How to handle user input of invalid UTF-8 characters?

Question

I\'m looking for general a strategy/advice on how to handle invalid UTF-8 input from users.

Even though my webapp uses UTF-8, somehow some users enter invalid chara

Answer 1

I put together a fairly simple class to check if input is in UTF-8 and to run through utf8_encode() as needs be:

class utf8
{

    /**
     * @param array $data
     * @param int $options
     * @return array
     */
    public static function encode(array $data)
    {
        foreach ($data as $key=>$val) {
            if (is_array($val)) {
                $data[$key] = self::encode($val, $options);
            } else {
                if (false === self::check($val)) {
                    $data[$key] = utf8_encode($val);
                }
            }
        }

        return $data;
    }

    /**
     * Regular expression to test a string is UTF8 encoded
     * 
     * RFC3629
     * 
     * @param string $string The string to be tested
     * @return bool
     * 
     * @link http://www.w3.org/International/questions/qa-forms-utf-8.en.php
     */
    public static function check($string)
    {
        return preg_match('%^(?:
            [\x09\x0A\x0D\x20-\x7E]              # ASCII
            | [\xC2-\xDF][\x80-\xBF]             # non-overlong 2-byte
            |  \xE0[\xA0-\xBF][\x80-\xBF]        # excluding overlongs
            | [\xE1-\xEC\xEE\xEF][\x80-\xBF]{2}  # straight 3-byte
            |  \xED[\x80-\x9F][\x80-\xBF]        # excluding surrogates
            |  \xF0[\x90-\xBF][\x80-\xBF]{2}     # planes 1-3
            | [\xF1-\xF3][\x80-\xBF]{3}          # planes 4-15
            |  \xF4[\x80-\x8F][\x80-\xBF]{2}     # plane 16
            )*$%xs',
            $string);
    }
}

// For example
$data = utf8::encode($_POST);