Fix token handling

Token was encoded as utf-8 string. However, token is a byte string
that is not required to be utf-8 encodable. This patch changes
token type in the Message class to string of bytes instead of string
of characters.

Signed-off-by: Hubert Miś <hubert.mis@gmail.com>

coapthon/messages/message.py

@@ -115,15 +115,15 @@ class Message(object):
         """
         Set the Token of the message.
 
-        :type value: String
+        :type value: Bytes
         :param value: the Token
         :raise AttributeError: if value is longer than 256
         """
         if value is None:
             self._token = value
             return
-        if not isinstance(value, str):
-            value = str(value)
+        if not isinstance(value, bytes):
+            value = bytes(value)
         if len(value) > 256:
             raise AttributeError
         self._token = value

coapthon/serializer.py

@@ -51,10 +51,7 @@ class Serializer(object):
             message.type = message_type
             message.mid = mid
             if token_length > 0:
-                fmt = "%ss" % token_length
-                s = struct.Struct(fmt)
-                token_value = s.unpack_from(datagram[pos:])[0]
-                message.token = token_value.decode("utf-8")
+                message.token = datagram[pos:pos+token_length]
             else:
                 message.token = None
 
@@ -152,10 +149,8 @@ class Serializer(object):
         values = [tmp, message.code, message.mid]
 
         if message.token is not None and tkl > 0:
-
-            for b in str(message.token):
-                fmt += "c"
-                values.append(bytes(b, "utf-8"))
+            fmt += "%ss" % tkl
+            values.append(message.token)
 
         options = Serializer.as_sorted_list(message.options)  # already sorted
         lastoptionnumber = 0