404 handler, default off for now

classes/autoptimizeCache.php

@@ -109,6 +109,16 @@ public function cache( $data, $mime )
         } else {
             // Write code to cache without doing anything else.
             file_put_contents( $this->cachedir . $this->filename, $data );
+
+            // save fallback .js or .css file if filter true (to be false by default) but not if snippet or single.
+            if ( self::do_fallback() && strpos( $this->filename, '_snippet_' ) === false && strpos( $this->filename, '_single_' ) === false ) {
+                $_extension     = pathinfo( $this->filename, PATHINFO_EXTENSION );
+                $_fallback_file = AUTOPTIMIZE_CACHEFILE_PREFIX . 'fallback.' . $_extension;
+                if ( ! file_exists( $this->cachedir . $_extension . '/' . $_fallback_file ) ) {
+                    file_put_contents( $this->cachedir . $_extension . '/' . $_fallback_file, $data );
+                }
+            }
+
             if ( apply_filters( 'autoptimize_filter_cache_create_static_gzip', false ) ) {
                 // Create an additional cached gzip file.
                 file_put_contents( $this->cachedir . $this->filename . '.gz', gzencode( $data, 9, FORCE_GZIP ) );
@@ -571,13 +581,50 @@ public static function cacheavail()
     </Files>
 </IfModule>';
             }
+
+            if ( self::do_fallback() ) {
+                $content .= "\nErrorDocument 404 " . trailingslashit( parse_url( content_url(), PHP_URL_PATH ) ) . 'autoptimize_404_handler.php';
+            }
             @file_put_contents( $htaccess, $content ); // @codingStandardsIgnoreLine
         }
 
+        if ( self::do_fallback() ) {
+            self::check_fallback_php();
+        }
+
         // All OK!
         return true;
     }
 
+    /**
+     * Checks if fallback-php file exists and create it if not.
+     *
+     * Return bool
+     */
+    public static function check_fallback_php() {
+        $_fallback_filename = 'autoptimize_404_handler.php';
+        $_fallback_php      = trailingslashit( WP_CONTENT_DIR ) . $_fallback_filename;
+        $_fallback_status   = true;
+
+        if ( ! file_exists( $_fallback_php ) ) {
+            $_fallback_php_contents = file_get_contents( AUTOPTIMIZE_PLUGIN_DIR . 'config/' . $_fallback_filename );
+            $_fallback_php_contents = str_replace( '<?php exit;', '<?php', $_fallback_php_contents );
+            $_fallback_status       = file_put_contents( $_fallback_php, $_fallback_php_contents );
+        }
+
+        return $_fallback_status;
+    }
+
+    /**
+     * Tells if AO should try to avoid 404's by creating fallback filesize
+     * and create a php 404 handler and tell .htaccess to redirect to said handler.
+     *
+     * Return bool
+     */
+    public static function do_fallback() {
+        return apply_filters( 'autoptimize_filter_cache_do_fallback', false );
+    }
+
     /**
      * Checks if cache dirs exist and create if not.
      * Returns false if not succesful.

config/autoptimize_404_handler.php

@@ -0,0 +1,31 @@
+<?php exit;
+/*
+ * Autoptimize's magic 404 handler.
+ * 
+ * Configure your webserver to have requests for files that are no longer in 
+ * /wp-content/cache/autoptimize/ to redirect to this file. AO's .htaccess file
+ * will have a "Errordocument:" directive to automatically do this.
+ * 
+ * This file has simple logic to redirect to the "fallback" files that are 
+ * created automatically by AO to avoid visitors seeing broken pages or 
+ * Googlebot getting utterly confused.
+ * 
+ * Warning: the fallback files might not apply to all pages, so this is a just
+ * a temporary solution, you really should clear any page cache to avoid requests
+ * to files that don't exist in AO's cache.
+ * 
+ */
+
+$original_request = $_SERVER[REQUEST_URI];
+$fallback_target  = preg_replace( '/(.*)_(?:[a-z0-9]{32})\.(js|css)$/', '${1}_fallback.${2}', $original_request );
+
+if ( $original_request !== $fallback_target ) {
+    error_log( 'Autoptimize file ' . $original_request . ' not found, using fallback instead.' );
+    header( 'HTTP/1.1 301 Moved Permanently' ); 
+    header( 'Location: ' . $fallback_target ); 
+} else {
+    error_log( 'Autoptimize file ' . $original_request . ' not found, sending 410 gone response.' );
+    header( 'HTTP/1.1 410 Gone' );
+}
+
+exit();