cmd/cli: add nextdns mode

Adding --nextdns flag to "ctrld start" command for generating ctrld
config with nextdns resolver id, then use nextdns as an upstream.

cmd/cli/cli.go

@@ -158,6 +158,7 @@ func initCLI() {
 		Run: func(cmd *cobra.Command, args []string) {
 			checkStrFlagEmpty(cmd, cdUidFlagName)
 			checkStrFlagEmpty(cmd, cdOrgFlagName)
+			validateCdAndNextDNSFlags()
 			sc := &service.Config{}
 			*sc = *svcConfig
 			osArgs := os.Args[2:]
@@ -231,6 +232,15 @@ func initCLI() {
 
 			initLogging()
 
+			if nextdns != "" {
+				removeNextDNSFromArgs(sc)
+				generateNextDNSConfig()
+				updateListenerConfig()
+				if err := writeConfigFile(); err != nil {
+					mainLog.Load().Error().Err(err).Msg("failed to write config with NextDNS resolver")
+				}
+			}
+
 			// Explicitly passing config, so on system where home directory could not be obtained,
 			// or sub-process env is different with the parent, we still behave correctly and use
 			// the expected config file.
@@ -281,7 +291,7 @@ func initCLI() {
 			}
 		},
 	}
-	// Keep these flags in sync with runCmd above, except for "-d".
+	// Keep these flags in sync with runCmd above, except for "-d"/"--nextdns".
 	startCmd.Flags().StringVarP(&configPath, "config", "c", "", "Path to config file")
 	startCmd.Flags().StringVarP(&configBase64, "base64_config", "", "", "Base64 encoded config")
 	startCmd.Flags().StringVarP(&listenAddress, "listen", "", "", "Listener address and port, in format: address:port")
@@ -295,6 +305,7 @@ func initCLI() {
 	startCmd.Flags().BoolVarP(&cdDev, "dev", "", false, "Use Control D dev resolver/domain")
 	_ = startCmd.Flags().MarkHidden("dev")
 	startCmd.Flags().StringVarP(&iface, "iface", "", "", `Update DNS setting for iface, "auto" means the default interface gateway`)
+	startCmd.Flags().StringVarP(&nextdns, nextdnsFlagName, "", "", "NextDNS resolver id")
 
 	routerCmd := &cobra.Command{
 		Use: "setup",
@@ -1216,6 +1227,11 @@ func selfCheckStatus(s service.Service) service.Status {
 		return service.StatusUnknown
 	}
 
+	// Not a ctrld upstream, return status as-is.
+	if cfg.FirstUpstream().VerifyDomain() == "" {
+		return status
+	}
+
 	mainLog.Load().Debug().Msg("ctrld listener is ready")
 	mainLog.Load().Debug().Msg("performing self-check")
 	bo := backoff.NewBackoff("self-check", logf, 10*time.Second)
@@ -1489,6 +1505,7 @@ func mobileListenerPort() int {
 func updateListenerConfig() (updated bool) {
 	lcc := make(map[string]*listenerConfigCheck)
 	cdMode := cdUID != ""
+	nextdnsMode := nextdns != ""
 	for n, listener := range cfg.Listener {
 		lcc[n] = &listenerConfigCheck{}
 		if listener.IP == "" {
@@ -1500,7 +1517,8 @@ func updateListenerConfig() (updated bool) {
 			lcc[n].Port = true
 		}
 		// In cd mode, we always try to pick an ip:port pair to work.
-		if cdMode {
+		// Same if nextdns resolver is used.
+		if cdMode || nextdnsMode {
 			lcc[n].IP = true
 			lcc[n].Port = true
 		}
@@ -1801,3 +1819,32 @@ func checkStrFlagEmpty(cmd *cobra.Command, flagName string) {
 		mainLog.Load().Fatal().Msgf(`flag "--%s"" value must be non-empty`, fl.Name)
 	}
 }
+
+func validateCdAndNextDNSFlags() {
+	if (cdUID != "" || cdOrg != "") && nextdns != "" {
+		mainLog.Load().Fatal().Msgf("--%s/--%s could not be used with --%s", cdUidFlagName, cdOrgFlagName, nextdnsFlagName)
+	}
+}
+
+// removeNextDNSFromArgs removes the --nextdns from command line arguments.
+func removeNextDNSFromArgs(sc *service.Config) {
+	a := sc.Arguments[:0]
+	skip := false
+	for _, x := range sc.Arguments {
+		if skip {
+			skip = false
+			continue
+		}
+		// For "--nextdns XXX", skip it and mark next arg skipped.
+		if x == "--"+nextdnsFlagName {
+			skip = true
+			continue
+		}
+		// For "--nextdns=XXX", just skip it.
+		if strings.HasPrefix(x, "--"+nextdnsFlagName+"=") {
+			continue
+		}
+		a = append(a, x)
+	}
+	sc.Arguments = a
+}

