all: preserve search domains settings

So bare hostname will be resolved as expected when ctrld is running.

cmd/cli/os_darwin.go

@@ -47,6 +47,9 @@ func setDnsIgnoreUnusableInterface(iface *net.Interface, nameservers []string) e
 // networksetup -setdnsservers Wi-Fi 8.8.8.8 1.1.1.1
 // TODO(cuonglm): use system API
 func setDNS(iface *net.Interface, nameservers []string) error {
+	// Note that networksetup won't modify search domains settings,
+	// This assignment is just a placeholder to silent linter.
+	_ = searchDomains
 	cmd := "networksetup"
 	args := []string{"-setdnsservers", iface.Name}
 	args = append(args, nameservers...)
@@ -88,7 +91,7 @@ func restoreDNS(iface *net.Interface) (err error) {
 }
 
 func currentDNS(_ *net.Interface) []string {
-	return resolvconffile.NameServers("")
+	return resolvconffile.NameServers()
 }
 
 // currentStaticDNS returns the current static DNS settings of given interface.

cmd/cli/os_freebsd.go

@@ -7,6 +7,7 @@ import (
 
 	"tailscale.com/control/controlknobs"
 	"tailscale.com/health"
+	"tailscale.com/util/dnsname"
 
 	"github.com/Control-D-Inc/ctrld/internal/dns"
 	"github.com/Control-D-Inc/ctrld/internal/resolvconffile"
@@ -50,7 +51,17 @@ func setDNS(iface *net.Interface, nameservers []string) error {
 		ns = append(ns, netip.MustParseAddr(nameserver))
 	}
 
-	if err := r.SetDNS(dns.OSConfig{Nameservers: ns}); err != nil {
+	osConfig := dns.OSConfig{
+		Nameservers:   ns,
+		SearchDomains: []dnsname.FQDN{},
+	}
+	if sds, err := searchDomains(); err == nil {
+		osConfig.SearchDomains = sds
+	} else {
+		mainLog.Load().Debug().Err(err).Msg("failed to get search domains list")
+	}
+
+	if err := r.SetDNS(osConfig); err != nil {
 		mainLog.Load().Error().Err(err).Msg("failed to set DNS")
 		return err
 	}
@@ -83,7 +94,7 @@ func restoreDNS(iface *net.Interface) (err error) {
 }
 
 func currentDNS(_ *net.Interface) []string {
-	return resolvconffile.NameServers("")
+	return resolvconffile.NameServers()
 }
 
 // currentStaticDNS returns the current static DNS settings of given interface.

cmd/cli/os_linux.go

@@ -71,6 +71,11 @@ func setDNS(iface *net.Interface, nameservers []string) error {
 		Nameservers:   ns,
 		SearchDomains: []dnsname.FQDN{},
 	}
+	if sds, err := searchDomains(); err == nil {
+		osConfig.SearchDomains = sds
+	} else {
+		mainLog.Load().Debug().Err(err).Msg("failed to get search domains list")
+	}
 	trySystemdResolve := false
 	if err := r.SetDNS(osConfig); err != nil {
 		if strings.Contains(err.Error(), "Rejected send message") &&
@@ -196,7 +201,8 @@ func restoreDNS(iface *net.Interface) (err error) {
 }
 
 func currentDNS(iface *net.Interface) []string {
-	for _, fn := range []getDNS{getDNSByResolvectl, getDNSBySystemdResolved, getDNSByNmcli, resolvconffile.NameServers} {
+	resolvconfFunc := func(_ string) []string { return resolvconffile.NameServers() }
+	for _, fn := range []getDNS{getDNSByResolvectl, getDNSBySystemdResolved, getDNSByNmcli, resolvconfFunc} {
 		if ns := fn(iface.Name); len(ns) > 0 {
 			return ns
 		}

cmd/cli/os_windows.go

@@ -100,6 +100,10 @@ func setDNS(iface *net.Interface, nameservers []string) error {
 		}
 	}
 
