Networkstack: easy happy eyeball (#411)

* Networkstack: easy happy eyeball

* Networkstack: drop own implementation of DNS-Server selection

Co-authored-by: Christian Schneppe <kriztan@users.noreply.github.com>

5 files changed, 158 insertions, 392 deletions

diff --git a/src/main/java/de/pixart/messenger/persistance/DatabaseBackend.java b/src/main/java/de/pixart/messenger/persistance/DatabaseBackend.java
index 9738bb8b3..36d9c945b 100644
--- a/src/main/java/de/pixart/messenger/persistance/DatabaseBackend.java
+++ b/src/main/java/de/pixart/messenger/persistance/DatabaseBackend.java
@@ -53,7 +53,6 @@ import de.pixart.messenger.services.ShortcutService;
 import de.pixart.messenger.utils.CryptoHelper;
 import de.pixart.messenger.utils.CursorUtils;
 import de.pixart.messenger.utils.FtsUtils;
-import de.pixart.messenger.utils.Resolver;
 import de.pixart.messenger.xmpp.InvalidJid;
 import de.pixart.messenger.xmpp.mam.MamReference;
 import rocks.xmpp.addr.Jid;
@@ -149,17 +148,6 @@ public class DatabaseBackend extends SQLiteOpenHelper {
             + ") ON CONFLICT IGNORE"
             + ");";
 
-    private static String RESOLVER_RESULTS_TABLENAME = "resolver_results";
-    private static String CREATE_RESOLVER_RESULTS_TABLE = "create table " + RESOLVER_RESULTS_TABLENAME + "("
-            + Resolver.Result.DOMAIN + " TEXT,"
-            + Resolver.Result.HOSTNAME + " TEXT,"
-            + Resolver.Result.IP + " BLOB,"
-            + Resolver.Result.PRIORITY + " NUMBER,"
-            + Resolver.Result.DIRECT_TLS + " NUMBER,"
-            + Resolver.Result.AUTHENTICATED + " NUMBER,"
-            + Resolver.Result.PORT + " NUMBER,"
-            + "UNIQUE(" + Resolver.Result.DOMAIN + ") ON CONFLICT REPLACE"
-            + ");";
     private static String CREATE_MESSAGE_TIME_INDEX = "create INDEX message_time_index ON " + Message.TABLENAME + "(" + Message.TIME_SENT + ")";
     private static String CREATE_MESSAGE_CONVERSATION_INDEX = "create INDEX message_conversation_index ON " + Message.TABLENAME + "(" + Message.CONVERSATION + ")";
     private static String CREATE_MESSAGE_DELETED_INDEX = "create index message_deleted_index ON " + Message.TABLENAME + "(" + Message.DELETED + ")";
@@ -258,7 +246,6 @@ public class DatabaseBackend extends SQLiteOpenHelper {
         db.execSQL(CREATE_SIGNED_PREKEYS_STATEMENT);
         db.execSQL(CREATE_IDENTITIES_STATEMENT);
         db.execSQL(CREATE_PRESENCE_TEMPLATES_STATEMENT);
-        db.execSQL(CREATE_RESOLVER_RESULTS_TABLE);
         db.execSQL(CREATE_MESSAGE_INDEX_TABLE);
         db.execSQL(CREATE_MESSAGE_INSERT_TRIGGER);
         db.execSQL(CREATE_MESSAGE_UPDATE_TRIGGER);
@@ -528,10 +515,6 @@ public class DatabaseBackend extends SQLiteOpenHelper {
             db.execSQL("ALTER TABLE " + Message.TABLENAME + " ADD COLUMN " + Message.MARKABLE + " NUMBER DEFAULT 0");
         }
 
-        if (oldVersion < 40 && newVersion >= 40) {
-            db.execSQL(CREATE_RESOLVER_RESULTS_TABLE);
-        }
-
         if (oldVersion < 42 && newVersion >= 42) {
             db.execSQL(CREATE_MESSAGE_INDEX_TABLE);
             db.execSQL(CREATE_MESSAGE_INSERT_TRIGGER);
@@ -561,14 +544,6 @@ public class DatabaseBackend extends SQLiteOpenHelper {
             }
         }
 
