我正在开发一个插件来替换标题、帖子和评论中一些用户代理的角色，但过滤器不起作用。以下是插件：

<?php
/*
Plugin Name: WP-HalfSpace
Description: نمایش فاصله به‌جای نیم‌فاصله برای گوگل برای خراب‌نشدن نوشته در نتایج جست‌وجوی گوگل
Version: 1.0.0
Author: ahmadalli
Author URI: http://2barnamenevis.com
*/
function HalfSpace_filter($content)
{

    $u_agent = $_SERVER[\'HTTP_USER_AGENT\'];
    echo "hi";
    if(($u_agent=="Mozilla/5.0 (compatible; Googlebot/2.1; +http://www.google.com/bot.html)" )
    || ($u_agent=="Googlebot/2.1 (+http://www.googlebot.com/bot.html)")
    || ($u_agent=="Googlebot/2.1 (+http://www.google.com/bot.html)")
    || ($u_agent=="Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.2; WOW64; Trident/6.0)")
    )
    { 
        echo "aaaaaaaaa";
        $content=str_ireplace("‌‌"," ",$content); //"" is not empty. it\'s a persian character names halfspace.
    }
    return $content;
}

register_activation_hook( __FILE__, \'HalfSpacePlugin_activate\' );

function HalfSpacePlugin_activate()
{
    add_filter(\'the_title\',\'HalfSpace_filter\',1,1);
    add_filter(\'the_content\',\'HalfSpace_filter\',1,1);
    add_filter(\'comment_text\',\'HalfSpace_filter\',1,1);
}



register_deactivation_hook( __FILE__, \'HalfSpacePlugin_deactivate\' );

function HalfSpacePlugin_deactivate()
{
    remove_filter(\'the_title\',\'HalfSpace_filter\');
    remove_filter(\'the_content\',\'HalfSpace_filter\');
    remove_filter(\'comment_text\',\'HalfSpace_filter\');
}
?>

有人能帮我吗？