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add mx preference to smtpclient.GatherDestinations

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mostly so moxtools can show the mx preferences in its output
This commit is contained in:
Mechiel Lukkien
2025-05-15 16:37:53 +02:00
parent cc627af263
commit 91bfff220e
6 changed files with 55 additions and 43 deletions
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20
smtpclient/gather.go
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@ -26,6 +26,12 @@ var (
errNoMail = errors.New("domain does not accept email as indicated with single dot for mx record")
)
// HostPref is a host for delivery, with preference for MX records.
type HostPref struct {
Host dns.IPDomain
Pref int // -1 when not an MX record.
}
// GatherDestinations looks up the hosts to deliver email to a domain ("next-hop").
// If it is an IP address, it is the only destination to try. Otherwise CNAMEs of
// the domain are followed. Then MX records for the expanded CNAME are looked up.
@ -46,14 +52,14 @@ var (
// were found, both the original and expanded next-hops must be authentic for DANE
// to be option. For a non-IP with no MX records found, the authentic result can
// be used to decide which of the names to use as TLSA base domain.
func GatherDestinations(ctx context.Context, elog *slog.Logger, resolver dns.Resolver, origNextHop dns.IPDomain) (haveMX, origNextHopAuthentic, expandedNextHopAuthentic bool, expandedNextHop dns.Domain, hosts []dns.IPDomain, permanent bool, err error) {
func GatherDestinations(ctx context.Context, elog *slog.Logger, resolver dns.Resolver, origNextHop dns.IPDomain) (haveMX, origNextHopAuthentic, expandedNextHopAuthentic bool, expandedNextHop dns.Domain, hostPrefs []HostPref, permanent bool, err error) {
// ../rfc/5321:3824
log := mlog.New("smtpclient", elog)
// IP addresses are dialed directly, and don't have TLSA records.
if len(origNextHop.IP) > 0 {
return false, false, false, expandedNextHop, []dns.IPDomain{origNextHop}, false, nil
return false, false, false, expandedNextHop, []HostPref{{origNextHop, -1}}, false, nil
}
// We start out assuming the result is authentic. Updated with each lookup.
@ -133,8 +139,8 @@ func GatherDestinations(ctx context.Context, elog *slog.Logger, resolver dns.Res
}
// No MX record, attempt delivery directly to host. ../rfc/5321:3842
hosts = []dns.IPDomain{{Domain: expandedNextHop}}
return false, origNextHopAuthentic, expandedNextHopAuthentic, expandedNextHop, hosts, false, nil
hostPrefs = []HostPref{{dns.IPDomain{Domain: expandedNextHop}, -1}}
return false, origNextHopAuthentic, expandedNextHopAuthentic, expandedNextHop, hostPrefs, false, nil
} else if err != nil {
log.Infox("mx record has some invalid records, keeping only the valid mx records", err)
}
@ -158,12 +164,12 @@ func GatherDestinations(ctx context.Context, elog *slog.Logger, resolver dns.Res
err = fmt.Errorf("%w: invalid host name in mx record %q: %v", errDNS, mx.Host, err)
return true, origNextHopAuthentic, expandedNextHopAuthentic, expandedNextHop, nil, true, err
}
hosts = append(hosts, dns.IPDomain{Domain: host})
hostPrefs = append(hostPrefs, HostPref{dns.IPDomain{Domain: host}, int(mx.Pref)})
}
if len(hosts) > 0 {
if len(hostPrefs) > 0 {
err = nil
}
return true, origNextHopAuthentic, expandedNextHopAuthentic, expandedNextHop, hosts, false, err
return true, origNextHopAuthentic, expandedNextHopAuthentic, expandedNextHop, hostPrefs, false, err
}
}