Fix decoding error with trailing comment extension blocks

src/Decoders/GifDataStreamDecoder.php

@@ -4,7 +4,9 @@
 
 namespace Intervention\Gif\Decoders;
 
+use Intervention\Gif\AbstractExtension;
 use Intervention\Gif\Blocks\ColorTable;
+use Intervention\Gif\Blocks\CommentExtension;
 use Intervention\Gif\Blocks\FrameBlock;
 use Intervention\Gif\Blocks\Header;
 use Intervention\Gif\Blocks\LogicalScreenDescriptor;
@@ -38,7 +40,16 @@ public function decode(): GifDataStream
         }
 
         while ($this->viewNextByte() != Trailer::MARKER) {
-            $gif->addFrame(FrameBlock::decode($this->handle));
+            match ($this->viewNextBytes(2)) {
+                // trailing "global" comment blocks which are not part of "FrameBlock"
+                AbstractExtension::MARKER . CommentExtension::LABEL
+                => $gif->addComment(
+                    CommentExtension::decode($this->handle)
+                ),
+                default => $gif->addFrame(
+                    FrameBlock::decode($this->handle)
+                ),
+            };
         }
 
         return $gif;

src/Encoders/GifDataStreamEncoder.php

@@ -30,6 +30,7 @@ public function encode(): string
             $this->source->getLogicalScreenDescriptor()->encode(),
             $this->maybeEncodeGlobalColorTable(),
             $this->encodeFrames(),
+            $this->encodeComments(),
             $this->source->getTrailer()->encode(),
         ]);
     }
@@ -54,4 +55,16 @@ protected function encodeFrames(): string
             return $frame->encode();
         }, $this->source->getFrames()));
     }
+
+    /**
+     * Encode comment extension blocks of source
+     *
+     * @return string
+     */
+    protected function encodeComments(): string
+    {
+        return implode('', array_map(function ($commentExtension) {
+            return $commentExtension->encode();
+        }, $this->source->getComments()));
+    }
 }

src/GifDataStream.php

@@ -5,6 +5,7 @@
 namespace Intervention\Gif;
 
 use Intervention\Gif\Blocks\ColorTable;
+use Intervention\Gif\Blocks\CommentExtension;
 use Intervention\Gif\Blocks\FrameBlock;
 use Intervention\Gif\Blocks\Header;
 use Intervention\Gif\Blocks\LogicalScreenDescriptor;
@@ -20,7 +21,8 @@ public function __construct(
         protected Header $header = new Header(),
         protected LogicalScreenDescriptor $logicalScreenDescriptor = new LogicalScreenDescriptor(),
         protected ?ColorTable $globalColorTable = null,
-        protected array $frames = []
+        protected array $frames = [],
+        protected array $comments = []
     ) {
     }
 
@@ -122,6 +124,16 @@ public function getFrames(): array
         return $this->frames;
     }
 
+    /**
+     * Return array of "global" comments
+     *
+     * @return array
+     */
+    public function getComments(): array
+    {
+        return $this->comments;
+    }
+
     /**
      * Return first frame
      *
@@ -149,6 +161,19 @@ public function addFrame(FrameBlock $frame): self
         return $this;
     }
 
+    /**
+     * Add comment extension
+     *
+     * @param CommentExtension $comment
+     * @return GifDataStream
+     */
+    public function addComment(CommentExtension $comment): self
+    {
+        $this->comments[] = $comment;
+
+        return $this;
+    }
+
     /**
      * Set the current data
      *

tests/GifDataStreamTest.php

@@ -33,6 +33,7 @@ public function testEncode()
         $gif = new GifDataStream();
         $gif->setLogicalScreenDescriptor($this->getTestLogicalScreenDescriptor());
         $gif->addFrame($this->getTestFrame());
+        $gif->addComment($this->getTestCommentExtension());
 
         $result = implode('', [
             (string) $this->getTestHeader(),
@@ -42,6 +43,7 @@ public function testEncode()
             (string) $this->getTestGraphicControlExtension(),
             (string) $this->getTestImageDescriptor(),
             (string) $this->getTestImageData(),
+            (string) $this->getTestCommentExtension(),
             Trailer::MARKER,
         ]);
 
@@ -153,4 +155,16 @@ public function testDecode()
         }, $gif->getFrames()));
         $this->assertEquals([0, 0, 0, 0, 0, 0, 0, 0], $sizes);
     }
+
+    public function testDecodeTrailingComment(): void
+    {
+        $gif = GifDataStream::decode(
+            $this->getTestHandle(
+                file_get_contents(__DIR__ . '/images/animation_trailing_comment.gif')
+            ),
+        );
+
+        $this->assertInstanceOf(GifDataStream::class, $gif);
+        $this->assertCount(1, $gif->getComments());
+    }
 }