HTTP Cache

Overview

A Skinny application provides built-in support for HTTP caching with its etag(), lastModified(), and expires() helper methods. It is best to use one of etag() or lastModified() — in conjunction with expires() - per route; never use both etag() and lastModified() together in the same route callback.

The etag() and lastModified() methods should be invoked in a route callback before other code; this allows Skinny to check conditional GET requests before processing the route callback’s remaining code.

Boths etag() and lastModified() instruct the HTTP client to store the resource response in a client-side cache. The expires() method indicates to the HTTP client when the client-side cache should be considered stale.

ETag

A Skinny application provides built-in support for HTTP caching using ETags. An ETag is a unique identifier for a resource URI. When an ETag header is set with the Skinny application’s etag() method, the HTTP client will send an If-None-Match header with each subsequent HTTP request of the same resource URI. If the ETag value for the resource URI matches the If-None-Match HTTP request header, the Skinny application will return a 304 Not Modified HTTP response that will prompt the HTTP client to continue using its cache; this also prevents the Skinny application from serving the entire markup for the resource URI, saving bandwidth and response time.

Setting an ETag with Skinny is very simple. Invoke the Skinny application’s etag() method in your route callback, passing it a unique ID as the first and only argument.

<?php
$app->get('/foo', function () use ($app) {
    $app->etag('unique-id');
    echo "This will be cached after the initial request!";
});

That’s it. Make sure the ETag ID is unique for the given resource. Also make sure the ETag ID changes as your resource changes; otherwise, the HTTP client will continue serving its outdated cache.

Last Modified

A Skinny application provides built-in support for HTTP caching using the resource’s last modified date. When you specify a last modified date, Skinny tells the HTTP client the date and time the current resource was last modified. The HTTP client will then send a If-Modified-Since header with each subsequent HTTP request for the given resource URI. If the last modification date you specify matches the If-Modified-Since HTTP request header, the Skinny application will return a 304 Not Modified HTTP response that will prompt the HTTP client to use its cache; this also prevents the Skinny application from serving the entire markup for the resource URI saving bandwidth and response time.

Setting a last modified date with Skinny is very simple. You only need to invoke the Skinny application’s lastModified() method in your route callback passing in a UNIX timestamp of the last modification date for the given resource. Be sure the lastModified() method’s timestamp updates along with the resource’s last modification date; otherwise, the browser client will continue serving its outdated cache.

<?php
$app->get('/foo', function () use ($app) {
    $app->lastModified(1286139652);
    echo "This will be cached after the initial request!";
});

Expires

Used in conjunction with the Skinny application’s etag() or lastModified() methods, the expires() method sets an Expires header on the HTTP response informing the HTTP client when its client-side cache for the current resource should be considered stale. The HTTP client will continue serving from its client-side cache until the expiration date is reached, at which time the HTTP client will send a conditional GET request to the Skinny application.

The expires() method accepts one argument: an integer UNIX timestamp, or a string to be parsed with strtotime().

<?php
$app->get('/foo', function () use ($app) {
    $app->etag('unique-resource-id');
    $app->expires('+1 week');
    echo "This will be cached client-side for one week";
});