feat: Implement trace command handshake to check whether capture perm…

…issions are available or not before switching to capture view

Signed-off-by: Felicitas Pojtinger <felicitas@pojtinger.com>

main.go

@@ -34,7 +34,7 @@ var (
 )
 
 func main() {
-	if trace := os.Getenv(backend.EnvTrace); trace == "true" {
+	if trace := os.Getenv(backend.TraceCommandEnv); trace == "true" {
 		flag.Parse()
 
 		if flag.NArg() < 2 {
@@ -50,15 +50,17 @@ func main() {
 		if err != nil {
 			// GoPacket doesn't export the permission error, so we need to compare error strings
 			if strings.HasSuffix(err.Error(), "(socket: Operation not permitted)") {
-				fmt.Println(errors.Join(errors.New("could not start capturing, capture permission denied"), err))
-
-				os.Exit(backend.PermissionDeniedExitCode)
+				fmt.Print(backend.TraceCommandHandshakeHandlePermissionDenied)
 			} else {
-				panic(err)
+				fmt.Print(backend.TraceCommandHandshakeHandleUnexpectedError)
 			}
+
+			panic(err)
 		}
 		defer handle.Close()
 
+		fmt.Print(backend.TraceCommandHandshakeHandleAcquired)
+
 		source := gopacket.NewPacketSource(handle, handle.LinkType())
 
 		encoder := json.NewEncoder(os.Stdout)

pkg/backend/server.go

@@ -35,15 +35,20 @@ import (
 )
 
 var (
-	ErrDatabaseNotInArchive = errors.New("database not in archive")
+	ErrDatabaseNotInArchive                     = errors.New("database not in archive")
+	ErrUnexpectedErrorWhileStartingTraceCommand = errors.New("unexpected error while starting trace command")
 )
 
 const (
 	flatpakSpawnCmd = "flatpak-spawn"
 
-	EnvTrace = "CONNMAPPER_TRACE"
+	TraceCommandEnv = "CONNMAPPER_TRACE"
 
-	PermissionDeniedExitCode = 13
+	traceCommandHandshakeLen = 2
+
+	TraceCommandHandshakeHandleAcquired         = "AQ"
+	TraceCommandHandshakeHandlePermissionDenied = "PD"
+	TraceCommandHandshakeHandleUnexpectedError  = "UE"
 )
 
 func lookupLocation(db *geoip2.Reader, ip net.IP) (
@@ -385,7 +390,7 @@ func (l *local) TraceDevice(ctx context.Context, device Device) error {
 	}
 
 	cmd := exec.Command(os.Args[0], device.PcapName, fmt.Sprintf("%v", device.MTU))
-	cmd.Env = append(cmd.Env, EnvTrace+"=true")
+	cmd.Env = append(cmd.Env, TraceCommandEnv+"=true")
 
 	stdout, err := cmd.StdoutPipe()
 	if err != nil {
@@ -396,10 +401,46 @@ func (l *local) TraceDevice(ctx context.Context, device Device) error {
 		return err
 	}
 
+	handshake := make([]byte, traceCommandHandshakeLen)
+	if _, err := stdout.Read(handshake); err != nil {
+		if cmd.Process != nil {
+			_ = cmd.Process.Kill()
+
+			_ = cmd.Wait()
+		}
+
+		return err
+	}
+
+	switch string(handshake) {
+	case TraceCommandHandshakeHandleAcquired:
+		break
+
+	case TraceCommandHandshakeHandlePermissionDenied:
+		if cmd.Process != nil {
+			_ = cmd.Process.Kill()
+
+			_ = cmd.Wait()
+		}
+
+		return l.RestartApp(ctx, true)
+
+	default:
+		if cmd.Process != nil {
+			_ = cmd.Process.Kill()
+
+			_ = cmd.Wait()
+		}
+
+		return errors.Join(ErrUnexpectedErrorWhileStartingTraceCommand, errors.New(string(handshake)))
+	}
+
 	go func() {
 		defer func() {
 			if cmd.Process != nil {
 				_ = cmd.Process.Kill()
+
+				_ = cmd.Wait()
 			}
 			_ = db.Close()
 
@@ -412,21 +453,8 @@ func (l *local) TraceDevice(ctx context.Context, device Device) error {
 		for {
 			var rawPacket Packet
 			if err := decoder.Decode(&rawPacket); err != nil {
-				if cmd.Process != nil {
-					_ = cmd.Process.Kill()
-
-					_ = cmd.Wait()
-				}
-
-				if cmd.ProcessState.ExitCode() == PermissionDeniedExitCode {
-					if err := l.RestartApp(ctx, true); err != nil {
-						log.Println("Could not restart app:", err)
-
-						return
-					}
-				}
 
-				log.Println("Could not capture:", err)
+				log.Println("Could not continue capturing:", err)
 
 				return
 			}