Question

today i built a UDP based chatting software which uses a UDP listener and server to form the chat app.

When i gave it to my friend to test, he, he had to port forward so that my messages can reach him through is router and so did I.

i am curious, that how does IM client like msn messenger and skype work. like how do they receive messages without having to port forward?

thanks,
Vidhu

Answer 1

The MSN, etc. clients connect to a third party remote server that technically also has port forwarding/routing but it’s exposed to the public via a static IP address. You download a client application like MSN and it connects to a remote server, but the client does not act as a server itself, thus not requiring port forwarding. It most likely consumes messages and blocks until more come in, so the server doesn’t need to have access to it via IP address to send messages to it.

In your case, since you are hosting the remote server on a private network, you need to route traffic to that IP address to the proper internal device that is connecting to it, just like if you hosted anything else like a website on one of your computers.

With your friend also having to port forward to get the application to work, it seems that their client is also acting as a server and does not maintain a connection/socket with your server. If the client were to maintain a socket with the server, only you would have to port forward and your friend would not because their client would just listen for requests and block until they come in, and send requests to your server.

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You might want to look into a real message bus like RabbitMQ and you could host this message bus and then build your client to subscribe to it and send/receive messages. Another option would be Redis and you could use the POP functionality to remove “read” messages that are retrieved from the queue by a client.