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In Pubsubhubbub, the Publisher is the party who publishes a live feed and frequently updates it with new content. This may be a blog, an aggregator, or even a web service with a public feed based API. In order for these updates to be pushed to Subscribers, the Publisher must notify all of its supported Hubs that an update has occured using a simple HTTP POST request containing the URI or the updated Topic (i.e the updated RSS or Atom feed). The Hub will confirm receipt of the notification, fetch the updated feed, and forward any updates to any Subscribers who have subscribed to that Hub for updates from the relevant feed.

By design, this means the Publisher has very little to do except send these Hub pings whenever its feeds change. As a result, the Publisher implementation is extremely simple to use and requires very little work to setup and use when feeds are updated.

Zend_Feed_Pubsubhubbub_Publisher implements a full Pubsubhubbub Publisher. Its setup for use is also simple, requiring mainly that it is configured with the URI endpoint for all Hubs to be notified of updates, and the URIs of all Topics to be included in the notifications.

The following example shows a Publisher notifying a collection of Hubs about updates to a pair of local RSS and Atom feeds. The class retains a collection of errors which include the Hub URLs, so the notification can be re-attempted later and/or logged if any notifications happen to fail. Each resulting error array also includes a "response" key containing the related HTTP response object. In the event of any errors, it is strongly recommended to attempt the operation for failed Hub Endpoints at least once more at a future time. This may require the use of either a scheduled task for this purpose or a job queue though such extra steps are optional.

= new Zend_Feed_Pubsubhubbub_Publisher;

if (!
$publisher->isSuccess()) {
// check for errors
$errors     $publisher->getErrors();
$failedHubs = array()
    foreach (
$errors as $error) {
$failedHubs[] = $error['hubUrl'];

// reschedule notifications for the failed Hubs in $failedHubs

If you prefer having more concrete control over the Publisher, the methods addHubUrls() and addUpdatedTopicUrls() pass each array value to the singular addHubUrl() and addUpdatedTopicUrl() public methods. There are also matching removeUpdatedTopicUrl() and removeHubUrl() methods.

You can also skip setting Hub URIs, and notify each in turn using the notifyHub() method which accepts the URI of a Hub endpoint as its only argument.

There are no other tasks to cover. The Publisher implementation is very simple since most of the feed processing and distribution is handled by the selected Hubs. It is however important to detect errors and reschedule notifications as soon as possible (with a reasonable maximum number of retries) to ensure notifications reach all Subscribers. In many cases as a final alternative, Hubs may frequently poll your feeds to offer some additional tolerance for failures both in terms of their own temporary downtime or Publisher errors or downtime.

Zend Framework