silverstripe-versionfeed/docs/en/developer.md

Version Feed

Development

Feed actions

Creating functions called changes or allchanges on any of your page types or controllers will cause confusion with the extensions defined on the extension.

Enabling / Disabling

The allchanges feed can be disabled by setting the VersionFeed.allchanges_enabled config to false.

Likewise, the changes feed for each page can be globally disabled by setting the VersionFeed.changes_enabled config to false. If this left true, then each page can still be individually disabled by unchecking the 'Make History Public' checkbox in the CMS under page settings. See user documentation on enabling / disabling.

Default RSS action

Templates can offer a "Subscribe" link with a link to the most relevant RSS feed. This will default to the changes feed for the current page. You can override this behaviour by defining the getDefaultRSSLink function in your page type and returning the URL of your desired RSS feed:

:::php
class MyPage extends Page {
	function getDefaultRSSLink() {
		return $this->Link('myrssfeed');
	}
}

This can be used in templates as $DefaultRSSLink.

Rate limiting and caching

By default all content is filtered based on the rules specified in versionfeed/_config/versionfeed.yml. Two filters are applied on top of one another:

• CachedContentFilter provides caching of versions based on an identifier built up of the record ID and the most recently saved version number. There is no configuration required for this class.
• RateLimitFilter provides rate limiting to ensure that requests to uncached data does not overload the server. This filter will only be applied if the CachedContentFilter does not have any cached record for a request.

Either one of these can be replaced, added to, or removed, by adjusting the VersionFeed_Controller.dependencies config to point to a replacement (or no) filter.

For smaller servers where it's reasonable to apply a strict approach to rate limiting the default settings should be sufficient. The RateLimitFilter.lock_bypage config defaults to false, meaning that a single limit will be applied to all URLs. If set to true, then each URL will have its own rate limit, and on smaller servers with lots of concurrent requests this can still overwhelm capacity. This will also leave smaller servers vulnerable to DDoS attacks which target many URLs simultaneously. This config will have no effect on the allchanges method.

RateLimitFilter.lock_byuserip can be set to true in order to prevent requests from different users interfering with one another. However, this can provide an ineffective safeguard against malicious DDoS attacks which use multiple IP addresses.

Another important variable is the RateLimitFilter.lock_timeout config, which is set to 5 seconds by default. This should be increased on sites which may be slow to generate page versions, whether due to lower server capacity or volume of content (number of page versions). Requests to this page after the timeout will not trigger any rate limit safeguard, so you should be sure that this is set to an appropriate level.

You can set the ContentFilter.cache_lifetime config in order to control the maximum age of the cache. This is an integer value in seconds, and defaults to 300 (five minutes). Set it to 0 or null to make this cache unlimited.