Zend_Feed_Reader supports using an
instance of Zend_Cache to cache feeds (as
XML) to avoid unnecessary network requests. Adding a cache is as
simple here as it is for other Zend Framework components, create
and configure your cache and then tell
Zend_Feed_Reader to use it! The cache key
used is "Zend_Feed_Reader_" followed by the
MD5 hash of the feed's URI.
<?php
$frontendOptions = array(
'lifetime' => 7200,
'automatic_serialization' => true
);
$backendOptions = array('cache_dir' => './tmp/');
$cache = Zend_Cache::factory(
'Core', 'File', $frontendOptions, $backendOptions
);
Zend_Feed_Reader::setCache($cache);
Note
While it's a little off track, you should also consider
adding a cache to
Zend_Loader_PluginLoader which is
used by Zend_Feed_Reader to load
Extensions.
The big question often asked when importing a feed frequently, is
if it has even changed. With a cache enabled, you can add HTTP
Conditional GET support to your arsenal to answer that
question.
Using this method, you can request feeds from URIs and include
their last known ETag and Last-Modified response header values
with the request (using the If-None-Match and If-Modified-Since
headers). If the feed on the server remains unchanged, you
should receive a 304 response which tells
Zend_Feed_Reader to use the cached
version. If a full feed is sent in a response with a status code
of 200, this means the feed has changed and
Zend_Feed_Reader will parse the new
version and save it to the cache. It will also cache the new
ETag and Last-Modified header values for future use.
These "conditional" requests are not guaranteed to be supported
by the server you request a URI of, but can be attempted
regardless. Most common feed sources like blogs should however
have this supported. To enable conditional requests, you will
need to provide a cache to Zend_Feed_Reader.
<?php
$frontendOptions = array(
'lifetime' => 86400,
'automatic_serialization' => true
);
$backendOptions = array('cache_dir' => './tmp/');
$cache = Zend_Cache::factory(
'Core', 'File', $frontendOptions, $backendOptions
);
Zend_Feed_Reader::setCache($cache);
Zend_Feed_Reader::useHttpConditionalGet();
$feed = Zend_Feed_Reader::import('http://www.planet-php.net/rdf/');
In the example above, with HTTP Conditional
GET requests enabled, the response header values for ETag and
Last-Modified will be cached along with the feed. For the next 24hrs (the cache
lifetime), feeds will only be updated on the cache if a non-304 response is received
containing a valid RSS or Atom XML document.
If you intend on managing request headers from outside
Zend_Feed_Reader, you can set the
relevant If-None-Matches and If-Modified-Since request headers
via the URI import method.
<?php
$lastEtagReceived = '5e6cefe7df5a7e95c8b1ba1a2ccaff3d';
$lastModifiedDateReceived = 'Wed, 08 Jul 2009 13:37:22 GMT';
$feed = Zend_Feed_Reader::import(
$uri, $lastEtagReceived, $lastModifiedDateReceived
);