如何从RESTful Web服务提供AJAX定期更新？

Question

I am writing a small demo web service.

I want to use this web service to provide periodic updates to the service consumer.

I must point out that I am interested only in the high level layer (ie HTTP and Javascript). I am not concerned with how the HTTP commands or dynamic javascript is generated. I am interested in the underlying concepts of the mechanism, and do not want to get tied into a particular implementation language (I could decide to use C/C++, PHP, Python, C#, Java, Ruby or even Lua so its best to leave the language specific aspects out).

This is the sequence of events in a typical use case scenario:

• The consumer first makes an intial request via an AJAX HTTP GET command

• the service responds with first set of data

• after a random time, the service sends more data to the client

• if no more data available, the service sends the last data to the client and tell the client to effectively, stop 'polling' or 'listening' for new data arrivals

IIRC, the required behavior (as described above), can be achieved by:

1. inserting a hidden frame in the page of the service consumer
2. generating a JSON response from the server which contains both the latest data, as well as dynamic Javascript which is inserted into the hidden frame. The javascript on the clientside 'polls' the service for new data
3. final data from the service no longer contains the dynamic Javascript, thereby effectively stopping the client from continuously polling the service

Can someone explain the correct (best practices) steps required to implement the behavior described above?

[Edit]

As you may realize, this is a form of (lightweight) server push. I am aware of Comet etc, but they are too clunky/heavy for my needs (plus they require additional third party software etc). I just want to roll my own lightweight version using Javascript and HTTP.

Answer 1

I think you want to investigate Comet . "Push technology" and "server push" are broader terms for this kind of thing.