Obtain DNS server automatically from VPN service

Demote DNS settings to fallback usages only.

mobile/src/main/java/be/mygod/vpnhotspot/App.kt

@@ -28,7 +28,6 @@ class App : Application() {
 
     val handler = Handler()
     val pref: SharedPreferences by lazy { PreferenceManager.getDefaultSharedPreferences(this) }
-    val dns: String get() = pref.getString("service.dns", "8.8.8.8")
 
     fun toast(@StringRes resId: Int) = handler.post { Toast.makeText(this, resId, Toast.LENGTH_SHORT).show() }
 }

mobile/src/main/java/be/mygod/vpnhotspot/RepeaterService.kt

@@ -138,7 +138,7 @@ class RepeaterService : Service(), WifiP2pManager.ChannelListener, VpnMonitor.Ca
             App.ACTION_CLEAN_ROUTINGS -> {
                 val routing = routing
                 routing!!.started = false
-                if (status == Status.ACTIVE) resetup(routing, upstream)
+                if (status == Status.ACTIVE) resetup(routing, upstream, dns)
             }
         }
     }
@@ -147,6 +147,7 @@ class RepeaterService : Service(), WifiP2pManager.ChannelListener, VpnMonitor.Ca
     val password get() = if (status == Status.ACTIVE) group?.passphrase else null
 
     private var upstream: String? = null
+    private var dns: List<InetAddress> = emptyList()
     private var routing: Routing? = null
 
     var status = Status.IDLE
@@ -194,13 +195,14 @@ class RepeaterService : Service(), WifiP2pManager.ChannelListener, VpnMonitor.Ca
     /**
      * startService 2nd stop, also called when VPN re-established
      */
-    private fun setup(ifname: String? = null) {
+    private fun setup(ifname: String? = null, dns: List<InetAddress> = emptyList()) {
         val matcher = patternNetworkInfo.matcher(loggerSu("dumpsys ${Context.WIFI_P2P_SERVICE}") ?: "")
         when {
             !matcher.find() -> startFailure(getString(R.string.root_unavailable))
             matcher.group(2) == "true" -> {
                 unregisterReceiver()
                 upstream = ifname
+                this.dns = dns
                 registerReceiver(receiver, intentFilter(WifiP2pManager.WIFI_P2P_STATE_CHANGED_ACTION,
                         WifiP2pManager.WIFI_P2P_CONNECTION_CHANGED_ACTION))
                 LocalBroadcastManager.getInstance(this)
@@ -228,18 +230,18 @@ class RepeaterService : Service(), WifiP2pManager.ChannelListener, VpnMonitor.Ca
         }
     }
 
-    private fun resetup(routing: Routing, ifname: String? = null) =
-            initRouting(ifname, routing.downstream, routing.hostAddress)
+    private fun resetup(routing: Routing, ifname: String? = null, dns: List<InetAddress> = emptyList()) =
+            initRouting(ifname, routing.downstream, routing.hostAddress, dns)
 
-    override fun onAvailable(ifname: String) = when (status) {
-        Status.STARTING -> setup(ifname)
+    override fun onAvailable(ifname: String, dns: List<InetAddress>) = when (status) {
+        Status.STARTING -> setup(ifname, dns)
         Status.ACTIVE -> {
             val routing = routing!!
             if (routing.started) {
                 routing.stop()
                 check(routing.upstream == null)
             }
-            resetup(routing, ifname)
+            resetup(routing, ifname, dns)
             while (false) { }
         }
         else -> throw IllegalStateException("RepeaterService is in unexpected state when receiving onAvailable")
@@ -280,23 +282,21 @@ class RepeaterService : Service(), WifiP2pManager.ChannelListener, VpnMonitor.Ca
         val downstream = group.`interface` ?: return
         receiverRegistered = true
         try {
-            if (initRouting(upstream, downstream, owner)) doStart(group)
+            if (initRouting(upstream, downstream, owner, dns)) doStart(group)
         } catch (e: Routing.InterfaceNotFoundException) {
             startFailure(e.message, group)
             return
         }
     }
-    private fun initRouting(upstream: String?, downstream: String, owner: InetAddress): Boolean {
+    private fun initRouting(upstream: String?, downstream: String,
+                            owner: InetAddress, dns: List<InetAddress>): Boolean {
         val routing = Routing(upstream, downstream, owner)
         this.routing = routing
+        this.dns = dns
         val strict = app.pref.getBoolean("service.repeater.strict", false)
-        if (strict && upstream == null) return true // in this case, nothing to be done
-        return if (routing
-                        .ipForward()   // Wi-Fi direct doesn't enable ip_forward
-                        .rule()
-                        .forward(strict)
-                        .dnsRedirect(app.dns)
-                        .start()) true else {
+        return if (strict && upstream == null ||    // in this case, nothing to be done
+                routing.ipForward()                 // Wi-Fi direct doesn't enable ip_forward
+                        .rule().forward(strict).dnsRedirect(dns).start()) true else {
             routing.stop()
             Toast.makeText(this, getText(R.string.noisy_su_failure), Toast.LENGTH_SHORT).show()
             false

