fix: dns server boostrapping with underlying dns servers

#1241

app/src/main/java/com/zaneschepke/wireguardautotunnel/core/orchestration/TunnelCoordinator.kt

@@ -32,6 +32,7 @@ import kotlinx.coroutines.sync.withLock
 class TunnelCoordinator(
     private val tunnelProvider: TunnelProvider,
     private val serviceManager: ServiceManager,
+    private val bootstrapCoordinator: AppBoostrapCoordinator,
     settingsRepository: GeneralSettingRepository,
     private val tunnelRepository: TunnelRepository,
     dnsSettingsRepository: RoomDnsSettingsRepository,
@@ -86,7 +87,11 @@ class TunnelCoordinator(
     suspend fun startTunnel(
         config: TunnelConfig,
         source: TunnelActionSource = TunnelActionSource.USER,
-    ) = tunnelMutex.withLock { startTunnelInternal(config, source) }
+    ) = tunnelMutex.withLock {
+        // wait for app to be bootstrapped
+        bootstrapCoordinator.isReady.first { it }
+        startTunnelInternal(config, source)
+    }
 
     suspend fun stopTunnel(id: Int, source: TunnelActionSource = TunnelActionSource.USER) =
         tunnelMutex.withLock {

app/src/main/java/com/zaneschepke/wireguardautotunnel/di/CoordinatorModule.kt

@@ -24,6 +24,7 @@ val coordinatorModule = module {
             get(),
             get(),
             get(),
+            get(),
             get(named(Scope.APPLICATION)),
         )
     }

tunnel/src/main/java/com/zaneschepke/tunnel/DnsConfigManager.kt

@@ -3,25 +3,27 @@ package com.zaneschepke.tunnel
 import com.zaneschepke.tunnel.model.DnsBootstrapResult
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
-import org.json.JSONObject
 
 internal object DnsConfigManager {
-    private external fun setDNSConfig(configJson: String)
 
-    fun update(protocol: String, upstream: String) {
-        val config =
-            JSONObject().apply {
-                put("protocol", protocol)
-                put("upstream", upstream)
-            }
-        setDNSConfig(config.toString())
-    }
+    private external fun resolveBootstrap(
+        host: String,
+        protocol: String,
+        upstream: String,
+        underlyingDnsServers: String,
+        bypass: Int,
+    ): String
 
-    private external fun resolveBootstrap(host: String, bypass: Int): String
-
-    suspend fun resolveHostBootstrap(host: String, bypass: Boolean): DnsBootstrapResult =
+    suspend fun resolveHostBootstrap(
+        host: String,
+        protocol: String,
+        upstream: String,
+        underlyingDnsServers: String,
+        bypass: Boolean,
+    ): DnsBootstrapResult =
         withContext(Dispatchers.IO) {
-            val raw = resolveBootstrap(host, if (bypass) 1 else 0)
+            val bypassOption = if (bypass) 1 else 0
+            val raw = resolveBootstrap(host, protocol, upstream, underlyingDnsServers, bypassOption)
 
             if (raw.startsWith("ERR|")) {
                 throw RuntimeException(raw.removePrefix("ERR|"))

tunnel/src/main/java/com/zaneschepke/tunnel/backend/TunnelActor.kt

@@ -5,6 +5,7 @@ import com.zaneschepke.tunnel.DnsConfigManager
 import com.zaneschepke.tunnel.Tunnel
 import com.zaneschepke.tunnel.event.ActorEvent
 import com.zaneschepke.tunnel.event.ActorEvent.ActiveConfigUpdated
+import com.zaneschepke.tunnel.event.ActorEvent.BootstrapConfigUpdated
 import com.zaneschepke.tunnel.event.ActorEvent.BootstrapStateChanged
 import com.zaneschepke.tunnel.event.ActorEvent.EngineStatus
 import com.zaneschepke.tunnel.event.ActorEvent.KillSwitchStateChanged
@@ -12,7 +13,9 @@ import com.zaneschepke.tunnel.event.ActorEvent.PeersUpdated
 import com.zaneschepke.tunnel.event.ActorEvent.ResolvedPeersApplied
 import com.zaneschepke.tunnel.event.ActorEvent.TunnelStarted
 import com.zaneschepke.tunnel.event.ActorEvent.TunnelStopped
+import com.zaneschepke.tunnel.event.ActorEvent.UnderlyingDnsServersUpdated
 import com.zaneschepke.tunnel.event.TunnelEvent
+import com.zaneschepke.tunnel.event.TunnelEvent.NoRootShellAccess
 import com.zaneschepke.tunnel.model.BackendMode
 import com.zaneschepke.tunnel.model.DnsBootstrapResult
 import com.zaneschepke.tunnel.model.PublicKey
@@ -122,6 +125,10 @@ internal class TunnelActor(
                             engine.stop(runtime.running.handle, runtime.running.mode)
                         }
 
+                        is TunnelCommand.SetBootstrapConfig -> {
+                            apply(BootstrapConfigUpdated(cmd.config))
+                        }
+
                         is TunnelCommand.UpdatePeers -> {
                             val runtime = _state.value.byTunnelId[cmd.tunnelId] ?: continue
                             val running = runtime.running
@@ -209,9 +216,7 @@ internal class TunnelActor(
                             } catch (t: Throwable) {
                                 Timber.w(t, "Root shell commands failed")
                                 if (t is RootShellException.NoRootAccess) {
-                                    _events.emit(
-                                        TunnelEvent.NoRootShellAccess(tunnelId = cmd.tunnelId)
-                                    )
+                                    _events.emit(NoRootShellAccess(tunnelId = cmd.tunnelId))
                                 }
                             } finally {
                                 if (isPostDown) {
@@ -219,6 +224,10 @@ internal class TunnelActor(
                                 }
                             }
                         }
+
+                        is TunnelCommand.UpdateUnderlyingDnsServers -> {
+                            apply(UnderlyingDnsServersUpdated(cmd.servers))
+                        }
                     }
                 } catch (t: Throwable) {
                     Timber.e(t, "Tunnel command failed: $cmd")
@@ -621,6 +630,14 @@ internal class TunnelActor(
             is KillSwitchStateChanged -> {
                 state.copy(killSwitchEnabled = event.enabled)
             }
+
+            is BootstrapConfigUpdated -> {
+                state.copy(dnsConfig = event.config)
+            }
+
+            is UnderlyingDnsServersUpdated -> {
+                state.copy(dnsConfig = state.dnsConfig.copy(underlyingDnsServers = event.servers))
+            }
         }
     }
 
