问题
This is my first experience with P2P and i need some help regarding the design.
I am developing a simple messenger application. I have a directory server on which every user authenticates and announces an open port on which every user is reachable. The directory server maintains the users and the ports and I can query the directory server for any specific user. This part is done. The second part is the chat which i think should be P2P. I can start a chat as well as I can be end point of a chat (client as well as server)
What is confusing me is how do I deal with P2P? Do I create two different sockets? One on which I am listening for TCP requests for incoming connections and another one from which I would send TCP requests to start chat.
In this case do I need 3 sockets, one to talk with server and two for P2P?
回答1:
If you want to go P2P, you'd better use a framework, such as JXTA for example if you are coding in Java. Creating sockets may not be enough by itself, because there are more complicated issues you need to deal with such as NAT traversal if you are operating beyond your LAN.
It seems like you have a central peer (some of server). If it has a public IP address, then you could implement a TURN-like architecture (peers communicate via this central peer). If you want direct connection between peers, you are looking a STUN solutions, but you still need a central peer to facilitate the communication.
TCP Stun is not easy. UDP is not very complicated, you just need to punch a hole in your NAT. Now, keep in mind that NAT traversal is not always possible (it depends of the NAT itself). In this case, the backup solution in a STUN one.
来源：https://stackoverflow.com/questions/8719581/writing-a-simple-p2p-chat-application