Server-sent event received after 3-4 seconds - html

Question

While reading about Server-Sent Events from this page, I got confused about the timing of events. Basically, the example shown has a PHP script sending the system time to the web page:
<?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();
?>
While the page receives and renders it:
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...";
}
My confusion is that the server seems to be sending messages every 3-4 seconds:
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
However, I don't see this delay either at the server end or at the client end. Is it the network lag between the website's server and my browser? Or is it something else?

Answer 1

Default retry is 3 seconds as shown on http://www.html5rocks.com/en/tutorials/eventsource/basics/
Check out the "Controlling the Reconnection-timeout section" on that link.
You may customize it by sending a line retry:100
to enforce just 100ms retry time interval.