PubSubHubbub support

I can't see any Drupal modules on that thread but I left a comment pointing to this issue.

There is PHP source code for PubSubHubub available on http://code.google.com/p/pubsubhubbub/source/checkout

I just realized that we will need to support pausing single feeds for this feature as a importer configuration will decide on a feed by feed basis on whether a feed needs to be refreshed on cron or not depending on whether a pubsub hub could be found for it. #629372: Pause single feeds

This is a first shot, building on subscriber.php included in http://code.google.com/p/pubsubhubbub/source/checkout

Completely untested and not functional. I'm posting this here to share where I'm going. Most likely, I won't have much time for working on this in the next week.

#8 Always welcome. The issue queue is a great place to start. Soon I will come up with a roadmap, too.

#7: I thought more about implementing pub/sub. I think the approach taken in #7 of breaking it out into its own fetcher/parser is not the way to go as pub sub is fundamentally a problem that concerns the importer configuration. I. e. only specific Atom/RSS parsers can actually detect the pubsub hub URL in a feed and then this URL is to be used only if the fetcher supports HTTP GET (or in the case of PuSH receiving HTTP POST requests). Will roll a new patch if I can get more time.

This patch implements pubsubhubbub support. Very close now. Will test with superfeedr.

Improvements:

* Implemented authenticated content distribution.
* Implemented unsubscribe on delete.
* Bunch of smaller bug fixes

For testing I opened an account with Superfeedr and hooked up to http://superfeedr.com/dummy.xml . You can send notifications for http://superfeedr.com/dummy.xml when going to Superfeedr's console on the dashboard and hitting the 'click here' button. You can observe notifications and subscription requests by following the debug log (see feeds_dbg() in feeds.module after patching).

Patch applies to HEAD. If you have applied #16, a reinstall is required.

- Fix fallback to $url when self can't be found.

The latest patched version is available on github here: http://github.com/lxbarth/Feeds

Setup:

* using the PubsubHubbub Fetcher instead of the HTTP Fetcher will automatically use pubsubhubbub if available.
* See README.txt on how to set up a designated hub (e. g. Superfeedr) with Feeds.

Outstanding:

* Do not automatically refresh feeds if they are successfully subscribed through PuSH (right now feeds will continue to import feeds at the given setting even if they are successfully subscribed).
* Automatically adjust re-subscription frequency to hub's verification response.

Both will require a significant rework of FeedsScheduler class that currently does not allow for different refresh frequencies per source.

Latest updated patch:

- Removed resubscription handling: Waiting on #721428: Make scheduler next scheduled time based to build this properly.
- Factored FeedsPubsubFetcher into FeedsHTTPFetcher
- More clean ups.
- Made sure all tests pass.

[Edit, hit save too fast:]

Removing RSSCloud from title as this patch won't implement RSSCloud support.

http://github.com/lxbarth/feeds is up to date

- Renamed fetcher menu callbacks from feeds/fetcher/[importer_id] to feeds/importer/[importer_id] - more generic
- Cleaned up PuSHSubscriber.inc for release

Clean up description on designated hub field.

Reroll after http://github.com/lxbarth/PuSHSubscriber was released.

Committed.

I will do a blog post on PuSH support in Feeds tomorrow. Will post a quick notification here when it's out.

Fyi, a little while ago I posted this summary of PuSH subscriber support on our blog: http://developmentseed.org/blog/2010/feb/23/pubsubhubbub-support-drupal