plugin.php

<?php
/**
 * Plugin Name: No-Admin-Ajax
 * Plugin URI: https://github.com/devgeniem/wp-no-admin-ajax
 * Description: A plugin that lightens the WP AJAX routine and directs the requests to front-end rather than admin back-end.
 * Author: Miika Arponen / Geniem Oy
 * Author URI: http://www.geniem.com
 * License: MIT
 * License URI: https://github.com/devgeniem/wp-no-admin-ajax/blob/master/LICENSE
 * Version: 1.0.2
 */
namespace Geniem\Helper;

class No_Admin_Ajax {
  public $keyword;

  protected static $already_run = false;

  public function __construct() {
    // This class should be run only once
    if ( self::$already_run === true ) {
      return false;
    }
    else {
      self::$already_run = true;
    }

    add_action( "after_setup_theme", array( $this, "init" ) );
  }

  public function init() {
    // Rewrite only public side admin urls
    if ( ! is_admin() ) {
      add_filter( 'admin_url', array( $this, 'redirect_ajax_url' ), 11, 3 );

      add_action( "template_redirect", array( $this, "run_ajax" ) );
    }

    // Register activation hook to flush the rewrites
    register_activation_hook( __FILE__, array( $this, "activate" ) );
    add_action( "init", array( $this, "rewrite" ) );

    // Url keyword to use for the ajax calls. Is modifiable with filter "no-admin-ajax/keyword"
    if ( defined('WP_NO_ADMIN_AJAX_URL') ) {
        // keyword doesn't need to contain slashes because they are set in redirect_ajax_url()
        // trim slashes to avoid confusion
        $default_keyword = trim(WP_NO_ADMIN_AJAX_URL,'/');
    } else {
        $default_keyword = "no-admin-ajax";
    }

    $this->keyword = apply_filters( "no-admin-ajax/keyword", $default_keyword );
  }

  // Function that handles rewriting the admin-ajax url to the one we want
  public function redirect_ajax_url( $url, $path, $blog_id ) {
    if( strpos( $url, 'admin-ajax' ) ) {
      return home_url( "/". $this->keyword ."/" );
    }
    else {
      return $url;
    }
  }

  // Creates the rewrite
  public function rewrite() {
    global $wp_rewrite;

    add_rewrite_tag( "%no-admin-ajax%", "([0-9]+)" );

    // The whole ajax url matching pattern can be altered with filter "no-admin-ajax/rule"
    $default_rule = "^". $this->keyword ."/?$";

    $rule = apply_filters( "no-admin-ajax/rule", $default_rule );

    add_rewrite_rule(
      $rule,
      "index.php?no-admin-ajax=true",
      "top"
    );
  }

  // Runs the ajax calls. Equivalent to the real admin-ajax.php
  public function run_ajax() {
    global $wp_query;

    if ( $wp_query->get("no-admin-ajax") ) {
      // Constant for plugins to know that we are on an AJAX request
      define("DOING_AJAX", true);

      // If we don't have an action, do nothing
      if ( ! isset( $_REQUEST["action"] ) ) {
          die(0);
      }

      // Escape the parameter to prevent disastrous things
      $action = esc_attr( $_REQUEST["action"] );

      // Run customized no-admin-ajax methods with action "no-admin-ajax/before"
      do_action( "no-admin-ajax/before" );

      // Run customized no-admin-ajax methods for specific ajax actions with "no-admin-ajax/before/{action}"
      do_action( "no-admin-ajax/before/". $action );

      // Same headers as WordPress normal AJAX routine sends
      $default_headers = array(
        "Content-Type: text/html; charset=" . get_option( "blog_charset" ),
        "X-Robots-Tag: noindex"
      );

      // Filter to customize the headers sent by ajax calls
      $headers = apply_filters( "no-admin-ajax/headers", $default_headers );

      // Send the headers to the user
      if ( is_array( $headers ) && count( $headers ) > 0 ) {
        foreach ( $headers as $header ) {
          @header( $header );
        }
      }

      send_nosniff_header();
      nocache_headers();

      // Run the actions
      if(is_user_logged_in()) {
          do_action( "wp_ajax_" . $action );
      }
      else {
          do_action( "wp_ajax_nopriv_" . $action );
      }

      die(0);
    }
  }

  // Run activate during plugin activation
  public function activate() {
    global $wp_rewrite;
    $this->rewrite();
    $wp_rewrite->flush_rules();
  }
}

new No_Admin_Ajax();