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GIF: Check for end of stream when reading comments. #2954

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Jun 24, 2025
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GIF: Check for end of stream when reading comments. #2954

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5 changes: 5 additions & 0 deletions src/ImageSharp/Formats/Gif/GifDecoderCore.cs
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Expand Up @@ -414,6 +414,11 @@ private void ReadComments(BufferedReadStream stream)
GifThrowHelper.ThrowInvalidImageContentException($"Gif comment length '{length}' exceeds max '{GifConstants.MaxCommentSubBlockLength}' of a comment data block");
}

if (length == -1)
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Copilot AI Jun 24, 2025

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[nitpick] Consider moving the EOF check (length < 0) before the max-length validation to follow a consistent ordering of bounds checks and avoid any accidental fall-through.

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{
GifThrowHelper.ThrowInvalidImageContentException("Unexpected end of stream while reading gif comment");
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[nitpick] The exception message uses lowercase 'gif'; for consistency with other GIF-related messages in the codebase, consider capitalizing it to 'GIF'.

Suggested change
GifThrowHelper.ThrowInvalidImageContentException("Unexpected end of stream while reading gif comment");
GifThrowHelper.ThrowInvalidImageContentException("Unexpected end of stream while reading GIF comment");

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}

if (this.skipMetadata)
{
stream.Seek(length, SeekOrigin.Current);
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17 changes: 17 additions & 0 deletions tests/ImageSharp.Tests/Formats/Gif/GifDecoderTests.cs
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Expand Up @@ -381,4 +381,21 @@ public void Issue2859_LZWPixelStackOverflow<TPixel>(TestImageProvider<TPixel> pr
image.DebugSaveMultiFrame(provider);
image.CompareToReferenceOutputMultiFrame(provider, ImageComparer.Exact);
}

// https://github.com/SixLabors/ImageSharp/issues/2953
[Theory]
[WithFile(TestImages.Gif.Issues.Issue2953, PixelTypes.Rgba32)]
public void Issue2953<TPixel>(TestImageProvider<TPixel> provider)
where TPixel : unmanaged, IPixel<TPixel>
{
// We should throw a InvalidImageContentException when trying to identify or load an invalid GIF file.
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Replace 'a InvalidImageContentException' with 'an InvalidImageContentException' to correct the article usage.

Suggested change
// We should throw a InvalidImageContentException when trying to identify or load an invalid GIF file.
// We should throw an InvalidImageContentException when trying to identify or load an invalid GIF file.

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TestFile testFile = TestFile.Create(provider.SourceFileOrDescription);

Assert.Throws<InvalidImageContentException>(() => Image.Identify(testFile.FullPath));
Assert.Throws<InvalidImageContentException>(() => Image.Load(testFile.FullPath));

DecoderOptions options = new() { SkipMetadata = true };
Assert.Throws<InvalidImageContentException>(() => Image.Identify(options, testFile.FullPath));
Assert.Throws<InvalidImageContentException>(() => Image.Load(options, testFile.FullPath));
}
}
1 change: 1 addition & 0 deletions tests/ImageSharp.Tests/TestImages.cs
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Expand Up @@ -581,6 +581,7 @@ public static class Issues
public const string Issue2866 = "Gif/issues/issue_2866.gif";
public const string Issue2859_A = "Gif/issues/issue_2859_A.gif";
public const string Issue2859_B = "Gif/issues/issue_2859_B.gif";
public const string Issue2953 = "Gif/issues/issue_2953.gif";
}

public static readonly string[] Animated =
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3 changes: 3 additions & 0 deletions tests/Images/Input/Gif/issues/issue_2953.gif
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