due to a closed pipe.
 func isPipeClosedError(err error) bool {
 	if err == nil {