retry key loading on hash mismatch

internal/backend/utils.go

@@ -6,6 +6,8 @@ import (
 	"fmt"
 	"io"
 
+	"github.com/restic/restic/internal/debug"
+	"github.com/restic/restic/internal/errors"
 	"github.com/restic/restic/internal/restic"
 )
 
@@ -13,6 +15,7 @@ import (
 // buffer, which is truncated. If the buffer is not large enough or nil, a new
 // one is allocated.
 func LoadAll(ctx context.Context, buf []byte, be restic.Backend, h restic.Handle) ([]byte, error) {
+	retriedInvalidData := false
 	err := be.Load(ctx, h, 0, 0, func(rd io.Reader) error {
 		// make sure this is idempotent, in case an error occurs this function may be called multiple times!
 		wr := bytes.NewBuffer(buf[:0])
@@ -21,6 +24,18 @@ func LoadAll(ctx context.Context, buf []byte, be restic.Backend, h restic.Handle
 			return cerr
 		}
 		buf = wr.Bytes()
+
+		// retry loading damaged data only once. If a file fails to download correctly
+		// the second time, then it  is likely corrupted at the backend. Return the data
+		// to the caller in that case to let it decide what to do with the data.
+		if !retriedInvalidData && h.Type != restic.ConfigFile {
+			id, err := restic.ParseID(h.Name)
+			if err == nil && !restic.Hash(buf).Equal(id) {
+				debug.Log("retry loading broken blob %v", h)
+				retriedInvalidData = true
+				return errors.Errorf("loadAll(%v): invalid data returned", h)
+			}
+		}
 		return nil
 	})