ManaPHP\Http\Response::send PHP Method

    public function send()
    {
        if ($this->_sent === true) {
            throw new ResponseException('Response was already sent');
        }
        if ($this->_file) {
            if (!$this->filesystem->fileExists($this->_file)) {
                throw new ResponseException('Sent file is not exists: `:file`', ['file' => $this->_file]);
            }
            $this->setHeader('Content-Length', $this->filesystem->fileSize($this->_file));
        }
        if (!headers_sent()) {
            $this->sendHeaders();
        }
        if ($this->_content !== null) {
            echo $this->_content;
        } else {
            if ($this->_file) {
                readfile($this->alias->resolve($this->_file));
            }
        }
        $this->_sent = true;
        return $this;
    }