cmd/ctrld: add self check for better error message reported

After telling service manager to start ctrld, performing self check
status by sending DNS query to ctrld listener. So if ctrld could not
start for any reason, an error message will be reported to user instead
of simply telling service started.

Updates #56

cmd/ctrld/cli.go

@@ -2,6 +2,7 @@ package main
 
 import (
 	"bytes"
+	"context"
 	"encoding/base64"
 	"errors"
 	"fmt"
@@ -14,12 +15,15 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
+	"time"
 
 	"github.com/go-playground/validator/v10"
 	"github.com/kardianos/service"
+	"github.com/miekg/dns"
 	"github.com/pelletier/go-toml/v2"
 	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
+	"tailscale.com/logtail/backoff"
 	"tailscale.com/net/interfaces"
 
 	"github.com/Control-D-Inc/ctrld"
@@ -27,6 +31,8 @@ import (
 	ctrldnet "github.com/Control-D-Inc/ctrld/internal/net"
 )
 
+const selfCheckFQDN = "verify.controld.com"
+
 var (
 	v                    = viper.NewWithOptions(viper.KeyDelimiter("::"))
 	defaultConfigWritten = false
@@ -234,8 +240,24 @@ func initCLI() {
 				{s.Start, true},
 			}
 			if doTasks(tasks) {
+				status, err := s.Status()
+				if err != nil {
+					mainLog.Warn().Err(err).Msg("could not get service status")
+					return
+				}
+
+				status = selfCheckStatus(status)
+				switch status {
+				case service.StatusRunning:
+					mainLog.Info().Msg("Service started")
+				default:
+					mainLog.Error().Msg("Service did not start, please check system/service log for details error")
+					if runtime.GOOS == "linux" {
+						prog.resetDNS()
+					}
+					os.Exit(1)
+				}
 				prog.setDNS()
-				mainLog.Info().Msg("Service started")
 			}
 		},
 	}
@@ -549,7 +571,7 @@ func processCDFlags() {
 		iface = "auto"
 	}
 	logger := mainLog.With().Str("mode", "cd").Logger()
-	logger.Info().Msg("fetching Controld-D configuration")
+	logger.Info().Msgf("fetching Controld D configuration from API: %s", cdUID)
 	resolverConfig, err := controld.FetchResolverConfig(cdUID)
 	if uer, ok := err.(*controld.UtilityErrorResponse); ok && uer.ErrorField.Code == controld.InvalidConfigCode {
 		s, err := service.New(&prog{}, svcConfig)
@@ -681,3 +703,27 @@ func defaultIfaceName() string {
 	}
 	return dri
 }
+
+func selfCheckStatus(status service.Status) service.Status {
+	c := new(dns.Client)
+	lc := cfg.Listener["0"]
+	bo := backoff.NewBackoff("self-check", logf, 10*time.Second)
+	bo.LogLongerThan = 500 * time.Millisecond
+	ctx := context.Background()
+	err := errors.New("query failed")
+	maxAttempts := 10
+	mainLog.Debug().Msg("Performing self-check")
+	for i := 0; i < maxAttempts; i++ {
+		m := new(dns.Msg)
+		m.SetQuestion(selfCheckFQDN+".", dns.TypeA)
+		m.RecursionDesired = true
+		r, _, _ := c.ExchangeContext(ctx, m, net.JoinHostPort(lc.IP, strconv.Itoa(lc.Port)))
+		if r != nil && r.Rcode == dns.RcodeSuccess && len(r.Answer) > 0 {
+			mainLog.Debug().Msgf("self-check against %q succeeded", selfCheckFQDN)
+			return status
+		}
+		bo.BackOff(ctx, err)
+	}
+	mainLog.Debug().Msgf("self-check against %q failed", selfCheckFQDN)
+	return service.StatusUnknown
+}

cmd/ctrld/os_linux.go

@@ -23,10 +23,6 @@ import (
 	"github.com/Control-D-Inc/ctrld/internal/resolvconffile"
 )
 
-var logf = func(format string, args ...any) {
-	mainLog.Debug().Msgf(format, args...)
-}
-
 // allocate loopback ip
 // sudo ip a add 127.0.0.2/24 dev lo
 func allocateIP(ip string) error {

cmd/ctrld/prog.go

@@ -16,6 +16,10 @@ import (
 	ctrldnet "github.com/Control-D-Inc/ctrld/internal/net"
 )
 
+var logf = func(format string, args ...any) {
+	mainLog.Debug().Msgf(format, args...)
+}
+
 var errWindowsAddrInUse = syscall.Errno(0x2740)
 
 var svcConfig = &service.Config{