cmd/cli/main.go

@@ -32,6 +32,7 @@ var (
 	cdDev             bool
 	iface             string
 	ifaceStartStop    string
+	nextdns           string
 
 	mainLog       atomic.Pointer[zerolog.Logger]
 	consoleWriter zerolog.ConsoleWriter
@@ -39,8 +40,9 @@ var (
 )
 
 const (
-	cdUidFlagName = "cd"
-	cdOrgFlagName = "cd-org"
+	cdUidFlagName   = "cd"
+	cdOrgFlagName   = "cd-org"
+	nextdnsFlagName = "nextdns"
 )
 
 func init() {

cmd/cli/nextdns.go

@@ -0,0 +1,31 @@
+package cli
+
+import (
+	"fmt"
+
+	"github.com/Control-D-Inc/ctrld"
+)
+
+const nextdnsURL = "https://dns.nextdns.io"
+
+func generateNextDNSConfig() {
+	if nextdns == "" {
+		return
+	}
+	mainLog.Load().Info().Msg("generating ctrld config for NextDNS resolver")
+	cfg = ctrld.Config{
+		Listener: map[string]*ctrld.ListenerConfig{
+			"0": {
+				IP:   "0.0.0.0",
+				Port: 53,
+			},
+		},
+		Upstream: map[string]*ctrld.UpstreamConfig{
+			"0": {
+				Type:     ctrld.ResolverTypeDOH3,
+				Endpoint: fmt.Sprintf("%s/%s", nextdnsURL, nextdns),
+				Timeout:  5000,
+			},
+		},
+	}
+}

config.go

@@ -323,7 +323,7 @@ func (uc *UpstreamConfig) UpstreamSendClientInfo() bool {
 	}
 	switch uc.Type {
 	case ResolverTypeDOH, ResolverTypeDOH3:
-		if uc.isControlD() {
+		if uc.isControlD() || uc.isNextDNS() {
 			return true
 		}
 	}
@@ -520,6 +520,16 @@ func (uc *UpstreamConfig) isControlD() bool {
 	return false
 }
 
+func (uc *UpstreamConfig) isNextDNS() bool {
+	domain := uc.Domain
+	if domain == "" {
+		if u, err := url.Parse(uc.Endpoint); err == nil {
+			domain = u.Hostname()
+		}
+	}
+	return domain == "dns.nextdns.io"
+}
+
 func (uc *UpstreamConfig) dohTransport(dnsType uint16) http.RoundTripper {
 	uc.transportOnce.Do(func() {
 		uc.SetupTransport()

doh.go

@@ -76,7 +76,6 @@ func newDohResolver(uc *UpstreamConfig) *dohResolver {
 		endpoint:          uc.u,
 		isDoH3:            uc.Type == ResolverTypeDOH3,
 		http3RoundTripper: uc.http3RoundTripper,
-		sendClientInfo:    uc.UpstreamSendClientInfo(),
 		uc:                uc,
 	}
 	return r
@@ -87,9 +86,9 @@ type dohResolver struct {
 	endpoint          *url.URL
 	isDoH3            bool
 	http3RoundTripper http.RoundTripper
-	sendClientInfo    bool
 }
 
