Wayback Cache

A PHP class for intelligently requesting and cataloging a history of data. Helpful when needing to cache requests from third-party API's and fall back to previous data if a new request is unsuccessful.

<?php require_once('Cache.class.php'); ?>
<?php

    $requestUrl = 'http://ip-api.com/json/wired.com';

    $cacheInstance = new Cache(array(
        'url'    => $requestUrl,
        'key'    => 'ip_lookup',
        'expire' => 'hourly'
    ));

    $ipData = $cacheInstance->get();

    echo $ipData;

?>

See also: http://chrisullyott.com/blog/2014-11-24-wayback-cache/

Initialization

container (string)

Sets the path to the parent cache directory, where this cache instance will be stored. If the path does not exist, it is created. The default is _cache. For websites, it's recommended to use:

$_SERVER['DOCUMENT_ROOT'] . '/_cache'

key (string)

The identifier of this specific cache instance (i.e., instagram_feed or weather_data). This will be used for the name of a subdirectory inside the cache container directory.

url (string)

The API's endpoint from which we will request a response.

expiration (string)

offset (integer)

Pushes back the expiration time by a number of seconds. For example, to make the cache expire at 2:00 am, use nightly and the value of 2 * 60 * 60. The default is 0.

cacheEmpty

Whether to consider an empty response as valid. If true, an empty response is cached and will not be updated until the expiration time. If false, an empty response is not cached and will be requested again on the next run. Default is false.

retry (boolean)

With retry set to TRUE, multiple fetch attempts are made if the data received from $url is either:

1. NULL
2. Equal to the data from the previous history state

If after all attempts either of these are still true, the previous history state is returned.

requestLimit (integer)

Sets the maximum number of requests that can be made with the url in a day. Requests are tallied against the domain of the url to help avoid reaching rate limits. The default is 100 requests.

historyLimit (integer)

Sets the number of history states (cache files) that are saved. Once the cache has stored this many files, the oldest ones will soon be deleted (on the first page load after midnight). Default is 100 history states.

mustMatch (string)

A regular expression pattern which incoming data must match in order for the cache to be updated. Example: /<img/

mustNotMatch (string)

A regular expression pattern which incoming data must not match in order for the cache to be updated. Example: /error/

Methods

get()

Reads the latest data from the cache. If the cache is expired, data is fetched and a new history state is created with the response.

Query strings

?clearCache

The cache is first erased and then set up again with one new history state.