header_register_callback

(PHP 5 >= 5.4.0, PHP 7, PHP 8)

header_register_callback — Call a header function

Description

header_register_callback(callable $callback): bool

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.

Parameters

callback: Function called just before the headers are sent. It gets no parameters and the return value is ignored.

Return Values

Returns true on success or false on failure.

Examples

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

Notes

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.

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User Contributed Notes 1 note

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matt@kafene ¶

11 years ago

Note that this function only registers a single callback as of php 5.4. The most recent callback set is the one that will be executed, they will not be executed in order like with register_shutdown_function(), just overwritten.

Here is my test:

<?php

$i = $j = 0;
header_register_callback(function() use(&$i){ $i+=2; });
header_register_callback(function() use(&$i){ $i+=3; });
register_shutdown_function(function() use(&$j){ $j+=2; });
register_shutdown_function(function() use(&$j){ $j+=3; });
register_shutdown_function(function() use(&$j){ var_dump($j); });
while(!headers_sent()) { echo "<!-- ... flushing ... -->"; }
var_dump(headers_sent(), $i);
exit;

?>

Results:

headers_sent() - true
$i = 3
$j = 5