Improver restorer error reporting

changelog/unreleased/pull-4624

@@ -0,0 +1,11 @@
+Bugfix: Correct restore progress information if an error occurs
+
+If an error occurred while restoring a snapshot, this could cause the restore
+progress bar to show incorrect information. In addition, if a data file could
+not be loaded completely, then errors would also be reported for some already
+restored files.
+
+We have improved the error reporting of the restore command to be more accurate.
+
+https://github.com/restic/restic/pull/4624
+https://forum.restic.net/t/errors-restoring-with-restic-on-windows-server-s3/6943

internal/repository/repository.go

@@ -881,9 +881,9 @@ type BackendLoadFn func(ctx context.Context, h backend.Handle, length int, offse
 const maxUnusedRange = 4 * 1024 * 1024
 
 // StreamPack loads the listed blobs from the specified pack file. The plaintext blob is passed to
-// the handleBlobFn callback or an error if decryption failed or the blob hash does not match. In
-// case of download errors handleBlobFn might be called multiple times for the same blob. If the
-// callback returns an error, then StreamPack will abort and not retry it.
+// the handleBlobFn callback or an error if decryption failed or the blob hash does not match.
+// handleBlobFn is never called multiple times for the same blob. If the callback returns an error,
+// then StreamPack will abort and not retry it.
 func StreamPack(ctx context.Context, beLoad BackendLoadFn, key *crypto.Key, packID restic.ID, blobs []restic.Blob, handleBlobFn func(blob restic.BlobHandle, buf []byte, err error) error) error {
 	if len(blobs) == 0 {
 		// nothing to do
@@ -945,7 +945,9 @@ func streamPackPart(ctx context.Context, beLoad BackendLoadFn, key *crypto.Key,
 		currentBlobEnd := dataStart
 		var buf []byte
 		var decode []byte
-		for _, entry := range blobs {
+		for len(blobs) > 0 {
+			entry := blobs[0]
+
 			skipBytes := int(entry.Offset - currentBlobEnd)
 			if skipBytes < 0 {
 				return errors.Errorf("overlapping blobs in pack %v", packID)
@@ -1008,6 +1010,8 @@ func streamPackPart(ctx context.Context, beLoad BackendLoadFn, key *crypto.Key,
 				cancel()
 				return backoff.Permanent(err)
 			}
+			// ensure that each blob is only passed once to handleBlobFn
+			blobs = blobs[1:]
 		}
 		return nil
 	})

internal/repository/repository_test.go

@@ -5,6 +5,7 @@ import (
 	"context"
 	"crypto/sha256"
 	"encoding/json"
+	"errors"
 	"fmt"
 	"io"
 	"math/rand"
@@ -14,6 +15,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/cenkalti/backoff/v4"
 	"github.com/google/go-cmp/cmp"
 	"github.com/klauspost/compress/zstd"
 	"github.com/restic/restic/internal/backend"
@@ -529,7 +531,9 @@ func testStreamPack(t *testing.T, version uint) {
 	packfileBlobs, packfile := buildPackfileWithoutHeader(blobSizes, &key, compress)
 
 	loadCalls := 0
-	load := func(ctx context.Context, h backend.Handle, length int, offset int64, fn func(rd io.Reader) error) error {
+	shortFirstLoad := false
+
+	loadBytes := func(length int, offset int64) []byte {
 		data := packfile
 
 		if offset > int64(len(data)) {
@@ -541,32 +545,56 @@ func testStreamPack(t *testing.T, version uint) {
 		if length > len(data) {
 			length = len(data)
 		}
+		if shortFirstLoad {
+			length /= 2
+			shortFirstLoad = false
+		}
+
+		return data[:length]
+	}
+
+	load := func(ctx context.Context, h backend.Handle, length int, offset int64, fn func(rd io.Reader) error) error {
+		data := loadBytes(length, offset)
+		if shortFirstLoad {
+			data = data[:len(data)/2]
+			shortFirstLoad = false
+		}
 
-		data = data[:length]
 		loadCalls++
 
-		return fn(bytes.NewReader(data))
+		err := fn(bytes.NewReader(data))
+		if err == nil {
+			return nil
+		}
+		var permanent *backoff.PermanentError
+		if errors.As(err, &permanent) {
+			return err
+		}
 
+		// retry loading once
+		return fn(bytes.NewReader(loadBytes(length, offset)))
 	}
 