+	// Note that Windows won't modify the current search domains if passing nil to luid.SetDNS function.
+	// searchDomains is still implemented for Windows just in case Windows API changes in future versions.
+	_ = searchDomains
+
 	if len(serversV4) == 0 && len(serversV6) == 0 {
 		return errors.New("invalid DNS nameservers")
 	}

cmd/cli/search_domains_unix.go

@@ -0,0 +1,14 @@
+//go:build unix
+
+package cli
+
+import (
+	"tailscale.com/util/dnsname"
+
+	"github.com/Control-D-Inc/ctrld/internal/resolvconffile"
+)
+
+// searchDomains returns the current search domains config.
+func searchDomains() ([]dnsname.FQDN, error) {
+	return resolvconffile.SearchDomains()
+}

cmd/cli/search_domains_windows.go

@@ -0,0 +1,43 @@
+package cli
+
+import (
+	"fmt"
+	"syscall"
+
+	"golang.zx2c4.com/wireguard/windows/tunnel/winipcfg"
+	"tailscale.com/util/dnsname"
+)
+
+// searchDomains returns the current search domains config.
+func searchDomains() ([]dnsname.FQDN, error) {
+	flags := winipcfg.GAAFlagIncludeGateways |
+		winipcfg.GAAFlagIncludePrefix
+
+	aas, err := winipcfg.GetAdaptersAddresses(syscall.AF_UNSPEC, flags)
+	if err != nil {
+		return nil, fmt.Errorf("winipcfg.GetAdaptersAddresses: %w", err)
+	}
+
+	var sds []dnsname.FQDN
+	for _, aa := range aas {
+		if aa.OperStatus != winipcfg.IfOperStatusUp {
+			continue
+		}
+
+		// Skip if software loopback or other non-physical types
+		// This is to avoid the "Loopback Pseudo-Interface 1" issue we see on windows
+		if aa.IfType == winipcfg.IfTypeSoftwareLoopback {
+			continue
+		}
+
+		for a := aa.FirstDNSSuffix; a != nil; a = a.Next {
+			d, err := dnsname.ToFQDN(a.String())
+			if err != nil {
+				mainLog.Load().Debug().Err(err).Msgf("failed to parse domain: %s", a.String())
+				continue
+			}
+			sds = append(sds, d)
+		}
+	}
+	return sds, nil
+}

internal/resolvconffile/dns.go

@@ -6,6 +6,7 @@ import (
 	"net"
 
 	"tailscale.com/net/dns/resolvconffile"
+	"tailscale.com/util/dnsname"
 )
 
 const resolvconfPath = "/etc/resolv.conf"
@@ -22,7 +23,7 @@ func NameServersWithPort() []string {
 	return ns
 }
 
-func NameServers(_ string) []string {
+func NameServers() []string {
 	c, err := resolvconffile.ParseFile(resolvconfPath)
 	if err != nil {
 		return nil
@@ -33,3 +34,12 @@ func NameServers(_ string) []string {
 	}
 	return ns
 }
+
+// SearchDomains returns the current search domains config in /etc/resolv.conf file.
+func SearchDomains() ([]dnsname.FQDN, error) {
+	c, err := resolvconffile.ParseFile(resolvconfPath)
+	if err != nil {
+		return nil, err
+	}
+	return c.SearchDomains, nil
+}

internal/resolvconffile/dns_test.go

@@ -9,7 +9,7 @@ import (
 )
 
 func TestNameServers(t *testing.T) {
-	ns := NameServers("")
+	ns := NameServers()
 	require.NotNil(t, ns)
 	t.Log(ns)
 }

nameservers_unix.go

@@ -14,7 +14,7 @@ import (
 
 // currentNameserversFromResolvconf returns the current nameservers set from /etc/resolv.conf file.
 func currentNameserversFromResolvconf() []string {
-	return resolvconffile.NameServers("")
+	return resolvconffile.NameServers()
 }
 
 // dnsFromResolvConf reads usable nameservers from /etc/resolv.conf file.
@@ -34,7 +34,7 @@ func dnsFromResolvConf() []string {
 			time.Sleep(retryInterval)
 		}
 
-		nss := resolvconffile.NameServers("")
+		nss := resolvconffile.NameServers()
 		var localDNS []string
 		seen := make(map[string]bool)