@@ -667,9 +684,17 @@ internal class TunnelActor(
                 val endpoint = peer.endpoint ?: continue
                 val host = endpoint.substringBeforeLast(":")
 
+                val dnsConfig = state.value.dnsConfig
+
                 val dnsResult =
                     try {
-                        DnsConfigManager.resolveHostBootstrap(host = host, bypass = bypassNeeded)
+                        DnsConfigManager.resolveHostBootstrap(
+                            host = host,
+                            dnsConfig.protocol,
+                            dnsConfig.upstream,
+                            dnsConfig.underlyingDnsServers,
+                            bypass = bypassNeeded,
+                        )
                     } catch (e: Exception) {
                         Timber.w(e, "DNS failed for $host")
                         continue

tunnel/src/main/java/com/zaneschepke/tunnel/backend/TunnelBackend.kt

@@ -1,8 +1,9 @@
 package com.zaneschepke.tunnel.backend
 
+import com.zaneschepke.networkmonitor.ActiveNetwork
+import com.zaneschepke.networkmonitor.DnsInfo
 import com.zaneschepke.networkmonitor.NetworkMonitor
 import com.zaneschepke.networkmonitor.PrivateDnsMode
-import com.zaneschepke.tunnel.DnsConfigManager
 import com.zaneschepke.tunnel.NotificationProvider
 import com.zaneschepke.tunnel.Tunnel
 import com.zaneschepke.tunnel.event.TunnelEvent
@@ -14,6 +15,7 @@ import com.zaneschepke.tunnel.model.TunnelCommand
 import com.zaneschepke.tunnel.service.VpnService
 import com.zaneschepke.tunnel.state.BackendStatus
 import com.zaneschepke.tunnel.state.KillSwitchState
+import com.zaneschepke.tunnel.state.RuntimeDnsConfig
 import com.zaneschepke.tunnel.util.BackendException
 import java.lang.ref.WeakReference
 import kotlin.reflect.KClass
@@ -27,8 +29,10 @@ import kotlinx.coroutines.flow.asSharedFlow
 import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.flow.distinctUntilChangedBy
 import kotlinx.coroutines.flow.first
+import kotlinx.coroutines.flow.firstOrNull
 import kotlinx.coroutines.flow.update
 import kotlinx.coroutines.launch
+import kotlinx.coroutines.withTimeoutOrNull
 import org.koin.java.KoinJavaComponent.inject
 import timber.log.Timber
 
@@ -191,24 +195,90 @@ class TunnelBackend(
     override suspend fun setBootstrapDnsMode(mode: DnsBoostrapMode) {
         _status.update { it.copy(dnsMode = mode) }
 
+        dnsConfigJob?.cancel()
+        dnsConfigJob = null
+
         when (mode) {
             is DnsBoostrapMode.Custom -> {
-                Timber.d("DNS Boostrap mode set to custom, disabling system dns monitoring")
-                dnsConfigJob?.cancel()
-                dnsConfigJob = null
-
-                DnsConfigManager.update(
-                    mode.config.protocol,
-                    mode.config.upstream ?: DnsBoostrapConfig.DEFAULT_UPSTREAM,
+                Timber.d(
+                    "DNS Bootstrap mode set to custom: ${mode.config.protocol} -> ${mode.config.upstream}"
                 )
+
+                emitInitialDnsConfig(mode.config.protocol, mode.config.upstream)
+                startUnderlyingDnsMonitoring()
             }
 
             DnsBoostrapMode.System -> {
+                Timber.d("DNS Bootstrap mode set to System")
+                emitInitialDnsConfig()
                 startSystemDnsMonitoring()
             }
         }
     }
 
+    private suspend fun emitInitialDnsConfig(protocol: String? = null, upstream: String? = null) {
+        val state =
+            withTimeoutOrNull(2_500L) {
+                networkMonitor.connectivityStateFlow.first { connectivityState ->
+                    val dns = connectivityState.underlyingDnsInfo
+                    dns.servers.isNotEmpty() ||
+                        connectivityState.activeNetwork is ActiveNetwork.Disconnected
+                }
+            } ?: networkMonitor.connectivityStateFlow.firstOrNull()
+
+        val dns = state?.underlyingDnsInfo ?: DnsInfo()
+
+        val finalProtocol =
+            protocol
+                ?: when (dns.privateDnsMode) {
+                    PrivateDnsMode.HOSTNAME -> "dot"
+                    else -> "plain"
+                }
+
+        val finalUpstream =
+            upstream
+                ?: when (dns.privateDnsMode) {
+                    PrivateDnsMode.HOSTNAME ->
+                        dns.privateDnsHostname?.takeIf { it.isNotBlank() }
+                            ?: DnsBoostrapConfig.DEFAULT_UPSTREAM
+                    else -> dns.servers.firstOrNull() ?: DnsBoostrapConfig.DEFAULT_UPSTREAM
+                }
+
+        val underlying =
+            dns.servers.joinToString(",").ifBlank { DnsBoostrapConfig.DEFAULT_UPSTREAM }
+
+        Timber.d(
+            "DNS initial emission: protocol=$finalProtocol upstream=$finalUpstream underlying=$underlying"
+        )
+
+        actor.send(
+            TunnelCommand.SetBootstrapConfig(
+                RuntimeDnsConfig(
+                    protocol = finalProtocol,
+                    upstream = finalUpstream,
+                    underlyingDnsServers = underlying,
+                )
+            )
+        )
+    }
+
+    private fun startUnderlyingDnsMonitoring() {
+        if (dnsConfigJob?.isActive == true) return
+
+        dnsConfigJob = scope.launch {
+            networkMonitor.connectivityStateFlow
+                .distinctUntilChangedBy { it.underlyingDnsInfo.servers }
+                .collect { state ->
+                    val dns = state.underlyingDnsInfo
+                    val underlying = dns.servers.joinToString(",")
+
+                    Timber.d("Underlying DNS servers changed: $underlying")
+
+                    actor.send(TunnelCommand.UpdateUnderlyingDnsServers(underlying))
+                }
+        }
+    }
+
     override fun emergencyStopAllOfTypeSync(modeClass: KClass<out BackendMode>) {
         actor.emergencyStopAllOfType(modeClass)
     }
@@ -236,13 +306,12 @@ class TunnelBackend(
                     val config =
                         when (dns.privateDnsMode) {
                             PrivateDnsMode.OFF,
-                            PrivateDnsMode.AUTOMATIC -> {
+                            PrivateDnsMode.AUTOMATIC ->
                                 DnsBoostrapConfig.Plain(
                                     dns.servers.firstOrNull() ?: DnsBoostrapConfig.DEFAULT_UPSTREAM
                                 )
-                            }
 
