wgengine/router/dns: create

Signed-off-by: Dmytro Shynkevych <dmytro@tailscale.com>

wgengine/router/dns/config.go

@@ -2,23 +2,29 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-package router
+package dns
 
 import (
 	"inet.af/netaddr"
 )
 
-// DNSConfig is the subset of Config that contains DNS parameters.
+// Config is the subset of router.Config that contains DNS parameters.
 type DNSConfig struct {
 	// Nameservers are the IP addresses of the nameservers to use.
 	Nameservers []netaddr.IP
 	// Domains are the search domains to use.
 	Domains []string
+	// PerDomain indicates whether it is preferred to use Nameservers
+	// only for queries for subdomains of Domains.
+	//
+	// Note that Nameservers may still be applied to all queries
+	// if the selected configuration mode does not support per-domain settings.
+	PerDomain bool
 }
 
 // EquivalentTo determines whether its argument and receiver
 // represent equivalent DNS configurations (then DNS reconfig is a no-op).
-func (lhs DNSConfig) EquivalentTo(rhs DNSConfig) bool {
+func (lhs Config) EquivalentTo(rhs Config) bool {
 	if len(lhs.Nameservers) != len(rhs.Nameservers) {
 		return false
 	}
@@ -27,6 +33,10 @@ func (lhs DNSConfig) EquivalentTo(rhs DNSConfig) bool {
 		return false
 	}
 
+	if lhs.PerDomain != rhs.PerDomain {
+		return false
+	}
+
 	// With how we perform resolution order shouldn't matter,
 	// but it is unlikely that we will encounter different orders.
 	for i, server := range lhs.Nameservers {
@@ -35,6 +45,7 @@ func (lhs DNSConfig) EquivalentTo(rhs DNSConfig) bool {
 		}
 	}
 
+	// The order of domains, on the other hand, is significant.
 	for i, domain := range lhs.Domains {
 		if rhs.Domains[i] != domain {
 			return false

wgengine/router/dns/direct.go

@@ -25,8 +25,8 @@ const (
 	resolvConf = "/etc/resolv.conf"
 )
 
-// dnsWriteConfig writes DNS configuration in resolv.conf format to the given writer.
-func dnsWriteConfig(w io.Writer, servers []netaddr.IP, domains []string) {
+// writeResolvConf writes DNS configuration in resolv.conf format to the given writer.
+func writeResolvConf(w io.Writer, servers []netaddr.IP, domains []string) {
 	io.WriteString(w, "# resolv.conf(5) file generated by tailscale\n")
 	io.WriteString(w, "# DO NOT EDIT THIS FILE BY HAND -- CHANGES WILL BE OVERWRITTEN\n\n")
 	for _, ns := range servers {
@@ -44,8 +44,8 @@ func dnsWriteConfig(w io.Writer, servers []netaddr.IP, domains []string) {
 	}
 }
 
-// dnsReadConfig reads DNS configuration from /etc/resolv.conf.
-func dnsReadConfig() (DNSConfig, error) {
+// readResolvConf reads DNS configuration from /etc/resolv.conf.
+func readResolvConf() (DNSConfig, error) {
 	var config DNSConfig
 
 	f, err := os.Open("/etc/resolv.conf")
@@ -89,7 +89,7 @@ func dnsReadConfig() (DNSConfig, error) {
 func dnsDirectUp(config DNSConfig) error {
 	// Write the tsConf file.
 	buf := new(bytes.Buffer)
-	dnsWriteConfig(buf, config.Nameservers, config.Domains)
+	writeResolvConf(buf, config.Nameservers, config.Domains)
 	if err := atomicfile.WriteFile(tsConf, buf.Bytes(), 0644); err != nil {
 		return err
 	}

wgengine/router/dns/manager.go

@@ -0,0 +1,56 @@
+// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package dns
+
+import (
+	"time"
+
+	"tailscale.com/types/logger"
+)
+
+// setTimeout is the time interval within which Manager.Set should complete.
+//
+// This is particularly useful because certain conditions can cause indefinite hangs
+// (such as improper dbus auth followed by contextless dbus.Object.Call).
+// Such operations should be wrapped in a timeout context.
+const setTimeout = time.Second
+
+type managerImpl interface {
+	Set(Config) error
+	Get() Config
+	Reset() error
+}
+
+type Manager struct {
+	impl      managerImpl
+	oldConfig Config
+}
+
+func NewManager(logf logger.Logf, interfaceName string) *Manager {
+	return &Manager{
+		impl: newManager(logf, interfaceName),
+	}
+}
+
+func (m *Manager) Up(config Config) error {
+	if len(config.Nameservers) == 0 {
+		return m.impl.Down()
+	}
+
+	if config.EquivalentTo(m.oldConfig) {
+		return nil
+	}
+
+	err := m.impl.Up(config)
+	if err == nil {
+		m.oldConfig = config
+	}
+
+	return err
+}
+
+func (m *Manager) Down() error {
+	return m.impl.Down()
+}

wgengine/router/router.go

@@ -11,6 +11,7 @@ import (
 	"github.com/tailscale/wireguard-go/tun"
 	"inet.af/netaddr"
 	"tailscale.com/types/logger"
+	"tailscale.com/wgengine/router/dns"
 )
 
 // Router is responsible for managing the system network stack.
@@ -72,7 +73,7 @@ type Config struct {
 	LocalAddrs []netaddr.IPPrefix
 	Routes     []netaddr.IPPrefix // routes to point into the Tailscale interface
 
-	DNSConfig
+	DNS dns.Config
 
 	// Linux-only things below, ignored on other platforms.