File System Caching in Slim Framework 3

In the past month, I've been learning Slim 3 PHP framework through a website as a real experiment of how powerful Slim Framework is. In this post, I'm sharing a code snippet of how I implemented the Filesystem caching.

The summary is:
- Add a middleware for caching successful responses (200 OK) by saving the response in a file. To avoid long file names or deep paths, I hash the response URL.
- When receiving a request, check its hashed path in the cached files. If found, return the content. Else, continue with initializing the app, routes, and everything else. This way, there is no initialization overhead for cached requests.

Here is the beginning of my index.php:

require './lib/initializer.php';

function getCachePath($uri) {
    $webpage_handle = md5($uri);
    return ROOT."/public/cache/".$webpage_handle;
}

/* Check for cached file here before loading anything or opening DB */
if(CACHING_ENABLED) {
    $requestedURI = "http://$_SERVER[HTTP_HOST]$_SERVER[REQUEST_URI]";
    $cachedFilePath = getCachePath($requestedURI);
    if (file_exists($cachedFilePath) && (filemtime($cachedFilePath) > (time() - CACHE_SECONDS ))) {
        $cacheFile = file_get_contents($cachedFilePath);
        die($cacheFile);
    }
}

$cacheMiddleware = function ($request, $response, $next) {
    /* process the request */
    $response = $next($request, $response);

    /* cache response */
    if(CACHING_ENABLED && ($response->getStatusCode()==200) && ($request->getMethod() == 'GET')) {
        $cachedFilePath = getCachePath($request->getUri());
        $file = fopen($cachedFilePath,"w");
        fwrite($file, $response->getBody());
        fclose($file);
    }

    return $response;
};

First, I require a file where I initialize some configs and constants, like CACHE_SECONDS.

Then, I create a function for deciding the cache path for requests. To use it in both reads and writes.

Then, -if caching is enabled- I check for the existence of the requested file and the creation date. This way I override the file if it was older. (*check the end of the post for another better way for expiry)

Next, you can see the caching middleware I use with some routes I wish to cache. Here is an example:

$app->get('/', function ($request, $response, $args) {
    // some app-related code
})->setName('home')->add($cacheMiddleware);

And that's it. The file system is now implemented with minimal code. Of course there are many changes and upgrades depending on your case.

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Notes:
*Better than just checking for file creation date (and leaving the files to increase), you can remove the date-check part and add a cron job for removing files older than a specific duration. Here is how my cron job script looks like:

CACHE_DIR=$1;
cd $CACHE_DIR && find * -type f -cmin +5 -exec rm {} \;

It takes the path to clean in the cron job command. And removes any file older than 5 minutes.

The cron job looks like:

*/5 * * * * bash ~/path/to/cache/expiry/script.sh ~/path/to/cache/folder/