Description

The following code:

<?php

var_dump(headers_sent());

while (ob_get_level() !== 0) {
    ob_end_flush();
}
flush();

var_dump(headers_sent());
var_dump(ob_get_level());

Resulted in this output:

bool(false)
bool(false)
int(0)

But I expected this output instead:

bool(false)
bool(true)
int(0)

This issue is reproducible with fastcgi on Windows together with nginx.

When I output/echo any data, the headers are always sent (expected).

When I use the php internal webserver instead, the flush is enough to force the headers to be send without any data/body (expected).

I belive this is a bug, as sending headers early must be supported. Some apps might need non trivial amount of time until first byte of the response is ready, also, some apps might not output any body at all, and the headers are not sent until the script ends.

PHP Version

8.1

Operating System

Windows 10