Test if string is URL encoded in PHP

Here is something i just put together.

if ( urlencode(urldecode($data)) === $data){
    echo 'string urlencoded';
} else {
    echo 'string is NOT urlencoded';
}

i have one trick :

you can do this to prevent doubly encode. Every time first decode then again encode;

$string = urldecode($string);

Then do again

$string = urlencode($string);

Performing this way we can avoid double encode :)

You'll never know for sure if a string is URL-encoded or if it was supposed to have the sequence %2B in it. Instead, it probably depends on where the string came from, i.e. if it was hand-crafted or from some application.

Is it better to search the string for characters which would be encoded, which aren't, and if any exist then its not encoded.

I think this is a better approach, since it would take care of things that have been done programmatically (assuming the application would not have left a non-encoded character behind).

One thing that will be confusing here... Technically, the % "should be" encoded if it will be present in the final value, since it is a special character. You might have to combine your approaches to look for should-be-encoded characters as well as validating that the string decodes successfully if none are found.