all: add pull API config based on special DNS query

For query domain that matches "uid.verify.controld.com" in cd mode, and
the uid has the same value with "--cd" flag, ctrld will fetch uid config
from ControlD API, using this config if valid.

This is useful for force syncing API without waiting until the API
reload ticker fire.

cmd/cli/cli.go

@@ -1141,6 +1141,7 @@ func run(appCallback *AppCallback, stopCh chan struct{}) {
 		reloadDoneCh:     make(chan struct{}),
 		dnsWatcherStopCh: make(chan struct{}),
 		apiReloadCh:      make(chan *ctrld.Config),
+		apiForceReloadCh: make(chan struct{}),
 		cfg:              &cfg,
 		appCallback:      appCallback,
 	}

cmd/cli/dns_proxy.go

@@ -151,6 +151,7 @@ func (p *prog) serveDNS(listenerNum string) error {
 				ufr:            ur,
 			})
 			go p.doSelfUninstall(pr.answer)
+
 			answer = pr.answer
 			rtt := time.Since(t)
 			ctrld.Log(ctx, mainLog.Load().Debug(), "received response of %d bytes in %s", answer.Len(), rtt)
@@ -168,6 +169,7 @@ func (p *prog) serveDNS(listenerNum string) error {
 		go func() {
 			p.WithLabelValuesInc(statsQueriesCount, labelValues...)
 			p.WithLabelValuesInc(statsClientQueriesCount, []string{ci.IP, ci.Mac, ci.Hostname}...)
+			p.forceFetchingAPI(domain)
 		}()
 		if err := w.WriteMsg(answer); err != nil {
 			ctrld.Log(ctx, mainLog.Load().Error().Err(err), "serveDNS: failed to send DNS response to client")
@@ -926,6 +928,41 @@ func (p *prog) performCaptivePortalDetection() {
 	mainLog.Load().Warn().Msg("captive portal login finished, stop leaking query")
 }
 
+// forceFetchingAPI sends signal to force syncing API config if run in cd mode,
+// and the domain == "cdUID.verify.controld.com"
+func (p *prog) forceFetchingAPI(domain string) {
+	if cdUID == "" {
+		return
+	}
+	resolverID, parent, _ := strings.Cut(domain, ".")
+	if resolverID != cdUID {
+		return
+	}
+	switch {
+	case cdDev && parent == "verify.controld.dev":
+		// match ControlD dev
+	case parent == "verify.controld.com":
+		// match ControlD
+	default:
+		return
+	}
+	_ = p.apiForceReloadGroup.DoChan("force_sync_api", func() (interface{}, error) {
+		p.apiForceReloadCh <- struct{}{}
+		// Wait here to prevent abusing API if we are flooded.
+		time.Sleep(timeDurationOrDefault(p.cfg.Service.ForceRefetchWaitTime, 30) * time.Second)
+		return nil, nil
+	})
+}
+
+// timeDurationOrDefault returns time duration value from n if not nil.
+// Otherwise, it returns time duration value defaultN.
+func timeDurationOrDefault(n *int, defaultN int) time.Duration {
+	if n != nil && *n > 0 {
+		return time.Duration(*n)
+	}
+	return time.Duration(defaultN)
+}
+
 // queryFromSelf reports whether the input IP is from device running ctrld.
 func queryFromSelf(ip string) bool {
 	netIP := netip.MustParseAddr(ip)

cmd/cli/prog.go

@@ -21,11 +21,11 @@ import (
 	"syscall"
 	"time"
 
-	"tailscale.com/net/netmon"
-
 	"github.com/kardianos/service"
 	"github.com/rs/zerolog"
 	"github.com/spf13/viper"
+	"golang.org/x/sync/singleflight"
+	"tailscale.com/net/netmon"
 	"tailscale.com/net/tsaddr"
 
 	"github.com/Control-D-Inc/ctrld"
@@ -69,19 +69,21 @@ var svcConfig = &service.Config{
 var useSystemdResolved = false
 
 type prog struct {
-	mu               sync.Mutex
-	waitCh           chan struct{}
-	stopCh           chan struct{}
-	reloadCh         chan struct{} // For Windows.
-	reloadDoneCh     chan struct{}
-	apiReloadCh      chan *ctrld.Config
-	logConn          net.Conn
-	cs               *controlServer
-	csSetDnsDone     chan struct{}
-	csSetDnsOk       bool
-	dnsWatchDogOnce  sync.Once
-	dnsWg            sync.WaitGroup
-	dnsWatcherStopCh chan struct{}
+	mu                  sync.Mutex
+	waitCh              chan struct{}
+	stopCh              chan struct{}
+	reloadCh            chan struct{} // For Windows.
+	reloadDoneCh        chan struct{}
+	apiReloadCh         chan *ctrld.Config
+	apiForceReloadCh    chan struct{}
+	apiForceReloadGroup singleflight.Group
+	logConn             net.Conn
+	cs                  *controlServer
+	csSetDnsDone        chan struct{}
+	csSetDnsOk          bool
+	dnsWatchDogOnce     sync.Once
+	dnsWg               sync.WaitGroup
+	dnsWatcherStopCh    chan struct{}
 
 	cfg                  *ctrld.Config
 	localUpstreams       []string
@@ -255,47 +257,48 @@ func (p *prog) apiConfigReload() {
 		return
 	}
 
