Merge pull request #3658 from Glandos/fast_mpo_open

Fast MPO open

src/PIL/JpegImagePlugin.py

@@ -827,7 +827,8 @@ def jpeg_factory(fp=None, filename=None):
         if mpheader[45057] > 1:
             # It's actually an MPO
             from .MpoImagePlugin import MpoImageFile
-            im = MpoImageFile(fp, filename)
+            # Don't reload everything, just convert it.
+            im = MpoImageFile.adopt(im, mpheader)
     except (TypeError, IndexError):
         # It is really a JPEG
         pass

src/PIL/MpoImagePlugin.py

@@ -47,7 +47,10 @@ class MpoImageFile(JpegImagePlugin.JpegImageFile):
     def _open(self):
         self.fp.seek(0)  # prep the fp in order to pass the JPEG test
         JpegImagePlugin.JpegImageFile._open(self)
-        self.mpinfo = self._getmp()
+        self._after_jpeg_open()
+
+    def _after_jpeg_open(self, mpheader=None):
+        self.mpinfo = mpheader if mpheader is not None else self._getmp()
         self.__framecount = self.mpinfo[0xB001]
         self.__mpoffsets = [mpent['DataOffset'] + self.info['mpoffset']
                             for mpent in self.mpinfo[0xB002]]
@@ -110,6 +113,22 @@ class MpoImageFile(JpegImagePlugin.JpegImageFile):
         finally:
             self.__fp = None
 
+    @staticmethod
+    def adopt(jpeg_instance, mpheader=None):
+        """
+        Transform the instance of JpegImageFile into
+        an instance of MpoImageFile.
+        After the call, the JpegImageFile is extended
+        to be an MpoImageFile.
+
+        This is essentially useful when opening a JPEG
+        file that reveals itself as an MPO, to avoid
+        double call to _open.
+        """
+        jpeg_instance.__class__ = MpoImageFile
+        jpeg_instance._after_jpeg_open(mpheader)
+        return jpeg_instance
+
 
 # ---------------------------------------------------------------------
 # Registry stuff