Nicer handling of PTR queries

[Daniel15]

amphp DNS doesn't handle calls like this:

yield Amp\Dns\resolve('209.141.56.29', $options = ['types' => Amp\Dns\Record::PTR])

Currently, you need to manually convert the IP address to the right PTR query:

yield Amp\Dns\resolve('29.56.141.209.in-addr.arpa', $options = ['types' => Amp\Dns\Record::PTR])

The legacy Net_DNS library has some code to handle PTR queries correctly, when the input looks like an IP address:

        /*
         * If the name looks like an IP address then do an appropriate
         * PTR query.
         */
        if (preg_match('/^(\d+)\.(\d+)\.(\d+)\.(\d+)$/', $name, $regs)) {
            $name = $regs[4].'.'.$regs[3].'.'.$regs[2].'.'.$regs[1].'.in-addr.arpa.';
            $type = 'PTR';
        }

https://github.com/pear/Net_DNS/blob/5786b8c6f21c3cc8915fe251dac1571fa524a417/Net/DNS/Resolver.php#L552-L559

It would be nice for amphp to do this too.

[kelunik]

You should use Amp\Dns\query for everything that doesn't resolve to an IP address. So in this case yield Amp\Dns\query('8.8.8.8.in-addr.arpa', Amp\Dns\Record::PTR); But you're right, we could add auto-rewrite here.

@bwoebi Didn't we have a protection that restricts resolve to A and AAAA queries?

[Daniel15]

Amp\Dns\resolve actually seems to work properly, Amp\Dns\resolve('29.56.141.209.in-addr.arpa', ['types' => Amp\Dns\Record::PTR]) gives me the right result.

[kelunik]

Yes, I know that it works, but it's not supposed to work. I think we had a restriction in there before.

[kelunik]

Do you have any suggestion for a better function name? I'm not sure what to do with an invalid IP, probably throw an exception, but not sure which one. InvalidAddressException might make sense, but it should probably not extend the ResolutionException in this case.

function ip2arpa($ip) {
    $packedIp = inet_pton($ip);

    if ($packedIp === false) {
        return null; // FIXME
    }

    if (isset($packedIp[5])) { // IPv6
        return wordwrap(strrev(bin2hex($packedIp)), 1, ".", true) . ".ip6.arpa";
    }

    return inet_ntop(strrev($packedIp)) . ".in-addr.arpa";
}

[kelunik]

I created a PR now. It doesn't use a separate function, see #52.

[kelunik]

It's now included in https://github.com/amphp/dns/releases/tag/v0.8.14.