PHP: Using special characters in bad word obfuscator

Question

I'm using this bad word detector/obfuscator in php (to be Adsense compliant). It shows the first letter of the bad word, and replaces the remaining letters with this character: ▪

It works fine, except when I'm using words that contain special characters in Spanish, for example: ñ, á, ó, etc.

This is my current code:

<?    
function badwords_full($string, &$bad_references) {
    static $bad_counter;
    static $bad_list;
    static $bad_list_q;
    if(!isset($bad_counter)) {
        $bad_counter = 0;
        $bad_list = badwords_list();
        $bad_list_q = array_map('preg_quote', $bad_list);
    }
    return preg_replace_callback('~('.implode('|', $bad_list_q).')~',
        function($matches) use (&$bad_counter, &$bad_references) {
            $bad_counter++;
            $bad_references[$bad_counter] = $matches[0];
            return substr($matches[0], 0, 1).str_repeat('&squf;', strlen($matches[0]) - 1);
    }, $string);
}

function badwords_list() {
    # spanish
    $es = array(
        "gallina",
        "ñoño"
    );

    # english
    $en = array(
        "chicken",
        "horse"
    );

    # join all languages
    $list = array_merge($es, $en);
    usort($list, function($a,$b) {
        return strlen($b) < strlen($b);
    });
    return $list;
}

$bad = []; //holder for bad words

Test 1:

echo badwords_full('Hello, you are a chicken!', $bad);

Result 1:

Hello, you are a c▪▪▪▪▪▪! (works fine)

Test 2:

echo badwords_full('Hola en español eres un ñoño!', $bad);

Result 2:

Hola en español eres un �▪▪▪▪▪!

Any ideas on how to solve this issue? Thanks!

Answer 1

You are splitting a multibyte character in half. Use mb_substr in place of substr.

return mb_substr($matches[0], 0, 1).str_repeat('▪', strlen($matches[0]) - 1);

https://3v4l.org/AnPJl

You also probably want to use mb_strlen in place of strlen.