GuzzleHttp\Psr7\MultipartStream::getHeader PHP Метод

    private function getHeader(array $headers, $key)
    {
        $lowercaseHeader = strtolower($key);
        foreach ($headers as $k => $v) {
            if (strtolower($k) === $lowercaseHeader) {
                return $v;
            }
        }
        return null;
    }