PHP/MySQL: Filtering POST & GET Data

Possible Duplicate:
What are the best PHP input sanitizing functions?

A while back I found this, what I thought to be great, snippet in someones code to filter POST and GET data from injections.

function filter($data) { //Filters data against security risks.

    $data = trim(htmlentities(strip_tags($data)));
    if(get_magic_quotes_gpc()) $data = stripslashes($data);
    $data = mysql_real_escape_string($data);
    return $data;
}
foreach($_GET as $key => $value) $filterGet[$key] = filter($value);
foreach($_POST as $key => $value) $filterPost[$key] = filter($value);

And I've been using it ever since. But today, while sending an array through ajax I got tons of errors. Most of them say strip_tags() expects parameter 1 to be string, array given in...

What the best way to filter data? All this data is going to a database. But what about cases where it isn't going to a database?

Answer

Here is the function you need:

function filter($data) { //Filters data against security risks.
    if (is_array($data)) {
        foreach ($data as $key => $element) {
            $data[$key] = filter($element);
        }

    } else {
        $data = trim(htmlentities(strip_tags($data)));
        if(get_magic_quotes_gpc()) $data = stripslashes($data);
        $data = mysql_real_escape_string($data);
    }
    return $data;
}