CI: Mysqli - Broken

Do you try with socket option? Try to config default socket in your system.

e.g: in my localhost, I'm using XAMPP on Mac OS and mysqli defaul socket is: /Applications/XAMPP/xamppfiles/var/mysql/mysql.sock

PHP Code:

$servername = "127.0.0.1";
$username = "username";
$password = "password";
$port = 3306;
$socket = "/Applications/XAMPP/xamppfiles/var/mysql/mysql.sock";
// Create connection
$conn = new mysqli($servername, $username, $password, $port, $socket);
var_dump($conn); 


Note: use 127.0.0.1 instead localhost