added a get_header() method to class chat_message

chat_messages.hpp

@@ -35,6 +35,9 @@ namespace chat
 
         size_t length() const
         { return sizeof(char) + _content.size() + sizeof(char); }
+
+        message get_header() const
+        { return _header; }
     };
 
     inline std::ostream& operator<<(std::ostream& os, const chat_message& msg)