Restore dns on unclean shutdown (#1494)

client/internal/dns/host_linux.go

@@ -4,7 +4,9 @@ package dns
 
 import (
 	"bufio"
+	"errors"
 	"fmt"
+	"io"
 	"os"
 	"strings"
 
@@ -19,8 +21,27 @@ const (
 	resolvConfManager
 )
 
+var ErrUnknownOsManagerType = errors.New("unknown os manager type")
+
 type osManagerType int
 
+func newOsManagerType(osManager string) (osManagerType, error) {
+	switch osManager {
+	case "netbird":
+		return fileManager, nil
+	case "file":
+		return netbirdManager, nil
+	case "networkManager":
+		return networkManager, nil
+	case "systemd":
+		return systemdManager, nil
+	case "resolvconf":
+		return resolvConfManager, nil
+	default:
+		return 0, ErrUnknownOsManagerType
+	}
+}
+
 func (t osManagerType) String() string {
 	switch t {
 	case netbirdManager:
@@ -38,13 +59,17 @@ func (t osManagerType) String() string {
 	}
 }
 
-func newHostManager(wgInterface WGIface) (hostManager, error) {
+func newHostManager(wgInterface string) (hostManager, error) {
 	osManager, err := getOSDNSManagerType()
 	if err != nil {
 		return nil, err
 	}
 
 	log.Debugf("discovered mode is: %s", osManager)
+	return newHostManagerFromType(wgInterface, osManager)
+}
+
+func newHostManagerFromType(wgInterface string, osManager osManagerType) (hostManager, error) {
 	switch osManager {
 	case networkManager:
 		return newNetworkManagerDbusConfigurator(wgInterface)
@@ -58,12 +83,15 @@ func newHostManager(wgInterface WGIface) (hostManager, error) {
 }
 
 func getOSDNSManagerType() (osManagerType, error) {
-
 	file, err := os.Open(defaultResolvConfPath)
 	if err != nil {
-		return 0, fmt.Errorf("unable to open %s for checking owner, got error: %s", defaultResolvConfPath, err)
+		return 0, fmt.Errorf("unable to open %s for checking owner, got error: %w", defaultResolvConfPath, err)
 	}
-	defer file.Close()
+	defer func() {
+		if err := file.Close(); err != nil {
+			log.Errorf("close file %s: %s", defaultResolvConfPath, err)
+		}
+	}()
 
 	scanner := bufio.NewScanner(file)
 	for scanner.Scan() {
@@ -101,6 +129,10 @@ func getOSDNSManagerType() (osManagerType, error) {
 			return resolvConfManager, nil
 		}
 	}
+	if err := scanner.Err(); err != nil && err != io.EOF {
+		return 0, fmt.Errorf("scan: %w", err)
+	}
+
 	return fileManager, nil
 }