added a length() method for checking message length

chat_messages.hpp

@@ -36,6 +36,9 @@ namespace chat
 
         std::string get_content() const
         { return _content; }
+
+        size_t length() const
+        { return sizeof(char) + _content.size() + sizeof(char); }
     };
 
     std::ostream& operator<<(std::ostream& os, const chat_message& msg)