core: fix serialization of empty bytes() on 3.x.

mitogen/core.py

@@ -425,6 +425,8 @@ class Message(object):
                 return Kwargs
         elif module == '_codecs' and func == 'encode':
             return self._unpickle_bytes
+        elif module == '__builtin__' and func == 'bytes':
+            return BytesType
         raise StreamError('cannot unpickle %r/%r', module, func)
 
     @property

tests/serialization_test.py

@@ -0,0 +1,37 @@
+
+try:
+    from io import StringIO
+    from io import BytesIO
+except ImportError:
+    from StringIO import StringIO as StringIO
+    from StringIO import StringIO as BytesIO
+
+import unittest2
+
+import mitogen.core
+from mitogen.core import b
+
+
+def roundtrip(v):
+    msg = mitogen.core.Message.pickled(v)
+    return mitogen.core.Message(data=msg.data).unpickle()
+
+
+class BlobTest(unittest2.TestCase):
+    klass = mitogen.core.Blob
+
+    # Python 3 pickle protocol 2 does weird stuff depending on whether an empty
+    # or nonempty bytes is being serialized. For non-empty, it yields a
+    # _codecs.encode() call. For empty, it yields a bytes() call.
+
+    def test_nonempty_bytes(self):
+        v = mitogen.core.Blob(b('dave'))
+        self.assertEquals(b('dave'), roundtrip(v))
+
+    def test_empty_bytes(self):
+        v = mitogen.core.Blob(b(''))
+        self.assertEquals(b(''), roundtrip(v))
+
+
+if __name__ == '__main__':
+    unittest2.main()