Updating data in a client application, how to avoid polling?

Question

I have a desktop client application that is talking to a server application through a REST API using simple HTTP posts. I currently have the client polling every X minutes, but I would like the data to be refreshed more frequently. Is it possible to have the server notify the client of any new data, or is that outside the scope of what an HTTP server is meant to do? Any thoughts on the best way to approach this would be much appreciated. Thanks!

Answer 1

If you hold the HTTP connection open on the server side then you can send data whenever there's an update, followed by flushing the connection to actually send the data. This may cause issues with the TCP/IP stack if tens of thousands of connections are required though.

Answer 2

You may want to check the accepted answer to the following Stack Overflow post, which describes with a very basic example how to implement Long Polling using php on the server-side:

• Simple “Long Polling” example code

When using Long Polling, your client application starts a request to the HTTP server, with an infinite timeout (or a very long one). Now as soon as new data is available, the server will find an active connection ready, so it can push the data immediately. In traditional polling, you would have to wait until the application initiates a new poll, plus the network latency to reach the server before new data is sent.

Then when the data is sent, the connection is closed, but your application should open a new one immediately in order to have a constantly open connection to the server. Actually there will be a very small gap where there will not be an active connection, but this is often negligible in many applications.