restore: split downloadPack into smaller methods

internal/restorer/filerestorer.go

@@ -197,12 +197,13 @@ func (r *fileRestorer) restoreFiles(ctx context.Context) error {
 	return wg.Wait()
 }
 
-func (r *fileRestorer) downloadPack(ctx context.Context, pack *packInfo) error {
+type blobToFileOffsetsMapping map[restic.ID]struct {
+	files map[*fileInfo][]int64 // file -> offsets (plural!) of the blob in the file
+}
 
+func (r *fileRestorer) downloadPack(ctx context.Context, pack *packInfo) error {
 	// calculate blob->[]files->[]offsets mappings
-	blobs := make(map[restic.ID]struct {
+	blobs := make(blobToFileOffsetsMapping)
-		files map[*fileInfo][]int64 // file -> offsets (plural!) of the blob in the file
-	})
 	var blobList []restic.Blob
 	for file := range pack.files {
 		addBlob := func(blob restic.Blob, fileOffset int64) {
@@ -239,60 +240,9 @@ func (r *fileRestorer) downloadPack(ctx context.Context, pack *packInfo) error {
 		}
 	}
 
-	sanitizeError := func(file *fileInfo, err error) error {
-		if err != nil {
-			err = r.Error(file.location, err)
-		}
-		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 {
+	err := r.downloadBlobs(ctx, pack.id, blobList, blobs, processedBlobs)
-		processedBlobs.Insert(h)
-		blob := blobs[h.ID]
-		if err != nil {
-			for file := range blob.files {
-				if errFile := sanitizeError(file, err); errFile != nil {
-					return errFile
-				}
-			}
-			return nil
-		}
-		for file, offsets := range blob.files {
-			for _, offset := range offsets {
-				writeToFile := func() error {
-					// this looks overly complicated and needs explanation
-					// two competing requirements:
-					// - must create the file once and only once
-					// - should allow concurrent writes to the file
-					// so write the first blob while holding file lock
-					// write other blobs after releasing the lock
-					createSize := int64(-1)
-					file.lock.Lock()
-					if file.inProgress {
-						file.lock.Unlock()
-					} else {
-						defer file.lock.Unlock()
-						file.inProgress = true
-						createSize = file.size
-					}
-					writeErr := r.filesWriter.writeToFile(r.targetPath(file.location), blobData, offset, createSize, file.sparse)
-
-					if r.progress != nil {
-						r.progress.AddProgress(file.location, uint64(len(blobData)), uint64(file.size))
-					}
-
-					return writeErr
-				}
-				err := sanitizeError(file, writeToFile())
-				if err != nil {
-					return err
-				}
-			}
-		}
-		return nil
-	})
 
 	if err != nil {
 		// only report error for not yet processed blobs
@@ -308,7 +258,7 @@ func (r *fileRestorer) downloadPack(ctx context.Context, pack *packInfo) error {
 		}
 
 		for file := range affectedFiles {
-			if errFile := sanitizeError(file, err); errFile != nil {
+			if errFile := r.sanitizeError(file, err); errFile != nil {
 				return errFile
 			}
 		}
@@ -316,3 +266,61 @@ func (r *fileRestorer) downloadPack(ctx context.Context, pack *packInfo) error {
 
 	return nil
 }
+
+func (r *fileRestorer) sanitizeError(file *fileInfo, err error) error {
+	if err != nil {
+		err = r.Error(file.location, err)
+	}
+	return err
+}
+
+func (r *fileRestorer) downloadBlobs(ctx context.Context, packID restic.ID, blobList []restic.Blob,
+	blobs blobToFileOffsetsMapping, processedBlobs restic.BlobSet) error {
+
+	return repository.StreamPack(ctx, r.packLoader, r.key, packID, 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 {
+					if errFile := r.sanitizeError(file, err); errFile != nil {
+						return errFile
+					}
+				}
+				return nil
+			}
+			for file, offsets := range blob.files {
+				for _, offset := range offsets {
+					writeToFile := func() error {
+						// this looks overly complicated and needs explanation
+						// two competing requirements:
+						// - must create the file once and only once
+						// - should allow concurrent writes to the file
+						// so write the first blob while holding file lock
+						// write other blobs after releasing the lock
+						createSize := int64(-1)
+						file.lock.Lock()
+						if file.inProgress {
+							file.lock.Unlock()
+						} else {
+							defer file.lock.Unlock()
+							file.inProgress = true
+							createSize = file.size
+						}
+						writeErr := r.filesWriter.writeToFile(r.targetPath(file.location), blobData, offset, createSize, file.sparse)
+
+						if r.progress != nil {
+							r.progress.AddProgress(file.location, uint64(len(blobData)), uint64(file.size))
+						}
+
+						return writeErr
+					}
+					err := r.sanitizeError(file, writeToFile())
+					if err != nil {
+						return err
+					}
+				}
+			}
+			return nil
+		})
+}