code: private function addParsedHeader($line)
      {
          if (strpos($line, ':') === false) {
              $this->responseCode = HttpStatus::parseStatus($line)->getCode();
          } else {
              $line = trim($line);
              list ($headerName, $headerValue) = explode(':', $line, 2);
              $this->headers[$headerName] = trim($headerValue);
          }
      }
docs: Try to parse line as header and add the results to local header list
  
  @param string $line