CODEWITHSUNDEEP
websocket
user2594604
user2594604

Reputation: 105

Requests from server to client

I know already about the web-sockets, and they are great, the problem with them is that they have to keep the connection open in order to be able to communicate.

I have a small system where from time to time the server has to update the status and notify the clients about that, and keeping the connection open from every client is not so optimal. At same time is very important that the update on the client side to be made just in time.

So my question is, if the server has a unique address does the client have a public temporary address where the server can send request? So when the client will connect to the server it will provide it's unique address and the server will cache it, and when there will be an update the server will send the request to that address?

I understand that there many problems as the address will constantly change, but this is already other question.

Upvotes: 1

Views: 372

Answers (1)

Alex Myznikov
Alex Myznikov

Reputation: 969

If client does not have a dedicated IP-address then it is not available from WAN unless it has an open connection with any node in it.

When client from local network sends request to a server it's (client's) router remembers client's local IP-address and port and translates it using NAT protocol to one of router's free ports and then sends data further with router's own 'IP-address of the sender' in IP protocol header and 'Sender's port' in TCP header. When router get's server's response it uses NAT table from it's memory to translate addresses back and deliver data to the client. Addresses are normally kept in NAT table while connection between server and client is open. So if there are no opened connections between server and local network client then server will not be able to connect with client because server does not know how to reach it.

You say you have a small system. Why then do you think that you will not have enough free ports at your server to work with websockets? If you just want to get updates from the server (not to both send and get data through a persistently opened connection) you'll probably find long polling or SSE more suitable. It is definitely easier to implement than websockets.

Upvotes: 1

Related Questions