Added basic support for references while marshalling

This allows to be closer to what the Java ObjectOutputStream does and reduces the size of the output files.

Author: tcalmant

javaobj.py

@@ -1084,6 +1084,7 @@ def __init__(self, stream=None):
         self.object_stream = stream
         self.object_obj = None
         self.object_transformers = []
+        self.references = []
 
     def add_transformer(self, transformer):
         """
@@ -1097,6 +1098,7 @@ def dump(self, obj):
         """
         Dumps the given object in the Java serialization format
         """
+        self.references = []
         self.object_obj = obj
         self.object_stream = BytesIO()
         self._writeStreamHeader()
@@ -1282,6 +1284,9 @@ def write_classdesc(self, obj, parent=None):
         :param obj: Class description to write
         :param parent:
         """
+        # Add reference
+        self.references.append(obj.name)
+
         self._writeStruct(">B", 1, (self.TC_CLASSDESC,))
         self._writeString(obj.name)
         self._writeStruct(">qB", 1, (obj.serialVersionUID, obj.flags))
@@ -1292,14 +1297,30 @@ def write_classdesc(self, obj, parent=None):
                 ">B", 1, (self._convert_type_to_char(field_type),))
             self._writeString(field_name)
             if field_type[0] in (self.TYPE_OBJECT, self.TYPE_ARRAY):
-                self.write_string(field_type)
+                try:
+                    idx = self.references.index(field_type)
+                except ValueError:
+                    # First appearance of the type
+                    self.write_string(field_type)
+                    self.references.append(field_type)
+                else:
+                    # Write a reference to the previous type
+                    self.write_reference(idx)
 
         self._writeStruct(">B", 1, (self.TC_ENDBLOCKDATA,))
         if obj.superclass:
             self.write_classdesc(obj.superclass)
         else:
             self.write_null()
 
+    def write_reference(self, ref_index):
+        """
+        Writes a reference
+        :param ref_index: Local index (0-based) to the reference
+        """
+        self._writeStruct(
+            ">BL", 1, (self.TC_REFERENCE, ref_index + self.BASE_REFERENCE_IDX))
+
     def write_array(self, obj):
         """
         Writes a JavaArray

tests/tests.py

@@ -190,8 +190,10 @@ def test_fields(self):
 
         self.assertEqual(len(classdesc.fields_names), 3)
 
-       # jobj_ = javaobj.dumps(pobj)
-       # self.assertEqual(jobj, jobj_)
+        jobj_ = javaobj.dumps(pobj)
+        # Reloading the new dump allows to compare the decoding sequence
+        javaobj.loads(jobj_)
+        self.assertEqual(jobj, jobj_)
 
     def test_class(self):
         """