backends: clean reader closing

internal/backend/gs/gs.go

@@ -263,18 +263,6 @@ func (be *Backend) Save(ctx context.Context, h restic.Handle, rd restic.RewindRe
 	return nil
 }
 
-// wrapReader wraps an io.ReadCloser to run an additional function on Close.
-type wrapReader struct {
-	io.ReadCloser
-	f func()
-}
-
-func (wr wrapReader) Close() error {
-	err := wr.ReadCloser.Close()
-	wr.f()
-	return err
-}
-
 // Load runs fn with a reader that yields the contents of the file at h at the
 // given offset.
 func (be *Backend) Load(ctx context.Context, h restic.Handle, length int, offset int64, fn func(rd io.Reader) error) error {
@@ -303,21 +291,16 @@ func (be *Backend) openReader(ctx context.Context, h restic.Handle, length int,
 
 	be.sem.GetToken()
 
+	ctx, cancel := context.WithCancel(ctx)
+
 	r, err := be.bucket.Object(objName).NewRangeReader(ctx, offset, int64(length))
 	if err != nil {
+		cancel()
 		be.sem.ReleaseToken()
 		return nil, err
 	}
 
-	closeRd := wrapReader{
-		ReadCloser: r,
-		f: func() {
-			debug.Log("Close()")
-			be.sem.ReleaseToken()
-		},
-	}
-
-	return closeRd, err
+	return be.sem.ReleaseTokenOnClose(r, cancel), err
 }
 
 // Stat returns information about a blob.