images: Make sure all jpegs work everywhere

Apply #1545 to a public function used everywhere

beets/art.py

@@ -22,7 +22,6 @@
 import subprocess
 import platform
 from tempfile import NamedTemporaryFile
-import imghdr
 import os
 
 from beets.util import displayable_path, syspath, bytestring_path

beets/mediafile.py

@@ -308,6 +308,17 @@ def _sc_encode(gain, peak):
 
 
 # Cover art and other images.
+def _imghdr_what_wrapper(data):
+    """A wrapper around imghdr.what to account for jpeg files that can only be
+    identified as such using their magic bytes
+    See #1545
+    See https://github.com/file/file/blob/master/magic/Magdir/jpeg#L12
+    """
+    # imghdr.what returns none for jpegs with only the magic bytes, so
+    # _wider_test_jpeg is run in that case. It still returns None if it didn't
+    # match such a jpeg file.
+    return imghdr.what(None, h=data) or _wider_test_jpeg(data)
+
 
 def _wider_test_jpeg(data):
     """Test for a jpeg file following the UNIX file implementation which
@@ -318,14 +329,14 @@ def _wider_test_jpeg(data):
         return 'jpeg'
 
 
-def _image_mime_type(data):
+def image_mime_type(data):
     """Return the MIME type of the image data (a bytestring).
     """
     # This checks for a jpeg file with only the magic bytes (unrecognized by
     # imghdr.what). imghdr.what returns none for that type of file, so
     # _wider_test_jpeg is run in that case. It still returns None if it didn't
     # match such a jpeg file.
-    kind = imghdr.what(None, h=data) or _wider_test_jpeg(data)
+    kind = _imghdr_what_wrapper(data)
     if kind in ['gif', 'jpeg', 'png', 'tiff', 'bmp']:
         return 'image/{0}'.format(kind)
     elif kind == 'pgm':
@@ -394,7 +405,7 @@ def __init__(self, data, desc=None, type=None):
     @property
     def mime_type(self):
         if self.data:
-            return _image_mime_type(self.data)
+            return image_mime_type(self.data)
 
     @property
     def type_index(self):

beetsplug/fetchart.py

@@ -29,7 +29,7 @@
 from beets import ui
 from beets import util
 from beets import config
-from beets.mediafile import _image_mime_type
+from beets.mediafile import image_mime_type
 from beets.util.artresizer import ArtResizer
 from beets.util import confit
 from beets.util import syspath, bytestring_path, py3_path
@@ -250,7 +250,7 @@ def fetch_image(self, candidate, extra):
                     # server didn't return enough data, i.e. corrupt image
                     return
 
-                real_ct = _image_mime_type(header)
+                real_ct = image_mime_type(header)
                 if real_ct is None:
                     # detection by file magic failed, fall back to the
                     # server-supplied Content-Type

test/test_mediafile_edge.py

@@ -91,7 +91,7 @@ def test_only_magic_bytes_jpeg(self):
         with open(magic_bytes_file, 'rb') as f:
             jpg_data = f.read()
         self.assertEqual(
-            beets.mediafile._image_mime_type(jpg_data),
+            beets.mediafile.image_mime_type(jpg_data),
             'image/jpeg')
 
     def test_soundcheck_non_ascii(self):