TUN-10387: Add no-prechecks flag

Add a new no-prechecks flag to cloudflared. This will allow skipping connectivity pre-checks at startup.

cmd/cloudflared/flags/flags.go

@@ -120,6 +120,9 @@ const (
 	// NoAutoUpdate is the command line flag to disable cloudflared from checking for updates
 	NoAutoUpdate = "no-autoupdate"
 
+	// NoPrechecks is the command line flag to skip connectivity pre-checks at startup.
+	NoPrechecks = "no-prechecks"
+
 	// LogLevel is the command line flag for the cloudflared logging level
 	LogLevel = "loglevel"
 

cmd/cloudflared/tunnel/cmd.go

@@ -77,6 +77,7 @@ var (
 		"config",
 		cfdflags.AutoUpdateFreq,
 		cfdflags.NoAutoUpdate,
+		cfdflags.NoPrechecks,
 		cfdflags.Metrics,
 		"pidfile",
 		"url",
@@ -881,6 +882,13 @@ func configureCloudflaredFlags(shouldHide bool) []cli.Flag {
 			Value:   false,
 			Hidden:  shouldHide,
 		}),
+		altsrc.NewBoolFlag(&cli.BoolFlag{
+			Name:    cfdflags.NoPrechecks,
+			Usage:   "Skip connectivity pre-checks at startup.",
+			EnvVars: []string{"TUNNEL_NO_PRECHECKS"},
+			Value:   false,
+			Hidden:  shouldHide,
+		}),
 		altsrc.NewStringFlag(&cli.StringFlag{
 			Name:  cfdflags.Metrics,
 			Value: metrics.GetMetricsDefaultAddress(metrics.Runtime),

cmd/cloudflared/tunnel/configuration.go

@@ -261,6 +261,7 @@ func prepareTunnelConfig(
 		DisableQUICPathMTUDiscovery:         c.Bool(flags.QuicDisablePathMTUDiscovery),
 		QUICConnectionLevelFlowControlLimit: c.Uint64(flags.QuicConnLevelFlowControlLimit),
 		QUICStreamLevelFlowControlLimit:     c.Uint64(flags.QuicStreamLevelFlowControlLimit),
+		NoPrechecks:                         c.Bool(flags.NoPrechecks),
 		OriginDNSService:                    dnsService,
 		OriginDialerService:                 originDialerService,
 	}
@@ -300,7 +301,7 @@ func gracePeriod(c *cli.Context) (time.Duration, error) {
 }
 
 func isRunningFromTerminal() bool {
-	return term.IsTerminal(int(os.Stdout.Fd()))
+	return term.IsTerminal(int(os.Stdout.Fd())) // nolint:gosec
 }
 
 // ParseConfigIPVersion returns the IP version from possible expected values from config
@@ -341,7 +342,7 @@ func testIPBindable(ip net.IP) error {
 	if err != nil {
 		return err
 	}
-	listener.Close()
+	_ = listener.Close()
 	return nil
 }
 
@@ -503,7 +504,7 @@ func findLocalAddr(dst net.IP, port int) (netip.Addr, error) {
 	if err != nil {
 		return netip.Addr{}, err
 	}
-	defer udpConn.Close()
+	defer func() { _ = udpConn.Close() }()
 	localAddrPort, err := netip.ParseAddrPort(udpConn.LocalAddr().String())
 	if err != nil {
 		return netip.Addr{}, err

supervisor/tunnel.go

@@ -61,6 +61,9 @@ type TunnelConfig struct {
 
 	NeedPQ bool
 
+	// NoPrechecks disables connectivity pre-checks at startup.
+	NoPrechecks bool
+
 	NamedTunnel         *connection.TunnelProperties
 	ProtocolSelector    connection.ProtocolSelector
 	EdgeTLSConfigs      map[connection.Protocol]*tls.Config