From f90c9c91d2bc9e2642260b0c1bb332a5616701cf Mon Sep 17 00:00:00 2001
From: Viktor Liu <viktor@netbird.io>
Date: Sat, 11 Jan 2025 23:02:32 +0100
Subject: [PATCH] Support non-openresolv for DNS on Linux

---
 client/internal/dns/resolvconf_unix.go | 72 +++++++++++++++++++++++---
 1 file changed, 66 insertions(+), 6 deletions(-)

diff --git a/client/internal/dns/resolvconf_unix.go b/client/internal/dns/resolvconf_unix.go
index a5d1cc8a225..6b5fdaf8698 100644
--- a/client/internal/dns/resolvconf_unix.go
+++ b/client/internal/dns/resolvconf_unix.go
@@ -7,6 +7,7 @@ import (
 	"fmt"
 	"net/netip"
 	"os/exec"
+	"strings"
 
 	log "github.com/sirupsen/logrus"
 
@@ -15,23 +16,64 @@ import (
 
 const resolvconfCommand = "resolvconf"
 
+// resolvconfType represents the type of resolvconf implementation
+type resolvconfType int
+
+func (r resolvconfType) String() string {
+	switch r {
+	case typeOpenresolv:
+		return "openresolv"
+	case typeResolvconf:
+		return "resolvconf"
+	default:
+		return "unknown"
+	}
+}
+
+const (
+	typeOpenresolv resolvconfType = iota
+	typeResolvconf
+)
+
 type resolvconf struct {
 	ifaceName string
+	implType  resolvconfType
 
 	originalSearchDomains []string
 	originalNameServers   []string
 	othersConfigs         []string
 }
 
-// supported "openresolv" only
+func detectResolvconfType() (resolvconfType, error) {
+	cmd := exec.Command(resolvconfCommand, "--version")
+	out, err := cmd.Output()
+	if err != nil {
+		return typeOpenresolv, fmt.Errorf("failed to determine resolvconf type: %w", err)
+	}
+
+	if strings.Contains(string(out), "openresolv") {
+		return typeOpenresolv, nil
+	}
+	return typeResolvconf, nil
+}
+
 func newResolvConfConfigurator(wgInterface string) (*resolvconf, error) {
 	resolvConfEntries, err := parseDefaultResolvConf()
 	if err != nil {
 		log.Errorf("could not read original search domains from %s: %s", defaultResolvConfPath, err)
 	}
 
+	implType, err := detectResolvconfType()
+	if err != nil {
+		log.Warnf("failed to detect resolvconf type, defaulting to openresolv: %v", err)
+		implType = typeOpenresolv
+	} else {
+		log.Infof("detected resolvconf type: %v", implType)
+	}
+
 	return &resolvconf{
 		ifaceName:             wgInterface,
+		implType:              implType,
 		originalSearchDomains: resolvConfEntries.searchDomains,
 		originalNameServers:   resolvConfEntries.nameServers,
 		othersConfigs:         resolvConfEntries.others,
@@ -80,8 +122,15 @@ func (r *resolvconf) applyDNSConfig(config HostDNSConfig, stateManager *stateman
 }
 
 func (r *resolvconf) restoreHostDNS() error {
-	// openresolv only, debian resolvconf doesn't support "-f"
-	cmd := exec.Command(resolvconfCommand, "-f", "-d", r.ifaceName)
+	var cmd *exec.Cmd
+
+	switch r.implType {
+	case typeOpenresolv:
+		cmd = exec.Command(resolvconfCommand, "-f", "-d", r.ifaceName)
+	case typeResolvconf:
+		cmd = exec.Command(resolvconfCommand, "-d", r.ifaceName)
+	}
+
 	_, err := cmd.Output()
 	if err != nil {
 		return fmt.Errorf("removing resolvconf configuration for %s interface: %w", r.ifaceName, err)
@@ -91,10 +140,21 @@ func (r *resolvconf) restoreHostDNS() error {
 }
 
 func (r *resolvconf) applyConfig(content bytes.Buffer) error {
-	// openresolv only, debian resolvconf doesn't support "-x"
-	cmd := exec.Command(resolvconfCommand, "-x", "-a", r.ifaceName)
+	var cmd *exec.Cmd
+
+	switch r.implType {
+	case typeOpenresolv:
+		// OpenResolv supports exclusive mode with -x
+		cmd = exec.Command(resolvconfCommand, "-x", "-a", r.ifaceName)
+	case typeResolvconf:
+		cmd = exec.Command(resolvconfCommand, "-a", r.ifaceName)
+	default:
+		return fmt.Errorf("unsupported resolvconf type: %v", r.implType)
+	}
+
 	cmd.Stdin = &content
-	_, err := cmd.Output()
+	out, err := cmd.Output()
+	log.Tracef("resolvconf output: %s", out)
 	if err != nil {
 		return fmt.Errorf("applying resolvconf configuration for %s interface: %w", r.ifaceName, err)
 	}