Chapter 16: Asset Management & Caching Strategies

Introduction: Managing Your Application's Assets

In a modern web application, "assets" are more than just CSS, JavaScript and core image files. They also include a critical and often complex category: user-generated content. For sites like ours, this means the images, videos, and documents that users upload to accompany their posts. Managing these assets effectively is crucial for performance, security, and maintainability. This chapter provides a complete guide to our application's asset management strategy, from secure uploading to efficient delivery.

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Case Study: Building a Secure File Uploader

The most complex asset management task in our application is handling user file uploads. This is a multi-stage process that involves a front-end interface built with JavaScript, a secure back-end PHP script to process the files, and a robust database layer to store the metadata.

The Front-End: HTML & JavaScript

The user interface for our file uploader is built from three key HTML components: the main <form>, a <template> for displaying existing files, and a <template> for previewing new files. Using the <template> tag is a modern approach that allows our JavaScript to efficiently clone these structures as needed. All client-side interactivity is handled by a single block of vanilla JavaScript, which is responsible for displaying existing files, handling new file selections (including validation), and sending the uploads to the server via an asynchronous AJAX request.

The Back-End: The PHP Upload Handler

The JavaScript sends the files and metadata to a dedicated PHP script that acts as our upload endpoint. This script is responsible for security, validation, and processing.

1. Security: The script first validates the formToken to prevent CSRF attacks( see our chapter on Web Security) and checks user permissions to ensure the logged-in user has the authority to upload files to the specified advert.
2. File Processing: For each valid file, the script generates a unique fileHash (a UUID), creates a dedicated directory, and moves the uploaded file to its permanent location. If the file is an image, it uses the GD library to create several resized, optimised .webp versions.
3. Database Interaction: Once the file is processed, the script calls a stored procedure (files_insertRecord) to save the file's metadata to the database and then calls another procedure to update the JSON array in the main aircraft table.
4. The JSON Response: Finally, the script sends a JSON response back to the browser, which the JavaScript uses to update the UI.

The Secure Gateway (fetchFile.php)

A critical security principle is to never expose your internal file structure to the public. A far more secure approach is to use a PHP "gateway" script to serve files. This script takes a public-facing fileHash as a parameter, uses a stored procedure to look up the file's real location on the server, and then securely outputs the file's contents with the correct HTTP headers. This acts as a secure proxy, completely hiding your server's internal filesystem from the user's browser.

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Caching Strategies

Caching is one of the most effective ways to improve an application's performance. Our architecture uses a multi-layered approach to caching.

1. Application-Level File Caching

For our most frequently viewed pages, fetching the data from the database and generating the HTML using Smarty on every single request is inefficient. We gain a significant performance boost by caching the fully rendered HTML page as a static file. This "Cache-on-Demand" strategy is controlled from the HttpController. Before executing a model, the controller checks if the page is marked as cacheable and if a fresh cache file exists. A "cache hit" serves the static file immediately, providing a massive improvement to the Time To First Byte (TTFB).

2. In-Memory Data Caching with Memcached

Memcached is a high-speed, in-memory key-value store. Its purpose is to cache the results of expensive database queries or calculations before they are rendered into HTML. A classic example is caching the data for a site's main navigation menu, which is the same for all users and rarely changes. By storing this data in Memcached, we avoid hitting the database for it on every single page load.

3. Browser-Level Caching with Apache

The final layer of caching happens in the user's browser. We use Apache's mod_expires module to add an Expires HTTP header to static assets like CSS, JavaScript, and images. This tells the browser how long it should keep a local copy of the file before requesting it again, dramatically reducing HTTP requests for repeat visitors.

<IfModule mod_expires.c>
    ExpiresActive On
    ExpiresByType image/jpeg "access plus 60 days"
    ExpiresByType text/css "access plus 1 day"
</IfModule>
'''
##Conclusion: A Complete Asset Strategy
> A professional application requires a professional strategy for managing its assets. By combining a secure, asynchronous file uploader for user-generated content with a multi-layered caching strategy, we have created a system that is both secure and performant, giving us full control over the entire lifecycle of an asset.