private function getBody()
    {
        if ($this->body) {
            return $this->body;
        } elseif ($this->files || $this->forceMultipart) {
            return $this->body = $this->createMultipart();
        } elseif ($this->fields) {
            return $this->body = $this->createUrlEncoded();
        } else {
            return $this->body = Stream::factory();
        }
    }