Notifications (push notifications) via HTTP or WebDAV protocol without using third-party protocols using HTTP or WebDAV?

Question

Computer networks

Tell me how you can implement a PUSH notification system without using third-party libraries or protocols using the HTTP (HTTPS) and / or WebDAV protocols? Those. the HTTP (HTTPS) and/or WebDAV server notifies that there has been a change on the server, for example, or simply "hello world" in the body of a PUSH message.
Is this even possible?
If very briefly, there is a self-written client that downloads a file using the WebDAV protocol, I want to make sure that if the contents of the file change, the server will let the client know about it and the client will start downloading the file. Instead of downloading a file and comparing whether it has changed or not after a time interval.

Answer 1

I advise you to look in the direction of SignalR here is a good article with an implementation example