Version

5.1.2

Context

The JavaDoc for DnsClient.resolveMX() says the returned list is sorted by priority:

@return a future notified with a List that contains all resolved {@link MxRecord}s, sorted by
        their {@link MxRecord#priority()}.

The DNS guide also says MX and SRV records with smaller priority values should come first.

However, Vert.x appears to keep the order from the DNS response. For example, if the server returns priorities 20 and then 10, Vert.x returns them in that order instead of 10 and then 20.

Applications relying on this ordering may then select the wrong mail exchanger or service endpoint.

Steps to reproduce

mockDnsServer.store(question -> Arrays.asList(
  MockDnsServer.mx("vertx.io", 100, "mx-high.vertx.io", 20),
  MockDnsServer.mx("vertx.io", 100, "mx-low.vertx.io", 10)
));

DnsClient dns = prepareDns();

List<MxRecord> records = dns.resolveMX("vertx.io").await();
records.forEach(record ->
  System.out.println(record.priority() + ": " + record.name()));

Expected output

10: mx-low.vertx.io
20: mx-high.vertx.io

Actual output

20: mx-high.vertx.io
10: mx-low.vertx.io

Do you have a reproducer?

No response