Specify pickle protocol in REPLICATE()

The default pickle protocol in python3 is version 3. This is not
readable by a python2 interpreter.

Force the use of version 2 in the object server REPLICATE() function,
for compatibility with python 2.

Change-Id: I19d23570ff3a084d288de1308e059cfd8134d6ad

swift/obj/server.py

@@ -1256,7 +1256,8 @@ class ObjectController(BaseStorageServer):
         except DiskFileDeviceUnavailable:
             resp = HTTPInsufficientStorage(drive=device, request=request)
         else:
-            resp = Response(body=pickle.dumps(hashes))
+            # force pickle protocol for compatibility with py2 nodes
+            resp = Response(body=pickle.dumps(hashes, protocol=2))
         return resp
 
     @public

test/unit/obj/test_server.py

@@ -6812,6 +6812,34 @@ class TestObjectController(unittest.TestCase):
             tpool.execute = was_tpool_exe
             diskfile.DiskFileManager._get_hashes = was_get_hashes
 
+    def test_REPLICATE_pickle_protocol(self):
+
+        def fake_get_hashes(*args, **kwargs):
+            return 0, {1: 2}
+
+        def my_tpool_execute(func, *args, **kwargs):
+            return func(*args, **kwargs)
+
+        was_get_hashes = diskfile.DiskFileManager._get_hashes
+        was_tpool_exe = tpool.execute
+        try:
+            diskfile.DiskFileManager._get_hashes = fake_get_hashes
+            tpool.execute = my_tpool_execute
+            req = Request.blank('/sda1/p/suff',
+                                environ={'REQUEST_METHOD': 'REPLICATE'},
+                                headers={})
+            with mock.patch('swift.obj.server.pickle.dumps') as fake_pickle:
+                fake_pickle.return_value = b''
+                req.get_response(self.object_controller)
+                # This is the key assertion: starting in Python 3.0, the
+                # default protocol version is 3, but such pickles can't be read
+                # on Python 2. As long as we may need to talk to a Python 2
+                # process, we need to cap our protocol version.
+                fake_pickle.assert_called_once_with({1: 2}, protocol=2)
+        finally:
+            tpool.execute = was_tpool_exe
+            diskfile.DiskFileManager._get_hashes = was_get_hashes
+
     def test_REPLICATE_timeout(self):
 
         def fake_get_hashes(*args, **kwargs):