From: Francis Hwang <sera@...>
Date: 2004-11-14T03:56:28+09:00
Subject: Re: [OT] RSS: Howto get started?


On Nov 13, 2004, at 11:57 AM, Sam Roberts wrote:

> Quoteing sera@fhwang.net, on Sat, Nov 13, 2004 at 04:14:37PM +0900:
>>
>> I tried out Gush (for OS X, I think it's mostly the same thing) and
>> didn't like it either. Its polling model is quite interesting, though:
>> It opens a Jabber connection to the PubSub server so it receives
>> updates from PubSub instead of asking for them periodically. Bob Wyman
>> (PubSub CTO, also I know him since he sits on the board of the
>> non-profit I work at) writes about this issue quite a lot on his own
>> blog. POP clients get updates every few minutes, and we should be able
>> to get the same update rate with feeds like RSS and Atom.
>
> Yeah, but pop clients do it by polling. Theres not difference between
> that and polling for RSS with http.
>

There is. If you've downloaded 30 items from an RSS feed, and then the 
feed gets updated with item 31, the basic HTTP get will download all 
the items and leave it up to the client to sort out what's new or not. 
POP doesn't work this way: If you've downloaded 2000 emails off of your 
mail server, then your mail server receives email 2001, when you check 
your email again you won't download all 2001 emails just to get the 
last one.

RFC3229 ("Delta Encoding in HTTP") describes a way to solve this, 
though nobody's implemented it for RSS or Atom. Here's a blog entry 
that describes the details at a finer grain of detail than I can 
manage:

http://bobwyman.pubsub.com/main/2004/09/using_rfc3229_w.html

Of course, for many feed consumers this is pretty far-out, most of us 
are still getting to work with conditional GET.

F.