回答

<?php
$server = new Swoole\Server("0.0.0.0", 9503);

$server->on('connect', function ($server, $fd) {
    echo "connection open: {$fd}\n";
});

$server->on('receive', function ($server, $fd, $reactor_id, $data) {

    $response = new Response();

    $_htmlstr = "hello world 你好 朋友";

    $response->withHeader('Content-Type', 'text/html;charset=utf-8')
    ->withHeader('Content-Length', strlen($_htmlstr))
    ->withBody($_htmlstr);

    $server->send($fd, $response->getPackage());


    $server->close($fd);
});

$server->on('close', function ($server, $fd) {
    echo "connection close: {$fd}\n";
});

$server->start();



/**
* 用来简单组装 header 和 body
* Class Response
*/
class Response {

    private $header = "HTTP/1.1 200 OK\r\n";
    private $body = '';

    public function withHeader($name, $value) {
        $name = strtolower($name);
        if ($name == 'content-type') {
            $this->header .= "Content-Type: {$value}\r\n";
        } elseif ($name == 'content-length') {
            $this->header .= "Content-Length: " . $value . "\r\n";
        }
        return $this;
    }

    public function withBody($body) {
        $this->body .= $body;
        return $this;
    }

    /**
    * 获取组装好的 http 报文
    * @return string
    */
    public function getPackage() {
        return $this->header ."\r\n" . $this->body;
    }

}