-                            PrivateDnsMode.HOSTNAME -> {
+                            PrivateDnsMode.HOSTNAME ->
                                 dns.privateDnsHostname
                                     ?.takeIf { it.isNotBlank() }
                                     ?.let { DnsBoostrapConfig.DoT(it) }
@@ -250,12 +319,16 @@ class TunnelBackend(
                                         dns.servers.firstOrNull()
                                             ?: DnsBoostrapConfig.DEFAULT_UPSTREAM
                                     )
-                            }
                         }
 
-                    DnsConfigManager.update(
-                        config.protocol,
-                        config.upstream ?: DnsBoostrapConfig.DEFAULT_UPSTREAM,
+                    actor.send(
+                        TunnelCommand.SetBootstrapConfig(
+                            RuntimeDnsConfig(
+                                protocol = config.protocol,
+                                upstream = config.upstream ?: DnsBoostrapConfig.DEFAULT_UPSTREAM,
+                                underlyingDnsServers = dns.servers.joinToString(","),
+                            )
+                        )
                     )
                 }
         }

tunnel/src/main/java/com/zaneschepke/tunnel/event/ActorEvent.kt

@@ -6,6 +6,7 @@ import com.zaneschepke.tunnel.model.TunnelCommand
 import com.zaneschepke.tunnel.state.BootstrapState
 import com.zaneschepke.tunnel.state.EngineStartResult
 import com.zaneschepke.tunnel.state.NativeTunnelStatus
+import com.zaneschepke.tunnel.state.RuntimeDnsConfig
 import com.zaneschepke.wireguardautotunnel.parser.ActiveConfig
 import com.zaneschepke.wireguardautotunnel.parser.PeerSection
 
@@ -23,6 +24,10 @@ sealed class ActorEvent {
         val preferIpv6: Boolean,
     ) : ActorEvent()
 
+    data class BootstrapConfigUpdated(val config: RuntimeDnsConfig) : ActorEvent()
+
+    data class UnderlyingDnsServersUpdated(val servers: String) : ActorEvent()
+
     data class ResolvedPeersApplied(
         val tunnelId: Int,
         val cache: Map<PublicKey, DnsBootstrapResult>,

tunnel/src/main/java/com/zaneschepke/tunnel/model/DnsBootstrap.kt

@@ -17,7 +17,7 @@ sealed class DnsBoostrapConfig(open val upstream: String?) {
 
     data class DoH(override val upstream: String?) : DnsBoostrapConfig(upstream) {
         override val protocol: String
-            get() = "dot"
+            get() = "doh"
     }
 
     data class DoT(override val upstream: String?) : DnsBoostrapConfig(upstream) {

tunnel/src/main/java/com/zaneschepke/tunnel/model/TunnelCommand.kt

@@ -2,6 +2,7 @@ package com.zaneschepke.tunnel.model
 
 import com.zaneschepke.tunnel.Tunnel
 import com.zaneschepke.tunnel.state.BootstrapState
+import com.zaneschepke.tunnel.state.RuntimeDnsConfig
 import com.zaneschepke.wireguardautotunnel.parser.PeerSection
 
 sealed class TunnelCommand {
@@ -24,6 +25,10 @@ sealed class TunnelCommand {
 
     data class SetBootstrapState(val tunnelId: Int, val state: BootstrapState) : TunnelCommand()
 
+    data class SetBootstrapConfig(val config: RuntimeDnsConfig) : TunnelCommand()
+
+    data class UpdateUnderlyingDnsServers(val servers: String) : TunnelCommand()
+
     data class RunHook(val tunnelId: Int, val phase: Phase, val cmds: List<String>?) :
         TunnelCommand() {
         enum class Phase {

tunnel/src/main/java/com/zaneschepke/tunnel/state/ActorState.kt

@@ -4,4 +4,5 @@ data class ActorState(
     val byTunnelId: Map<Int, TunnelRuntimeState>,
     val byHandle: Map<Int, Int>,
     val killSwitchEnabled: Boolean = false,
+    val dnsConfig: RuntimeDnsConfig = RuntimeDnsConfig(),
 )

tunnel/src/main/java/com/zaneschepke/tunnel/state/RuntimeDnsConfig.kt

@@ -0,0 +1,9 @@
+package com.zaneschepke.tunnel.state
+
+import com.zaneschepke.tunnel.model.DnsBoostrapConfig
+
+data class RuntimeDnsConfig(
+    val protocol: String = "plain",
+    val upstream: String = DnsBoostrapConfig.DEFAULT_UPSTREAM,
+    val underlyingDnsServers: String = DnsBoostrapConfig.DEFAULT_UPSTREAM,
+)

tunnel/tools/libwg-go/dns/dns.go

@@ -9,7 +9,6 @@ import (
 	"bytes"
 	"context"
 	"crypto/tls"
-	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
@@ -18,7 +17,6 @@ import (
 	"net/netip"
 	"net/url"
 	"strings"
-	"sync"
 	"syscall"
 	"time"
 
