cmd/ctrld: add --iface for setting DNS on specific interface

internal/resolvconffile/dns.go

@@ -0,0 +1,35 @@
+//go:build !js && !windows
+
+package resolvconffile
+
+import (
+	"net"
+
+	"tailscale.com/net/dns/resolvconffile"
+)
+
+const resolvconfPath = "/etc/resolv.conf"
+
+func NameServersWithPort() []string {
+	c, err := resolvconffile.ParseFile(resolvconfPath)
+	if err != nil {
+		return nil
+	}
+	ns := make([]string, 0, len(c.Nameservers))
+	for _, nameserver := range c.Nameservers {
+		ns = append(ns, net.JoinHostPort(nameserver.String(), "53"))
+	}
+	return ns
+}
+
+func NameServers(_ string) []string {
+	c, err := resolvconffile.ParseFile(resolvconfPath)
+	if err != nil {
+		return nil
+	}
+	ns := make([]string, 0, len(c.Nameservers))
+	for _, nameserver := range c.Nameservers {
+		ns = append(ns, nameserver.String())
+	}
+	return ns
+}

internal/resolvconffile/dns_test.go

@@ -0,0 +1,13 @@
+package resolvconffile
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestNameServers(t *testing.T) {
+	ns := NameServers("")
+	require.NotNil(t, ns)
+	t.Log(ns)
+}