3-4 秒后收到服务器发送的事件

Question

虽然从 this page, I got confused about the timing of events. Basically, the example shown 读取有关服务器发送的事件有一个 PHP 脚本将系统时间发送到网页：

<?php
    header('Content-Type: text/event-stream');
    header('Cache-Control: no-cache');

    $time = date('r');
    echo "data: The server time is: {$time}\n\n";
    flush();
?>

当页面接收并呈现它时：

if(typeof(EventSource) !== "undefined") {
    var source = new EventSource("demo_sse.php");
    source.onmessage = function(event) {
        document.getElementById("result").innerHTML += event.data + "<br>";
    };
} else {
    document.getElementById("result").innerHTML = "Sorry, your browser does not support server-sent events...";
}

我的困惑是服务器似乎每 3-4 秒发送一次消息：

The server time is: Tue, 20 Sep 2016 11:55:12 -0400
The server time is: Tue, 20 Sep 2016 11:55:16 -0400
The server time is: Tue, 20 Sep 2016 11:55:20 -0400
The server time is: Tue, 20 Sep 2016 11:55:23 -0400
The server time is: Tue, 20 Sep 2016 11:55:28 -0400
The server time is: Tue, 20 Sep 2016 11:55:32 -0400
The server time is: Tue, 20 Sep 2016 11:55:35 -0400
The server time is: Tue, 20 Sep 2016 11:55:39 -0400
The server time is: Tue, 20 Sep 2016 11:55:43 -0400
The server time is: Tue, 20 Sep 2016 11:55:46 -0400
The server time is: Tue, 20 Sep 2016 11:55:50 -0400
The server time is: Tue, 20 Sep 2016 11:55:53 -0400
The server time is: Tue, 20 Sep 2016 11:55:57 -0400
The server time is: Tue, 20 Sep 2016 11:56:01 -0400
The server time is: Tue, 20 Sep 2016 11:56:04 -0400
The server time is: Tue, 20 Sep 2016 11:56:08 -0400
The server time is: Tue, 20 Sep 2016 11:56:12 -0400
The server time is: Tue, 20 Sep 2016 11:56:15 -0400

但是，我在服务器端或客户端都没有看到这种延迟。是网站服务器和我的浏览器之间的网络延迟吗？还是其他原因？

Answer 1

默认重试时间为 3 秒，如 http://www.html5rocks.com/en/tutorials/eventsource/basics/ 所示查看 link 上的 "Controlling the Reconnection-timeout section"。您可以通过发送一行 retry:100 来自定义它强制执行仅 100 毫秒的重试时间间隔。

3-4 秒后收到服务器发送的事件

Server-sent event received after 3-4 seconds

html

server-sent-events