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.

django/core/files/images.py

@@ -4,7 +4,11 @@ Utility functions for handling images.
 Requires PIL, as you might imagine.
 """
 
+import zlib
+import sys
+
 from django.core.files import File
+from django.utils import six
 
 class ImageFile(File):
     """
@@ -55,7 +59,15 @@ def get_image_dimensions(file_or_path, close=False):
             data = file.read(chunk_size)
             if not data:
                 break
-            p.feed(data)
+            try:
+                p.feed(data)
+            except zlib.error as e:
+                # ignore zlib complaining on truncated stream, just feed more
+                # data to parser (ticket #19457).
+                if e.message.startswith("Error -5"):
+                    pass
+                else:
+                    six.reraise(*sys.exc_info())
             if p.image:
                 return p.image.size
             chunk_size = chunk_size*2

tests/regressiontests/file_storage/tests.py

@@ -7,6 +7,7 @@ import shutil
 import sys
 import tempfile
 import time
+import zlib
 from datetime import datetime, timedelta
 from io import BytesIO
 
@@ -559,6 +560,20 @@ class InconsistentGetImageDimensionsBug(unittest.TestCase):
         self.assertEqual(image_pil.size, size_1)
         self.assertEqual(size_1, size_2)
 
+    @unittest.skipUnless(Image, "PIL not installed")
+    def test_bug_19457(self):
+        """
+        Regression test for #19457
+        get_image_dimensions fails on some pngs, while Image.size is working good on them
+        """
+        img_path = os.path.join(os.path.dirname(upath(__file__)), "magic.png")
+        try:
+            size = get_image_dimensions(img_path)
+        except zlib.error:
+            self.fail("Exception raised from get_image_dimensions().")
+        self.assertEqual(size, Image.open(img_path).size)
+
+
 class ContentFileTestCase(unittest.TestCase):
 
     def setUp(self):