Shortening an IPv6 address ending in 0's via PHP - php

Question

I'm using an IPv6 class found on GitHub to do some IP manipulation but I noticed that there is an issue with shortening certain address, typically ending in 0.
When I enter the address 2001::6dcd:8c74:0:0:0:0, it results in 2001::6dcd:8c74::::.
$address = '2001::6dcd:8c74:0:0:0:0';
// Check to see if address is already compacted
if (strpos($address, '::') === FALSE) {
$parts = explode(':', $address);
$new_parts = array();
$ignore = FALSE;
$done = FALSE;
for ($i = 0; $i < count($parts); $i++) {
if (intval(hexdec($parts[$i])) === 0 && $ignore == FALSE && $done == FALSE) {
$ignore = TRUE;
$new_parts[] = '';
if ($i == 0) {
$new_parts = '';
}
} else if (intval(hexdec($parts[$i])) === 0 && $ignore == TRUE && $done == FALSE) {
continue;
} else if (intval(hexdec($parts[$i])) !== 0 && $ignore == TRUE) {
$done = TRUE;
$ignore = FALSE;
$new_parts[] = $parts[$i];
} else {
$new_parts[] = $parts[$i];
}
}
// Glue everything back together
$address = implode(':', $new_parts);
}
// Remove the leading 0's
$new_address = preg_replace("/:0{1,3}/", ":", $address);
// $this->compact = $new_address;
// return $this->compact;
echo $new_address; // Outputs: 2001::6dcd:8c74::::

Answer 1

To compress ipv6 addresses, use php functions inet_ntop and inet_pton to do the formatting, by converting the ipv6 to binary and back.
Sample ipv6 - 2001::6dcd:8c74:0:0:0:0
Test usage:
echo inet_ntop(inet_pton('2001::6dcd:8c74:0:0:0:0'));
Output : 2001:0:6dcd:8c74::

Answer 2

Without that problem line at the bottom you get 2001::6dcd:8c74:0:0:0:0.
Now, before the leading 0's are all replaced, the function checks to see if the address ends in :0 before removing all leading 0's.
if (substr($address, -2) != ':0') {
$new_address = preg_replace("/:0{1,3}/", ":", $address);
} else {
$new_address = $address;
}
Another check is added to catch other possible valid IPv6 addresses from being malformed.
if (isset($new_parts)) {
if (count($new_parts) < 8 && array_pop($new_parts) == '') {
$new_address .= ':0';
}
}
The new full function looks like this:
// Check to see if address is already compacted
if (strpos($address, '::') === FALSE) {
$parts = explode(':', $address);
$new_parts = array();
$ignore = FALSE;
$done = FALSE;
for ($i = 0; $i < count($parts); $i++) {
if (intval(hexdec($parts[$i])) === 0 && $ignore == FALSE && $done == FALSE) {
$ignore = TRUE;
$new_parts[] = '';
if ($i == 0) {
$new_parts = '';
}
} else if (intval(hexdec($parts[$i])) === 0 && $ignore == TRUE && $done == FALSE) {
continue;
} else if (intval(hexdec($parts[$i])) !== 0 && $ignore == TRUE) {
$done = TRUE;
$ignore = FALSE;
$new_parts[] = $parts[$i];
} else {
$new_parts[] = $parts[$i];
}
}
// Glue everything back together
$address = implode(':', $new_parts);
}
// Check to see if this ends in a shortened :0 before replacing all
// leading 0's
if (substr($address, -2) != ':0') {
// Remove the leading 0's
$new_address = preg_replace("/:0{1,3}/", ":", $address);
} else {
$new_address = $address;
}
// Since new_parts isn't always set, check to see if it's set before
// trying to fix possibly broken shortened addresses ending in 0.
// (Ex: Trying to shorten 2001:19f0::0 will result in unset array)
if (isset($new_parts)) {
// Some addresses (Ex: starting addresses for a range) can end in
// all 0's resulting in the last value in the new parts array to be
// an empty string. Catch that case here and add the remaining :0
// for a complete shortened address.
if (count($new_parts) < 8 && array_pop($new_parts) == '') {
$new_address .= ':0';
}
}
// $this->compact = $new_address;
// return $this->compact;
echo $new_address; // Outputs: 2001::6dcd:8c74:0:0:0:0
It's not the cleanest solution and could possibly have holes in its logic depending on what the address is. If I find any other issues with it I will update this question/answer.