Get network DNS server

app/src/main/java/eu/faircode/email/ConnectionHelper.java

@@ -3,6 +3,7 @@ package eu.faircode.email;
 import android.content.Context;
 import android.content.SharedPreferences;
 import android.net.ConnectivityManager;
+import android.net.LinkProperties;
 import android.net.Network;
 import android.net.NetworkCapabilities;
 import android.net.NetworkInfo;
@@ -16,6 +17,7 @@ import com.bugsnag.android.BreadcrumbType;
 import com.bugsnag.android.Bugsnag;
 import com.sun.mail.imap.IMAPStore;
 
+import java.net.InetAddress;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
@@ -26,6 +28,11 @@ import java.util.Map;
 import javax.mail.MessagingException;
 
 public class ConnectionHelper {
+    private static final String DEFAULT_DNS = "8.8.8.8";
+
+    static final int AUTH_TYPE_PASSWORD = 1;
+    static final int AUTH_TYPE_GMAIL = 2;
+
     // Roam like at home
     // https://en.wikipedia.org/wiki/European_Union_roaming_regulations
     private static final List<String> RLAH_COUNTRY_CODES = Collections.unmodifiableList(Arrays.asList(
@@ -62,9 +69,6 @@ public class ConnectionHelper {
             "GB" // United Kingdom
     ));
 
-    static final int AUTH_TYPE_PASSWORD = 1;
-    static final int AUTH_TYPE_GMAIL = 2;
-
     static class NetworkState {
         private Boolean connected = null;
         private Boolean suitable = null;
@@ -269,4 +273,23 @@ public class ConnectionHelper {
         return Settings.System.getInt(context.getContentResolver(),
                 Settings.Global.AIRPLANE_MODE_ON, 0) != 0;
     }
+
+    static String getDnsServer(Context context) {
+        if (android.os.Build.VERSION.SDK_INT < android.os.Build.VERSION_CODES.M)
+            return DEFAULT_DNS;
+        ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
+        if (cm == null)
+            return DEFAULT_DNS;
+        Network active = cm.getActiveNetwork();
+        if (active == null)
+            return DEFAULT_DNS;
+        LinkProperties props = cm.getLinkProperties(active);
+        if (props == null)
+            return DEFAULT_DNS;
+        List<InetAddress> dns = props.getDnsServers();
+        if (dns.size() == 0)
+            return DEFAULT_DNS;
+        else
+            return dns.get(0).getHostAddress();
+    }
 }

app/src/main/java/eu/faircode/email/EmailProvider.java

@@ -167,17 +167,17 @@ public class EmailProvider {
     private static EmailProvider fromDomainInternal(Context context, String domain) throws IOException {
         try {
             Log.i("Provider from DNS domain=" + domain);
-            return addSpecials(context, fromDNS(domain));
+            return addSpecials(context, fromDNS(context, domain));
         } catch (Throwable ex) {
             Log.w(ex);
             try {
                 Log.i("Provider from ISPDB domain=" + domain);
-                return addSpecials(context, fromISPDB(domain));
+                return addSpecials(context, fromISPDB(context, domain));
             } catch (Throwable ex1) {
                 Log.w(ex1);
                 try {
                     Log.i("Provider from template domain=" + domain);
-                    return addSpecials(context, fromTemplate(domain));
+                    return addSpecials(context, fromTemplate(context, domain));
                 } catch (Throwable ex2) {
                     Log.w(ex2);
                     throw new UnknownHostException(context.getString(R.string.title_setup_no_settings, domain));
@@ -186,7 +186,7 @@ public class EmailProvider {
         }
     }
 
-    private static EmailProvider fromISPDB(String domain) throws IOException, XmlPullParserException {
+    private static EmailProvider fromISPDB(Context context, String domain) throws IOException, XmlPullParserException {
         EmailProvider provider = new EmailProvider(domain);
 
         // https://wiki.mozilla.org/Thunderbird:Autoconfiguration:ConfigFileFormat
@@ -366,10 +366,10 @@ public class EmailProvider {
         return provider;
     }
 
-    private static EmailProvider fromDNS(String domain) throws TextParseException, UnknownHostException {
+    private static EmailProvider fromDNS(Context context, String domain) throws TextParseException, UnknownHostException {
         // https://tools.ietf.org/html/rfc6186
-        SRVRecord imap = lookup("_imaps._tcp." + domain);
+        SRVRecord imap = lookup(context, "_imaps._tcp." + domain);
-        SRVRecord smtp = lookup("_submission._tcp." + domain);
+        SRVRecord smtp = lookup(context, "_submission._tcp." + domain);
 