-        if (oldVersion < 48 && newVersion >= 48) {
-            try {
-                db.execSQL(CREATE_RESOLVER_RESULTS_TABLE);
-            } catch (Exception e) {
-                //ignore
-            }
-        }
-
         if (oldVersion < 49 && newVersion >= 49) {
             db.execSQL("ALTER TABLE " + Message.TABLENAME + " ADD COLUMN " + Message.BODY_LANGUAGE);
         }
@@ -581,6 +556,8 @@ public class DatabaseBackend extends SQLiteOpenHelper {
             final long diff = SystemClock.elapsedRealtime() - start;
             Log.d(Config.LOGTAG, "deleted old edit information in " + diff + "ms");
         }
+
+        db.execSQL("DROP TABLE IF EXISTS resolver_results");
     }
 
     private boolean isColumnExisting(SQLiteDatabase db, String TableName, String ColumnName) {
@@ -717,34 +694,6 @@ public class DatabaseBackend extends SQLiteOpenHelper {
         return result;
     }
 
-    public void saveResolverResult(String domain, Resolver.Result result) {
-        SQLiteDatabase db = this.getWritableDatabase();
-        ContentValues contentValues = result.toContentValues();
-        contentValues.put(Resolver.Result.DOMAIN, domain);
-        db.insert(RESOLVER_RESULTS_TABLENAME, null, contentValues);
-    }
-
-    public synchronized Resolver.Result findResolverResult(String domain) {
-        SQLiteDatabase db = this.getReadableDatabase();
-        String where = Resolver.Result.DOMAIN + "=?";
-        String[] whereArgs = {domain};
-        final Cursor cursor = db.query(RESOLVER_RESULTS_TABLENAME, null, where, whereArgs, null, null, null);
-        Resolver.Result result = null;
-        if (cursor != null) {
-            try {
-                if (cursor.moveToFirst()) {
-                    result = Resolver.Result.fromCursor(cursor);
-                }
-            } catch (Exception e) {
-                Log.d(Config.LOGTAG, "unable to find cached resolver result in database " + e.getMessage());
-                return null;
-            } finally {
-                cursor.close();
-            }
-        }
-        return result;
-    }
-
     public void insertPresenceTemplate(PresenceTemplate template) {
         SQLiteDatabase db = this.getWritableDatabase();
         String whereToDelete = PresenceTemplate.MESSAGE + "=?";
diff --git a/src/main/java/de/pixart/messenger/utils/AndroidUsingExecLowPriority.java b/src/main/java/de/pixart/messenger/utils/AndroidUsingExecLowPriority.java
deleted file mode 100644
index 6097fcd03..000000000
--- a/src/main/java/de/pixart/messenger/utils/AndroidUsingExecLowPriority.java
+++ /dev/null
@@ -1,92 +0,0 @@
-/*
- * Copyright 2015-2016 the original author or authors
- *
- * This software is licensed under the Apache License, Version 2.0,
- * the GNU Lesser General Public License version 2 or later ("LGPL")
- * and the WTFPL.
- * You may choose either license to govern your use of this software only
- * upon the condition that you accept all of the terms of either
- * the Apache License 2.0, the LGPL 2.1+ or the WTFPL.
- */
-
-package de.pixart.messenger.utils;
-
-import java.io.IOException;
-import java.io.InputStream;
-import java.io.InputStreamReader;
-import java.io.LineNumberReader;
-import java.net.InetAddress;
-import java.util.HashSet;
-import java.util.logging.Level;
-
-import de.measite.minidns.dnsserverlookup.AbstractDNSServerLookupMechanism;
-import de.measite.minidns.dnsserverlookup.AndroidUsingReflection;
-import de.measite.minidns.dnsserverlookup.DNSServerLookupMechanism;
-import de.measite.minidns.util.PlatformDetection;
-
-/**
- * Try to retrieve the list of DNS server by executing getprop.
- */
-public class AndroidUsingExecLowPriority extends AbstractDNSServerLookupMechanism {
-
-    public static final DNSServerLookupMechanism INSTANCE = new AndroidUsingExecLowPriority();
-    public static final int PRIORITY = AndroidUsingReflection.PRIORITY + 1;
-
-    private AndroidUsingExecLowPriority() {
-        super(AndroidUsingExecLowPriority.class.getSimpleName(), PRIORITY);
-    }
-
-    @Override
-    public String[] getDnsServerAddresses() {
-        try {
-            Process process = Runtime.getRuntime().exec("getprop");
-            InputStream inputStream = process.getInputStream();
-            LineNumberReader lnr = new LineNumberReader(
-                    new InputStreamReader(inputStream));
-            String line;
-            HashSet<String> server = new HashSet<>(6);
-            while ((line = lnr.readLine()) != null) {
-                int split = line.indexOf("]: [");
-                if (split == -1) {
-                    continue;
-                }
-                String property = line.substring(1, split);
-                String value = line.substring(split + 4, line.length() - 1);
-
-                if (value.isEmpty()) {
-                    continue;
-                }
-
-                if (property.endsWith(".dns") || property.endsWith(".dns1") ||
-                        property.endsWith(".dns2") || property.endsWith(".dns3") ||
