如何从没有文档的客户端/服务器通信中提取信息？

What are methods for undocumented client/server communication to be captured and analyzed for information you want and then have your program looking for this information in real time? For example, programs that look at online game client/server communication and get information and use it to do things like show location on a 3rd party map, etc.What are methods for undocumented client/server