@@ -27,21 +25,6 @@ import (
 	"golang.org/x/sys/unix"
 )
 
-const defaultPlain = "udp://1.1.1.1:53"
-
-var (
-	currentConfig DNSConfig = DNSConfig{
-		"plain",
-		"1.1.1.1:53",
-	}
-	configMu sync.RWMutex
-)
-
-type DNSConfig struct {
-	Protocol string `json:"protocol"` // plain, doh, or dot
-	Upstream string `json:"upstream"`
-}
-
 type Resolved struct {
 	V4 []netip.Addr
 	V6 []netip.Addr
@@ -52,36 +35,34 @@ type ResolverOptions struct {
 	Timeout     time.Duration
 }
 
-func DefaultOptions() ResolverOptions {
-	return ResolverOptions{
-		UpstreamURL: defaultPlain,
-		Timeout:     5 * time.Second,
-	}
-}
-
-//export SetDNSConfig
-func SetDNSConfig(config string) {
-	var cfg DNSConfig
-	if err := json.Unmarshal([]byte(config), &cfg); err != nil {
-		shared.LogError("DNS", "Failed to parse DNSConfig: %v", err)
-		return
-	}
-	if cfg.Protocol != "plain" && cfg.Protocol != "doh" && cfg.Protocol != "dot" {
-		cfg.Protocol = "plain"
-	}
-	configMu.Lock()
-	currentConfig = cfg
-	configMu.Unlock()
-	shared.LogDebug("DNS", "DNS config updated: %s %s", cfg.Protocol, cfg.Upstream)
+type Transport interface {
+	Query(ctx context.Context, msg *dns.Msg) (*dns.Msg, error)
 }
 
 //export ResolveBootstrap
-func ResolveBootstrap(host *C.char, bypass C.int) *C.char {
+func ResolveBootstrap(
+	host *C.char,
+	protocol *C.char,
+	upstream *C.char,
+	underlyingDnsServers *C.char,
+	bypass C.int,
+) *C.char {
 	h := C.GoString(host)
+	p := C.GoString(protocol)
+	u := C.GoString(upstream)
+	underlying := C.GoString(underlyingDnsServers)
 	bp := bypass == 1
-	shared.LogDebug("DNS", "ResolveBootstrap called for host=%s (bypass=%t)", h, bp)
 
-	v4, v6, err := Resolve(h, bp)
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+
+	shared.LogDebug(
+		"DNS",
+		"ResolveBootstrap called host=%s protocol=%s upstream=%s bypass=%t",
+		h, p, u, bp,
+	)
+
+	v4, v6, err := Resolve(ctx, h, p, u, bp, underlying)
 	if err != nil {
 		shared.LogError("DNS", "ResolveBootstrap failed for %s: %v", h, err)
 		return C.CString("ERR|" + err.Error())
@@ -96,15 +77,76 @@ func ResolveBootstrap(host *C.char, bypass C.int) *C.char {
 		v6Str[i] = ip.String()
 	}
 
-	result := "v4=" + strings.Join(v4Str, ",") + ";v6=" + strings.Join(v6Str, ",")
+	result := "v4=" + strings.Join(v4Str, ",") +
+		";v6=" + strings.Join(v6Str, ",")
+
 	shared.LogDebug("DNS", "ResolveBootstrap success for %s: %s", h, result)
 	return C.CString(result)
 }
 
-func getConfig() DNSConfig {
-	configMu.RLock()
-	defer configMu.RUnlock()
-	return currentConfig
+type DoTTransport struct {
+	Client  *dns.Client
+	Servers []string
+}
+
+type DoHTransport struct {
+	Client   *http.Client
+	URL      string
+	Servers  []string // IPv4 first, IPv6 fallback
+	Hostname string   // for SNI and Host header
+}
+
+type PlainTransport struct {
+	Client  *dns.Client
+	Servers []string
+}
+
+func resolveHost(
+	ctx context.Context,
+	t Transport,
+	host string,
+) (v4, v6 []netip.Addr, err error) {
+	a4, e4 := resolveQ(ctx, t, host, dns.TypeA)
+	if e4 == nil {
+		v4 = a4
+	}
+	a6, e6 := resolveQ(ctx, t, host, dns.TypeAAAA)
+	if e6 == nil {
+		v6 = a6
+	}
+
+	if len(v4) > 0 || len(v6) > 0 {
+		return v4, v6, nil
+	}
+	return nil, nil, errors.Join(e4, e6)
+}
+
+func resolveQ(
+	ctx context.Context,
+	t Transport,
+	host string,
+	qtype uint16,
+) ([]netip.Addr, error) {
+	req := &dns.Msg{}
+	req.SetQuestion(dns.Fqdn(host), qtype)
+	req.SetEdns0(4096, true)
+
+	res, err := t.Query(ctx, req)
+	if err != nil {
+		return nil, err
+	}
+	if res == nil {
+		return nil, fmt.Errorf("nil DNS response")
+	}
+	if res.Rcode != dns.RcodeSuccess {
+		return nil, fmt.Errorf("rcode %d", res.Rcode)
+	}
+
+	addrs := parseDNSAnswers(res, qtype)
+	if len(addrs) == 0 {
+		return nil, fmt.Errorf("no answers for qtype %d", qtype)
+	}
+	return addrs, nil
 }
 
 func parseUpstream(upstreamURL string) (network, address string, err error) {
@@ -113,7 +155,6 @@ func parseUpstream(upstreamURL string) (network, address string, err error) {
 	if !strings.Contains(u, "://") {
 		u = "udp://" + u
 	}
-
 	parsed, err := url.Parse(u)
 	if err != nil {
 		shared.LogError("DNS", "parseUpstream failed for %q: %v", upstreamURL, err)
@@ -141,189 +182,127 @@ func parseUpstream(upstreamURL string) (network, address string, err error) {
 	return network, address, nil
 }
 
