I'm currently trying to use Server-Sent Events using PHP, but they are not firing instantly on the browser.

Here is my code:

<?php
    
    // Headers must be processed line by line.
    header('Content-Type: text/event-stream');
    header('Cache-Control: no-cache');
    header('X-Accel-Buffering: no');
    while(true)
    {
    
        // Set data line
        echo "event: server-time";
        echo "data: " . date( 'G:H:s', time() );
        //echo str_repeat(" ", 4096);
    
        ob_end_flush();     // Strange behaviour, will not work
        flush();            // Unless both are called !
    
        // Wait one second.
        sleep(1);

}

While it works, it seems like there is a minimum size for the buffer to flush and send data to the browser. In fact, if I uncomment the str_repeat line, I get almost instantaneous events (as in, one every second). However, if I keep it commented, the browser keeps loading for around 2 minutes, before sending all the data from the past 2 minutes.

I've looked around on Stack Overflow but I couldn't find an answer that works within all of them.

Here are some infos from phpinfo() that I find useful in this context, don't hesitate to ask for more:

PHPINFO