 	// first, test regular usage
 	t.Run("regular", func(t *testing.T) {
 		tests := []struct {
-			blobs []restic.Blob
-			calls int
+			blobs          []restic.Blob
+			calls          int
+			shortFirstLoad bool
 		}{
-			{packfileBlobs[1:2], 1},
-			{packfileBlobs[2:5], 1},
-			{packfileBlobs[2:8], 1},
+			{packfileBlobs[1:2], 1, false},
+			{packfileBlobs[2:5], 1, false},
+			{packfileBlobs[2:8], 1, false},
 			{[]restic.Blob{
 				packfileBlobs[0],
 				packfileBlobs[4],
 				packfileBlobs[2],
-			}, 1},
+			}, 1, false},
 			{[]restic.Blob{
 				packfileBlobs[0],
 				packfileBlobs[len(packfileBlobs)-1],
-			}, 2},
+			}, 2, false},
+			{packfileBlobs[:], 1, true},
 		}
 
 		for _, test := range tests {
@@ -593,6 +621,7 @@ func testStreamPack(t *testing.T, version uint) {
 				}
 
 				loadCalls = 0
+				shortFirstLoad = test.shortFirstLoad
 				err = repository.StreamPack(ctx, load, &key, restic.ID{}, test.blobs, handleBlob)
 				if err != nil {
 					t.Fatal(err)
@@ -605,6 +634,7 @@ func testStreamPack(t *testing.T, version uint) {
 			})
 		}
 	})
+	shortFirstLoad = false
 
 	// next, test invalid uses, which should return an error
 	t.Run("invalid", func(t *testing.T) {

internal/restorer/filerestorer.go

@@ -246,7 +246,10 @@ func (r *fileRestorer) downloadPack(ctx context.Context, pack *packInfo) error {
 		return err
 	}
 
+	// track already processed blobs for precise error reporting
+	processedBlobs := restic.NewBlobSet()
 	err := repository.StreamPack(ctx, r.packLoader, r.key, pack.id, blobList, func(h restic.BlobHandle, blobData []byte, err error) error {
+		processedBlobs.Insert(h)
 		blob := blobs[h.ID]
 		if err != nil {
 			for file := range blob.files {
@@ -292,7 +295,19 @@ func (r *fileRestorer) downloadPack(ctx context.Context, pack *packInfo) error {
 	})
 
 	if err != nil {
-		for file := range pack.files {
+		// only report error for not yet processed blobs
+		affectedFiles := make(map[*fileInfo]struct{})
+		for _, blob := range blobList {
+			if processedBlobs.Has(blob.BlobHandle) {
+				continue
+			}
+			blob := blobs[blob.ID]
+			for file := range blob.files {
+				affectedFiles[file] = struct{}{}
+			}
+		}
+
+		for file := range affectedFiles {
 			if errFile := sanitizeError(file, err); errFile != nil {
 				return errFile
 			}

internal/restorer/filerestorer_test.go

@@ -317,3 +317,47 @@ func testPartialDownloadError(t *testing.T, part int) {
 	rtest.OK(t, err)
 	verifyRestore(t, r, repo)
 }
+
+func TestFatalDownloadError(t *testing.T) {
+	tempdir := rtest.TempDir(t)
+	content := []TestFile{
+		{
+			name: "file1",
+			blobs: []TestBlob{
+				{"data1-1", "pack1"},
+				{"data1-2", "pack1"},
+			},
+		},
+		{
+			name: "file2",
+			blobs: []TestBlob{
+				{"data2-1", "pack1"},
+				{"data2-2", "pack1"},
+				{"data2-3", "pack1"},
+			},
+		}}
+
+	repo := newTestRepo(content)
+
+	loader := repo.loader
+	repo.loader = func(ctx context.Context, h backend.Handle, length int, offset int64, fn func(rd io.Reader) error) error {
+		// only return half the data to break file2
+		return loader(ctx, h, length/2, offset, fn)
+	}
+
+	r := newFileRestorer(tempdir, repo.loader, repo.key, repo.Lookup, 2, false, nil)
+	r.files = repo.files
+
+	var errors []string
+	r.Error = func(s string, e error) error {
+		// ignore errors as in the `restore` command
+		errors = append(errors, s)
+		return nil
+	}
+
+	err := r.restoreFiles(context.TODO())
+	rtest.OK(t, err)
+
+	rtest.Assert(t, len(errors) == 1, "unexpected number of restore errors, expected: 1, got: %v", len(errors))
+	rtest.Assert(t, errors[0] == "file2", "expected error for file2, got: %v", errors[0])
+}