-func resolveServerAddr(ctx context.Context, address string, bypass bool) (string, error) {
+func newUnderlyingResolver(bypass bool, underlying string) *net.Resolver {
+	if !bypass {
+		return &net.Resolver{PreferGo: false}
+	}
+
+	rawServers := strings.Split(underlying, ",")
+	var servers []string
+
+	for _, s := range rawServers {
+		s = strings.TrimSpace(s)
+		if s == "" {
+			continue
+		}
+
+		if !strings.Contains(s, ":") {
+			s = net.JoinHostPort(s, "53")
+		}
+		servers = append(servers, s)
+	}
+
+	if len(servers) == 0 {
+		servers = []string{"1.1.1.1:53"}
+	}
+
+	return &net.Resolver{
+		PreferGo: true,
+		Dial: func(ctx context.Context, network, _ string) (net.Conn, error) {
+			for _, server := range servers {
+				conn, err := GetDialer(true).DialContext(ctx, network, server)
+				if err == nil {
+					shared.LogDebug("DNS", "Using underlying bootstrap resolver: %s", server)
+					return conn, nil
+				}
+				shared.LogDebug("DNS", "Bootstrap resolver failed for %s: %v", server, err)
+			}
+			return nil, fmt.Errorf("all underlying DNS servers failed")
+		},
+	}
+}
+
+func resolveServerAddrs(
+	ctx context.Context,
+	address string,
+	bypass bool,
+	defaultPort string,
+	underlying string,
+) ([]string, string, error) {
 	host, port, err := net.SplitHostPort(address)
 	if err != nil {
-		shared.LogError("DNS", "resolveServerAddr: invalid address %q: %v", address, err)
-		return "", err
+		host = address
+		port = defaultPort
 	}
 
 	if net.ParseIP(host) != nil {
-		return address, nil
-	}
-
-	shared.LogDebug("DNS", "resolveServerAddr: bootstrapping upstream hostname %s (bypass=%t)", host, bypass)
-
-	bootstrapDialer := GetDialer(bypass)
-	resolver := &net.Resolver{
-		PreferGo: true,
-		Dial: func(ctx context.Context, network, _ string) (net.Conn, error) {
-			return bootstrapDialer.DialContext(ctx, network, "1.1.1.1:53")
-		},
+		return []string{net.JoinHostPort(host, port)}, host, nil
 	}
 
+	resolver := newUnderlyingResolver(bypass, underlying)
 	ips, err := resolver.LookupIP(ctx, "ip", host)
 	if err != nil {
-		shared.LogError("DNS", "Failed to resolve upstream hostname %s (bypass=%t): %v", host, bypass, err)
-		return "", fmt.Errorf("failed to resolve upstream hostname %s: %w", host, err)
-	}
-	if len(ips) == 0 {
-		err = errors.New("no IPs found for upstream hostname")
-		shared.LogError("DNS", "%v for %s", err, host)
-		return "", err
+		shared.LogError("DNS", "Failed to resolve upstream %s (bypass=%t): %v", host, bypass, err)
+		return nil, "", err
 	}
 
-	addr := net.JoinHostPort(ips[0].String(), port)
-	shared.LogDebug("DNS", "Resolved upstream %s -> %s", host, addr)
-	return addr, nil
-}
-func resolveInner(host string, ipType uint16, network, serverAddr string, bypass bool) ([]netip.Addr, error) {
-	req := &dns.Msg{}
-	req.Id = dns.Id()
-	req.RecursionDesired = true
-	req.SetQuestion(dns.Fqdn(host), ipType)
-	req.SetEdns0(4096, true)
-
-	client := &dns.Client{
-		Net:     network,
-		Dialer:  GetDialer(bypass),
-		Timeout: 5 * time.Second,
-		UDPSize: 4096,
-	}
-
-	res, _, err := client.Exchange(req, serverAddr)
-	if err != nil {
-		shared.LogError("DNS", "resolveInner: DNS exchange failed for %s (type=%d, server=%s, bypass=%t): %v", host, ipType, serverAddr, bypass, err)
-		return nil, err
-	}
-	if res.Rcode != dns.RcodeSuccess {
-		shared.LogError("DNS", "resolveInner: DNS query failed with Rcode %d for %s", res.Rcode, host)
-		return nil, fmt.Errorf("DNS query failed with Rcode: %d", res.Rcode)
-	}
-
-	var addr []netip.Addr
-	for _, ans := range res.Answer {
-		switch ipType {
-		case dns.TypeA:
-			if a, ok := ans.(*dns.A); ok {
-				if ip, err := netip.ParseAddr(a.A.String()); err == nil {
-					addr = append(addr, ip)
-				}
-			}
-		case dns.TypeAAAA:
-			if aaaa, ok := ans.(*dns.AAAA); ok {
-				if ip, err := netip.ParseAddr(aaaa.AAAA.String()); err == nil {
-					addr = append(addr, ip)
-				}
-			}
+	var v4, v6 []string
+	for _, ip := range ips {
+		addr := net.JoinHostPort(ip.String(), port)
+		if ip.To4() != nil {
+			v4 = append(v4, addr)
+		} else {
+			v6 = append(v6, addr)
 		}
 	}
-	return addr, nil
+
+	return append(v4, v6...), host, nil
 }
 
