ByteStringSplitter can now take kwargs and can be added to other splitters.

nkms/crypto/utils.py

@@ -47,17 +47,33 @@ class BytestringSplitter(object):
     def __len__(self):
         return sum(self.get_message_meta(m)[1] for m in self.message_types)
 
+
     @staticmethod
     def get_message_meta(message_type):
-        if isinstance(message_type, tuple):
-            message_meta = message_type
-        else:
         try:
-                message_meta = message_type, message_type._EXPECTED_LENGTH
+            message_class = message_type[0]
+        except TypeError:
+            message_class = message_type
+
+        try:
+            message_length = message_type[1]
+        except TypeError:
+            message_length = message_type._EXPECTED_LENGTH
         except AttributeError:
             raise TypeError("No way to know the expected length.  Either pass it as the second member of a tuple or set _EXPECTED_LENGTH on the class you're passing.")
 
-        return message_meta
+        try:
+            kwargs = message_type[2]
+        except (IndexError, TypeError):
+            kwargs = {}
+
+        return message_class, message_length, kwargs
+
+    def __add__(self, splitter):
+        return self.__class__(*self.message_types + splitter.message_types)
+
+    def __radd__(self, other):
+        return other + bytes(self)
 
 
 class RepeatingBytestringSplitter(BytestringSplitter):