How to increase Server-Sent Event's reopen time? - php

Question

I'm working to show notifications from Server-Sent Event. I checked that every time the browser tries to reconnect with the source about 3 seconds after each connection is closed. That event is getting a call too fast, so my server is loaded too.
So how do I change the reopening time to increase? I have to do at least 60 seconds, so tell me how to do it?
I'm trying the following code.
<table class="table" id="notification"></table>
<script type="text/javascript">
var ssevent = null;
if (!!window.EventSource) {
ssevent = new EventSource('ssevent.php');
ssevent.addEventListener('message', function(e){
if(e.data){
json = JSON.parse(e.data);
if(json){
json.forEach(function(v,i){
html = "<tr><td>"+ v.text +"</td><td>"+ v.date +"</td></tr>";
});
$('#notification').append(html);
}
}
}, false);
ssevent.addEventListener('error', function(e) {
if (e.readyState == EventSource.CLOSED){
console.log("Connection was closed.");
}
}, false);
} else {
console.log('Server-Sent Events not support in your browser');
}
</script>
The file of event stream is as follow.
header('Content-Type: text/event-stream');
header('Cache-Control: no-cache');
include_once "config.php";
$time = isset($_SESSION['last_event_time']) ? $_SESSION['last_event_time'] : time();
$result = $db->quesry("SELECT * FROM event_noti WHERE event_time < {$time} ")->rows;
$_SESSION['last_event_time'] = time();
if($result){
$json = array();
foreach ($result as $row){
$json[] = array(
'text' => $row['event_text'],
'date' => date("Y-m-d H:i", $row['event_time']),
);
}
echo "data: ". json_encode($json) . "\n\n";
flush();
}

Answer 1

Fundamentally you cannot control this: it is a browser-specific setting.
If your browser is Firefox it appears to be controlled by this setting: dom.server-events.default-reconnection-time with a default of 5000ms.
Taking a step back: the reconnect only happens if the server closes the connection. Why are you closing the connection? (*) Why is a 3-second re-connection too fast?
The point of SSE is to minimize latency; the trade-off is more resource usage, in particular having to keep a dedicated socket open for each client.
So it sounds like you don't want to be using SSE, and instead want to use a simple AJAX poll, on a 60-second setInterval() call?
*: If you did intend to keep it open, you need to wrap your query and processing the result code in a while(true){...} loop. Put e.g. a one-second sleep at the end of the while loop to stop the DB server being overloaded.

Answer 2

Now I have my answer.
Controlling Reconnection-Timeout:
The browser attempts to reconnect the connection to the source within about 3 seconds after each server-sent event connection is closed. Before trying to reconnect, you can change that timeout by starting the line with retry: and then adding the millisecond number to wait.
I changed the code below and started working as I wanted.
header('Content-Type: text/event-stream');
header('Cache-Control: no-cache');
include_once "config.php";
$time = isset($_SESSION['last_event_time']) ? $_SESSION['last_event_time'] : time();
$result = $db->quesry("SELECT * FROM event_noti WHERE event_time < {$time} ")->rows;
$_SESSION['last_event_time'] = time();
echo "retry: 60000\n"; // 60 seconds, to wait for next connection.
$json = array();
if($result){
foreach ($result as $row){
$json[] = array(
'text' => $row['event_text'],
'date' => date("Y-m-d H:i", $row['event_time']),
);
}
}
echo "data: ". json_encode($json) . "\n\n";
flush();
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