Zig

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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const std = @import("std");
const chilkat = @import("chilkat");

pub fn main(init: std.process.Init) !void {
    const alloc = init.arena.allocator();

    // 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.

    const dkim = try chilkat.Dkim.init();
    defer dkim.deinit();

    // 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.
    dkim.prefetchPublicKey("myselector", "example.com") catch {
        std.debug.print("{s}\n", .{try dkim.getLastErrorText(alloc)});
        return;
    };

    std.debug.print("Public key prefetched from DNS and cached.\n", .{});
}