stracker-phil · September 30, 2022 08:33 · Sep 20, 2022
diff --git a/asset-cache.php b/asset-cache.php
@@ -0,0 +1,74 @@
+<?php
+/**
+ * Proof of concept for https://github.com/divimode/gdpr-cache-script-styles
+ */
+
+
+/**
+ * Filter all scripts and style URLs.
+ * When an external URL is detected, download the file
+ * and replace it in the page source.
+ */
+add_filter( 'scripts_loader_src', 'maybe_replace_url' );
+add_filter( 'style_loader_src', 'maybe_replace_url' );
+
+/**
+ * Takes any URL as input, and always returns a local
+ * URL.
+ *
+ * If an external URL is provided, the external asset
+ * is downloaded to the uploads-folder and the function
+ * return value is a URL to that local file.
+ */
+function maybe_replace_url( $url ) {
+	if ( is_external_url( $url ) ) {
+		if ( cache_asset( $url ) ) {
+			$url = WP_CONTENT_URL .
+				'/uploads/gdpr-cache/' .
+				md5( $url );
+		}
+	}
+
+	return $url;
+}
+
+/**
+ * Returns true, if the specified URL points to an external asset.
+ */
+function is_external_url( string $url ) : bool {
+	// Relative URLs are always local to the current domain.
+	if ( 0 === strpos( $url, '/' ) ) {
+		return false;
+	}
+
+	// Get protocol-relative
+	$home_url = preg_replace( '/^\w+:/', '', home_url() );
+
+	return false === strpos( $url, $home_url );
+}
+
+/**
+ * Downloads the given URL to the websites uploads-folder.
+ * Returns true on success.
+ */
+function cache_asset( $url ) {
+	$cache_dir  = WP_CONTENT_DIR . '/uploads/gdpr-cache/';
+	$cache_path = $cache_dir . md5( $url );
+
+	$resp = wp_safe_remote_get(
+		$url,
+		[
+			'timeout'  => 300,
+			'stream'   => true,
+			'filename' => $cache_path,
+		]
+	);
+
+	if ( is_wp_error( $resp ) ) {
+		@unlink( $cache_path );
+
+		return false;
+	}
+
+	return true;
+}