-                        property.endsWith(".dns4")) {
-
-                    // normalize the address
-
-                    InetAddress ip = InetAddress.getByName(value);
-
-                    if (ip == null) continue;
-
-                    value = ip.getHostAddress();
-
-                    if (value == null) continue;
-                    if (value.length() == 0) continue;
-
-                    server.add(value);
-                }
-            }
-            if (server.size() > 0) {
-                return server.toArray(new String[server.size()]);
-            }
-        } catch (IOException e) {
-            LOGGER.log(Level.WARNING, "Exception in findDNSByExec", e);
-        }
-        return null;
-    }
-
-    @Override
-    public boolean isAvailable() {
-        return PlatformDetection.isAndroid();
-    }
-
-}
\ No newline at end of file
diff --git a/src/main/java/de/pixart/messenger/utils/AndroidUsingLinkProperties.java b/src/main/java/de/pixart/messenger/utils/AndroidUsingLinkProperties.java
deleted file mode 100644
index f2f33dc1b..000000000
--- a/src/main/java/de/pixart/messenger/utils/AndroidUsingLinkProperties.java
+++ /dev/null
@@ -1,90 +0,0 @@
-package de.pixart.messenger.utils;
-
-import android.annotation.TargetApi;
-import android.content.Context;
-import android.net.ConnectivityManager;
-import android.net.LinkProperties;
-import android.net.Network;
-import android.net.NetworkInfo;
-import android.net.RouteInfo;
-import android.os.Build;
-
-import java.net.Inet4Address;
-import java.net.InetAddress;
-import java.util.ArrayList;
-import java.util.List;
-
-import de.measite.minidns.dnsserverlookup.AbstractDNSServerLookupMechanism;
-import de.measite.minidns.dnsserverlookup.AndroidUsingExec;
-
-public class AndroidUsingLinkProperties extends AbstractDNSServerLookupMechanism {
-
-    private final Context context;
-
-    AndroidUsingLinkProperties(Context context) {
-        super(AndroidUsingLinkProperties.class.getSimpleName(), AndroidUsingExec.PRIORITY - 1);
-        this.context = context;
-    }
-
-    @Override
-    public boolean isAvailable() {
-        return Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP;
-    }
-
-    @Override
-    @TargetApi(21)
-    public String[] getDnsServerAddresses() {
-        final ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
-        final Network[] networks = connectivityManager == null ? null : connectivityManager.getAllNetworks();
-        if (networks == null) {
-            return new String[0];
-        }
-        final Network activeNetwork = getActiveNetwork(connectivityManager);
-        final List<String> servers = new ArrayList<>();
-        int vpnOffset = 0;
-        for (Network network : networks) {
-            LinkProperties linkProperties = connectivityManager.getLinkProperties(network);
-            if (linkProperties == null) {
-                continue;
-            }
-            final NetworkInfo networkInfo = connectivityManager.getNetworkInfo(network);
-            final boolean isActiveNetwork = network.equals(activeNetwork);
-            final boolean isVpn = networkInfo != null && networkInfo.getType() == ConnectivityManager.TYPE_VPN;
-            if (isActiveNetwork && isVpn) {
-                final List<String> tmp = getIPv4First(linkProperties.getDnsServers());
-                servers.addAll(0, tmp);
-                vpnOffset += tmp.size();
-            } else if (hasDefaultRoute(linkProperties) || isActiveNetwork || activeNetwork == null || isVpn) {
-                servers.addAll(vpnOffset, getIPv4First(linkProperties.getDnsServers()));
-            }
-        }
-        return servers.toArray(new String[0]);
-    }
-
-    @TargetApi(23)
-    private static Network getActiveNetwork(ConnectivityManager cm) {
-        return Build.VERSION.SDK_INT >= Build.VERSION_CODES.M ? cm.getActiveNetwork() : null;
-    }
-
-    private static List<String> getIPv4First(List<InetAddress> in) {
-        List<String> out = new ArrayList<>();
-        for (InetAddress address : in) {
-            if (address instanceof Inet4Address) {
-                out.add(0, address.getHostAddress());
-            } else {
-                out.add(address.getHostAddress());
-            }
-        }
-        return out;
-    }
-
-    @TargetApi(Build.VERSION_CODES.LOLLIPOP)
-    private static boolean hasDefaultRoute(LinkProperties linkProperties) {
-        for (RouteInfo route : linkProperties.getRoutes()) {
-            if (route.isDefaultRoute()) {
-                return true;
-            }
-        }
-        return false;
-    }
-}
\ No newline at end of file
diff --git a/src/main/java/de/pixart/messenger/utils/Resolver.java b/src/main/java/de/pixart/messenger/utils/Resolver.java
index 3fe7e2286..0221b08b7 100644
--- a/src/main/java/de/pixart/messenger/utils/Resolver.java
+++ b/src/main/java/de/pixart/messenger/utils/Resolver.java
@@ -8,11 +8,17 @@ import androidx.annotation.NonNull;
 
