User Defined Filter

The constants below are defined by this extension, and will only be available when the extension has either been compiled into PHP or dynamically loaded at runtime.

FILTER_CALLBACK (int)

This filter delegates the filtering to a user defined function. The callable is passed via the options parameter as the value associated to the 'options' key.

The callback should have the following signature:

function callback(string $value): mixed

value

The value that is being filtered.

Note:

The value returned by the callback will be the value returned by the invoked filter function.

Example #1 Example of using FILTER_CALLBACK to validate a login name

<?php
function validate_login(string $value): ?string
{
    if (strlen($value) >= 5 && ctype_alnum($value)) {
        return $value;
    }
    return null;
}

$login = "val1dL0gin";
$filtered_login = filter_var($login, FILTER_CALLBACK, ['options' => 'validate_login']);
var_dump($filtered_login);

$login = "f&ke login";
$filtered_login = filter_var($login, FILTER_CALLBACK, ['options' => 'validate_login']);
var_dump($filtered_login);
?>

The above example will output:

string(10) "val1dL0gin"
NULL

Note:

As of PHP 8.1.25 and 8.2.12, the structural flags FILTER_REQUIRE_ARRAY, FILTER_FORCE_ARRAY and FILTER_REQUIRE_SCALAR apply to this filter, and FILTER_NULL_ON_FAILURE changes how such a structural failure is reported. In earlier versions all flags were ignored. Filter specific flags are always ignored, and since the return value of the callback is the result, the callback itself cannot fail: no flag turns a false returned by the callback into null or an exception.