Keep confiured nameservers as fallback (#1036)

* keep existing nameserver as fallback when adding netbird resolver

* fix resolvconf

* fix imports

client/internal/dns/file_linux.go

@@ -15,7 +15,8 @@ const (
 	fileGeneratedResolvConfSearchBeginContent = "search "
 	fileGeneratedResolvConfContentFormat      = fileGeneratedResolvConfContentHeader +
 		"\n# If needed you can restore the original file by copying back %s\n\nnameserver %s\n" +
-		fileGeneratedResolvConfSearchBeginContent + "%s\n"
+		fileGeneratedResolvConfSearchBeginContent + "%s\n\n" +
+		"%s\n"
 )
 
 const (
@@ -91,7 +92,12 @@ func (f *fileConfigurator) applyDNSConfig(config hostDNSConfig) error {
 		searchDomains += " " + dConf.domain
 		appendedDomains++
 	}
-	content := fmt.Sprintf(fileGeneratedResolvConfContentFormat, fileDefaultResolvConfBackupLocation, config.serverIP, searchDomains)
+
+	originalContent, err := os.ReadFile(fileDefaultResolvConfBackupLocation)
+	if err != nil {
+		log.Errorf("Could not read existing resolv.conf")
+	}
+	content := fmt.Sprintf(fileGeneratedResolvConfContentFormat, fileDefaultResolvConfBackupLocation, config.serverIP, searchDomains, string(originalContent))
 	err = writeDNSConfig(content, defaultResolvConfPath, f.originalPerms)
 	if err != nil {
 		err = f.restore()

client/internal/dns/host_darwin.go

@@ -182,12 +182,11 @@ func (s *systemConfigurator) addDNSState(state, domains, dnsServer string, port
 }
 
 func (s *systemConfigurator) addDNSSetupForAll(dnsServer string, port int) error {
-	primaryServiceKey := s.getPrimaryService()
+	primaryServiceKey, existingNameserver := s.getPrimaryService()
 	if primaryServiceKey == "" {
 		return fmt.Errorf("couldn't find the primary service key")
 	}
-
+	err := s.addDNSSetup(getKeyWithInput(primaryServiceSetupKeyFormat, primaryServiceKey), dnsServer, port, existingNameserver)
-	err := s.addDNSSetup(getKeyWithInput(primaryServiceSetupKeyFormat, primaryServiceKey), dnsServer, port)
 	if err != nil {
 		return err
 	}
@@ -196,27 +195,32 @@ func (s *systemConfigurator) addDNSSetupForAll(dnsServer string, port int) error
 	return nil
 }
 
-func (s *systemConfigurator) getPrimaryService() string {
+func (s *systemConfigurator) getPrimaryService() (string, string) {
 	line := buildCommandLine("show", globalIPv4State, "")
 	stdinCommands := wrapCommand(line)
 	b, err := runSystemConfigCommand(stdinCommands)
 	if err != nil {
 		log.Error("got error while sending the command: ", err)
-		return ""
+		return "", ""
 	}
 	scanner := bufio.NewScanner(bytes.NewReader(b))
+	primaryService := ""
+	router := ""
 	for scanner.Scan() {
 		text := scanner.Text()
 		if strings.Contains(text, "PrimaryService") {
-			return strings.TrimSpace(strings.Split(text, ":")[1])
+			primaryService = strings.TrimSpace(strings.Split(text, ":")[1])
+		}
+		if strings.Contains(text, "Router") {
+			router = strings.TrimSpace(strings.Split(text, ":")[1])
 		}
 	}
-	return ""
+	return primaryService, router
 }
 
-func (s *systemConfigurator) addDNSSetup(setupKey, dnsServer string, port int) error {
+func (s *systemConfigurator) addDNSSetup(setupKey, dnsServer string, port int, existingDNSServer string) error {
 	lines := buildAddCommandLine(keySupplementalMatchDomainsNoSearch, digitSymbol+strconv.Itoa(0))
-	lines += buildAddCommandLine(keyServerAddresses, arraySymbol+dnsServer)
+	lines += buildAddCommandLine(keyServerAddresses, arraySymbol+dnsServer+" "+existingDNSServer)
 	lines += buildAddCommandLine(keyServerPort, digitSymbol+strconv.Itoa(port))
 	addDomainCommand := buildCreateStateWithOperation(setupKey, lines)
 	stdinCommands := wrapCommand(addDomainCommand)

client/internal/dns/resolvconf_linux.go

@@ -4,6 +4,7 @@ package dns
 
 import (
 	"fmt"
+	"os"
 	"os/exec"
 	"strings"
 
@@ -59,7 +60,11 @@ func (r *resolvconf) applyDNSConfig(config hostDNSConfig) error {
 		appendedDomains++
 	}
 
-	content := fmt.Sprintf(fileGeneratedResolvConfContentFormat, fileDefaultResolvConfBackupLocation, config.serverIP, searchDomains)
+	originalContent, err := os.ReadFile(fileDefaultResolvConfBackupLocation)
+	if err != nil {
+		log.Errorf("Could not read existing resolv.conf")
+	}
+	content := fmt.Sprintf(fileGeneratedResolvConfContentFormat, fileDefaultResolvConfBackupLocation, config.serverIP, searchDomains, string(originalContent))
 
 	err = r.applyConfig(content)
 	if err != nil {

client/internal/dns/systemd_linux.go

@@ -13,8 +13,6 @@ import (
 	"github.com/miekg/dns"
 	log "github.com/sirupsen/logrus"
 	"golang.org/x/sys/unix"
-
-	nbdns "github.com/netbirdio/netbird/dns"
 )
 
 const (
@@ -123,10 +121,6 @@ func (s *systemdDbusConfigurator) applyDNSConfig(config hostDNSConfig) error {
 		if err != nil {
 			return fmt.Errorf("setting link as default dns router, failed with error: %s", err)
 		}
-		domainsInput = append(domainsInput, systemdDbusLinkDomainsInput{
-			Domain:    nbdns.RootZone,
-			MatchOnly: true,
-		})
 		s.routingAll = true
 	} else if s.routingAll {
 		log.Infof("removing %s:%d as main DNS forwarder for this peer", config.serverIP, config.serverPort)