mobile/src/main/java/be/mygod/vpnhotspot/TetheringService.kt

@@ -7,6 +7,7 @@ import android.support.v4.content.LocalBroadcastManager
 import android.widget.Toast
 import be.mygod.vpnhotspot.App.Companion.app
 import be.mygod.vpnhotspot.net.*
+import java.net.InetAddress
 
 class TetheringService : Service(), VpnMonitor.Callback, IpNeighbourMonitor.Callback {
     companion object {
@@ -23,6 +24,7 @@ class TetheringService : Service(), VpnMonitor.Callback, IpNeighbourMonitor.Call
     private val routings = HashMap<String, Routing?>()
     private var neighbours = emptyList<IpNeighbour>()
     private var upstream: String? = null
+    private var dns: List<InetAddress> = emptyList()
     private var receiverRegistered = false
     private val receiver = broadcastReceiver { _, intent ->
         when (intent.action) {
@@ -49,7 +51,7 @@ class TetheringService : Service(), VpnMonitor.Callback, IpNeighbourMonitor.Call
                 for ((downstream, value) in routings) if (value == null) {
                     // system tethering already has working forwarding rules
                     // so it doesn't make sense to add additional forwarding rules
-                    val routing = Routing(upstream, downstream).rule().forward(true).dnsRedirect(app.dns)
+                    val routing = Routing(upstream, downstream).rule().forward(true).dnsRedirect(dns)
                     if (routing.start()) routings[downstream] = routing else {
                         failed = true
                         routing.stop()
@@ -81,15 +83,17 @@ class TetheringService : Service(), VpnMonitor.Callback, IpNeighbourMonitor.Call
         return START_NOT_STICKY
     }
 
-    override fun onAvailable(ifname: String) {
+    override fun onAvailable(ifname: String, dns: List<InetAddress>) {
         check(upstream == null || upstream == ifname)
         upstream = ifname
+        this.dns = dns
         updateRoutings()
     }
 
     override fun onLost(ifname: String) {
         check(upstream == null || upstream == ifname)
         upstream = null
+        this.dns = emptyList()
         var failed = false
         for ((iface, routing) in routings) {
             if (routing?.stop() == false) failed = true

mobile/src/main/java/be/mygod/vpnhotspot/net/Routing.kt

@@ -3,6 +3,7 @@ package be.mygod.vpnhotspot.net
 import android.os.Build
 import be.mygod.vpnhotspot.App.Companion.app
 import be.mygod.vpnhotspot.R
+import be.mygod.vpnhotspot.debugLog
 import be.mygod.vpnhotspot.noisySu
 import java.io.IOException
 import java.net.Inet4Address
@@ -82,8 +83,11 @@ class Routing(val upstream: String?, val downstream: String, ownerAddress: InetA
         return this
     }
 
-    fun dnsRedirect(dns: String): Routing {
+    fun dnsRedirect(dnses: List<InetAddress>): Routing {
         val hostAddress = hostAddress.hostAddress
+        val dns = dnses.firstOrNull { it is Inet4Address }?.hostAddress
+                ?: app.pref.getString("service.dns", "8.8.8.8")
+        debugLog("Routing", "Using $dns from ($dnses)")
         startScript.add("$IPTABLES -t nat -A PREROUTING -i $downstream -p tcp -d $hostAddress --dport 53 -j DNAT --to-destination $dns")
         startScript.add("$IPTABLES -t nat -A PREROUTING -i $downstream -p udp -d $hostAddress --dport 53 -j DNAT --to-destination $dns")
         stopScript.addFirst("$IPTABLES -t nat -D PREROUTING -i $downstream -p tcp -d $hostAddress --dport 53 -j DNAT --to-destination $dns")

mobile/src/main/java/be/mygod/vpnhotspot/net/VpnMonitor.kt

@@ -7,10 +7,11 @@ import android.net.NetworkCapabilities
 import android.net.NetworkRequest
 import be.mygod.vpnhotspot.App.Companion.app
 import be.mygod.vpnhotspot.debugLog
+import java.net.InetAddress
 
 object VpnMonitor : ConnectivityManager.NetworkCallback() {
     interface Callback {
-        fun onAvailable(ifname: String)
+        fun onAvailable(ifname: String, dns: List<InetAddress>)
         fun onLost(ifname: String)
     }
 
