add json.dumps and json.loads hook

Add properties for json.dumps and json.loads functions in JSONParser
and JSONRenderer class respectively. The classes can be easily extended
by providing custom dumps and/or loads functions.

rest_framework/parsers.py

@@ -48,6 +48,7 @@ class JSONParser(BaseParser):
 
     media_type = 'application/json'
     renderer_class = renderers.UnicodeJSONRenderer
+    loads_function = json.loads
 
     def parse(self, stream, media_type=None, parser_context=None):
         """
@@ -58,7 +59,7 @@ class JSONParser(BaseParser):
 
         try:
             data = stream.read().decode(encoding)
-            return json.loads(data)
+            return self.loads_function(data)
         except ValueError as exc:
             raise ParseError('JSON parse error - %s' % six.text_type(exc))
 

rest_framework/renderers.py

@@ -55,6 +55,7 @@ class JSONRenderer(BaseRenderer):
     encoder_class = encoders.JSONEncoder
     ensure_ascii = True
     charset = None
+    dumps_function = json.dumps
     # JSON is a binary encoding, that can be encoded as utf-8, utf-16 or utf-32.
     # See: http://www.ietf.org/rfc/rfc4627.txt
     # Also: http://lucumr.pocoo.org/2013/7/19/application-mimetypes-and-encodings/
@@ -81,7 +82,7 @@ class JSONRenderer(BaseRenderer):
             except (ValueError, TypeError):
                 indent = None
 
-        ret = json.dumps(data, cls=self.encoder_class,
+        ret = self.dumps_function(data, cls=self.encoder_class,
             indent=indent, ensure_ascii=self.ensure_ascii)
 
         # On python 2.x json.dumps() returns bytestrings if ensure_ascii=True,