all: rework routers ntp waiting mechanism

Currently, on routers that require NTP waiting, ctrld makes the cleanup
process, and restart dnsmasq for restoring default DNS config, so ntpd
can query the NTP servers. It did work, but the code will depends on
router platforms.

Instead, we can spawn a plain DNS listener before PreRun on routers,
this listener will serve NTP dns queries and once ntp is configured, the
listener is terminated and ctrld will start serving using its configured
upstreams.

While at it, also fix the userHomeDir function on freshtomato, which
must return the binary directory for routers that requires JFFS.

cmd/ctrld/cli.go

@@ -165,9 +165,13 @@ func initCLI() {
 			initLogging()
 
 			if setupRouter {
-				if err := router.PreStart(); err != nil {
+				s, _ := runDNSServerForNTPD()
+				if err := router.PreRun(); err != nil {
 					mainLog.Fatal().Err(err).Msg("failed to perform router pre-start check")
 				}
+				if err := s.Shutdown(); err != nil {
+					mainLog.Fatal().Err(err).Msg("failed to shutdown dns server for ntpd")
+				}
 			}
 
 			processCDFlags()
@@ -909,7 +913,7 @@ func unsupportedPlatformHelp(cmd *cobra.Command) {
 
 func userHomeDir() (string, error) {
 	switch router.Name() {
-	case router.DDWrt, router.Merlin:
+	case router.DDWrt, router.Merlin, router.Tomato:
 		exe, err := os.Executable()
 		if err != nil {
 			return "", err

cmd/ctrld/dns_proxy.go

@@ -459,3 +459,45 @@ func runDNSServer(addr, network string, handler dns.Handler) (*dns.Server, <-cha
 	waitLock.Lock()
 	return s, errCh
 }
+
+func runDNSServerForNTPD() (*dns.Server, <-chan error) {
+	dnsResolver := ctrld.NewBootstrapResolver()
+	s := &dns.Server{
+		Addr: router.ListenAddress(),
+		Net:  "udp",
+		Handler: dns.HandlerFunc(func(w dns.ResponseWriter, m *dns.Msg) {
+			mainLog.Debug().Msg("Serving query for ntpd")
+			resolveCtx, cancel := context.WithCancel(context.Background())
+			defer cancel()
+			if osUpstreamConfig.Timeout > 0 {
+				timeoutCtx, cancel := context.WithTimeout(resolveCtx, time.Millisecond*time.Duration(osUpstreamConfig.Timeout))
+				defer cancel()
+				resolveCtx = timeoutCtx
+			}
+			answer, err := dnsResolver.Resolve(resolveCtx, m)
+			if err != nil {
+				mainLog.Error().Err(err).Msgf("could not resolve: %v", m)
+				return
+			}
+			if err := w.WriteMsg(answer); err != nil {
+				mainLog.Error().Err(err).Msg("runDNSServerForNTPD: failed to send DNS response")
+			}
+		}),
+	}
+
+	waitLock := sync.Mutex{}
+	waitLock.Lock()
+	s.NotifyStartedFunc = waitLock.Unlock
+
+	errCh := make(chan error)
+	go func() {
+		defer close(errCh)
+		if err := s.ListenAndServe(); err != nil {
+			waitLock.Unlock()
+			mainLog.Error().Err(err).Msgf("could not listen and serve on: %s", s.Addr)
+			errCh <- err
+		}
+	}()
+	waitLock.Lock()
+	return s, errCh
+}

internal/router/merlin.go

@@ -2,16 +2,11 @@ package router
 
 import (
 	"bytes"
-	"context"
-	"errors"
 	"fmt"
 	"os"
 	"os/exec"
 	"strings"
-	"time"
 	"unicode"
-
-	"tailscale.com/logtail/backoff"
 )
 
