Server-sent events, WebSockets, and HTTP
In case people don't know, Mark Nottingham (the author) is the chair of the HTTP working group at the IETF. He isn't just some guy with opinions on the internet. (Sorry mnot!)<p>I've never found pub/sub quite the right abstraction, because almost every implementation I've seen has race conditions or issues on reconnect. Usually its possible to lose messages during reconnection, and there's often other issues too. I usually want an event queue abstraction, not pub/sub.<p>I met mnot a few years ago when we (the braid group) took a stab at writing a spec for HTTP based streaming updates[1]. Our proposal is to do state syncronization around a shared objects (the URL). Each event on the channel is (explicitly or implicitly) an update for some resource. So:<p>- The document (resource) has a version header (ETag?).<p>- Each event sent on the stream is a patch which changes the version from X to Y. Patches can either be incremental ("insert A at position 5") or if its small, just contain a new copy of the document.<p>- You can reconnect at any time, and specify a known version of the document. The server can bring you up to date by sending the patches you missed. If the server doesn't store historical changes, it should be able to just send you a fresh copy of the document. After that, the subscription should drip feed events as they come in.<p>One nice thing about this is that CDNs can do highly efficient fan-out of changes. A cache could also use braid to subscribe to resources which change a lot on the origin server, in order to keep the cached values hot.<p>[1] <a href="https://datatracker.ietf.org/doc/html/draft-toomim-httpbis-braid-http-02" rel="nofollow">https://datatracker.ietf.org/doc/html/draft-toomim-httpbis-b...</a><p>We've done some revisions since then but have been working on getting more running code before pushing forward more with the approach. Most recent draft & issues: <a href="https://github.com/braid-org/braid-spec/blob/master/draft-toomim-httpbis-braid-http-03.txt" rel="nofollow">https://github.com/braid-org/braid-spec/blob/master/draft-to...</a>