How best to cache entire HTML output on the server - php

Question

I have a fairly basic website, written in pure php, no framework was used, running in a basic LAMP environment.
The site dynamically generates markup based on the HTTP User Agent header, and some query string parameters. For example "itemdetail.php" would inspect the querystring param "itemid" and the User Agent header and produce some markup.
I want to cache this markup, so that the next time a device with the same User Agent and itemid in the query string tries to request the page, it simply dumps out whatever markup is in its cache.
I realise I could do this manually in php using memcache, and just write some code at the top of the page to inspect the relevant params, and either try serve from memcached or render the page and store the markup in memcached, but I was thinking it might be possible to avoid the PHP layer altogether, using something like what is described here http://httpd.apache.org/docs/2.2/caching.html
So, my question, which I realise might be vague and this post will get killed is:
What is the recommended caching implementation here? Is it indeed to use memcache at the php level, or are the apache modules sufficient to meet my needs?

Answer 1

Generating different pages depending on User Agents is just bad practice. You shouldn't do that.
If you want to cache entire pages because your website is slow, the problem probably has to be searched in your code.
On-topic: Write a simple function that hashes the uri being served with a small footprint hash function (md5, sha1,...)
e.g.
<?php
$hash = md5('itemdetail.php-'.$itemid);
if ( file_exist('cache/'.$hash.'.html') {
echo file_get_contents('cache/'.$hash.'.html');
die();
}
and then at the end of your script save the result to 'cache/'.$hash.'.html';
You can offcourse use different kind of extension or folder or...
If you want to cache without using PHP, take a look at Varnish. Or the other example posted here.

Answer 2

If you are familiar with OpenCart at all here is something I wrote to do just this. hopefully you will get the idea given the possible unfamiliar
context.
ob_start();
$enableCaching = false; // Boolean flag
$route = !isset($_GET['route']) ? 'home' : str_replace("/",'-',$_GET['route']);
$cacheFile = DIR_CACHE . $route . '.' . md5($_SERVER['QUERY_STRING']) . ".cache.tpl";
if ($enableCaching !== false && in_array($_GET['route'], $cachePages) && file_exists($cacheFile) ||
$enableCaching !== false && file_exists($cacheFile) && !isset($_GET['route'])) {
/**
* This block of code will output the contents of the cache file.
*/
require ($cacheFile);
}
else {
/**
* Cache file doesn't exist, process the request
*/
$response->output();
if($enableCaching !== false && in_array($_GET['route'], $cachePages) ||
$enableCaching !== false && !isset($_GET['route'])){
file_put_contents($cacheFile, str_replace(array("\n","\r","\t"),'', str_replace(" "," ",ob_get_contents())));
}
}
Basically, create a variable generating a unique file name based on the file name and quest string.
Create that file, writing all HTML output to that file.
Then when it comes to processing request you can check if the unique cache file exists and just send that instead of processing the request.

Answer 3

use the memcached library...
you'll have to install it first and then memcached provides and in-memory caching system for php