all: add router client info detection

This commit add the ability for ctrld to gather client information,
including mac/ip/hostname, and send to Control-D server through a
config per upstream.

 - Add send_client_info upstream config.
 - Read/Watch dnsmasq leases files on supported platforms.
 - Add corresponding client info to DoH query header

All of these only apply for Control-D upstream, though.

cmd/ctrld/dns_proxy.go

@@ -20,7 +20,13 @@ import (
 	"github.com/Control-D-Inc/ctrld/internal/router"
 )
 
-const staleTTL = 60 * time.Second
+const (
+	staleTTL = 60 * time.Second
+	// EDNS0_OPTION_MAC is dnsmasq EDNS0 code for adding mac option.
+	// https://thekelleys.org.uk/gitweb/?p=dnsmasq.git;a=blob;f=src/dns-protocol.h;h=76ac66a8c28317e9c121a74ab5fd0e20f6237dc8;hb=HEAD#l81
+	// This is also dns.EDNS0LOCALSTART, but define our own constant here for clarification.
+	EDNS0_OPTION_MAC = 0xFDE9
+)
 
 var osUpstreamConfig = &ctrld.UpstreamConfig{
 	Name:    "OS resolver",
@@ -230,6 +236,12 @@ func (p *prog) proxy(ctx context.Context, upstreams []string, failoverRcodes []i
 		return dnsResolver.Resolve(resolveCtx, msg)
 	}
 	resolve := func(n int, upstreamConfig *ctrld.UpstreamConfig, msg *dns.Msg) *dns.Msg {
+		if upstreamConfig.UpstreamSendClientInfo() {
+			ci := router.GetClientInfoByMac(macFromMsg(msg))
+			if ci != nil {
+				ctx = context.WithValue(ctx, ctrld.ClientInfoCtxKey{}, ci)
+			}
+		}
 		answer, err := resolve1(n, upstreamConfig, msg)
 		if err != nil {
 			ctrld.Log(ctx, mainLog.Debug().Err(err), "could not resolve query on first attempt, retrying...")
@@ -386,3 +398,17 @@ func dnsListenAddress(lc *ctrld.ListenerConfig) string {
 	}
 	return net.JoinHostPort(lc.IP, strconv.Itoa(lc.Port))
 }
+
+func macFromMsg(msg *dns.Msg) string {
+	if opt := msg.IsEdns0(); opt != nil {
+		for _, s := range opt.Option {
+			switch e := s.(type) {
+			case *dns.EDNS0_LOCAL:
+				if e.Code == EDNS0_OPTION_MAC {
+					return net.HardwareAddr(e.Data).String()
+				}
+			}
+		}
+	}
+	return ""
+}

cmd/ctrld/dns_proxy_test.go

@@ -155,3 +155,39 @@ func TestCache(t *testing.T) {
 	assert.Equal(t, answer1.Rcode, got1.Rcode)
 	assert.Equal(t, answer2.Rcode, got2.Rcode)
 }
+
+func Test_macFromMsg(t *testing.T) {
+	tests := []struct {
+		name    string
+		mac     string
+		wantMac bool
+	}{
+		{"has mac", "4c:20:b8:ab:87:1b", true},
+		{"no mac", "4c:20:b8:ab:87:1b", false},
+	}
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			hw, err := net.ParseMAC(tc.mac)
+			if err != nil {
+				t.Fatal(err)
+			}
+			m := new(dns.Msg)
+			m.SetQuestion(selfCheckFQDN+".", dns.TypeA)
+			o := &dns.OPT{Hdr: dns.RR_Header{Name: ".", Rrtype: dns.TypeOPT}}
+			if tc.wantMac {
+				ec1 := &dns.EDNS0_LOCAL{Code: EDNS0_OPTION_MAC, Data: hw}
+				o.Option = append(o.Option, ec1)
+			}
+			m.Extra = append(m.Extra, o)
+			got := macFromMsg(m)
+			if tc.wantMac && got != tc.mac {
+				t.Errorf("mismatch, want: %q, got: %q", tc.mac, got)
+			}
+			if !tc.wantMac && got != "" {
+				t.Errorf("unexpected mac: %q", got)
+			}
+		})
+	}
+}

cmd/ctrld/prog.go

@@ -139,6 +139,9 @@ func (p *prog) Stop(s service.Service) error {
 		return err
 	}
 	p.preStop()
+	if err := router.Stop(); err != nil {
+		mainLog.Warn().Err(err).Msg("problem occurred while stopping router")
+	}
 	mainLog.Info().Msg("Service stopped")
 	close(p.stopCh)
 	return nil