How do I properly sanitize data received from a text area, when outputting it back into the text area?

Question

A user will input text in a textarea. It is then inserted directly into a mySQL database. I use trim, htmlentities, mysql_real_escape_string on it and I have magic quotes en

Answer 1

You shouldn't use htmlentities when saving it. You should use htmlentities when displaying it. The rule of thumb is not to encode/sanitize the data until you need to. If you do htmlentities on it when you save then you have to do html_entity_decode on the text when the user wants to edit the input. So you sanitize for what you need and nothing more. When saving it, you need to sanitize for SQL injection, so you mysql_real_escape_string it. When displaying, you need to sanitize for XSS, so you htmlentities it.

Also, I am not sure if you saw Darryl Hein's comment, but you really do not want magic_quotes enabled. They are a bad, bad, thing and have been deprecated as of PHP 5.3 and will be gone altogether in PHP 6.