 import java.io.IOException;
 import java.lang.reflect.Field;
-import java.net.Inet4Address;
 import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.net.Socket;
 import java.net.UnknownHostException;
 import java.util.ArrayList;
 import java.util.Collections;
+import java.util.concurrent.Callable;
+import java.util.concurrent.ExecutionException;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
 import java.util.List;
 
 import de.measite.minidns.AbstractDNSClient;
@@ -21,7 +27,6 @@ import de.measite.minidns.DNSName;
 import de.measite.minidns.Question;
 import de.measite.minidns.Record;
 import de.measite.minidns.dnssec.DNSSECResultNotAuthenticException;
-import de.measite.minidns.dnsserverlookup.AndroidUsingExec;
 import de.measite.minidns.hla.DnssecResolverApi;
 import de.measite.minidns.hla.ResolverApi;
 import de.measite.minidns.hla.ResolverResult;
@@ -34,22 +39,21 @@ import de.measite.minidns.record.InternetAddressRR;
 import de.measite.minidns.record.SRV;
 import de.pixart.messenger.Config;
 import de.pixart.messenger.R;
+import de.pixart.messenger.persistance.FileBackend;
 import de.pixart.messenger.services.XmppConnectionService;
 
 public class Resolver {
 
     public static final int DEFAULT_PORT_XMPP = 5222;
+
     private static final String DIRECT_TLS_SERVICE = "_xmpps-client";
-    private static final String STARTTLS_SERICE = "_xmpp-client";
+    private static final String STARTTLS_SERVICE = "_xmpp-client";
 
     private static XmppConnectionService SERVICE = null;
 
 
     public static void init(XmppConnectionService service) {
         Resolver.SERVICE = service;
-        DNSClient.removeDNSServerLookupMechanism(AndroidUsingExec.INSTANCE);
-        DNSClient.addDnsServerLookupMechanism(AndroidUsingExecLowPriority.INSTANCE);
-        DNSClient.addDnsServerLookupMechanism(new AndroidUsingLinkProperties(service));
         final AbstractDNSClient client = ResolverApi.INSTANCE.getClient();
         if (client instanceof ReliableDNSClient) {
             disableHardcodedDnsServers((ReliableDNSClient) client);
@@ -72,23 +76,25 @@ public class Resolver {
         }
     }
 
-    public static List<Result> fromHardCoded(String hostname, int port) {
-        Result result = new Result();
-        result.hostname = DNSName.from(hostname);
-        result.port = port;
-        result.directTls = useDirectTls(port);
-        result.authenticated = true;
-        return Collections.singletonList(result);
+    public static Result fromHardCoded(String hostname, int port) {
+        final Result ipResult = fromIpAddress(hostname, port);
+        if (ipResult != null) {
+            ipResult.connect();
+            return ipResult;
+        }
+        return happyEyeball(resolveNoSrvRecords(DNSName.from(hostname), port, true));
     }
 
+
     public static boolean useDirectTls(final int port) {
         return port == 443 || port == 5223;
     }
 
