HTTP streaming- This technique uses the HTTP protocol, but instead of responding to a request with a single piece of data, the server responds with many small pieces of data that are published as soon as they are available. It's as if you're using HTTP to retrieve a very, very, large file -- the server just keeps pushing out data, one piece at a time. Twitter uses this technique in its Streaming API.
Since HTTP Streaming doesn't work quite the same way that most HTTP-based services work, the program that reads the stream has to be written to process the incoming data, handle reconnects, and so on. It's also difficult to use in a web browser without doing some
JavaScript trickery; HTTP Streaming is mainly suitable for server-to-server communication.
WebHooks is a real-time tech with a simple concept: whenever something happens on server A, it makes an HTTP POST to server B and sends it the update directly. Like HTTP Streaming, it only works for server-to-server communications, but unlike HTTP Streaming the barrier to entry is very low for the programmer - anyone who can write a program or script that can process an HTTP POST can consume a WebHook. Unlike HTTP Streaming, however, a WebHook uses one HTTP request for each event, which means that with today's servers a WebHook is going to top out at several thousand events per second, whereas HTTP Streaming can theoretically process many more events.
WebSockets, unlike HTTP streaming and WebHooks, is designed for real-time streaming to the client- useful for creating real-time apps that run in the browser. WebSockets allows a client and server to use the HTTP protocol for some initial interchange, and then agree to communicate bidirectionally. The result is just like a TCP socket -- the client and server can send whatever data they'd like, in any order, in either direction, for as long as they want. WebSockets also supports JavaScript, ensuring you can easily build a high-fidelity, near-real-time application in a web browser using Internet-standard protocols. WebSockets is part of the HTML 5 family of standards, already implemented in Google Chrome and Apple Safari, and will eventually come to all the browsers.
It was good to see Kaazing, who is leading the development of WebSockets, hanging out at the RRW Real Time Summit.
With some existing technology out there and some new stuff on the way, the stage is set to build a real-time web that's a bit closer to real-time.
