From a814715ef874ee877d2aebc726f1176b1f844331 Mon Sep 17 00:00:00 2001
From: Maycon Santos <mlsmaycon@gmail.com>
Date: Tue, 29 Nov 2022 14:51:18 +0100
Subject: [PATCH] Add resolvconf configurator for linux (#592)

---
 client/internal/dns/file_linux.go       |  4 +-
 client/internal/dns/host_linux.go       |  2 +
 client/internal/dns/resolvconf_linux.go | 84 +++++++++++++++++++++++++
 3 files changed, 88 insertions(+), 2 deletions(-)
 create mode 100644 client/internal/dns/resolvconf_linux.go

diff --git a/client/internal/dns/file_linux.go b/client/internal/dns/file_linux.go
index ad6e3a37f..b9a7f4804 100644
--- a/client/internal/dns/file_linux.go
+++ b/client/internal/dns/file_linux.go
@@ -44,7 +44,7 @@ func (f *fileConfigurator) applyDNSConfig(config hostDNSConfig) error {
 				return fmt.Errorf("unable to configure DNS for this peer using file manager without a Primary nameserver group. Restoring the original file return err: %s", err)
 			}
 		}
-		return fmt.Errorf("unable to configure DNS for this peer using file manager without a Primary nameserver group")
+		return fmt.Errorf("unable to configure DNS for this peer using file manager without a nameserver group with all domains configured")
 	}
 	managerType, err := getOSDNSManagerType()
 	if err != nil {
@@ -92,7 +92,7 @@ func (f *fileConfigurator) applyDNSConfig(config hostDNSConfig) error {
 		}
 		return err
 	}
-	log.Infof("created a NetBird managed %s file with your DNS settings", defaultResolvConfPath)
+	log.Infof("created a NetBird managed %s file with your DNS settings. Added %d search domains. Search list: %s", defaultResolvConfPath, appendedDomains, searchDomains)
 	return nil
 }
 
diff --git a/client/internal/dns/host_linux.go b/client/internal/dns/host_linux.go
index 368c7e35e..e411280cc 100644
--- a/client/internal/dns/host_linux.go
+++ b/client/internal/dns/host_linux.go
@@ -35,6 +35,8 @@ func newHostManager(wgInterface *iface.WGIface) (hostManager, error) {
 		return newNetworkManagerDbusConfigurator(wgInterface)
 	case systemdManager:
 		return newSystemdDbusConfigurator(wgInterface)
+	case resolvConfManager:
+		return newResolvConfConfigurator(wgInterface)
 	default:
 		return newFileConfigurator()
 	}
diff --git a/client/internal/dns/resolvconf_linux.go b/client/internal/dns/resolvconf_linux.go
new file mode 100644
index 000000000..7bd4511ac
--- /dev/null
+++ b/client/internal/dns/resolvconf_linux.go
@@ -0,0 +1,84 @@
+package dns
+
+import (
+	"fmt"
+	"github.com/netbirdio/netbird/iface"
+	log "github.com/sirupsen/logrus"
+	"os/exec"
+	"strings"
+)
+
+const resolvconfCommand = "resolvconf"
+
+type resolvconf struct {
+	ifaceName string
+}
+
+func newResolvConfConfigurator(wgInterface *iface.WGIface) (hostManager, error) {
+	return &resolvconf{
+		ifaceName: wgInterface.GetName(),
+	}, nil
+}
+
+func (r *resolvconf) applyDNSConfig(config hostDNSConfig) error {
+	var err error
+	if !config.routeAll {
+		err = r.restoreHostDNS()
+		if err != nil {
+			log.Error(err)
+		}
+		return fmt.Errorf("unable to configure DNS for this peer using resolvconf manager without a nameserver group with all domains configured")
+	}
+
+	var searchDomains string
+	appendedDomains := 0
+	for _, dConf := range config.domains {
+		if dConf.matchOnly {
+			continue
+		}
+
+		if appendedDomains >= fileMaxNumberOfSearchDomains {
+			// lets log all skipped domains
+			log.Infof("already appended %d domains to search list. Skipping append of %s domain", fileMaxNumberOfSearchDomains, dConf.domain)
+			continue
+		}
+
+		if fileSearchLineBeginCharCount+len(searchDomains) > fileMaxLineCharsLimit {
+			// lets log all skipped domains
+			log.Infof("search list line is larger than %d characters. Skipping append of %s domain", fileMaxLineCharsLimit, dConf.domain)
+			continue
+		}
+
+		searchDomains += " " + dConf.domain
+		appendedDomains++
+	}
+
+	content := fmt.Sprintf(fileGeneratedResolvConfContentFormat, fileDefaultResolvConfBackupLocation, config.serverIP, searchDomains)
+
+	err = r.applyConfig(content)
+	if err != nil {
+		return err
+	}
+
+	log.Infof("added %d search domains. Search list: %s", appendedDomains, searchDomains)
+	return nil
+}
+
+func (r *resolvconf) restoreHostDNS() error {
+	cmd := exec.Command(resolvconfCommand, "-f", "-d", r.ifaceName)
+	_, err := cmd.Output()
+	if err != nil {
+		return fmt.Errorf("got an error while removing resolvconf configuration for %s interface, error: %s", r.ifaceName, err)
+	}
+	return nil
+}
+
+func (r *resolvconf) applyConfig(content string) error {
+	cmd := exec.Command(resolvconfCommand, "-x", "-a", r.ifaceName)
+	cmd.Stdin = strings.NewReader(content)
+	_, err := cmd.Output()
+	if err != nil {
+		return fmt.Errorf("got an error while appying resolvconf configuration for %s interface, error: %s", r.ifaceName, err)
+	}
+	return nil
+}