-    public static List<Result> resolve(String domain) {
-        final List<Result> ipResults = fromIpAddress(domain);
-        if (ipResults.size() > 0) {
-            return ipResults;
+    public static Result resolve(String domain) {
+        final Result ipResult = fromIpAddress(domain, DEFAULT_PORT_XMPP);
+        if (ipResult != null) {
+            ipResult.connect();
+            return ipResult;
         }
         final List<Result> results = new ArrayList<>();
         final List<Result> fallbackResults = new ArrayList<>();
@@ -114,7 +120,7 @@ public class Resolver {
             }
         });
         threads[2] = new Thread(() -> {
-            List<Result> list = resolveNoSrvRecords(DNSName.from(domain), true);
+            List<Result> list = resolveNoSrvRecords(DNSName.from(domain), DEFAULT_PORT_XMPP, true);
             synchronized (fallbackResults) {
                 fallbackResults.addAll(list);
             }
@@ -130,40 +136,40 @@ public class Resolver {
                 synchronized (results) {
                     Collections.sort(results);
                     Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + ": " + results.toString());
-                    return new ArrayList<>(results);
+                    return happyEyeball(results);
                 }
             } else {
                 threads[2].join();
                 synchronized (fallbackResults) {
                     Collections.sort(fallbackResults);
                     Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + ": " + fallbackResults.toString());
-                    return new ArrayList<>(fallbackResults);
+                    return happyEyeball(fallbackResults);
                 }
             }
         } catch (InterruptedException e) {
             for (Thread thread : threads) {
                 thread.interrupt();
             }
-            return Collections.emptyList();
+            return null;
         }
     }
 
-    private static List<Result> fromIpAddress(String domain) {
+    private static Result fromIpAddress(String domain, int port) {
         if (!IP.matches(domain)) {
-            return Collections.emptyList();
+            return null;
         }
         try {
             Result result = new Result();
             result.ip = InetAddress.getByName(domain);
-            result.port = DEFAULT_PORT_XMPP;
-            return Collections.singletonList(result);
+            result.port = port;
+            return result;
         } catch (UnknownHostException e) {
-            return Collections.emptyList();
+            return null;
         }
     }
 
     private static List<Result> resolveSrv(String domain, final boolean directTls) throws IOException {
-        DNSName dnsName = DNSName.from((directTls ? DIRECT_TLS_SERVICE : STARTTLS_SERICE) + "._tcp." + domain);
+        DNSName dnsName = DNSName.from((directTls ? DIRECT_TLS_SERVICE : STARTTLS_SERVICE) + "._tcp." + domain);
         ResolverResult<SRV> result = resolveWithFallback(dnsName, SRV.class);
         final List<Result> results = new ArrayList<>();
         final List<Thread> threads = new ArrayList<>();
@@ -172,21 +178,15 @@ public class Resolver {
                 continue;
             }
             threads.add(new Thread(() -> {
-                final List<Result> ipv4s = resolveIp(record, A.class, result.isAuthenticData(), directTls);
-                if (ipv4s.size() == 0) {
-                    Result resolverResult = Result.fromRecord(record, directTls);
-                    resolverResult.authenticated = resolverResult.isAuthenticated();
-                    ipv4s.add(resolverResult);
-                }
+                final List<Result> ipv6s = resolveIp(record, AAAA.class, result.isAuthenticData(), directTls);
                 synchronized (results) {
-                    results.addAll(ipv4s);
+                    results.addAll(ipv6s);
                 }
-
             }));
             threads.add(new Thread(() -> {
-                final List<Result> ipv6s = resolveIp(record, AAAA.class, result.isAuthenticData(), directTls);
+                final List<Result> ipv4s = resolveIp(record, A.class, result.isAuthenticData(), directTls);
                 synchronized (results) {
-                    results.addAll(ipv6s);
+                    results.addAll(ipv4s);
                 }
             }));
         }
@@ -219,24 +219,23 @@ public class Resolver {
         return list;
     }
 
-    private static List<Result> resolveNoSrvRecords(DNSName dnsName, boolean withCnames) {
+    private static List<Result> resolveNoSrvRecords(DNSName dnsName, int port, boolean withCnames) {
         List<Result> results = new ArrayList<>();
         try {
-            for (A a : resolveWithFallback(dnsName, A.class, false).getAnswersOrEmptySet()) {
-                results.add(Result.createDefault(dnsName, a.getInetAddress()));
-            }
             for (AAAA aaaa : resolveWithFallback(dnsName, AAAA.class, false).getAnswersOrEmptySet()) {
-                results.add(Result.createDefault(dnsName, aaaa.getInetAddress()));
+                results.add(Result.createDefault(dnsName, aaaa.getInetAddress(), port));
+            }
+            for (A a : resolveWithFallback(dnsName, A.class, false).getAnswersOrEmptySet()) {
+                results.add(Result.createDefault(dnsName, a.getInetAddress(), port));
             }
             if (results.size() == 0 && withCnames) {
                 for (CNAME cname : resolveWithFallback(dnsName, CNAME.class, false).getAnswersOrEmptySet()) {
-                    results.addAll(resolveNoSrvRecords(cname.name, false));
+                    results.addAll(resolveNoSrvRecords(cname.name, port, false));
                 }
             }
         } catch (Throwable throwable) {
             Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + "error resolving fallback records", throwable);
         }
-        results.add(Result.createDefault(dnsName));
         return results;
     }
 
