ImageField size detection fails for some files even when PIL could succeed

[Stephen Burrows]

Some PNG files can't have their size detected by django because the clever method of size detection Django employs (I suspect in order to be somewhat more efficient?) fails horribly in these cases.

>>> import Image
>>> with open('/path/to/file.png') as f:
...  im = Image.open(f)
... 
>>> im.size
(480, 362)
>>> from django.core.files.images import get_image_dimensions
>>> with open('/path/to/file.png') as f:
...  get_image_dimensions(f)
... 
Traceback (most recent call last):
  File "<console>", line 2, in <module>
  File "django/core/files/images.py", line 58, in get_image_dimensions
    p.feed(data)
  File "PIL/ImageFile.py", line 402, in feed
    im = Image.open(fp)
  File "PIL/Image.py", line 1965, in open
    return factory(fp, filename)
  File "PIL/ImageFile.py", line 91, in __init__
    self._open()
  File "PIL/PngImagePlugin.py", line 331, in _open
    s = self.png.call(cid, pos, len)
  File "PIL/PngImagePlugin.py", line 115, in call
    return getattr(self, "chunk_" + cid)(pos, len)
  File "PIL/PngImagePlugin.py", line 296, in chunk_zTXt
    self.im_info[k] = self.im_text[k] = zlib.decompress(v[1:])
error: Error -5 while decompressing data: incomplete or truncated stream

[Stephen Burrows]

I can't attach the file that I'm using for testing, since it's too big (276kb), but you can download it (at least for now) here: ​http://s3.mirocommunity.org.s3.amazonaws.com/tyhychi/localtv/video_thumbs/43/orig.png

[Anton Baklanov]

​failing test
i've used your png example there

[Anton Baklanov]

this is 'fixing' problem:

@@ -50,7 +50,7 @@ def get_image_dimensions(file_or_path, close=False):
         # Most of the time PIL only needs a small chunk to parse the image and
         # get the dimensions, but with some TIFF files PIL needs to parse the
         # whole file.
-        chunk_size = 1024
+        chunk_size = 2048
         while 1:
             data = file.read(chunk_size)
             if not data:

i will try to dig into that and find more robust solution.

[Anton Baklanov]

​pull request

maybe we also need to contact with PIL guys, because Parser.feed() does not supposed to raise zlib.error in case like our, it must silently wait for more data

[Florian Apolloner <florian@…>]

In 3aa4b8165da23a2f094d0eeffacbda5484f4c1f6:

Fixed #19457 -- ImageField size detection failed for some files.

This was caused by PIL raising a zlib truncated stream error since we fed
the parser with chunks instead of the whole image.

[KS Chan]

May I ask that why this fix is not backported to Django v1.4 LTS?

[Aymeric Augustin]

Only security fixes get backported.