yii\web\MultipartFormDataParser::parseHeaders PHP Method

    private function parseHeaders($headerContent)
    {
        $headers = [];
        $headerParts = preg_split("/\\R/s", $headerContent, -1, PREG_SPLIT_NO_EMPTY);
        foreach ($headerParts as $headerPart) {
            if (($separatorPos = strpos($headerPart, ':')) === false) {
                continue;
            }
            list($headerName, $headerValue) = explode(':', $headerPart, 2);
            $headerName = strtolower(trim($headerName));
            $headerValue = trim($headerValue);
            if (strpos($headerValue, ';') === false) {
                $headers[$headerName] = $headerValue;
            } else {
                $headers[$headerName] = [];
                foreach (explode(';', $headerValue) as $part) {
                    $part = trim($part);
                    if (strpos($part, '=') === false) {
                        $headers[$headerName][] = $part;
                    } else {
                        list($name, $value) = explode('=', $part, 2);
                        $name = strtolower(trim($name));
                        $value = trim(trim($value), '"');
                        $headers[$headerName][$name] = $value;
                    }
                }
            }
        }
        return $headers;
    }