@@ -261,24 +260,64 @@ public class Resolver {
         return ResolverApi.INSTANCE.resolve(question);
     }
 
+    private static Result happyEyeball(List<Result> r) {
+        if (r.size() == 0) return null;
+
+        Result result;
+        if (r.size() == 1) {
+            result = r.get(0);
+            result.connect();
+            return result;
+        }
+
+        ExecutorService executor = (ExecutorService) Executors.newFixedThreadPool(4);
+
+        try {
+            result = executor.invokeAny(r);
+            executor.shutdown();
+            Thread disconnector = new Thread(() -> {
+                while (true) {
+                    try {
+                        if (executor.awaitTermination(5, TimeUnit.SECONDS)) break;
+                        Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + ": happy eyeball wait for cleanup ...");
+                    } catch (InterruptedException e) {}
+                }
+                Log.i(Config.LOGTAG, Resolver.class.getSimpleName() + ": happy eyeball cleanup");
+                for (Result re : r) {
+                    if(!re.equals(result)) re.disconnect();
+                }
+            });
+            disconnector.start();
+            Log.i(Config.LOGTAG, Resolver.class.getSimpleName() + ": happy eyeball used: " + result.toString());
+            return result;
+        } catch (InterruptedException e) {
+            Log.e(Config.LOGTAG, Resolver.class.getSimpleName() + ": happy eyeball failed: ", e);
+            return null;
+        } catch (ExecutionException e) {
+            Log.e(Config.LOGTAG, Resolver.class.getSimpleName() + ": happy eyeball failed: ", e);
+            return null;
+        }
+    }
+
     private static boolean validateHostname() {
         return SERVICE != null && SERVICE.getBooleanPreference("validate_hostname", R.bool.validate_hostname);
     }
 
-    public static class Result implements Comparable<Result> {
-        public static final String DOMAIN = "domain";
+    public static class Result implements Comparable<Result>, Callable<Result> {
         public static final String IP = "ip";
         public static final String HOSTNAME = "hostname";
         public static final String PORT = "port";
         public static final String PRIORITY = "priority";
         public static final String DIRECT_TLS = "directTls";
         public static final String AUTHENTICATED = "authenticated";
+
         private InetAddress ip;
         private DNSName hostname;
         private int port = DEFAULT_PORT_XMPP;
         private boolean directTls = false;
         private boolean authenticated = false;
         private int priority;
+        private Socket socket;
 
         static Result fromRecord(SRV srv, boolean directTls) {
             Result result = new Result();
@@ -288,35 +327,15 @@ public class Resolver {
             result.priority = srv.priority;
             return result;
         }
-
-        static Result createDefault(DNSName hostname, InetAddress ip) {
+ 
+        static Result createDefault(DNSName hostname, InetAddress ip, int port) {
             Result result = new Result();
-            result.port = DEFAULT_PORT_XMPP;
+            result.port = port;
             result.hostname = hostname;
             result.ip = ip;
             return result;
         }
 
-        static Result createDefault(DNSName hostname) {
-            return createDefault(hostname, null);
-        }
-
-        public static Result fromCursor(Cursor cursor) {
-            final Result result = new Result();
-            try {
-                result.ip = InetAddress.getByAddress(cursor.getBlob(cursor.getColumnIndex(IP)));
-            } catch (UnknownHostException e) {
-                result.ip = null;
-            }
-            final String hostname = cursor.getString(cursor.getColumnIndex(HOSTNAME));
-            result.hostname = hostname == null ? null : DNSName.from(hostname);
-            result.port = cursor.getInt(cursor.getColumnIndex(PORT));
-            result.priority = cursor.getInt(cursor.getColumnIndex(PRIORITY));
-            result.authenticated = cursor.getInt(cursor.getColumnIndex(AUTHENTICATED)) > 0;
-            result.directTls = cursor.getInt(cursor.getColumnIndex(DIRECT_TLS)) > 0;
-            return result;
-        }
-
         @Override
         public boolean equals(Object o) {
             if (this == o) return true;
@@ -343,14 +362,6 @@ public class Resolver {
             return result;
         }
 
