How can I get the client's IP address in a PHP webservice? [duplicate]

This should be what you want:

$_SERVER['REMOTE_ADDR']

The IP address from which the user is viewing the current page.

http://php.net/manual/en/reserved.variables.server.php

Actually, I would suggest using this function to cover all of your bases, such as people using proxies, shared networks etc.:

function getUserIpAddr()
{
    if (!empty($_SERVER['HTTP_CLIENT_IP'])) //if from shared
    {
        return $_SERVER['HTTP_CLIENT_IP'];
    }
    else if (!empty($_SERVER['HTTP_X_FORWARDED_FOR']))   //if from a proxy
    {
        return $_SERVER['HTTP_X_FORWARDED_FOR'];
    }
    else
    {
        return $_SERVER['REMOTE_ADDR'];
    }
}