On Fri, Jun 15, 2012 at 5:13 PM, Maxim Lacrima <[email protected]>wrote:
> Hi Roman, > >> >> You should use feed URL as Topic. If you can wget the feed, it means you >> can also subscribe to it. >> > > The feed can have several URLs, like this > > http://devhubbub.blogspot.com/feeds/posts/default which correspnds to > link[@rel="http://schemas.google.com/g/2005#feed";] > > and this > > http://www.blogger.com/feeds/2243540998291553416/posts/default which > corresponds to link[@rel="self"] > > These URLs point to the same feed. If I subscribe to link[@rel=" > http://schemas.google.com/g/2005#feed";] (and it doesn't matter which > 'hub.mode' I use) then I get updates, but if I subscribe > to link[@rel="self"] I never get updates. > > Is it expected? > Ok, I got it now. When PubSubHubbub gets notified of topic changes (i.e., when publishing happens), it must fetch the feed and distribute changes to all subscribers on the topic. When you post something on http://devhubbub.blogspot.com<http://devhubbub.blogspot.com/feeds/posts/default>, Blogger tells pubsubhubbub.appspot.com that http://devhubbub.blogspot.com/feeds/posts/default has changed. The hub then propagates the changes to all subscribers of http://devhubbub.blogspot.com/feeds/posts/default. Ideally, the hub should figure out that http://www.blogger.com/feeds/2243540998291553416/posts/default is the same feed and notify its subscribers as well. Feed deduping is a non-trivial problem; pubsubhubbub.appspot.com uses a bunch of heuristics but unfortunately they did't work in this particular case. The good news is that the 0.4 PubSubHubbub spec avoids this problem by explicitly specifying which feed URL should be used as topic when subscribing and publishing. Things will get less confusing once Blogger and pubsubhubbub.appspot.com adopt it. Roman.
