Indefinite loop while counting frames in truncated tiff image

[bauerji]

What did you do?

I tried to count number of frames in a tiff image. However, the image is corrupted.

What did you expect to happen?

I expected some kind of exception (OSError).

What actually happened?

Warning is logged
.../lib/python3.9/site-packages/PIL/TiffImagePlugin.py:793: UserWarning: Truncated File Read
and code is trapped inside indefinite for loop.

What are your OS, Python and Pillow versions?

• OS: MacOS Big Sur
• Python: 3.9.4
• Pillow: 8.2.0

also occurs in docker container with

• OS: Ubuntu focal
• Python: 3.9.0
• Pillow: 8.2.0

from pathlib import Path
from PIL import Image

# path to the attached image
file_path = Path("truncated_img.tiff")

Image.open(file_path).n_frames

truncated_img.tiff.zip

[radarhere]

Thanks for reporting. Your file is telling Pillow that the next frame is in the same position as the current frame, leading to an infinite loop.

I've created PR #5473 to resolve this - although my change doesn't raise an error like you are expecting, it just concludes that your image only has 1 frame.

[bauerji]

Thank you for such a quick solution. This seems to work when the last frame is corrupted. But when the image contains e.g. 4 frames and the third one is corrupted, n_frames returns 2 which is incorrect.

[radarhere]

Would you be able to attach that image? The information that is incorrect is the information telling us where the next image is, so I'm not sure if there is a way to figure that out without it. The specification states that "This file offset may
point anywhere in the file, even after the image data."
If I create a multiframe image like you're describing and check to see if commercial software can handle it, I can't open it in Preview or GIMP.

[bauerji]

Unfortunately I cannot shared this file, it is confidential. As I tried to create another one, I also wasn't able to open it in such a software. That leads me to outcome that n_frames should really raise an exception rather than return an invalid number. It should be sufficient to add raise in here https://github.com/python-pillow/Pillow/blob/master/src/PIL/TiffImagePlugin.py#L794 (this change would cause 2 tests to fail)

[radarhere]

Just to be clear, my change doesn't affect the UserWarning that you're seeing for your image.

[bauerji]

Okay, your solution fits fine to our needs. Thank you!

[radarhere]

It's not clear to me - are you still interested in n_frames throwing an error? I've been mulling it over.

[bauerji]

I am sorry for not being clear enough. I like the solution just with UserWarning. Throwing an error is not necessary.