How to Replace Deprecated PHP 8.1 String Sanitization Filters (FILTER_SANITIZE_STRING and FILTER_SANITIZE_STRIPPED)?

Replacing Deprecated Filter Constants: FILTER_SANITIZE_STRING and FILTER_SANITIZE_STRIPPED

With PHP 8.1, the constant filters FILTER_SANITIZE_STRING and FILTER_SANITIZE_STRIPPED have become deprecated. This has sparked concerns among developers who previously used these filters for string sanitization.

The Reason for Deprecation

These filter constants were deemed confusing and unclear in their purpose. Their functionality overlapped with other string filters, leading to confusion and inconsistent results. The PHP community decided to discontinue their support.

Replacement Options

There are several options available to replace these deprecated filters:

• Use FILTER_UNSAFE_RAW: This is the default string filter that performs no filtering. It is suitable if you do not require any specific sanitization.
• Use htmlspecialchars() for XSS Prevention: If you were using FILTER_SANITIZE_STRING primarily to prevent XSS vulnerabilities, replace it with htmlspecialchars(). This function should be called on the output, not the input, to ensure effective protection.
• Create a Polyfill: If you require the exact behavior of the deprecated filters, you can create a polyfill using regular expressions.

The following code demonstrates a polyfill function for filter_string_polyfill:

function filter_string_polyfill(string $string): string
{
    $str = preg_replace('/\x00|<[^>]*>?/', '', $string);
    return str_replace([&quot;'&quot;, '&quot;'], ['&amp;#39;', '&amp;#34;'], $str);
}

Remember, sanitizing input is less effective than escaping output. Focus on encoding potentially vulnerable data before it is displayed or used.

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