-	secs := 3600
-	if p.cfg.Service.RefetchTime != nil && *p.cfg.Service.RefetchTime > 0 {
-		secs = *p.cfg.Service.RefetchTime
-	}
-
-	ticker := time.NewTicker(time.Duration(secs) * time.Second)
+	ticker := time.NewTicker(timeDurationOrDefault(p.cfg.Service.RefetchTime, 3600) * time.Second)
 	defer ticker.Stop()
 
 	logger := mainLog.Load().With().Str("mode", "api-reload").Logger()
 	logger.Debug().Msg("starting custom config reload timer")
 	lastUpdated := time.Now().Unix()
+
+	doReloadApiConfig := func(forced bool, logger zerolog.Logger) {
+		resolverConfig, err := controld.FetchResolverConfig(cdUID, rootCmd.Version, cdDev)
+		selfUninstallCheck(err, p, logger)
+		if err != nil {
+			logger.Warn().Err(err).Msg("could not fetch resolver config")
+			return
+		}
+
+		if resolverConfig.Ctrld.CustomConfig == "" {
+			return
+		}
+
+		if resolverConfig.Ctrld.CustomLastUpdate > lastUpdated || forced {
+			lastUpdated = time.Now().Unix()
+			cfg := &ctrld.Config{}
+			if err := validateCdRemoteConfig(resolverConfig, cfg); err != nil {
+				logger.Warn().Err(err).Msg("skipping invalid custom config")
+				if _, err := controld.UpdateCustomLastFailed(cdUID, rootCmd.Version, cdDev, true); err != nil {
+					logger.Error().Err(err).Msg("could not mark custom last update failed")
+				}
+				return
+			}
+			setListenerDefaultValue(cfg)
+			logger.Debug().Msg("custom config changes detected, reloading...")
+			p.apiReloadCh <- cfg
+		} else {
+			logger.Debug().Msg("custom config does not change")
+		}
+	}
 	for {
 		select {
+		case <-p.apiForceReloadCh:
+			doReloadApiConfig(true, logger.With().Bool("forced", true).Logger())
 		case <-ticker.C:
-			resolverConfig, err := controld.FetchResolverConfig(cdUID, rootCmd.Version, cdDev)
-			selfUninstallCheck(err, p, logger)
-			if err != nil {
-				logger.Warn().Err(err).Msg("could not fetch resolver config")
-				continue
-			}
-
-			if resolverConfig.Ctrld.CustomConfig == "" {
-				continue
-			}
-
-			if resolverConfig.Ctrld.CustomLastUpdate > lastUpdated {
-				lastUpdated = time.Now().Unix()
-				cfg := &ctrld.Config{}
-				if err := validateCdRemoteConfig(resolverConfig, cfg); err != nil {
-					logger.Warn().Err(err).Msg("skipping invalid custom config")
-					if _, err := controld.UpdateCustomLastFailed(cdUID, rootCmd.Version, cdDev, true); err != nil {
-						logger.Error().Err(err).Msg("could not mark custom last update failed")
-					}
-					break
-				}
-				setListenerDefaultValue(cfg)
-				logger.Debug().Msg("custom config changes detected, reloading...")
-				p.apiReloadCh <- cfg
-			} else {
-				logger.Debug().Msg("custom config does not change")
-			}
+			doReloadApiConfig(false, logger)
 		case <-p.stopCh:
 			return
 		}

config.go

@@ -217,6 +217,7 @@ type ServiceConfig struct {
 	DnsWatchdogEnabled      *bool          `mapstructure:"dns_watchdog_enabled" toml:"dns_watchdog_enabled,omitempty"`
 	DnsWatchdogInvterval    *time.Duration `mapstructure:"dns_watchdog_interval" toml:"dns_watchdog_interval,omitempty"`
 	RefetchTime             *int           `mapstructure:"refetch_time" toml:"refetch_time,omitempty"`
+	ForceRefetchWaitTime    *int           `mapstructure:"force_refetch_wait_time" toml:"force_refetch_wait_time,omitempty"`
 	Daemon                  bool           `mapstructure:"-" toml:"-"`
 	AllocateIP              bool           `mapstructure:"-" toml:"-"`
 }