A simple, open, server-to-server webhook-based pubsub (publish/subscribe) protocol for any web accessible resources.
Parties (servers) speaking the PubSubHubbub protocol can get near-instant notifications (via webhook callbacks) when a topic (resource URL) they’re interested in is updated.The protocol in a nutshell is as follows:
- An resource URL (a “topic”) declares its Hub server(s) in its HTTP Headers, via Link: <hub url>; rel=”hub” . The hub(s) can be run by the publisher of the resource, or can be acommunity hub that anybody can use: Google’s, or Superfeedr.
- A subscriber (a server that’s interested in a topic), initially fetches the resource URL as normal. If the response declares its hubs, the subscriber can then avoid lame, repeated polling of the URL and can instead register with the designated hub(s) and subscribe to updates.
- The subscriber subscribes to the Topic URL from the Topic URL’s declared Hub(s).
- When the Publisher next updates the Topic URL, the publisher software pings the Hub(s) saying that there’s an update.
- The hub efficiently fetches the published resource and multicasts the new/changed content out to all registered subscribers.
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