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php – Server sent events work, but with a massive time delay

Posted by: admin July 12, 2020 Leave a comment

Questions:

Ill start off by saying this works perfectly on my local machine, the js example below connects to stream.php and receives a continuous update of the servers current time every second.

index.php

var source = new EventSource("stream.php");

source.addEventListener('message', function(e) {
    console.log(e);
}, false);

source.addEventListener('open', function(e) {
    console.log(e);
}, false);

source.addEventListener('error', function(e) {
    if (e.readyState == EventSource.CLOSED) {
        console.log('closed');
    }
}, false);

stream.php

while(true)
{
    // Headers must be processed line by line.
    header('Content-Type: text/event-stream');
    header('Cache-Control: no-cache');

    // Set data line
    print "data: " . date( 'G:H:s', time() ) . PHP_EOL . PHP_EOL;

    // Toilet
    flush();

    // Wait one second.
    sleep(1);
}

I did expect a bit of a delay after uploading to the live dev. server. But there is a time delay of about 15 to 20 min. before I even see the first entry.

The connection does not drop. (Prob. been going 40 min. + now.) Is this just an Apache looping problem (means it time to look at web sockets) or is there something I can do to fix this?

How to&Answers:

Server.php needs to be as follows:

stream.php

while(true)
{
    // Headers must be processed line by line.
    header('Content-Type: text/event-stream');
    header('Cache-Control: no-cache');

    // Set data line
    print "Event: server-time" . PHP_EOL;
    print "data: " . date( 'G:H:s', time() ) . PHP_EOL;
    print PHP_EOL;

    ob_end_flush();     // Strange behaviour, will not work
    flush();            // Unless both are called !

    // Wait one second.
    sleep(1);
}

Answer:

@Derrick, your suggested ob_end_flush(); line got me close, but in more complex PHP than hello world code, I was still getting unwanted reopens on my SSE connections (I still don’t fully understand why ob_end_flush() was doing that to me). So here’s the pattern I’m now using (otherwise identical to your stream.php). In English, I’m turning off PHP output buffering before entering my infinite loop:

// per http://www.php.net/manual/en/book.outcontrol.php:
//     Clean (erase) the output buffer and turn off output buffering
ob_end_clean();

// how long PHP script stays running/SSE connection stays open (seconds)
set_time_limit(60);
while (true) {

  // use @Derrick's header/send code here

  ob_flush();  // note I don't turn off output buffering here again
  flush();
  sleep(1);
}

Answer:

Sleep is blocking the SSE. I too had the same problem. I was advised to use event driven programming.

Answer:

just add, ob_flush(); before flush() function in stream.php

updated stream.php script is as below, observe ob_flush() function before flush() function.

while(true)
{
    // Headers must be processed line by line.
    header('Content-Type: text/event-stream');
    header('Cache-Control: no-cache');

    // Set data line
    print "data: " . date( 'G:H:s', time() ) . PHP_EOL . PHP_EOL;

    // Toilet
    **ob_flush();**
    flush();

    // Wait one second.
    sleep(1);
}