Things to note when using the PHP flush function

ob_flush/flush are described in the manual as flushing the output buffer, and they need to be used together, so it will cause confusion to many people... In fact, they operate on different objects. In some cases, flush does nothing at all. Things

ob_* series functions operate the output buffer of PHP itself.

So, ob_flush is to refresh the buffer of PHP itself.

And flush, strictly speaking , this only has practical effect when PHP is installed as apache Module (handler or filter).
It is to refresh the buffer of WebServer (can be considered specifically apache).

In apache Under module's sapi, flush will indirectly call apache's api by calling the flush member function pointer of sapi_module,
: ap_rflush refreshes apache's output buffer. Of course, the manual also says that there are some other modules of apache,
The result of this action may be changed..

Some Apache modules, such as mod_gzip, may perform output caching themselves, which will cause the results generated by the flush() function to not be sent to the client browser immediately. .

Even the browser will cache the received content before displaying it. For example, the Netscape browser caches content until it receives a newline or the beginning of an html tag, and does not display the entire table until it receives the tag.

Some versions of Microsoft Internet Explorer
will only start displaying the page after receiving 256 bytes, so some extra spaces must be sent to allow these browsers to display the page content.

So, the correct order to use the two is. First ob_flush, then flush,

Of course, under other sapi, you can not call flush, just to ensure the portability of your code property, it is recommended to use it together.

<?php
// set_time_limit(0);
header(&#39;Content-Type: text/event-stream&#39;);
header(&#39;Cache-Control: no-cache&#39;);
// ob_end_flush();
// ini_set(&#39;output_buffering&#39;, 0);
// ini_set(&#39;implicit_flush&#39;, 1);
if (ob_get_level() == 0) ob_start();
echo str_repeat(&#39; &#39; ,4096);
$long = 60;
while($long > 0)
{
$time = date(&#39;r&#39;);
echo "data: The server time is: {$time}\n\n";
ob_flush();
flush();//break;
sleep(1);
$long --;
}
// var source=new EventSource("http://localhost:18000/sse.php");source.onmessage=function(event){console.info(event.data)};
?>

If you want to support nginx fpm php, you need to add a response header

header('X-Accel-Buffering: no');
This eliminates both proxy_buffering and (if you have nginx >= 1.5.6), fastcgi_buffering. The fastcgi bit is crucial if you're using php-fpm. The header is also far more convenient to do on an as-needed basis.
Docs on learning helps.

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