From 1b2dd919ca99a2ac2afcc9257d3707f6e5cd3761 Mon Sep 17 00:00:00 2001
From: Zoltan Papp <zoltan.pmail@gmail.com>
Date: Wed, 22 May 2024 11:16:28 +0200
Subject: [PATCH] Add hardcoded DNS server (#18)

Extend the host's DNS list with the hardcoded Cloudflare DNS server in case the first assigned server type is link local
---
 .../java/io/netbird/client/tool/DNSWatch.java | 21 +++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/android/tool/src/main/java/io/netbird/client/tool/DNSWatch.java b/android/tool/src/main/java/io/netbird/client/tool/DNSWatch.java
index 51aad1b..960aacf 100644
--- a/android/tool/src/main/java/io/netbird/client/tool/DNSWatch.java
+++ b/android/tool/src/main/java/io/netbird/client/tool/DNSWatch.java
@@ -12,6 +12,7 @@
 import androidx.annotation.NonNull;
 
 import java.net.InetAddress;
+import java.net.UnknownHostException;
 import java.util.List;
 
 import io.netbird.gomobile.android.DNSList;
@@ -26,7 +27,7 @@ public class DNSWatch {
 
 
     DNSWatch(Context context) {
-        connectivityManager = (ConnectivityManager) context.getSystemService(ConnectivityManager.class);
+        connectivityManager = context.getSystemService(ConnectivityManager.class);
         dnsServers  = readActiveDns();
     }
 
@@ -65,7 +66,10 @@ private DNSList readActiveDns() {
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
             isPrivateDnsActive = props.isPrivateDnsActive();
         }
-        return toDnsList(props.getDnsServers());
+
+        List<InetAddress> list = props.getDnsServers();
+        extendWithFallbackDNS(list);
+        return toDnsList(list);
     }
 
     private void registerNetworkCallback() {
@@ -81,6 +85,7 @@ private void registerNetworkCallback() {
 
     private synchronized void onNewDNSList(LinkProperties linkProperties) {
         List<InetAddress> newDNSList = linkProperties.getDnsServers();
+        extendWithFallbackDNS(newDNSList);
 
         if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.P) {
             isPrivateDnsActive = linkProperties.isPrivateDnsActive();
@@ -112,6 +117,18 @@ private synchronized void onNewDNSList(LinkProperties linkProperties) {
         }
     }
 
+    private void extendWithFallbackDNS(List<InetAddress> dnsServers) {
+        if (dnsServers.isEmpty()) {
+            return;
+        }
+        if (dnsServers.get(0).isLinkLocalAddress()) {
+            try {
+                InetAddress addr = InetAddress.getByName("1.1.1.1");
+                dnsServers.add(0, addr);
+            } catch (UnknownHostException e) {}
+        }
+    }
+
     private void notifyDnsWatcher(DNSList dnsServers) throws Exception {
         listener.onChanged(dnsServers);
     }