How can I verify a Googlebot

Question

I'm going to block all bots except the big search engines. One of my blocking methods will be to check for "language": Accept-Language: If it has no Accept-Language the bot's IP address will be blocked until 2037. Googlebot does not have Accept-Language, I want to verify it with DNS lookup

<?php
gethostbyaddr($_SERVER['REMOTE_ADDR']);
?>

Is it ok to use gethostbyaddr, can someone pass my "gethostbyaddr protection"?

Answer 1

//The function
function is_google() {
    return strpos($_SERVER['HTTP_USER_AGENT'],"Googlebot");
}

Answer 2

How to verify Googlebot.