-func resolvePlain(host, upstreamURL string, bypass bool) ([]netip.Addr, []netip.Addr, error) {
-	shared.LogDebug("DNS", "resolvePlain: %s with upstream=%s (bypass=%t)", host, upstreamURL, bypass)
-	network, addr, err := parseUpstream(upstreamURL)
-	if err != nil {
-		return nil, nil, err
+func (t PlainTransport) Query(ctx context.Context, msg *dns.Msg) (*dns.Msg, error) {
+	for _, server := range t.Servers {
+		m, _, err := t.Client.Exchange(msg, server)
+		if err == nil && m != nil && m.Rcode == dns.RcodeSuccess {
+			return m, nil
+		}
 	}
-
-	serverAddr, err := resolveServerAddr(context.Background(), addr, bypass)
-	if err != nil {
-		return nil, nil, err
-	}
-
-	var wg sync.WaitGroup
-	var v4, v6 []netip.Addr
-	var v4Err, v6Err error
-	wg.Add(2)
-	go func() { v4, v4Err = resolveInner(host, dns.TypeA, network, serverAddr, bypass); wg.Done() }()
-	go func() { v6, v6Err = resolveInner(host, dns.TypeAAAA, network, serverAddr, bypass); wg.Done() }()
-	wg.Wait()
-
-	if v4Err != nil && v6Err != nil {
-		shared.LogError("DNS", "resolvePlain failed for %s: both A and AAAA failed", host)
-		return nil, nil, errors.Join(v4Err, v6Err)
-	}
-	if len(v4) == 0 && len(v6) == 0 {
-		err = errors.New("no IP addresses found")
-		shared.LogError("DNS", "%v for %s", err, host)
-		return nil, nil, err
-	}
-	return v4, v6, nil
+	return nil, fmt.Errorf("all DNS servers failed")
 }
 
-func resolveDoH(host, dohURL string, bypass bool) ([]netip.Addr, []netip.Addr, error) {
-	shared.LogDebug("DNS", "Resolving DOH: %s with %s", host, dohURL)
-	var v4, v6 []netip.Addr
-	var v4Err, v6Err error
-
-	var wg sync.WaitGroup
-	wg.Add(2)
-
-	go func() {
-		defer wg.Done()
-		v4, v4Err = doDoHQuery(dohURL, host, dns.TypeA, bypass)
-	}()
-	go func() {
-		defer wg.Done()
-		v6, v6Err = doDoHQuery(dohURL, host, dns.TypeAAAA, bypass)
-	}()
-	wg.Wait()
-
-	if v4Err != nil && v6Err != nil {
-		shared.LogError("DNS", "resolveDoH failed for %s: both queries failed", host)
-		return nil, nil, errors.Join(v4Err, v6Err)
+func (t DoTTransport) Query(ctx context.Context, msg *dns.Msg) (*dns.Msg, error) {
+	for _, server := range t.Servers {
+		m, _, err := t.Client.Exchange(msg, server)
+		if err == nil && m != nil && m.Rcode == dns.RcodeSuccess {
+			return m, nil
+		}
 	}
-	return v4, v6, nil
+	return nil, fmt.Errorf("all DoT servers failed")
 }
 
-func doDoHQuery(dohURL, host string, qtype uint16, bypass bool) ([]netip.Addr, error) {
-	req := &dns.Msg{}
-	req.Id = dns.Id()
-	req.RecursionDesired = true
-	req.SetEdns0(4096, true)
-	req.SetQuestion(dns.Fqdn(host), qtype)
-
-	transport := &http.Transport{
-		DialContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
-			h, port, _ := net.SplitHostPort(addr)
-			if net.ParseIP(h) == nil {
-				ips, err := CustomResolver(bypass).LookupIP(ctx, "ip", h)
-				if err == nil && len(ips) > 0 {
-					h = ips[0].String()
-				}
-			}
-			return GetDialer(bypass).DialContext(ctx, network, net.JoinHostPort(h, port))
-		},
-	}
-
-	client := &http.Client{
-		Transport: transport,
-		Timeout:   5 * time.Second,
-	}
-
-	wire, err := req.Pack()
+func (t DoHTransport) Query(ctx context.Context, msg *dns.Msg) (*dns.Msg, error) {
+	wire, err := msg.Pack()
 	if err != nil {
 		return nil, err
 	}
 
-	httpReq, err := http.NewRequestWithContext(context.Background(), "POST", dohURL, bytes.NewReader(wire))
+	req, err := http.NewRequestWithContext(
+		ctx, "POST", t.URL, bytes.NewReader(wire),
+	)
 	if err != nil {
 		return nil, err
 	}
-	httpReq.Header.Set("Content-Type", "application/dns-message")
-	httpReq.Header.Set("Accept", "application/dns-message")
+	req.Header.Set("Content-Type", "application/dns-message")
+	req.Header.Set("Accept", "application/dns-message")
+	req.Host = t.Hostname // important for virtual hosting and cert validation
 
-	resp, err := client.Do(httpReq)
+	resp, err := t.Client.Do(req)
 	if err != nil {
 		return nil, err
 	}
 	defer resp.Body.Close()
 
 	if resp.StatusCode != http.StatusOK {
-		shared.LogError("DNS", "doDoHQuery: DoH server returned HTTP %d for %s", resp.StatusCode, host)
-		return nil, fmt.Errorf("DoH HTTP %d", resp.StatusCode)
+		return nil, fmt.Errorf("doh status %d", resp.StatusCode)
 	}
 
 	body, err := io.ReadAll(resp.Body)
@@ -335,158 +314,143 @@ func doDoHQuery(dohURL, host string, qtype uint16, bypass bool) ([]netip.Addr, e
 	if err := res.Unpack(body); err != nil {
 		return nil, err
 	}
-	if res.Rcode != dns.RcodeSuccess {
-		shared.LogError("DNS", "doDoHQuery: DoH Rcode %d for %s", res.Rcode, host)
-		return nil, fmt.Errorf("DoH Rcode %d", res.Rcode)
-	}
-
-	var addrs []netip.Addr
-	for _, ans := range res.Answer {
-		if qtype == dns.TypeA {
-			if a, ok := ans.(*dns.A); ok {
-				if ip, _ := netip.ParseAddr(a.A.String()); ip.Is4() {
-					addrs = append(addrs, ip)
-				}
-			}
-		} else if qtype == dns.TypeAAAA {
-			if aaaa, ok := ans.(*dns.AAAA); ok {
-				if ip, _ := netip.ParseAddr(aaaa.AAAA.String()); ip.Is6() {
-					addrs = append(addrs, ip)
-				}
-			}
-		}
-	}
-	return addrs, nil
+	return &res, nil
 }
 
