What are the Alternatives to the Deprecated PHP 8.1 Constants FILTER_SANITIZE_STRING and FILTER_SANITIZE_STRIPPED?

Consequences of Deprecating Constants

In PHP 8.1, constants FILTER_SANITIZE_STRING and FILTER_SANITIZE_STRIPPED are now deprecated. This raises concerns for developers who previously relied on these constants for sanitizing user input.

Rationale for Deprecation

The affected constants had an ambiguous purpose and potentially confusing behavior. They removed specific characters and encoded certain symbols without providing clear guidelines for when they should be used. The community recognized that this lack of clarity could lead to unintended consequences and decided to discourage their continued use.

Impact on Legacy Applications

Applications that still use these constants will encounter deprecation warnings. To avoid errors and ensure the continued functionality of their code, developers should find suitable replacements.

Alternative Solutions

1. FILTER_UNSAFE_RAW:
If you previously used FILTER_SANITIZE_STRING without a specific purpose, you can switch to the default string filter, FILTER_UNSAFE_RAW, which performs no filtering. This option is recommended if you require the raw string value without any sanitization.

2. htmlspecialchars:
If you used FILTER_SANITIZE_STRING for protection against cross-site scripting (XSS) attacks, consider using the htmlspecialchars() function on output data. This approach ensures that malicious scripts are rendered harmless before being displayed to users.

3. Custom Regex Filter:
For cases where you require specific filtering, a custom regex filter can be created. See the example code provided in the accepted answer. Remember that it is essential to escape output when protecting against XSS vulnerabilities.

Conclusion

The deprecation of FILTER_SANITIZE_STRING and FILTER_SANITIZE_STRIPPED in PHP 8.1 serves as a reminder to developers to critically evaluate their input sanitation practices. By understanding the rationale behind this change, they can make informed decisions about adopting alternative solutions that provide more clarity and security.

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