MOBI Input: Dont crash on corrupted JPG images

Use ImageMagick instead of PIL, which handles corrupted JPG files
better. Fixes #1404590 [calibre misbehaves when bad jpeg in mobi file](https://bugs.launchpad.net/calibre/+bug/1404590)

src/calibre/ebooks/metadata/mobi.py

@@ -9,7 +9,7 @@ __copyright__ = '2009, Kovid Goyal kovid@kovidgoyal.net and ' \
     'Marshall T. Vandegrift <llasram@gmail.com>'
 __docformat__ = 'restructuredtext en'
 
-import os, cStringIO
+import os
 from struct import pack, unpack
 from cStringIO import StringIO
 
@@ -467,14 +467,9 @@ def get_metadata(stream):
     from calibre.ptempfile import TemporaryDirectory
     from calibre.ebooks.mobi.reader.headers import MetadataHeader
     from calibre.ebooks.mobi.reader.mobi6 import MobiReader
+    from calibre.utils.magick.draw import save_cover_data_to
     from calibre import CurrentDir
 
-    try:
-        from PIL import Image as PILImage
-        PILImage
-    except ImportError:
-        import Image as PILImage
-
     stream.seek(0)
     try:
         raw = stream.read(3)
@@ -520,13 +515,9 @@ def get_metadata(stream):
             data  = mh.section_data(mh.first_image_index)
         except:
             data = ''
-    buf = cStringIO.StringIO(data)
-    try:
-        im = PILImage.open(buf)
-    except:
-        log.exception('Failed to read MOBI cover')
-    else:
-        obuf = cStringIO.StringIO()
-        im.convert('RGB').save(obuf, format='JPEG')
-        mi.cover_data = ('jpg', obuf.getvalue())
+    if data and what(None, data) in {'jpg', 'jpeg', 'gif', 'png', 'bmp', 'webp'}:
+        try:
+            mi.cover_data = ('jpg', save_cover_data_to(data, 'cover.jpg', return_data=True))
+        except Exception:
+            log.exception('Failed to read MOBI cover')
     return mi

src/calibre/ebooks/mobi/reader/mobi6.py

@@ -8,12 +8,6 @@ __docformat__ = 'restructuredtext en'
 
 import shutil, os, re, struct, textwrap, cStringIO
 
-try:
-    from PIL import Image as PILImage
-    PILImage
-except ImportError:
-    import Image as PILImage
-
 from lxml import html, etree
 
 from calibre import (xml_entity_to_unicode, entity_to_unicode)
@@ -27,6 +21,8 @@ from calibre.ebooks.metadata import MetaInformation
 from calibre.ebooks.metadata.opf2 import OPFCreator, OPF
 from calibre.ebooks.metadata.toc import TOC
 from calibre.ebooks.mobi.reader.headers import BookHeader
+from calibre.utils.magick.draw import save_cover_data_to
+from calibre.utils.imghdr import what
 
 class TopazError(ValueError):
     pass
@@ -851,16 +847,15 @@ class MobiReader(object):
                 # This record is a known non image type, not need to try to
                 # load the image
                 continue
-            buf = cStringIO.StringIO(data)
-            try:
-                im = PILImage.open(buf)
-                im = im.convert('RGB')
-            except IOError:
-                continue
 
             path = os.path.join(output_dir, '%05d.jpg' % image_index)
+            try:
+                if what(None, data) not in {'jpg', 'jpeg', 'gif', 'png', 'bmp', 'webp'}:
+                    continue
+                save_cover_data_to(data, path, minify_to=(10000, 10000))
+            except Exception:
+                continue
             self.image_names.append(os.path.basename(path))
-            im.save(open(path, 'wb'), format='JPEG')
 
 def test_mbp_regex():
     for raw, m in {