-        public InetAddress getIp() {
-            return ip;
-        }
-
-        public int getPort() {
-            return port;
-        }
-
         public DNSName getHostname() {
             return hostname;
         }
@@ -363,6 +374,10 @@ public class Resolver {
             return authenticated;
         }
 
+        public Socket getSocket() {
+            return socket;
+        }
+
         @Override
         public String toString() {
             return "Result{" +
@@ -375,21 +390,35 @@ public class Resolver {
                     '}';
         }
 
+        public void connect() {
+            if (this.socket != null) {
+                this.disconnect();
+            }
+            final InetSocketAddress addr = new InetSocketAddress(this.ip, this.port);
+            this.socket = new Socket();
+            try {
+                long time = System.currentTimeMillis();
+                this.socket.connect(addr, Config.SOCKET_TIMEOUT * 1000);
+                time = System.currentTimeMillis() - time;
+                Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + ": Result connect: " + toString() + " after: " + time + " ms");
+            } catch (IOException e) {
+                this.disconnect();
+            }
+        }
+
+        public void disconnect() {
+            if (this.socket != null ) {
+                FileBackend.close(this.socket);
+                this.socket = null;
+                Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + ": Result disconnect: " + toString());
+            }
+        }
+
         @Override
         public int compareTo(@NonNull Result result) {
             if (result.priority == priority) {
                 if (directTls == result.directTls) {
-                    if (ip == null && result.ip == null) {
-                        return 0;
-                    } else if (ip != null && result.ip != null) {
-                        if (ip instanceof Inet4Address && result.ip instanceof Inet4Address) {
-                            return 0;
-                        } else {
-                            return ip instanceof Inet4Address ? -1 : 1;
-                        }
-                    } else {
-                        return ip != null ? -1 : 1;
-                    }
+                    return 0;
                 } else {
                     return directTls ? -1 : 1;
                 }
@@ -397,6 +426,11 @@ public class Resolver {
                 return priority - result.priority;
             }
         }
+        @Override
+        public Result call() throws Exception {
+            this.connect();
+            return this.socket.isConnected() ? this : null;
+        }
 
         public ContentValues toContentValues() {
             final ContentValues contentValues = new ContentValues();
@@ -409,4 +443,5 @@ public class Resolver {
             return contentValues;
         }
     }
-}
\ No newline at end of file
+
+}
diff --git a/src/main/java/de/pixart/messenger/xmpp/XmppConnection.java b/src/main/java/de/pixart/messenger/xmpp/XmppConnection.java
index b8cddc170..be9fd5a3a 100644
--- a/src/main/java/de/pixart/messenger/xmpp/XmppConnection.java
+++ b/src/main/java/de/pixart/messenger/xmpp/XmppConnection.java
@@ -317,86 +317,50 @@ public class XmppConnection implements Runnable {
                 }
             } else {
                 final String domain = account.getJid().getDomain();
-                final List<Resolver.Result> results;
+                final Resolver.Result result;
                 final boolean hardcoded = extended && !account.getHostname().isEmpty();
                 if (hardcoded) {
-                    results = Resolver.fromHardCoded(account.getHostname(), account.getPort());
+                    result = Resolver.fromHardCoded(account.getHostname(), account.getPort());
                 } else {
-                    results = Resolver.resolve(domain);
+                    result = Resolver.resolve(domain);
+                }
+                if (result == null) {
+                    throw new UnknownHostException();
                 }
                 if (Thread.currentThread().isInterrupted()) {
                     Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": Thread was interrupted");
                     return;
                 }
-                if (results.size() == 0) {
-                    Log.e(Config.LOGTAG, account.getJid().asBareJid() + ": Resolver results were empty");
-                    return;
-                }
-                final Resolver.Result storedBackupResult;
-                if (hardcoded) {
-                    storedBackupResult = null;
-                } else {
-                    storedBackupResult = mXmppConnectionService.databaseBackend.findResolverResult(domain);
-                    if (storedBackupResult != null && !results.contains(storedBackupResult)) {
-                        results.add(storedBackupResult);
-                        Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": loaded backup resolver result from db: " + storedBackupResult);
-                    }
-                }
-                for (Iterator<Resolver.Result> iterator = results.iterator(); iterator.hasNext(); ) {
-                    final Resolver.Result result = iterator.next();
-                    if (Thread.currentThread().isInterrupted()) {
-                        Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": Thread was interrupted");
-                        return;
-                    }
-                    try {
-                        // if tls is true, encryption is implied and must not be started
-                        features.encryptionEnabled = result.isDirectTls();
-                        verifiedHostname = result.isAuthenticated() ? result.getHostname().toString() : null;
-                        Log.d(Config.LOGTAG, "verified hostname " + verifiedHostname);
-                        final InetSocketAddress addr;
-                        if (result.getIp() != null) {
-                            addr = new InetSocketAddress(result.getIp(), result.getPort());
-                            Log.d(Config.LOGTAG, account.getJid().asBareJid().toString()
-                                    + ": using values from resolver " + (result.getHostname() == null ? "" : result.getHostname().toString()
-                                    + "/") + result.getIp().getHostAddress() + ":" + result.getPort() + " tls: " + features.encryptionEnabled);
-                        } else {
-                            addr = new InetSocketAddress(IDN.toASCII(result.getHostname().toString()), result.getPort());
-                            Log.d(Config.LOGTAG, account.getJid().asBareJid().toString()
-                                    + ": using values from resolver "
-                                    + result.getHostname().toString() + ":" + result.getPort() + " tls: " + features.encryptionEnabled);
-                        }
+                try {
+                    // if tls is true, encryption is implied and must not be started
+                    features.encryptionEnabled = result.isDirectTls();
+                    verifiedHostname = result.isAuthenticated() ? result.getHostname().toString() : null;
+                    Log.d(Config.LOGTAG,"verified hostname " + verifiedHostname);
+                    Log.d(Config.LOGTAG, account.getJid().asBareJid().toString()
+                            + ": using values from resolver " + result.toString());
 
