restore: re-read block file while falling back to different decompres…

…sion method

Longhorn 7687

Signed-off-by: Derek Su <derek.su@suse.com>

backupbackingimage/backupbackingimage.go

@@ -497,17 +497,10 @@ func restoreBlock(bsDriver backupstore.BackupStoreDriver, backingImageFile *os.F
 
 func restoreBlockToFile(bsDriver backupstore.BackupStoreDriver, backingImageFile *os.File, decompression string, blk common.BlockMapping) error {
 	blkFile := getBackingImageBlockFilePath(blk.BlockChecksum)
-	rc, err := bsDriver.Read(blkFile)
+	r, err := backupstore.DecompressAndVerifyWithFallback(bsDriver, blkFile, decompression, blk.BlockChecksum)
 	if err != nil {
 		return err
 	}
-	defer rc.Close()
-	r, err := util.DecompressAndVerifyWithFallback(decompression, rc, blk.BlockChecksum)
-	if err != nil {
-		if r == nil {
-			return err
-		}
-	}
 
 	if _, err := backingImageFile.Seek(blk.Offset, 0); err != nil {
 		return err

deltablock.go

@@ -775,17 +775,9 @@ func RestoreDeltaBlockBackup(ctx context.Context, config *DeltaRestoreConfig) er
 
 func restoreBlockToFile(bsDriver BackupStoreDriver, volumeName string, volDev *os.File, decompression string, blk BlockMapping) error {
 	blkFile := getBlockFilePath(volumeName, blk.BlockChecksum)
-	rc, err := bsDriver.Read(blkFile)
+	r, err := DecompressAndVerifyWithFallback(bsDriver, blkFile, decompression, blk.BlockChecksum)
 	if err != nil {
-		return errors.Wrapf(err, "failed to read block %v with checksum %v", blkFile, blk.BlockChecksum)
-	}
-	defer rc.Close()
-
-	r, err := util.DecompressAndVerifyWithFallback(decompression, rc, blk.BlockChecksum)
-	if err != nil {
-		if r == nil {
-			return err
-		}
+		return errors.Wrapf(err, "failed to decompress and verify block %v with checksum %v", blkFile, blk.BlockChecksum)
 	}
 
 	if _, err := volDev.Seek(blk.Offset, 0); err != nil {

util.go

@@ -1,9 +1,16 @@
 package backupstore
 
 import (
+	"compress/gzip"
 	"context"
+	"io"
 	"path/filepath"
+	"strings"
 	"sync"
+
+	"github.com/pkg/errors"
+
+	"github.com/longhorn/backupstore/util"
 )
 
 func getBlockPath(volumeName string) string {
@@ -50,3 +57,53 @@ func mergeErrorChannels(ctx context.Context, channels ...<-chan error) <-chan er
 	}()
 	return out
 }
+
+// DecompressAndVerifyWithFallback decompresses the given data and verifies the data integrity.
+// If the decompression fails, it will try to decompress with the fallback method.
+func DecompressAndVerifyWithFallback(bsDriver BackupStoreDriver, blkFile, decompression, checksum string) (io.Reader, error) {
+	// Helper function to read block from backup store
+	readBlock := func() (io.ReadCloser, error) {
+		rc, err := bsDriver.Read(blkFile)
+		if err != nil {
+			return nil, errors.Wrapf(err, "failed to read block %v", blkFile)
+		}
+		return rc, nil
+	}
+
+	// First attempt to read and decompress/verify
+	rc, err := readBlock()
+	if err != nil {
+		return nil, err
+	}
+	defer rc.Close()
+
+	r, err := util.DecompressAndVerify(decompression, rc, checksum)
+	if err == nil {
+		return r, nil
+	}
+
+	// If there's an error, determine the alternative decompression method
+	alternativeDecompression := ""
+	if strings.Contains(err.Error(), gzip.ErrHeader.Error()) {
+		alternativeDecompression = "lz4"
+	} else if strings.Contains(err.Error(), "lz4: bad magic number") {
+		alternativeDecompression = "gzip"
+	}
+
+	// Second attempt with alternative decompression, if applicable
+	if alternativeDecompression != "" {
+		retriedRc, err := readBlock()
+		if err != nil {
+			return nil, err
+		}
+		defer retriedRc.Close()
+
+		r, err = util.DecompressAndVerify(alternativeDecompression, retriedRc, checksum)
+		if err != nil {
+			return nil, errors.Wrapf(err, "fallback decompression also failed for block %v", blkFile)
+		}
+		return r, nil
+	}
+
+	return nil, errors.Wrapf(err, "decompression verification failed for block %v", blkFile)
+}

util/util.go

@@ -23,7 +23,6 @@ import (
 	lz4 "github.com/pierrec/lz4/v4"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
-	"go.uber.org/multierr"
 	"golang.org/x/sys/unix"
 
 	"k8s.io/apimachinery/pkg/util/wait"
@@ -133,39 +132,6 @@ func DecompressAndVerify(method string, src io.Reader, checksum string) (io.Read
 	return bytes.NewReader(block), nil
 }
 
-// DecompressAndVerifyWithFallback decompresses the given data and verifies the data integrity.
-// If the decompression fails, it will try to decompress with the fallback method.
-func DecompressAndVerifyWithFallback(decompression string, rc io.ReadCloser, checksum string) (io.Reader, error) {
-	r, err := DecompressAndVerify(decompression, rc, checksum)
-	if err == nil {
-		return r, nil
-	}
-	// Fall back to other decompression method if the current one fails
-	// The mitigation will be removed after identifying https://github.com/longhorn/longhorn/issues/7687
-	// Seek rc to offset 0
-	seeker, ok := rc.(io.Seeker)
-	if !ok {
-		return nil, errors.Wrapf(err, "failed to cast to io.Seeker for block %v", checksum)
-	}
-
-	_, errFallback := seeker.Seek(0, io.SeekStart)
-	if errFallback != nil {
-		// Merge the err1 and err2 and error out
-		return nil, errors.Wrapf(multierr.Append(err, errFallback), "failed to seek to offset 0 for block %v", checksum)
-	}
-
-	if strings.Contains(err.Error(), gzip.ErrHeader.Error()) {
-		r, errFallback = DecompressAndVerify("lz4", rc, checksum)
-	} else if strings.Contains(err.Error(), "lz4: bad magic number") {
-		r, errFallback = DecompressAndVerify("gzip", rc, checksum)
-	}
-	if errFallback != nil {
-		return nil, errors.Wrapf(multierr.Append(err, errFallback), "failed to decompress and verify block %v with fallback", checksum)
-	}
-
-	return r, err
-}
-
 func newCompressionWriter(method string, buffer io.Writer) (io.WriteCloser, error) {
 	switch method {
 	case "gzip":