         EmailProvider provider = new EmailProvider(domain);
         provider.imap_host = imap.getTarget().toString(true);
@@ -383,7 +383,7 @@ public class EmailProvider {
         return provider;
     }
 
-    private static EmailProvider fromTemplate(String domain) throws UnknownHostException {
+    private static EmailProvider fromTemplate(Context context, String domain) throws UnknownHostException {
         if (checkTemplate(domain, null, 993, null, 587))
             return new EmailProvider(domain, domain, null, null);
 
@@ -403,7 +403,7 @@ public class EmailProvider {
                 isHostReachable((smtp_prefix == null ? "" : smtp_prefix + ".") + domain, smtp_port, 5000);
     }
 
-    static boolean isHostReachable(String host, int port, int timeoutms) {
+    private static boolean isHostReachable(String host, int port, int timeoutms) {
         Log.i("Checking " + host + ":" + port);
         try (Socket socket = new Socket()) {
             InetAddress iaddr = InetAddress.getByName(host);
@@ -439,24 +439,26 @@ public class EmailProvider {
         return provider;
     }
 
-    private static SRVRecord lookup(String dns) throws TextParseException, UnknownHostException {
+    private static SRVRecord lookup(Context context, String record) throws TextParseException, UnknownHostException {
-        Lookup lookup = new Lookup(dns, Type.SRV);
+        Lookup lookup = new Lookup(record, Type.SRV);
 
         // https://dns.watch/ 84.200.69.80
-        SimpleResolver resolver = new SimpleResolver(Helper.DEFAULT_DNS);
+        SimpleResolver resolver = new SimpleResolver(ConnectionHelper.getDnsServer(context));
         lookup.setResolver(resolver);
-        Log.i("Lookup dns=" + dns + " @" + resolver.getAddress());
+        Log.i("Lookup record=" + record + " @" + resolver.getAddress());
         Record[] records = lookup.run();
 
         if (lookup.getResult() != Lookup.SUCCESSFUL)
             if (lookup.getResult() == Lookup.HOST_NOT_FOUND ||
                     lookup.getResult() == Lookup.TYPE_NOT_FOUND)
-                throw new UnknownHostException(dns);
+                throw new UnknownHostException(record);
             else
                 throw new IllegalArgumentException(lookup.getErrorString());
 
-        Log.i("Found dns=" + (records == null ? -1 : records.length));
+        SRVRecord result = (records == null || records.length == 0 ? null : (SRVRecord) records[0]);
-        return (records == null || records.length == 0 ? null : (SRVRecord) records[0]);
+        Log.i("Found record=" + (records == null ? -1 : records.length) +
+                " result=" + (result == null ? "" : result.toString()));
+        return result;
     }
 
     @Override

app/src/main/java/eu/faircode/email/FragmentCompose.java

@@ -2769,14 +2769,16 @@ public class FragmentCompose extends FragmentBase {
 
             String domain = email.split("@")[1];
             Lookup lookup = new Lookup(domain, Type.MX);
-            SimpleResolver resolver = new SimpleResolver(Helper.DEFAULT_DNS);
+            SimpleResolver resolver = new SimpleResolver(ConnectionHelper.getDnsServer(context));
             lookup.setResolver(resolver);
-            Log.i("Lookup dns=" + domain + " @" + resolver.getAddress());
+            Log.i("Lookup MX=" + domain + " @" + resolver.getAddress());
 
             lookup.run();
             if (lookup.getResult() == Lookup.HOST_NOT_FOUND ||
-                    lookup.getResult() == Lookup.TYPE_NOT_FOUND)
+                    lookup.getResult() == Lookup.TYPE_NOT_FOUND) {
+                Log.i("Lookup MX=" + domain + " result=" + lookup.getErrorString());
                 throw new IllegalArgumentException(context.getString(R.string.title_no_server, domain));
+            }
         }
 
         private String getActionName(int id) {

app/src/main/java/eu/faircode/email/Helper.java

@@ -114,8 +114,6 @@ public class Helper {
 
     static final float LOW_LIGHT = 0.6f;
 
-    static final String DEFAULT_DNS = "8.8.8.8";
-
     static final String FAQ_URI = "https://github.com/M66B/FairEmail/blob/master/FAQ.md";
     static final String XDA_URI = "https://forum.xda-developers.com/android/apps-games/source-email-t3824168";