Quick way of expanding IPv6 Addresses with PHP

Question

I was working on a project where I needed to expand IPv6 addresses. There are not many functions out there created by other users, and the ones that exist are ugly. Some of them included multiple foreach's and gmp_init, which added a lot of overhead and harder to maintain code. I need a simple, non-taxing script to expand IPv6.

Posting this for the community.

Answer 1

The following is a two liner, where $ip is a condensed IPv6 address. Returns expanded $ip.

Example:

$ip = "fe80:01::af0";
echo expand($ip); // fe80:0001:0000:0000:0000:0000:0000:0af0

Function:

function expand($ip){
    $hex = unpack("H*hex", inet_pton($ip));         
    $ip = substr(preg_replace("/([A-f0-9]{4})/", "$1:", $hex['hex']), 0, -1);

    return $ip;
}

Answer 2

With the help from Mike Mackintosh and Yann Milin I came up with this function:

function expandIPv6($ip) {
    $hex = bin2hex(inet_pton($ip));
    return implode(':', str_split($hex, 4));
}

Below a more universal function witch will also extract IPv4 from an IPv4-mapped IPv6 addresses:

function expandIPv6($ip) {
    if (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV4))
        return $ip;
    elseif (filter_var($ip, FILTER_VALIDATE_IP, FILTER_FLAG_IPV6)) {
        $hex = bin2hex(inet_pton($ip));
        if (substr($hex, 0, 24) == '00000000000000000000ffff') // IPv4-mapped IPv6 addresses
            return long2ip(hexdec(substr($hex, -8)));
        return implode(':', str_split($hex, 4));
    }
    return false;
}