image/gif: avoid decoding past the first frame in decode()

The existing decode() method offers the ability to keep just one
frame of the GIF image, however it will read and decompress all
subsequent frames regardless.

Fixes #41142

Change-Id: I0c3c11f9c11cd487b6c365e9a8b98e617d555db0
GitHub-Last-Rev: 03ebc8ee7bb19ee80c62d0c935b783d7bc75c2e9
GitHub-Pull-Request: golang/go#46813
Reviewed-on: https://go-review.googlesource.com/c/go/+/329329
Auto-Submit: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Paul Tyng <paul@paultyng.net>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Nigel Tao (INACTIVE; USE @golang.org INSTEAD) <nigeltao@google.com>

diff --git a/src/image/gif/reader.go b/src/image/gif/reader.go
index 9e8268c86f3c018af93723a748a258b8c13870da..0867b1029567533182b3a95c3f7344c14b0c42d3 100644 (file)
--- a/src/image/gif/reader.go
+++ b/src/image/gif/reader.go
@@ -250,6 +250,10 @@ func (d *decoder) decode(r io.Reader, configOnly, keepAllFrames bool) error {
                                return err
                        }
 
+                       if !keepAllFrames && len(d.image) == 1 {
+                               return nil
+                       }
+
                case sTrailer:
                        if len(d.image) == 0 {
                                return fmt.Errorf("gif: missing image data")

diff --git a/src/image/gif/reader_test.go b/src/image/gif/reader_test.go
index 5eec5ecb4a6889e8a25abb2c4cadc38c97e31f3e..a7f943adeb76ea9c125a0a40fc9ffd0349c98105 100644 (file)
--- a/src/image/gif/reader_test.go
+++ b/src/image/gif/reader_test.go
@@ -379,7 +379,7 @@ func TestLoopCount(t *testing.T) {
 
 func TestUnexpectedEOF(t *testing.T) {
        for i := len(testGIF) - 1; i >= 0; i-- {
-               _, err := Decode(bytes.NewReader(testGIF[:i]))
+               _, err := DecodeAll(bytes.NewReader(testGIF[:i]))
                if err == errNotEnough {
                        continue
                }