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bpo-16512: one jpeg image added with different profile, code modified to detect all types of jpg #8322

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c27e101
issue16512: one image added, code modified to detect all types of jpe…
Jul 18, 2018
8192d9e
issue16512: added the blurb file in next/Library
Jul 18, 2018
af68a64
Update test_imghdr.py
gov-vj Jul 24, 2018
aaea47b
Update 2018-07-18-19-57-19.bpo-16512.Jh27PQ.rst
gov-vj Jul 24, 2018
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2 changes: 1 addition & 1 deletion Lib/imghdr.py
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Original file line number Diff line number Diff line change
Expand Up @@ -36,7 +36,7 @@ def what(file, h=None):

def test_jpeg(h, f):
"""JPEG data in JFIF or Exif format"""
if h[6:10] in (b'JFIF', b'Exif'):
if h.startswith(b'\xff\xd8'):
return 'jpeg'
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While technically this test is correct, there is a risk to have false positive. Would it be possible to design a stricter test?

My Hachoir parser for JPEG picture checks that it's able to parse at least 3 chunks:
https://github.com/vstinner/hachoir/blob/15f61aef34115a7ed1e76efc84b9176be55032a4/hachoir/parser/image/jpeg.py#L565-L578

A chunk must start with 0xFF, then have a tag in the 0xD0..0xD9 range.

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@vstinner Hi,

I think I understand your code. For example in b'\xff\xd8\xff\xdb\x00C....':

  1. First 2 bytes must equal to '\xff\xd8'
  2. Then you are looking for the tag (defined in JpegChunk.TAG_INFO) in the next 3 bytes( i.e. '\xff\xdb\x00C').

Am I correct?

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@vstinner Hi,

I had trouble understainding the code you provided. Can you please elebroate more?
Thanks.


tests.append(test_jpeg)
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3 changes: 2 additions & 1 deletion Lib/test/test_imghdr.py
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Expand Up @@ -14,6 +14,7 @@
('python.pgm', 'pgm'),
('python.pbm', 'pbm'),
('python.jpg', 'jpeg'),
('python2.jpeg', 'jpeg'),
('python.ras', 'rast'),
('python.sgi', 'rgb'),
('python.tiff', 'tiff'),
Expand Down Expand Up @@ -79,7 +80,7 @@ def test_bad_args(self):
imghdr.what()
with self.assertRaises(AttributeError):
imghdr.what(None)
with self.assertRaises(TypeError):
with self.assertRaises(AttributeError):
imghdr.what(self.testfile, 1)
with self.assertRaises(AttributeError):
imghdr.what(os.fsencode(self.testfile))
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1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Library/2018-07-18-19-57-19.bpo-16512.Jh27PQ.rst
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@@ -0,0 +1 @@
Fixed bug in ``imghdr`` that was causing some jpeg image files not being detected as such.