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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
View File

@ -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
}
}

36
smtpclient/gather_test.go
View File

@ -35,11 +35,11 @@ func ipdomain(s string) dns.IPDomain {
return dns.IPDomain{Domain: d}
}
func ipdomains(s ...string) (l []dns.IPDomain) {
for _, e := range s {
l = append(l, ipdomain(e))
func hostprefs(pref int, names ...string) (l []HostPref) {
for _, s := range names {
l = append(l, HostPref{Host: ipdomain(s), Pref: pref})
}
return
return l
}
// Test basic MX lookup case, but also following CNAME, detecting CNAME loops and
@ -86,10 +86,10 @@ func TestGatherDestinations(t *testing.T) {
resolver.CNAME[s] = next
}
test := func(ipd dns.IPDomain, expHosts []dns.IPDomain, expDomain dns.Domain, expPerm, expAuthic, expExpAuthic bool, expErr error) {
test := func(ipd dns.IPDomain, expHostPrefs []HostPref, expDomain dns.Domain, expPerm, expAuthic, expExpAuthic bool, expErr error) {
t.Helper()
_, authic, authicExp, ed, hosts, perm, err := GatherDestinations(ctxbg, log.Logger, resolver, ipd)
_, authic, authicExp, ed, hostPrefs, perm, err := GatherDestinations(ctxbg, log.Logger, resolver, ipd)
if (err == nil) != (expErr == nil) || err != nil && !errors.Is(err, expErr) {
// todo: could also check the individual errors? code currently does not have structured errors.
t.Fatalf("gather hosts: %v, expected %v", err, expErr)
@ -97,8 +97,8 @@ func TestGatherDestinations(t *testing.T) {
if err != nil {
return
}
if !reflect.DeepEqual(hosts, expHosts) || ed != expDomain || perm != expPerm || authic != expAuthic || authicExp != expExpAuthic {
t.Fatalf("got hosts %#v, effectiveDomain %#v, permanent %#v, authic %v %v, expected %#v %#v %#v %v %v", hosts, ed, perm, authic, authicExp, expHosts, expDomain, expPerm, expAuthic, expExpAuthic)
if !reflect.DeepEqual(hostPrefs, expHostPrefs) || ed != expDomain || perm != expPerm || authic != expAuthic || authicExp != expExpAuthic {
t.Fatalf("got hosts %#v, effectiveDomain %#v, permanent %#v, authic %v %v, expected %#v %#v %#v %v %v", hostPrefs, ed, perm, authic, authicExp, expHostPrefs, expDomain, expPerm, expAuthic, expExpAuthic)
}
}
@ -108,18 +108,18 @@ func TestGatherDestinations(t *testing.T) {
authic := i == 1
resolver.AllAuthentic = authic
// Basic with simple MX.
test(ipdomain("basic.example"), ipdomains("mail.basic.example"), domain("basic.example"), false, authic, authic, nil)
test(ipdomain("multimx.example"), ipdomains("mail1.multimx.example", "mail2.multimx.example"), domain("multimx.example"), false, authic, authic, nil)
test(ipdomain("basic.example"), hostprefs(10, "mail.basic.example"), domain("basic.example"), false, authic, authic, nil)
test(ipdomain("multimx.example"), hostprefs(10, "mail1.multimx.example", "mail2.multimx.example"), domain("multimx.example"), false, authic, authic, nil)
// Only an A record.
test(ipdomain("justhost.example"), ipdomains("justhost.example"), domain("justhost.example"), false, authic, authic, nil)
test(ipdomain("justhost.example"), hostprefs(-1, "justhost.example"), domain("justhost.example"), false, authic, authic, nil)
// Only an AAAA record.
test(ipdomain("justhost6.example"), ipdomains("justhost6.example"), domain("justhost6.example"), false, authic, authic, nil)
test(ipdomain("justhost6.example"), hostprefs(-1, "justhost6.example"), domain("justhost6.example"), false, authic, authic, nil)
// Follow CNAME.
test(ipdomain("cname.example"), ipdomains("mail.basic.example"), domain("basic.example"), false, authic, authic, nil)
test(ipdomain("cname.example"), hostprefs(10, "mail.basic.example"), domain("basic.example"), false, authic, authic, nil)
// No MX/CNAME, non-existence of host will be found out later.
test(ipdomain("absent.example"), ipdomains("absent.example"), domain("absent.example"), false, authic, authic, nil)
test(ipdomain("absent.example"), hostprefs(-1, "absent.example"), domain("absent.example"), false, authic, authic, nil)
// Followed CNAME, has no MX, non-existence of host will be found out later.
test(ipdomain("danglingcname.example"), ipdomains("absent.example"), domain("absent.example"), false, authic, authic, nil)
test(ipdomain("danglingcname.example"), hostprefs(-1, "absent.example"), domain("absent.example"), false, authic, authic, nil)
test(ipdomain("cnamelimit1.example"), nil, zerodom, true, authic, authic, errCNAMELimit)
test(ipdomain("cnameloop.example"), nil, zerodom, true, authic, authic, errCNAMELoop)
test(ipdomain("nullmx.example"), nil, zerodom, true, authic, authic, errNoMail)
@ -127,9 +127,9 @@ func TestGatherDestinations(t *testing.T) {
test(ipdomain("temperror-cname.example"), nil, zerodom, false, authic, authic, errDNS)
}
test(ipdomain("10.0.0.1"), ipdomains("10.0.0.1"), zerodom, false, false, false, nil)
test(ipdomain("cnameinauthentic.example"), ipdomains("mail.basic.example"), domain("basic.example"), false, false, false, nil)
test(ipdomain("cname-to-inauthentic.example"), ipdomains("mail.basic.example"), domain("basic.example"), false, true, false, nil)
test(ipdomain("10.0.0.1"), hostprefs(-1, "10.0.0.1"), zerodom, false, false, false, nil)
test(ipdomain("cnameinauthentic.example"), hostprefs(10, "mail.basic.example"), domain("basic.example"), false, false, false, nil)
test(ipdomain("cname-to-inauthentic.example"), hostprefs(10, "mail.basic.example"), domain("basic.example"), false, true, false, nil)
}
func TestGatherIPs(t *testing.T) {