When attempting to read the attached GIF (random example) it returns the following:

Exception in thread "main" java.lang.NegativeArraySizeException
	at com.adobe.xmp.impl.ByteBuffer.<init>(Unknown Source)
	at com.drew.metadata.xmp.XmpReader.extract(XmpReader.java:167)
	at com.drew.metadata.gif.GifReader.readApplicationExtensionBlock(GifReader.java:275)
	at com.drew.metadata.gif.GifReader.readGifExtensionBlock(GifReader.java:225)
	at com.drew.metadata.gif.GifReader.extract(GifReader.java:103)
	at com.drew.imaging.gif.GifMetadataReader.readMetadata(GifMetadataReader.java:60)
	at com.drew.imaging.ImageMetadataReader.readMetadata(ImageMetadataReader.java:158)
	at com.drew.imaging.ImageMetadataReader.readMetadata(ImageMetadataReader.java:121)
	at com.drew.imaging.ImageMetadataReader.readMetadata(ImageMetadataReader.java:197)

Running the file against exiftool generates (partly to verify the filetype):

• ExifTool Version Number : 10.93
• File Name : IMG_5602.gif
• Directory : /tmp
• File Size : 44 kB
• File Modification Date/Time : 2018:06:17 16:15:21+01:00
• File Access Date/Time : 2018:06:17 16:15:30+01:00
• File Inode Change Date/Time : 2018:06:17 16:15:21+01:00
• File Permissions : rw-------
• File Type : GIF
• File Type Extension : gif
• MIME Type : image/gif
• GIF Version : 87a
• Image Width : 840
• Image Height : 436
• Has Color Map : Yes
• Color Resolution Depth : 8
• Bits Per Pixel : 7
• Background Color : 0
• Warning : [minor] Empty XMP
• Image Size : 840x436
• Megapixels : 0.366

It looks like it could be an issue on this line in GifReader.java. In the case of the attached image, the XmpByte length is 4 bytes long so (xmpBytes.length - 257) raises the NegativeArraySizeException.

It looks like gatherBytes(SequentialReader reader) has a fixed byte array of size 257. Is there a reason that 257 is being subtracted from xmpBytes.length? Removing this appears to fix my issue but I'm not entirely familiar with the code.

Thanks.