 func setupMerlin() error {
@@ -92,43 +87,3 @@ func merlinParsePostConf(buf []byte) []byte {
 	}
 	return buf
 }
-
-func merlinPreStart() (err error) {
-	pidFile := "/tmp/ctrld.pid"
-
-	// Remove pid file and trigger dnsmasq restart, so NTP can resolve
-	// server name and perform time synchronization.
-	pid, err := os.ReadFile(pidFile)
-	if err != nil {
-		return fmt.Errorf("PreStart: os.Readfile: %w", err)
-	}
-	if err := os.Remove(pidFile); err != nil {
-		return fmt.Errorf("PreStart: os.Remove: %w", err)
-	}
-	defer func() {
-		if werr := os.WriteFile(pidFile, pid, 0600); werr != nil {
-			err = errors.Join(err, werr)
-			return
-		}
-		if rerr := restartDNSMasq(); rerr != nil {
-			err = errors.Join(err, rerr)
-			return
-		}
-	}()
-	if err := restartDNSMasq(); err != nil {
-		return fmt.Errorf("PreStart: restartDNSMasqFn: %w", err)
-	}
-
-	// Wait until `ntp_ready=1` set.
-	b := backoff.NewBackoff("PreStart", func(format string, args ...any) {}, 10*time.Second)
-	for {
-		out, err := nvram("get", "ntp_ready")
-		if err != nil {
-			return fmt.Errorf("PreStart: nvram: %w", err)
-		}
-		if out == "1" {
-			return nil
-		}
-		b.BackOff(context.Background(), errors.New("ntp not ready"))
-	}
-}

internal/router/router.go

@@ -2,14 +2,18 @@ package router
 
 import (
 	"bytes"
+	"context"
 	"errors"
+	"fmt"
 	"os"
 	"os/exec"
 	"sync"
 	"sync/atomic"
+	"time"
 
 	"github.com/fsnotify/fsnotify"
 	"github.com/kardianos/service"
+	"tailscale.com/logtail/backoff"
 
 	"github.com/Control-D-Inc/ctrld"
 )
@@ -106,14 +110,23 @@ func ConfigureService(sc *service.Config) error {
 	return nil
 }
 
-// PreStart blocks until the router is ready for running ctrld.
-func PreStart() (err error) {
+// PreRun blocks until the router is ready for running ctrld.
+func PreRun() (err error) {
 	// On some routers, NTP may out of sync, so waiting for it to be ready.
 	switch Name() {
-	case Merlin:
-		return merlinPreStart()
-	case Tomato:
-		return tomatoPreStart()
+	case Merlin, Tomato:
+		// Wait until `ntp_ready=1` set.
+		b := backoff.NewBackoff("PreStart", func(format string, args ...any) {}, 10*time.Second)
+		for {
+			out, err := nvram("get", "ntp_ready")
+			if err != nil {
+				return fmt.Errorf("PreStart: nvram: %w", err)
+			}
+			if out == "1" {
+				return nil
+			}
+			b.BackOff(context.Background(), errors.New("ntp not ready"))
+		}
 	default:
 		return nil
 	}

internal/router/tomato.go

@@ -1,13 +1,8 @@
 package router
 
 import (
-	"context"
-	"errors"
 	"fmt"
 	"os/exec"
-	"time"
-
-	"tailscale.com/logtail/backoff"
 )
 
 const (
@@ -72,27 +67,6 @@ func cleanupTomato() error {
 	return nil
 }
 
-func tomatoPreStart() (err error) {
-	// cleanup to trigger dnsmasq restart, so NTP can resolve
-	// server name and perform time synchronization.
-	if err = cleanupTomato(); err != nil {
-		return err
-	}
-
-	// Wait until `ntp_ready=1` set.
-	b := backoff.NewBackoff("PreStart", func(format string, args ...any) {}, 10*time.Second)
-	for {
-		out, err := nvram("get", "ntp_ready")
-		if err != nil {
-			return fmt.Errorf("PreStart: nvram: %w", err)
-		}
-		if out == "1" {
-			return nil
-		}
-		b.BackOff(context.Background(), errors.New("ntp not ready"))
-	}
-}
-
 func tomatoRestartService(name string) error {
 	return tomatoRestartServiceWithKill(name, false)
 }

resolver.go

@@ -201,3 +201,17 @@ func lookupIP(domain string, timeout int, withBootstrapDNS bool) (ips []string)
 	}
 	return ips
 }
+
+// NewBootstrapResolver returns an OS resolver, which use following nameservers:
+//
+//   - ControlD bootstrap DNS server.
+//   - Gateway IP address (depends on OS).
+//   - Input servers.
+func NewBootstrapResolver(servers ...string) Resolver {
+	resolver := &osResolver{nameservers: nameservers()}
+	resolver.nameservers = append([]string{net.JoinHostPort(bootstrapDNS, "53")}, resolver.nameservers...)
+	for _, ns := range servers {
+		resolver.nameservers = append([]string{net.JoinHostPort(ns, "53")}, resolver.nameservers...)
+	}
+	return resolver
+}