Revert "Stop using DHCP on iOS and tvOS"

dns/transport/dhcp/dhcp.go

@@ -49,6 +49,7 @@ type Transport struct {
 	interfaceCallback *list.Element[tun.DefaultInterfaceUpdateCallback]
 	transportLock     sync.RWMutex
 	updatedAt         time.Time
+	lastError         error
 	servers           []M.Socksaddr
 	search            []string
 	ndots             int
@@ -92,7 +93,7 @@ func (t *Transport) Start(stage adapter.StartStage) error {
 		t.interfaceCallback = t.networkManager.InterfaceMonitor().RegisterCallback(t.interfaceUpdated)
 	}
 	go func() {
-		_, err := t.Fetch()
+		_, err := t.fetch()
 		if err != nil {
 			t.logger.Error(E.Cause(err, "fetch DNS servers"))
 		}
@@ -108,7 +109,7 @@ func (t *Transport) Close() error {
 }
 
 func (t *Transport) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg, error) {
-	servers, err := t.Fetch()
+	servers, err := t.fetch()
 	if err != nil {
 		return nil, err
 	}
@@ -128,11 +129,20 @@ func (t *Transport) Exchange0(ctx context.Context, message *mDNS.Msg, servers []
 	}
 }
 
-func (t *Transport) Fetch() ([]M.Socksaddr, error) {
+func (t *Transport) Fetch() []M.Socksaddr {
+	servers, _ := t.fetch()
+	return servers
+}
+
+func (t *Transport) fetch() ([]M.Socksaddr, error) {
 	t.transportLock.RLock()
 	updatedAt := t.updatedAt
+	lastError := t.lastError
 	servers := t.servers
 	t.transportLock.RUnlock()
+	if lastError != nil {
+		return nil, lastError
+	}
 	if time.Since(updatedAt) < C.DHCPTTL {
 		return servers, nil
 	}
@@ -143,7 +153,7 @@ func (t *Transport) Fetch() ([]M.Socksaddr, error) {
 	}
 	err := t.updateServers()
 	if err != nil {
-		return nil, err
+		return servers, err
 	}
 	return t.servers, nil
 }
@@ -173,12 +183,15 @@ func (t *Transport) updateServers() error {
 	fetchCtx, cancel := context.WithTimeout(t.ctx, C.DHCPTimeout)
 	err = t.fetchServers0(fetchCtx, iface)
 	cancel()
+	t.updatedAt = time.Now()
 	if err != nil {
+		t.lastError = err
 		return err
 	} else if len(t.servers) == 0 {
-		return E.New("dhcp: empty DNS servers response")
+		t.lastError = E.New("dhcp: empty DNS servers response")
+		return t.lastError
 	} else {
-		t.updatedAt = time.Now()
+		t.lastError = nil
 		return nil
 	}
 }

dns/transport/local/local_darwin.go

@@ -43,7 +43,7 @@ type Transport struct {
 
 type dhcpTransport interface {
 	adapter.DNSTransport
-	Fetch() ([]M.Socksaddr, error)
+	Fetch() []M.Socksaddr
 	Exchange0(ctx context.Context, message *mDNS.Msg, servers []M.Socksaddr) (*mDNS.Msg, error)
 }
 
@@ -74,14 +74,12 @@ func (t *Transport) Start(stage adapter.StartStage) error {
 			break
 		}
 	}
-	if !C.IsIos {
-		if t.fallback {
-			t.dhcpTransport = newDHCPTransport(t.TransportAdapter, log.ContextWithOverrideLevel(t.ctx, log.LevelDebug), t.dialer, t.logger)
-			if t.dhcpTransport != nil {
-				err := t.dhcpTransport.Start(stage)
-				if err != nil {
-					return err
-				}
+	if t.fallback {
+		t.dhcpTransport = newDHCPTransport(t.TransportAdapter, log.ContextWithOverrideLevel(t.ctx, log.LevelDebug), t.dialer, t.logger)
+		if t.dhcpTransport != nil {
+			err := t.dhcpTransport.Start(stage)
+			if err != nil {
+				return err
 			}
 		}
 	}
@@ -105,12 +103,10 @@ func (t *Transport) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg,
 	if !t.fallback {
 		return t.exchange(ctx, message, question.Name)
 	}
-	if !C.IsIos {
-		if t.dhcpTransport != nil {
-			dhcpTransports, _ := t.dhcpTransport.Fetch()
-			if len(dhcpTransports) > 0 {
-				return t.dhcpTransport.Exchange0(ctx, message, dhcpTransports)
-			}
+	if t.dhcpTransport != nil {
+		dhcpTransports := t.dhcpTransport.Fetch()
+		if len(dhcpTransports) > 0 {
+			return t.dhcpTransport.Exchange0(ctx, message, dhcpTransports)
 		}
 	}
 	if t.preferGo {
@@ -134,9 +130,5 @@ func (t *Transport) Exchange(ctx context.Context, message *mDNS.Msg) (*mDNS.Msg,
 		}
 		return dns.FixedResponse(message.Id, question, addresses, C.DefaultDNSTTL), nil
 	}
-	if C.IsIos {
-		return nil, E.New("only A and AAAA queries are supported on iOS and tvOS when using NetworkExtension.")
-	} else {
-		return nil, E.New("only A and AAAA queries are supported on macOS when using NetworkExtension and DHCP unavailable.")
-	}
+	return nil, E.New("only A and AAAA queries are supported on Apple platforms when using TUN and DHCP unavailable.")
 }