Zend\Diactoros\Uri::filterScheme PHP Метод

    private function filterScheme($scheme)
    {
        $scheme = strtolower($scheme);
        $scheme = preg_replace('#:(//)?$#', '', $scheme);
        if (empty($scheme)) {
            return '';
        }
        if (!array_key_exists($scheme, $this->allowedSchemes)) {
            throw new InvalidArgumentException(sprintf('Unsupported scheme "%s"; must be any empty string or in the set (%s)', $scheme, implode(', ', array_keys($this->allowedSchemes))));
        }
        return $scheme;
    }