-func resolveDoT(host, dotUpstream string, bypass bool) ([]netip.Addr, []netip.Addr, error) {
-	shared.LogDebug("DNS", "resolveDoT: %s with upstream=%s (bypass=%t)", host, dotUpstream, bypass)
-
-	var v4, v6 []netip.Addr
-	var v4Err, v6Err error
-
-	var wg sync.WaitGroup
-	wg.Add(2)
-
-	go func() {
-		defer wg.Done()
-		v4, v4Err = doDoTQuery(dotUpstream, host, dns.TypeA, bypass)
-	}()
-	go func() {
-		defer wg.Done()
-		v6, v6Err = doDoTQuery(dotUpstream, host, dns.TypeAAAA, bypass)
-	}()
-	wg.Wait()
-
-	if v4Err != nil && v6Err != nil {
-		shared.LogError("DNS", "resolveDoT failed for %s: both A and AAAA queries failed (bypass=%t)", host, bypass)
-		return nil, nil, errors.Join(v4Err, v6Err)
-	}
-
-	shared.LogDebug("DNS", "resolveDoT success for %s: %d v4, %d v6 (bypass=%t)", host, len(v4), len(v6), bypass)
-	return v4, v6, nil
-}
-
-func doDoTQuery(dotUpstream, host string, qtype uint16, bypass bool) ([]netip.Addr, error) {
-	// Normalize upstream to host:port
-	sni, port, err := net.SplitHostPort(dotUpstream)
-	if err != nil {
-		sni = dotUpstream
-		port = "853"
-		dotUpstream = net.JoinHostPort(sni, port)
-	}
-
-	// Resolve hostname using bypass resolver
-	serverAddr, err := resolveServerAddr(context.Background(), dotUpstream, bypass)
-	if err != nil {
-		return nil, err
-	}
-
-	req := &dns.Msg{}
-	req.Id = dns.Id()
-	req.RecursionDesired = true
-	req.SetEdns0(4096, true)
-	req.SetQuestion(dns.Fqdn(host), qtype)
-
-	client := &dns.Client{
-		Net:     "tcp-tls",
-		Dialer:  GetDialer(bypass),
-		Timeout: 5 * time.Second,
-		TLSConfig: &tls.Config{
-			ServerName:         sni,
-			InsecureSkipVerify: false,
-		},
-	}
-
-	res, _, err := client.Exchange(req, serverAddr)
-	if err != nil {
-		return nil, err
-	}
-	if res.Rcode != dns.RcodeSuccess {
-		return nil, fmt.Errorf("DoT query failed with Rcode: %d", res.Rcode)
-	}
-
-	var addrs []netip.Addr
-	for _, ans := range res.Answer {
+func parseDNSAnswers(msg *dns.Msg, qtype uint16) []netip.Addr {
+	var out []netip.Addr
+	for _, ans := range msg.Answer {
 		switch qtype {
 		case dns.TypeA:
 			if a, ok := ans.(*dns.A); ok {
-				if ip, _ := netip.ParseAddr(a.A.String()); ip.Is4() {
-					addrs = append(addrs, ip)
+				if ip, err := netip.ParseAddr(a.A.String()); err == nil {
+					out = append(out, ip)
 				}
 			}
 		case dns.TypeAAAA:
 			if aaaa, ok := ans.(*dns.AAAA); ok {
-				if ip, _ := netip.ParseAddr(aaaa.AAAA.String()); ip.Is6() {
-					addrs = append(addrs, ip)
+				if ip, err := netip.ParseAddr(aaaa.AAAA.String()); err == nil {
+					out = append(out, ip)
 				}
 			}
 		}
 	}
-	return addrs, nil
+	return out
 }
 
-// Resolve runs the correct protocol based on the global config
-func Resolve(host string, bypass bool) ([]netip.Addr, []netip.Addr, error) {
-	cfg := getConfig()
-	shared.LogDebug("DNS", "Resolve(%s, bypass=%t) protocol=%s upstream=%s", host, bypass, cfg.Protocol, cfg.Upstream)
-
-	var v4, v6 []netip.Addr
-	var err error
-	switch cfg.Protocol {
-	case "doh":
-		v4, v6, err = resolveDoH(host, cfg.Upstream, bypass)
-	case "dot":
-		v4, v6, err = resolveDoT(host, cfg.Upstream, bypass)
-	default:
-		v4, v6, err = resolvePlain(host, cfg.Upstream, bypass)
-	}
-
+func Resolve(
+	ctx context.Context,
+	host, protocol, upstream string,
+	bypass bool,
+	underlying string,
+) ([]netip.Addr, []netip.Addr, error) {
+	t, err := buildTransport(ctx, protocol, upstream, bypass, underlying)
 	if err != nil {
-		shared.LogError("DNS", "Final Resolve failed for %s: %v", host, err)
-	} else {
-		shared.LogDebug("DNS", "Resolve success for %s: %d v4, %d v6", host, len(v4), len(v6))
+		return nil, nil, err
 	}
-	return v4, v6, err
+	return resolveHost(ctx, t, host)
 }
 
