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Semi HTTP Cache for Zend Framework 2

Exclamation

This module is still in development phase.

Introduction

What issues it solves?

• Wrong Last-Modified date when your application is running on Apache. This date in taken from index.php modification date which is not accurate and can cause that browser won't cache response.

What benefits it brings?

Enabling browser cache workflow.

• Handling If-Modified-Since which:
  • Reducing bandwidth. If browser has valid cached data then only 304 header is send.
  • Speed up response time, by omitting dispatch event if browser cache is not stale.
• Providing out of the box Cache-Control management.
• Providing more accurate Last-Modified date solution (but not perfect).

Why semi HTTP cache?

Because things like If-Modified-Since are calculated base of Cache-Control: max-age and not base to real modification date of requested entity. The max-age is set explicit per action or global for application. It's big simplification, but as solution out of the box is quite effective. If you looking for something more bespoke I recommend The Symfony framework approach: http://symfony.com/doc/2.0/book/http_cache.html

Simple workflow

1. Browser request resource /data.json. In application max-age is set for this resource for 60 seconds. Application return response with headers:

   • Last-Modified: 2013-04-01 10:00:00 GMT
   • Cache-Control: max-age=60

2. a) Browser try to request resource /data.json after 10 seconds, but it already has cached content so it return data from browser cache. No request is made.

3. b) Sometimes may happen that browser try to request resource /data.json after 10 seconds, and it want to validate if cached resource is stale. So it sends request wth header If-Modified-Since : 2013-04-01 10:00:00 GMT. But application knows that valid lifetime for this resource is 60 seconds so application return response without body but with headers:

   • 304 Not Modified
   • Last-Modified: 2013-04-01 10:00:00 GMT - note that last modified is old one.

4. Browser try to request resource after 70 seconds, but it already has cached content so it sends request with header If-Modified-Since : 2013-04-01 10:00:00 GMT to validate if cached resource is stale. Application knows that browser cache is stage so it's returning respond with headers and with new response body:

   • Last-Modified: 2013-04-01 10:01:10 GMT - note new last modified time.
   • Cache-Control: max-age=60

Installation

1. cd my/project/directory
2. Create a composer.json file with following content:

{
    "require": {
        "widmogrod/zf2-semi-http-cache": "dev-master"
    }
}

3. Run php composer.phar install
4. Open my/project/folder/configs/application.config.php and add 'WidHttpCache' to your 'modules' parameter.

Configuration

By default, HTTP Cache is disabled if you wan to enable it you should copy configuration file:

cp vendor/widmogrod/zf2-semi-http-cache/config/zf2-semi-http-cache.local.php config/autoload/

Or, add following config entry to your local.php configuration file:

<?php
return array(
    'zf2-semi-http-cache' => array(
        'enabled' => true,
        'default' => array(
             'max-age'  => 600,   // 10min in browser
        ),
    ),
);

Todo

1. create simple UML diagram describing workflow
2. example with Varnish cache.

Time saving tips & tricks

Does your application use session?

1. Remember to start session in action like login, do not do it every time.
2. If session is started, headers like Set-Cookie & Cache-Control can be send. To avoid caching headers in Varnish like Set-Cookie best decision will be to set:

session_cache_limiter('no-cache');
session_cache_expire(0);