have vtables consider size

Author: thejtshow

python/flatbuffers/builder.py

@@ -230,8 +230,10 @@ def WriteVtable(self):
             vtKey.append(elem)
 
         vtKey = tuple(vtKey)
-        vt2Offset = self.vtables.get(vtKey)
-        if vt2Offset is None:
+        # calculate the size of the object
+        objectSize = UOffsetTFlags.py_type(objectOffset - self.objectEnd)
+        vt2Offset, vt2Size = self.vtables.get(vtKey) or (None, None)
+        if vt2Offset is None or vt2Size != objectSize:
             # Did not find a vtable, so write this one to the buffer.
 
             # Write out the current vtable in reverse , because
@@ -259,7 +261,6 @@ def WriteVtable(self):
             # The two metadata fields are written last.
 
             # First, store the object bytesize:
-            objectSize = UOffsetTFlags.py_type(objectOffset - self.objectEnd)
             self.PrependVOffsetT(VOffsetTFlags.py_type(objectSize))
 
             # Second, store the vtable bytesize:
@@ -275,7 +276,7 @@ def WriteVtable(self):
 
             # Finally, store this vtable in memory for future
             # deduplication:
-            self.vtables[vtKey] = self.Offset()
+            self.vtables[vtKey] = (self.Offset(), objectSize)
         else:
             # Found a duplicate vtable.
             objectStart = SOffsetTFlags.py_type(len(self.Bytes) - objectOffset)