How to keep users unique id stored in session in addition to IP in Wordpress plugin?

Question

I want to get likes from two computers with the same IP in the post like plugin I developed for wordpress. Currently my plugin is working but when I like a post from a device with the same IP, the dislike button appears in the other device. How can i prevent this ?

Here is my main plugin file (.php):

<?php
/**
Plugin Name: LikeMyPost
Plugin URI:  https://github.com/basarballioz/Like-My-Post-WPPlugin
Description: It allows users to create a button that will make them like the posts, and monitor which tags are mostly liked.
Version:     1.0
Author:      Başar Ballıöz
Author URI:  https://github.com/basarballioz
License:     GPLv3
License URI: https://www.gnu.org/licenses/gpl-3.0.tr.html
 **/


//This will prevent public user to access your hidden files directly by using URL.
if (!defined('ABSPATH') ) {
    exit;
}

// Load plugin files
require_once plugin_dir_path(__FILE__) . 'likemypost-widget.php';           // plugin widget
require_once plugin_dir_path( __FILE__ ) . 'likemypost-admin.php';          // admin menu entry and page content

class likeMyPost {
    
    //REGISTER STYLE AND JQUERY
    public function register_script() {
        //($handle, $src, $deps, $ver, $media) 
        wp_register_script('lmpScript', plugins_url('js/lmpscript.js', __FILE__), array('jquery'), '3.5.1' );       
        wp_localize_script('lmpScript', 'LMPajax',
        array('ajax_url' => admin_url('admin-ajax.php'), 'nonce' => wp_create_nonce('worldsBestPluginEver'))); //SAFETY
    }

    public function loadScripts(){
        wp_enqueue_script('lmpScript');
    }

    //ADD A LIKE BUTTON TO BOTTOM OF THE POSTS
    public function addLikeButton($content) {
        if (get_post_type() == is_singular()) {
            $getPost = '<p class="getPostLiked" style="font-size: 1.1em; border-style: solid; border-width: thin; width: 200px"> You can, ';
        if ($this->alreadyLiked(get_the_ID())) {
            $getPost .= '<br> <a style="color: pink;" data-event="dislike" data-post_id="'.get_the_ID().'" href="#/"> Dislike this post ';
        } else {
            $getPost .= '<br> <a style="color: pink;" data-event="like" data-post_id="'.get_the_ID().'" href="#/"> Like this post! ';
        }
            $getPost .= '</a><span class="count">'.$this->likeCounter(get_the_ID());
            $getPost .= ' Likes <p></p></span></p>';
            $content .= $getPost;
        }
        return $content;
    }

    //AJAX RESPONSE
    public function like() {
        //SAFETY
        check_ajax_referer('worldsBestPluginEver', 'nonce');
        
        $post_id = $_POST['post_id'];
        $event = $_POST['event'];
        if ($event == "like") {
            $this->likePost($post_id);
        } else {
            $this->dislikePost($post_id);
        }
        die();
    }

    //IP CONTROL FOR ALREADY LIKED
    public function alreadyLiked($post_id) {
        $user_IP = $_SERVER['REMOTE_ADDR'];
        $meta_IP = get_post_meta($post_id, '_likers_IP');
        $likers_IP = $meta_IP[0];
        
        //SAFE ARRAYS (allows us to display the counter as zero when creating a new post - in order to prevent errors)
        if (!is_array($likers_IP)) {
            $likers_IP = array();
        }
        if (in_array($user_IP, $likers_IP)) {
            return true;                        //ALREADY LIKED (SHOW "like") button
        } else {
            return false;                       //SHOW "dislike" button
        }
    }

    //LIKING POSTS BY USING $POSTID
    public function likePost($post_id) {
        $likes_count = $this->likeCounter($post_id);
        $user_IP = $_SERVER['REMOTE_ADDR'];
        $meta_IP = get_post_meta($post_id,'_likers_IP');
        $likers_IP = $meta_IP[0];

        //SAFE ARRAYS
        if (!is_array($likers_IP)) {
            $likers_IP = array();
        }
        $likers_IP[] = $user_IP;
        
        if (update_post_meta($post_id, '_likes_count', ++$likes_count)) {
            update_post_meta($post_id, '_likers_IP', $likers_IP);
            echo " ";
            echo "$likes_count Likes";
        } else {
            echo "Try again please...";
        }
    }

    //DISLIKING POSTS BY USING $POSTID
    public function dislikePost($post_id) {
        
        $likes_count = $this->likeCounter($post_id);
        $user_IP = $_SERVER['REMOTE_ADDR'];
        $meta_IP = get_post_meta($post_id,'_likers_IP');
        $likers_IP = $meta_IP[0];

        //SAFE ARRAYS
        if (!is_array($likers_IP)) {
            $likers_IP = array();
        }
        if ($this->alreadyLiked($post_id)) {
            $key = array_search($user_IP,$likers_IP);
            unset($likers_IP[$key]);
        }
        if (update_post_meta($post_id, '_likes_count', --$likes_count)) {
            update_post_meta($post_id, '_likers_IP', $likers_IP);
            echo " ";
            echo "$likes_count Likes";
        } else {
            echo "Try again please...";
        }
    }

    public function likeCounter($post_id) {
        return get_post_meta($post_id, '_likes_count', true);
    }

    //HOOKS
    public function run() {      
        add_action('init', array($this,'register_script'));
        add_action('wp_enqueue_scripts', array($this,'loadScripts'));

        add_filter('the_content', array($this, 'addLikeButton' ));

        add_action('wp_ajax_nopriv_like', array($this,'like'));
        add_action('wp_ajax_like', array($this,'like'));
    }
}

//LIKE MY POST PLUGIN INITIALIZER
$plugin = new likeMyPost();  //Plugin object
$plugin->run();              //Call run function

And it is my jquery file:

jQuery(document).ready(function () {
   jQuery('.getPostLiked a').click(function () {
       
       let likeButton = jQuery(this);
       let post_id = likeButton.data('post_id');
       let event = likeButton.data('event');
       
       if (event == 'like') {
          likeButton.text('Dislike this post!');
          likeButton.data('event','unlike');
       } else {
          likeButton.text('Like this post!');
          likeButton.data('event','like');
       }
       
       jQuery.ajax({
           type : 'post',
           url : LMPajax.ajax_url,
           data : {
               action : 'like',
               post_id : post_id,
               event : event,
               nonce : LMPajax.nonce
           },
           success : function (response) {   //WHEN ENDS
                        jQuery('.count').text(response);
                     }
        });
    });
});

Answer 1

It depends how you want to uniquely identify users. Some options to uniquely identify people might be the:

• The Wordpress User ID. If people are logged in then using their WP User ID is a good option.
• The Wordpress session ID. This is unique to the session; People will get a new session after some amount of time, and if they change browser or clear their cache, etc.
• The Browser User Agent. This is another option that will change less frequently but still might change, but will solve your problem quickly

Whatever you choose, you can simply change both of these lines in your code to user more specific method. E.g. I would suggest trying IP + User Agent:

$user_IP = $_SERVER['REMOTE_ADDR'] . $_SERVER['HTTP_USER_AGENT'];

This will mean each like is then unique to IP plus browser user agent string, which should solve the problem you stated.