protected function encodeHeader($header) { return preg_replace_callback('/(?:[^A-Za-z0-9_\\-\\.~!\\$@#?&\'\\(\\)\\[\\]\\*\\+,:;=\\/% ]+|%(?![A-Fa-f0-9]{2}))/', function (array $matches) { return rawurlencode($matches[0]); }, $header); }