Refactored superbox parsing. #175

glymur/jp2box.py

@@ -120,6 +120,53 @@ class Jp2kBox(object):
         fptr.write(struct.pack('>I', end_pos - orig_pos))
         fptr.seek(end_pos)
 
+    def parse_this_box(self, fptr, box_id, start, num_bytes):
+        """Parse the current box.
+
+        Parameters
+        ----------
+        fptr : file
+            Open file object.
+        box_id : str
+            4-letter identifier for the current box.
+        start, num_bytes: int
+            Byte offset and length of the current box. 
+
+        Returns
+        -------
+        box : Jp2kBox
+            object corresponding to the current box
+        """
+        try:
+            box = _BOX_WITH_ID[box_id].parse(fptr, start, num_bytes)
+        except KeyError as err:
+            msg = 'Unrecognized box ({0}) encountered.'.format(box_id)
+            warnings.warn(msg)
+            box = Jp2kBox(box_id, offset=start, length=num_bytes,
+                          longname='Unknown box')
+
+            if fptr.tell() != start + 8:
+                # If the file pointer has advanced, then the KeyError
+                # ocurred during the parsing of the box.
+                pass
+            else:
+                # Could it be a superbox with recognizable child boxes?
+                # Peek ahead to see.
+                pos = fptr.tell()
+                read_buffer = fptr.read(8)
+                sub_length, sub_id = struct.unpack('>I4s', read_buffer)
+                sub_id = sub_id.decode('utf-8')
+
+                # Regardless of whether or not we recognize the box, rewind back
+                # to properly advance to the next box.
+                fptr.seek(pos)
+
+                # Now process any child boxes if we actually did recognize it.
+                if sub_id in _BOX_WITH_ID.keys():
+                    box.box = box.parse_superbox(fptr)
+
+        return box
+
     def parse_superbox(self, fptr):
         """Parse a superbox (box consisting of nothing but other boxes.
 
@@ -159,36 +206,10 @@ class Jp2kBox(object):
                 num_bytes, = struct.unpack('>Q', read_buffer)
 
             else:
+                # The box_length value really is the length of the box!
                 num_bytes = box_length
 
-            # Call the proper parser for the given box with ID "T".
-            try:
-                box = _BOX_WITH_ID[box_id].parse(fptr, start, num_bytes)
-            except KeyError as err:
-                msg = 'Unrecognized box ({0}) encountered.'.format(box_id)
-                warnings.warn(msg)
-                box = Jp2kBox(box_id, offset=start, length=num_bytes,
-                              longname='Unknown box')
-
-                if fptr.tell() != start + 8:
-                    # If the file pointer has advanced, then the KeyError
-                    # ocurred during the parsing of the box.
-                    pass
-                else:
-                    # Could it be a superbox with recognizable child boxes?
-                    # Peek ahead to see.
-                    pos = fptr.tell()
-                    read_buffer = fptr.read(8)
-                    sub_length, sub_id = struct.unpack('>I4s', read_buffer)
-                    sub_id = sub_id.decode('utf-8')
-
-                    # Regardless of whether or not we recognize the box, rewind back
-                    # to properly advance to the next box.
-                    fptr.seek(pos)
-
-                    # Now process any child boxes if we actually did recognize it.
-                    if sub_id in _BOX_WITH_ID.keys():
-                        box.box = box.parse_superbox(fptr)
+            box = self.parse_this_box(fptr, box_id, start, num_bytes)
 
             superbox.append(box)