From e8bbb05328652cae3fd7ae65eb37c2bcf51d44ad Mon Sep 17 00:00:00 2001
From: Michael Eischer <michael.eischer@fau.de>
Date: Tue, 29 Jun 2021 20:54:16 +0200
Subject: [PATCH] restore: Correctly handle partial pack download errors

Failed pack/blob downloads should be retried. For blobs that fail
decryption assume that the pack file is really damaged and try to
restore the remaining blobs.
---
 internal/restorer/filerestorer.go | 23 ++++++++++++++++-------
 1 file changed, 16 insertions(+), 7 deletions(-)

diff --git a/internal/restorer/filerestorer.go b/internal/restorer/filerestorer.go
index d2f71ce8f..2e503c4aa 100644
--- a/internal/restorer/filerestorer.go
+++ b/internal/restorer/filerestorer.go
@@ -258,7 +258,11 @@ func (r *fileRestorer) downloadPack(ctx context.Context, pack *packInfo) error {
 			if err != nil {
 				return err
 			}
-			blobData, buf, err = r.loadBlob(bufRd, blobID, blob.length, buf)
+			buf, err = r.downloadBlob(bufRd, blobID, blob.length, buf)
+			if err != nil {
+				return err
+			}
+			blobData, err = r.decryptBlob(blobID, buf)
 			if err != nil {
 				for file := range blob.files {
 					if errFile := sanitizeError(file, err); errFile != nil {
@@ -309,7 +313,7 @@ func (r *fileRestorer) downloadPack(ctx context.Context, pack *packInfo) error {
 	return nil
 }
 
-func (r *fileRestorer) loadBlob(rd io.Reader, blobID restic.ID, length int, buf []byte) ([]byte, []byte, error) {
+func (r *fileRestorer) downloadBlob(rd io.Reader, blobID restic.ID, length int, buf []byte) ([]byte, error) {
 	// TODO reconcile with Repository#loadBlob implementation
 
 	if cap(buf) < length {
@@ -320,24 +324,29 @@ func (r *fileRestorer) loadBlob(rd io.Reader, blobID restic.ID, length int, buf
 
 	n, err := io.ReadFull(rd, buf)
 	if err != nil {
-		return nil, nil, err
+		return nil, err
 	}
 
 	if n != length {
-		return nil, nil, errors.Errorf("error loading blob %v: wrong length returned, want %d, got %d", blobID.Str(), length, n)
+		return nil, errors.Errorf("error loading blob %v: wrong length returned, want %d, got %d", blobID.Str(), length, n)
 	}
+	return buf, nil
+}
+
+func (r *fileRestorer) decryptBlob(blobID restic.ID, buf []byte) ([]byte, error) {
+	// TODO reconcile with Repository#loadBlob implementation
 
 	// decrypt
 	nonce, ciphertext := buf[:r.key.NonceSize()], buf[r.key.NonceSize():]
 	plaintext, err := r.key.Open(ciphertext[:0], nonce, ciphertext, nil)
 	if err != nil {
-		return nil, nil, errors.Errorf("decrypting blob %v failed: %v", blobID, err)
+		return nil, errors.Errorf("decrypting blob %v failed: %v", blobID, err)
 	}
 
 	// check hash
 	if !restic.Hash(plaintext).Equal(blobID) {
-		return nil, nil, errors.Errorf("blob %v returned invalid hash", blobID)
+		return nil, errors.Errorf("blob %v returned invalid hash", blobID)
 	}
 
-	return plaintext, buf, nil
+	return plaintext, nil
 }