Use Android's DNS resolver

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

@@ -29,14 +29,11 @@ import android.os.Build;
 
 import androidx.annotation.NonNull;
 
-import org.xbill.DNS.Flags;
 import org.xbill.DNS.Lookup;
 import org.xbill.DNS.MXRecord;
 import org.xbill.DNS.Message;
-import org.xbill.DNS.OPTRecord;
 import org.xbill.DNS.Record;
 import org.xbill.DNS.SRVRecord;
-import org.xbill.DNS.Section;
 import org.xbill.DNS.SimpleResolver;
 import org.xbill.DNS.TextParseException;
 import org.xbill.DNS.Type;
@@ -46,6 +43,7 @@ import java.net.InetAddress;
 import java.net.UnknownHostException;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.concurrent.Executor;
 import java.util.concurrent.Semaphore;
 import java.util.concurrent.TimeUnit;
 
@@ -129,60 +127,70 @@ public class DnsHelper {
 
                 @Override
                 public Message send(Message query) throws IOException {
-                    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q || !BuildConfig.DEBUG)
+                    if (Build.VERSION.SDK_INT < Build.VERSION_CODES.Q)
                         return super.send(query);
                     else {
                         Log.i("Using Android DNS resolver");
                         Semaphore sem = new Semaphore(0);
                         DnsResolver resolver = DnsResolver.getInstance();
-                        OPTRecord optRecord = new OPTRecord(4096, 0, 0, Flags.DO, null);
-                        query.addRecord(optRecord, Section.ADDITIONAL);
-                        query.getHeader().setFlag(Flags.AD);
+                        //OPTRecord optRecord = new OPTRecord(4096, 0, 0, Flags.DO, null);
+                        //query.addRecord(optRecord, Section.ADDITIONAL);
+                        //query.getHeader().setFlag(Flags.AD);
                         Log.i("DNS query=" + query.toString());
                         resolver.rawQuery(
                                 null,
                                 query.toWire(),
                                 DnsResolver.FLAG_EMPTY,
-                                Helper.getBackgroundExecutor(1, "dns"),
+                                new Executor() {
+                                    @Override
+                                    public void execute(Runnable command) {
+                                        command.run();
+                                    }
+                                },
                                 null,
                                 new DnsResolver.Callback<byte[]>() {
                                     @Override
                                     public void onAnswer(@NonNull byte[] answer, int rcode) {
-                                        Log.i("DNS rcode=" + rcode);
                                         try {
                                             if (rcode == 0)
                                                 result = new Message(answer);
                                             else
-                                                throw new IOException("rcode=" + rcode);
+                                                ex = new IOException("rcode=" + rcode);
                                         } catch (Throwable e) {
                                             ex = new IOException(e.getMessage());
+                                        } finally {
+                                            sem.release();
                                         }
-                                        sem.release();
                                     }
 
                                     @Override
                                     public void onError(@NonNull DnsResolver.DnsException e) {
-                                        Log.w(e);
-                                        ex = new IOException(e.getMessage());
-                                        sem.release();
+                                        try {
+                                            Log.w(e);
+                                            ex = new IOException(e.getMessage());
+                                        } finally {
+                                            sem.release();
+                                        }
                                     }
                                 });
                         try {
                             if (!sem.tryAcquire(LOOKUP_TIMEOUT, TimeUnit.SECONDS))
-                                throw new IOException("timeout");
+                                ex = new IOException("timeout");
                         } catch (InterruptedException e) {
                             ex = new IOException("interrupted");
                         }
 
                         if (ex == null) {
-                            ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
-                            Network active = (cm == null ? null : cm.getActiveNetwork());
-                            LinkProperties props = (active == null ? null : cm.getLinkProperties(active));
-                            Log.i("DNS private=" + (props == null ? null : props.isPrivateDnsActive()));
+                            //ConnectivityManager cm = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
+                            //Network active = (cm == null ? null : cm.getActiveNetwork());
+                            //LinkProperties props = (active == null ? null : cm.getLinkProperties(active));
+                            //Log.i("DNS private=" + (props == null ? null : props.isPrivateDnsActive()));
                             Log.i("DNS answer=" + result.toString() + " flags=" + result.getHeader().printFlags());
                             return result;
-                        } else
+                        } else {
+                            Log.w(ex);
                             throw ex;
+                        }
                     }
                 }
             };