If you use JPSpan to augment a normal website you may have noticed that your page loads now take quite a bit longer. The reason for this is loading the JPSpan client javascript code, its generated on each load and so it can’t be cached on the client. This file can become huge if you register lots of classes with lots of methods to create stubs for.
So the solution is to allow this page to be cached, to allow for that, im using HTTP_Cache, i’ll also be caching the output generated by PHP since the client files shouldn’t change often.
When you start caching the most important question to answer is, “How do I know when I need to regenerate my cache”. In the JPSpan case two things can cause a cache regen, the server url changing (the url of the JPSpan server is embedded in the file) or the api your exporting changing. The server url changing might not ever happen for some people, but in my usage the ip is different depending on if your using the VPN or the public url so this needs to be taken into account. Its also good to take into account so that a stale cache file from development doesn’t ruin things.
Now the api is a little harder, but since JPSpan has to know what to export, its something that must be available.
In fact its in the descriptions array on the JPSpan_Server_PostOffice Object. So to know if its change you just make a hash of it, and check for a change in that. Code to make our API hash is shown below.
<?php
// create a hash from the api of the handlers
// turn the descriptions into a string
$api = “”;
foreach($S->descriptions as $key => $val)
$api .= $key;
foreach($val->methods as $method) {
$api .= $method;
}
}
$apihash = md5($api);
?>
Now that we have the information we need on when to regenerate our cache its just a matter of implementing it. First will implement the client side cache, to do this we Use HTTP_Cache to send 304 codes when nothing is changed. The code to do this is shown below, notice that were not compressing the generated JavaScript yet (strip whitespace comments) since its a really expensive operation, that will have to wait until we cache that part too. Also take not that were not calling displayClient anymore, its echo’s it output and then calls exit, so that makes its pretty useless for caching.
<?php
// setup HTTP_Cache give it our custom etag and see if we need to generate the client
require_once ‘HTTP/Cache.php’;
$cache = &new HTTP_Cache();
$cache->setEtag($etag);
if (!$cache->isValid()) {
// Compress the output Javascript (e.g. strip whitespace)
//define(’JPSPAN_INCLUDE_COMPRESS’,TRUE);
// Display the Javascript client
$G = & $S->getGenerator();
require_once JPSPAN . ‘Include.php’;
$I = & JPSpan_Include::instance();
// HACK - this needs to change
$I->loadString(__FILE__,$G->getClient());
$client = $I->getCode();
header(‘Content-Type: application/x-javascript’);
$cache->setBody($client);
}
else {
// something is setting Cache-Control
header(‘Cache-Control: must-revalidate’);
}
$cache->send();
?>
Now if things are working correctly the web browser shouldn’t be fetching the entire page after the first time, it should just be getting a 304 header as the result. There are a couple ways to test that this is working, the easiest it too just view the client page, get the page info in firefox and see if its in your browsers cache, if not then something is broken. In debugging these types of problems i’ve found the LiveHTTPHeaders firefox extension to be useful. What your looking for is the server to send the ETag and then the client to respond with it on the next reload. The server should then respond with a 304 instead of a 200.
Now the next step in the process is to add a file cache in php for the generated client stubs so that we can turn on whitespace stripping and make the first download faster. Thats pretty simple stuff, just make your filename, check if the file exists, if so use it, otherwise generate the client as write it out to file for latter use. I’m using file_put_contents to write to the file so if your on php4 you’ll want to replace that code or check out PHP_Compat. Complete code showing both client side caching using HTTP_Cache and 304, and server side caching is shown below.
<?php
// Include JPSpan and setup your server here
// now our new updated client serving code with lots o caching
if (isset($_SERVER['QUERY_STRING']) && strcasecmp($_SERVER['QUERY_STRING'], ‘client’)==0) {
// cache dir
$cacheDir = APP_ROOT.“/tmp/”;
// create a hash from the api of the handlers
// turn the descriptions into a string
$api = “”;
foreach($S->descriptions as $key => $val) {
$api .= $key;
foreach($val->methods as $method) {
$api .= $method;
}
}
$apihash = md5($api);
// get the host the request is being made with since it gets embedded in the client file
$server = preg_replace(‘/[^a-zA-Z0-9._]/’,”,$_SERVER['HTTP_HOST']);
// create the filename
$cacheFile = “client-$apihash-$server.js”;
// create the etag
$etag = md5($cacheFile);
// setup HTTP_Cache give it our custom etag and see if we need to generate the client
require_once ‘HTTP/Cache.php’;
$cache = &new HTTP_Cache();
$cache->setEtag($etag);
if (!$cache->isValid()) {
if (!file_exists($cacheDir.$cacheFile)) {
// Compress the output Javascript (e.g. strip whitespace)
define(‘JPSPAN_INCLUDE_COMPRESS’,TRUE);
// Display the Javascript client
$G = & $S->getGenerator();
require_once JPSPAN . ‘Include.php’;
$I = & JPSpan_Include::instance();
// HACK - this needs to change
$I->loadString(__FILE__,$G->getClient());
$client = $I->getCode();
file_put_contents($cacheDir.$cacheFile,$client);
}
else {
$client = file_get_contents($cacheDir.$cacheFile);
}
header(‘Content-Type: application/x-javascript’);
$cache->setBody($client);
}
else {
// something is setting Cache-Control
header(‘Cache-Control: must-revalidate’);
}
$cache->send();
} else {
// This is where the real serving happens…
// Include error handler
// PHP errors, warnings and notices serialized to JS
require_once JPSPAN . ‘ErrorHandler.php’;
// Start serving requests…
$S->serve();
}
?>
Update: added data cleaning around HTTP_HOST since I use that in a file name
