Our architecture is HTTP servers (custom written) which whereby custom clients send a HTTP request for some information and information is returned just as HTTP works. But we need a special custom 'extension' which is a request which is a subscription for receiving asynchronous 'events' on a resource.

For example the client sends an http request subscribing for events on some entity. As the 'entity' generates events they are passed to the http server and the http server must then lookup subscriptions for that entity and send the event message to all subscribed clients. Hope that makes sense.

So my questions are:

• Has this been done before / or is there a standard I should be looking at?
• If no standard, any suggestions on how to implement?
• How does a http server send an unsolicited 'message' to a client?