public function stream(string $partialBodyChunk) : \Amp\Promise
{
if ($this->status === 101) {
throw new \DomainException("Cannot stream(); entity body content disallowed for Switching Protocols Response");
}
if (!$this->isStarted) {
$this->handshake();
}
$this->isStarted = true;
return $this->response->stream($partialBodyChunk);
}