-                        localSocket = new Socket();
-                        localSocket.connect(addr, Config.SOCKET_TIMEOUT * 1000);
+                    localSocket = result.getSocket();
 
-                        if (features.encryptionEnabled) {
-                            localSocket = upgradeSocketToTls(localSocket);
-                        }
+                    if (features.encryptionEnabled) {
+                        localSocket = upgradeSocketToTls(localSocket);
+                    }
 
-                        localSocket.setSoTimeout(Config.SOCKET_TIMEOUT * 1000);
-                        if (startXmpp(localSocket)) {
-                            localSocket.setSoTimeout(0); //reset to 0; once the connection is established we don’t want this
-                            if (!hardcoded && !result.equals(storedBackupResult)) {
-                                mXmppConnectionService.databaseBackend.saveResolverResult(domain, result);
-                            }
-                            break; // successfully connected to server that speaks xmpp
-                        } else {
-                            FileBackend.close(localSocket);
-                            throw new StateChangingException(Account.State.STREAM_OPENING_ERROR);
-                        }
-                    } catch (final StateChangingException e) {
-                        if (!iterator.hasNext()) {
-                            throw e;
-                        }
-                    } catch (InterruptedException e) {
-                        Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": thread was interrupted before beginning stream");
-                        return;
-                    } catch (final Throwable e) {
-                        Log.d(Config.LOGTAG, account.getJid().asBareJid().toString() + ": " + e.getMessage() + "(" + e.getClass().getName() + ")");
-                        if (!iterator.hasNext()) {
-                            throw new UnknownHostException();
-                        }
+                    localSocket.setSoTimeout(Config.SOCKET_TIMEOUT * 1000);
+                    if (startXmpp(localSocket)) {
+                        localSocket.setSoTimeout(0); //reset to 0; once the connection is established we don’t want this
+                        // successfully connected to server that speaks xmpp
+                    } else {
+                        FileBackend.close(localSocket);
+                        throw new StateChangingException(Account.State.STREAM_OPENING_ERROR);
                     }
+                } catch (final StateChangingException e) {
+                    throw e;
+                } catch (InterruptedException e) {
+                    Log.d(Config.LOGTAG, account.getJid().asBareJid() + ": thread was interrupted before beginning stream");
+                    return;
+                } catch (final Throwable e) {
+                    Log.d(Config.LOGTAG, account.getJid().asBareJid().toString() + ": " + e.getMessage() + "(" + e.getClass().getName() + ")");
+                    throw new UnknownHostException();
                 }
             }
             processStream();