(PHP 5 >= 5.4.0, PHP 7, PHP 8)
header_register_callback — Call a header function
Registers a function that will be called when PHP starts sending output.
The callback is executed just after PHP prepares all
headers to be sent, and before any other output is sent, creating a window
to manipulate the outgoing headers before being sent.
callbackFunction called just before the headers are sent. It gets no parameters and the return value is ignored.
Returns true on success or false on failure.
Example #1 header_register_callback() example
<?php
header('Content-Type: text/plain');
header('X-Test: foo');
function foo() {
foreach (headers_list() as $header) {
if (strpos($header, 'X-Powered-By:') !== false) {
header_remove('X-Powered-By');
}
header_remove('X-Test');
}
}
$result = header_register_callback('foo');
echo "a";
?>
The above example will output something similar to:
Content-Type: text/plain a
header_register_callback() is executed just as the headers are about to be sent out, so any output from this function can break output.
Note:
Headers will only be accessible and output when a SAPI that supports them is in use.