+// Resolve performs DNS query with given DNS message using DOH protocol.
 func (r *dohResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, error) {
 	data, err := msg.Pack()
 	if err != nil {
@@ -106,7 +105,7 @@ func (r *dohResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, erro
 	if err != nil {
 		return nil, fmt.Errorf("could not create request: %w", err)
 	}
-	addHeader(ctx, req, r.sendClientInfo)
+	addHeader(ctx, req, r.uc)
 	dnsTyp := uint16(0)
 	if len(msg.Question) > 0 {
 		dnsTyp = msg.Question[0].Qtype
@@ -146,26 +145,19 @@ func (r *dohResolver) Resolve(ctx context.Context, msg *dns.Msg) (*dns.Msg, erro
 	return answer, nil
 }
 
-func addHeader(ctx context.Context, req *http.Request, sendClientInfo bool) {
+func addHeader(ctx context.Context, req *http.Request, uc *UpstreamConfig) {
 	req.Header.Set("Content-Type", headerApplicationDNS)
 	req.Header.Set("Accept", headerApplicationDNS)
-	req.Header.Set(dohOsHeader, dohOsHeaderValue())
 
 	printed := false
-	if sendClientInfo {
+	if uc.UpstreamSendClientInfo() {
 		if ci, ok := ctx.Value(ClientInfoCtxKey{}).(*ClientInfo); ok && ci != nil {
 			printed = ci.Mac != "" || ci.IP != "" || ci.Hostname != ""
-			if ci.Mac != "" {
-				req.Header.Set(dohMacHeader, ci.Mac)
-			}
-			if ci.IP != "" {
-				req.Header.Set(dohIPHeader, ci.IP)
-			}
-			if ci.Hostname != "" {
-				req.Header.Set(dohHostHeader, ci.Hostname)
-			}
-			if ci.Self {
-				req.Header.Set(dohOsHeader, dohOsHeaderValue())
+			switch {
+			case uc.isControlD():
+				addControlDHeaders(req, ci)
+			case uc.isNextDNS():
+				addNextDNSHeaders(req, ci)
 			}
 		}
 	}
@@ -173,3 +165,35 @@ func addHeader(ctx context.Context, req *http.Request, sendClientInfo bool) {
 		Log(ctx, ProxyLogger.Load().Debug().Interface("header", req.Header), "sending request header")
 	}
 }
+
+// addControlDHeaders set DoH/Doh3 HTTP request headers for ControlD upstream.
+func addControlDHeaders(req *http.Request, ci *ClientInfo) {
+	req.Header.Set(dohOsHeader, dohOsHeaderValue())
+	if ci.Mac != "" {
+		req.Header.Set(dohMacHeader, ci.Mac)
+	}
+	if ci.IP != "" {
+		req.Header.Set(dohIPHeader, ci.IP)
+	}
+	if ci.Hostname != "" {
+		req.Header.Set(dohHostHeader, ci.Hostname)
+	}
+	if ci.Self {
+		req.Header.Set(dohOsHeader, dohOsHeaderValue())
+	}
+}
+
+// addNextDNSHeaders set DoH/Doh3 HTTP request headers for nextdns upstream.
+// https://github.com/nextdns/nextdns/blob/v1.41.0/resolver/doh.go#L100
+func addNextDNSHeaders(req *http.Request, ci *ClientInfo) {
+	if ci.Mac != "" {
+		// https: //github.com/nextdns/nextdns/blob/v1.41.0/run.go#L543
+		req.Header.Set("X-Device-Model", "mac:"+ci.Mac[:8])
+	}
+	if ci.IP != "" {
+		req.Header.Set("X-Device-Ip", ci.IP)
+	}
+	if ci.Hostname != "" {
+		req.Header.Set("X-Device-Name", ci.Hostname)
+	}
+}