为什么FILTER_VALIDATE_URL不适用于波斯字符？

Here is my code:

$url = "http://localhost/myweb/qanda/1/";
var_dump(filter_var($url, FILTER_VALIDATE_URL));
//=> string(31) "http://localhost/myweb/qanda/1/"

It is known as a valid URL and all fine. But my code doesn't work when there is a Persian character in the URL:

$url = "http://localhost/myweb/qanda/1/س";
var_dump(filter_var($url, FILTER_VALIDATE_URL));
//=> bool(false)

Why? And how can I fix it?

Well, basically because the string you've entered isn't a valid URL according to the RFC:

"Only alphanumerics [0-9a-zA-Z], the special characters "$-_.+!*'()," [not including the quotes - ed], and reserved characters used for their reserved purposes may be used unencoded within a URL"

Your client (the browser) will translate your character to %D8%B3 which is valid and send that to the server, but your client will probably still show س (mine does).

So basically, the correct URL would be validated like so:

$url = "http://localhost/myweb/qanda/1/%D8%B3";
var_dump(filter_var($url, FILTER_VALIDATE_URL));

You can safely use urlencode() to translate foreign characters.