Error handling in case of corrupt images

[ptamarit]

Testing of corrupted images

Creation of the corrupted image files

• Text file: echo -e 'Some text file\nwith some content.' > vips.txt
• XML (SVG-ish) file: echo -e '<?xml version="1.0" encoding="UTF-8"?>\n<Some><XML>File</XML><Message>With some comment</Message></Some>' > vips.xml
• Truncated PNG file:

  wget https://upload.wikimedia.org/wikipedia/commons/4/47/PNG_transparency_demonstration_1.png
  mv PNG_transparency_demonstration_1.png vips-truncated.png
  truncate -s 100k vips-truncated.png

• Truncated and padded PNG file:

  cp vips-truncated.png vips-padded.png
  truncate -s +100k vips-padded.png

Execution of the processing of the corrupted files

for filename in vips*.*; do
    echo "-------------------------------"
    echo "$filename"
    vips tiffsave "$filename" "output-$filename.tif" --tile --pyramid --tile-width 256 --tile-height 256 --compression "jpeg"
    echo "Exit code: $?"
done

Output:

-------------------------------
vips-padded.png

(vips:97162): VIPS-WARNING **: 16:21:31.715: pngload: end of stream
...
(vips:97162): VIPS-WARNING **: 16:21:31.720: pngload: end of stream
Exit code: 0
-------------------------------
vips-truncated.png

(vips:97177): VIPS-WARNING **: 16:21:31.768: pngload: end of stream
...
(vips:97177): VIPS-WARNING **: 16:21:31.773: pngload: end of stream
Exit code: 0
-------------------------------
vips.txt
VipsForeignLoad: "vips.txt" is not a known file format
Exit code: 1
-------------------------------
vips.xml
magickload: Magick: unable to read image data `vips.xml' @ error/svg.c/RenderRSVGImage/457 (null)
Exit code: 1

Conclusion

• The vips CLI does not care about the filename extension, it tries to guess the type of the file from its content.
• When handling fully corrupted images (e.g. TXT or XML file), the vips CLI returns an error code of 1 and prints an error message in stderr.
• When handling partially corrupted images (e.g. truncated or padded PNG file), the vips CLI generates valid outputs (but with an incomplete image), returns without any error code (i.e. 0), but does print some errors in stderr indicating that some of the processing went wrong.

Adapting the usage of pyvips to properly handle corrupted images

• The pyvips library throws the pyvips.Error exception in case of problems when processing an input image.
• The linked pull request adds a try/except around the image generation and logs an exception in order to not let the celery task fail in case of image processing problem.