PHP

Prefetch a DKIM Public Key from DNS

Demonstrates the Chilkat Dkim.PrefetchPublicKey method, which retrieves a DKIM public key from DNS and caches it for a specific selector and domain. The arguments are the selector and the domain. The TXT lookup is made at selector._domainkey.domain.

Background: DkimVerify already fetches the key from DNS on demand, so prefetching is about when the lookup happens: doing it up front lets you separate a potentially slow network step from the verification itself, warm the cache before a batch of messages from the same domain, or confirm the key is publishable before relying on it. After a successful prefetch, verification of a matching signature uses the cached key with no further DNS traffic.

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<?php

use Chilkat2\Dkim;

// Demonstrates the Dkim.PrefetchPublicKey method, which retrieves a DKIM public key from DNS and
// caches it for a specific selector and domain.  The 1st argument is the selector and the 2nd is
// the domain.

$dkim = new Dkim();

// Retrieve the public key from the DNS TXT record at selector._domainkey.domain and cache it.
// A later DkimVerify for the same selector and domain then uses the cached key.
try {
    $dkim->PrefetchPublicKey('myselector', 'example.com');
} catch (\Chilkat2\Exception $e) {
    echo $e->getMessage(), "\n";
    exit;
}

echo "Public key prefetched from DNS and cached.\n";