Fix GIF parser #7
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Previously, the GIF parser would assume a GIF is animated if it had the Netscape Application Extension. This can lead to false positives where a GIF can have all the indicators of an animated GIF but only one Image Descriptor. Now, the code checks for the absence of the Graphic Control Extension before an Image Descriptor to mean non-animated and otherwise checks if there are multiple Image Descriptors. This unfortunately requires parsing much further into the data stream. The example cli now also supports specifiying the buffer size.
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| if let Some(size) = color_table_size(flags) { | ||
| cursor.seek(SeekFrom::Current(size))?; |
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:nit:
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| if let Some(size) = color_table_size(flags) { | |
| cursor.seek(SeekFrom::Current(size))?; | |
| if let Some(size) = color_table_size(flags) { | |
| // skip Local Color Table | |
| cursor.seek(SeekFrom::Current(size))?; |
FurqanHabibi
approved these changes
Aug 23, 2024
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The parsing part LGTM.
Ref : https://www.w3.org/Graphics/GIF/spec-gif89a.txt
Usually, the "NETSCAPE2.0" Application Extension is used for looping GIFs and the Graphic Control Extension is used for animated GIFs. However, such files can still have only a single image, resulting in a non-animated GIF. While rather nonsensical, these files should still be handled correctly, so one such file was crafted for testing.
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Previously, the GIF parser would assume a GIF is animated if it had the Netscape Application Extension. This can lead to false positives where a GIF can have all the indicators of an animated GIF but only one Image Descriptor.
Now, the code checks for the absence of the Graphic Control Extension before an Image Descriptor to mean non-animated and otherwise checks if there are multiple Image Descriptors. This unfortunately requires parsing much further into the data stream.
The example cli now also supports specifiying the buffer size.
Fixes #7