@@ -27,13 +28,14 @@ object VpnMonitor : ConnectivityManager.NetworkCallback() {
     /**
      * Obtaining ifname in onLost doesn't work so we need to cache it in onAvailable.
      */
-    val available = HashMap<Network, String>()
+    private val available = HashMap<Network, String>()
     override fun onAvailable(network: Network) {
-        val ifname = manager.getLinkProperties(network)?.interfaceName ?: return
+        val properties = manager.getLinkProperties(network)
+        val ifname = properties?.interfaceName ?: return
         synchronized(this) {
             if (available.put(network, ifname) != null) return
-            debugLog(TAG, "onAvailable: $ifname")
-            callbacks.forEach { it.onAvailable(ifname) }
+            debugLog(TAG, "onAvailable: $ifname, ${properties.dnsServers.joinToString()}")
+            callbacks.forEach { it.onAvailable(ifname, properties.dnsServers) }
         }
     }
 
@@ -55,7 +57,9 @@ object VpnMonitor : ConnectivityManager.NetworkCallback() {
                                     cap.hasCapability(NetworkCapabilities.NET_CAPABILITY_NOT_VPN)
                         }
                     } else if (available.isEmpty()) true else {
-                        available.forEach { callback.onAvailable(it.value) }
+                        available.forEach {
+                            callback.onAvailable(it.value, manager.getLinkProperties(it.key)?.dnsServers ?: emptyList())
+                        }
                         false
                     }
         }) failfast?.invoke()

mobile/src/main/res/values-zh-rCN/strings.xml

@@ -40,9 +40,9 @@
     <string name="connected_state_failed">%s (已断开)</string>
 
     <string name="settings_service">服务</string>
-    <string name="settings_service_dns">下游 DNS 服务器[:端口]</string>
     <string name="settings_service_repeater_strict">严格模式 (仅用于中继)</string>
     <string name="settings_service_repeater_strict_summary">只允许通过 VPN 隧道的包通过</string>
+    <string name="settings_service_dns">备用 DNS 服务器[:端口]</string>
     <string name="settings_service_clean">清理/重新应用路由规则</string>
     <string name="settings_misc">杂项</string>
     <string name="settings_misc_logcat">导出日志</string>

mobile/src/main/res/values/strings.xml

@@ -42,9 +42,9 @@
     <string name="connected_state_failed">%s (lost)</string>
 
     <string name="settings_service">Service</string>
-    <string name="settings_service_dns">Downstream DNS server[:port]</string>
     <string name="settings_service_repeater_strict">Strict mode (repeater only)</string>
     <string name="settings_service_repeater_strict_summary">Only allow packets that goes through VPN tunnel</string>
+    <string name="settings_service_dns">Fallback DNS server[:port]</string>
     <string name="settings_service_clean">Clean/reapply routing rules</string>
     <string name="settings_misc">Misc</string>
     <string name="settings_misc_logcat">Export logcat</string>

mobile/src/main/res/xml/pref_settings.xml

@@ -2,16 +2,16 @@
 <PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
     <PreferenceCategory
         android:title="@string/settings_service">
+        <SwitchPreference
+            android:key="service.repeater.strict"
+            android:title="@string/settings_service_repeater_strict"
+            android:summary="@string/settings_service_repeater_strict_summary"/>
         <AutoSummaryEditTextPreference
             android:key="service.dns"
             android:title="@string/settings_service_dns"
             android:summary="%s"
             android:singleLine="true"
             android:defaultValue="8.8.8.8"/>
-        <SwitchPreference
-            android:key="service.repeater.strict"
-            android:title="@string/settings_service_repeater_strict"
-            android:summary="@string/settings_service_repeater_strict_summary"/>
         <Preference
             android:key="service.clean"
             android:title="@string/settings_service_clean"/>