-func CustomResolver(bypass bool) *net.Resolver {
-	return &net.Resolver{
-		PreferGo: true,
-		Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
-			d := GetDialer(bypass)
-			return d.DialContext(ctx, network, address)
-		},
+func buildTransport(
+	ctx context.Context,
+	protocol, upstream string,
+	bypass bool,
+	underlying string,
+) (Transport, error) {
+	switch protocol {
+	case "doh":
+		u, err := url.Parse(upstream)
+		if err != nil {
+			return nil, err
+		}
+		hostname := u.Hostname()
+		port := u.Port()
+		if port == "" {
+			port = "443"
+		}
+		u.Host = net.JoinHostPort(hostname, port)
+
+		// Pre-resolve with IPv4-first ordering + bypass
+		servers, _, err := resolveServerAddrs(ctx, u.Host, bypass, "443", underlying)
+		if err != nil {
+			return nil, err
+		}
+		if len(servers) == 0 {
+			return nil, fmt.Errorf("no addresses resolved for DoH server")
+		}
+
+		// Custom dialer that tries servers in order (IPv4 → IPv6)
+		dialer := GetDialer(bypass)
+		transport := &http.Transport{
+			DialContext: func(ctx context.Context, network, _ string) (net.Conn, error) {
+				for _, addr := range servers {
+					conn, err := dialer.DialContext(ctx, network, addr)
+					if err == nil {
+						return conn, nil
+					}
+				}
+				return nil, fmt.Errorf("all DoH addresses failed")
+			},
+			TLSClientConfig: &tls.Config{
+				ServerName: hostname,
+			},
+		}
+
+		return DoHTransport{
+			Client:   &http.Client{Timeout: 5 * time.Second, Transport: transport},
+			URL:      u.String(),
+			Servers:  servers,
+			Hostname: hostname,
+		}, nil
+
+	case "dot":
+		servers, sni, err := resolveServerAddrs(ctx, upstream, bypass, "853", underlying)
+		if err != nil {
+			return nil, err
+		}
+		if len(servers) == 0 {
+			return nil, fmt.Errorf("no addresses resolved for DoT server")
+		}
+
+		client := &dns.Client{
+			Net:     "tcp-tls",
+			Dialer:  GetDialer(bypass),
+			Timeout: 5 * time.Second,
+			TLSConfig: &tls.Config{
+				ServerName: sni,
+			},
+		}
+		return DoTTransport{
+			Client:  client,
+			Servers: servers,
+		}, nil
+
+	default: // plain DNS
+		_, addr, err := parseUpstream(upstream)
+		if err != nil {
+			return nil, err
+		}
+		servers, _, err := resolveServerAddrs(ctx, addr, bypass, "53", underlying)
+		if err != nil {
+			return nil, err
+		}
+
+		client := &dns.Client{
+			Net:     "udp",
+			Dialer:  GetDialer(bypass),
+			Timeout: 5 * time.Second,
+		}
+		return PlainTransport{
+			Client:  client,
+			Servers: servers,
+		}, nil
 	}
 }
 
 func GetDialer(bypass bool) *net.Dialer {
 	if !bypass {
-		return &net.Dialer{
-			LocalAddr: nil,
-		}
+		return &net.Dialer{LocalAddr: nil}
 	}
-
 	return &net.Dialer{
 		Control: func(network, address string, c syscall.RawConn) error {
 			var opErr error

tunnel/tools/libwg-go/dns/dns_jni.c

@@ -3,54 +3,51 @@
 
 struct go_string { const char *str; long n; };
 
-extern void SetDNSConfig(struct go_string handle);
-extern char* ResolveBootstrap(const char* host, int bypass);
-
-JNIEXPORT void JNICALL Java_com_zaneschepke_tunnel_DnsConfigManager_setDNSConfig(
-        JNIEnv* env, jclass clazz, jstring json)
-{
-    if (json == NULL) {
-        return;
-    }
-
-    const char* cjson = (*env)->GetStringUTFChars(env, json, 0);
-    if (cjson != NULL) {
-        size_t len = (*env)->GetStringUTFLength(env, json);
-
-        SetDNSConfig((struct go_string){
-            .str = cjson,
-            .n = (long)len
-        });
-
-        (*env)->ReleaseStringUTFChars(env, json, cjson);
-    }
-}
+extern char* ResolveBootstrap(
+        const char* host,
+        const char* protocol,
+        const char* upstream,
+        const char* underlyingDnsServers,
+        int bypass);
 
 JNIEXPORT jstring JNICALL
 Java_com_zaneschepke_tunnel_DnsConfigManager_resolveBootstrap(
         JNIEnv* env,
         jclass clazz,
         jstring host,
-        jboolean bypass)
+        jstring protocol,
+        jstring upstream,
+        jstring underlyingDnsServers,
+        jint bypass)
 {
-    if (host == NULL) {
-        return (*env)->NewStringUTF(env, "{\"error\":\"invalid host\"}");
+    if (host == NULL || protocol == NULL || upstream == NULL || underlyingDnsServers == NULL) {
+        return (*env)->NewStringUTF(env, "ERR|invalid arguments");
     }
 
-    const char* chost = (*env)->GetStringUTFChars(env, host, NULL);
-    if (chost == NULL) {
-        return (*env)->NewStringUTF(env, "{\"error\":\"out of memory\"}");
+    const char* chost       = (*env)->GetStringUTFChars(env, host, NULL);
+    const char* cprotocol   = (*env)->GetStringUTFChars(env, protocol, NULL);
+    const char* cupstream   = (*env)->GetStringUTFChars(env, upstream, NULL);
+    const char* cunderlying = (*env)->GetStringUTFChars(env, underlyingDnsServers, NULL);
+
+    if (chost == NULL || cprotocol == NULL || cupstream == NULL || cunderlying == NULL) {
+        return (*env)->NewStringUTF(env, "ERR|out of memory");
     }
 
     char* resultC = ResolveBootstrap(
-        (char*)chost,
-        bypass ? 1 : 0
+            chost,
+            cprotocol,
+            cupstream,
+            cunderlying,
+            bypass ? 1 : 0
     );
 
     (*env)->ReleaseStringUTFChars(env, host, chost);
+    (*env)->ReleaseStringUTFChars(env, protocol, cprotocol);
+    (*env)->ReleaseStringUTFChars(env, upstream, cupstream);
+    (*env)->ReleaseStringUTFChars(env, underlyingDnsServers, cunderlying);
 
     if (resultC == NULL) {
-        return (*env)->NewStringUTF(env, "{\"error\":\"null response\"}");
+        return (*env)->NewStringUTF(env, "ERR|null response");
     }
 
     jstring jresult = (*env)->NewStringUTF(env, resultC);