Trying to save a (0, 0) image creates an unreadable file

[NewUserHa]

What did you do?

from PIL import Image
Image.new("RGB",(0,0)).save('test.png') # `.png` or `.jpg` or `.tiff`

What did you expect to happen?

no file should be created on disk because there's an SystemError: tile cannot extend outside image error.
(#5931 (comment) for jpg, libjpeg seems not support size 0 0)

What actually happened?

throw SystemError: tile cannot extend outside image
a ~33 bytes file is on disk, which is unable to read via pillow and other viewer No matter the extension is .png or .jpg or .tiff

What are your OS, Python and Pillow versions?

• OS: win10 1803
• Python: 3.8.10
• Pillow: 9.0.0

[radarhere]

I've created PR #5947 to resolve this.

[NewUserHa]

rather than removing file, why not create file only if there's no error? (i.e. don't open file if there's any known error)

[radarhere]

Ok, i've updated #5947 to use that method, rather than my original suggestion of removing the saved image after an error.

[radarhere]

I've restored my original idea of removing the file after the error as a new PR, #6134. I'm skeptical about the idea of forcing files to live in memory simply to handle this edge case.

[NewUserHa]

What happens if there's user's file with that filename??

btw, shouldn't created = not os.path.exists(filename) from your PR be after the open probably?

[radarhere]

Yes, if the user is asking Pillow to overwrite an existing file with the image, a corrupted image will still be saved.
But I think that this is a rare situation, and forcing all users to keep their images in memory to handle this is an extreme solution.

I don't understand your comment about created = not os.path.exists(filename). It is before builtins.open because it is checking whether or not Pillow is creating the file. If Pillow is creating the file, then I feel ok about removing it. If the file was already on disk, then I think the user would not expect their file to be deleted after Pillow failed to save to it.

[NewUserHa]

what about: "before modifying on disk, check if it is saveable" OR
"use temp file then move to the place, like that the browsers download files does"?

ok. I thought it was to check if the file is created by the pillow

[radarhere]

It's unclear what "check if it is saveable" means without a significant change to how Pillow plugins work.

Using a temporary file is possible, but again, it seems like a sizeable change to how Pillow operates, and this issue seems like a rare situation. Feel free to argue otherwise if you think this is a common situation, and my PR doesn't address it.

[NewUserHa]

about "check if saveable before saving", because most formats don't support (0,0) image, what about if img.size == (0,0) and format != the supported ones just before saving at the lines in your PR ?

[radarhere]

There is room for users to create their own plugins and add them to Pillow. Your suggestion could conceivably break plugins written by users.

[NewUserHa]

ok. This issue then probably could be a low priority.

[radarhere]

#6134 has now been merged, meaning that the broken file will be removed after the error has been raised. That should be part of Pillow 9.1.0, due out on April 1.

If you don't think this is resolved, could you explain a bit more? I don't understand why it is important that a broken file not exist temporarily on disk.