Revert "Networkstack - let OS decide IPv4 or IPv6 (#267)"

This reverts commit e6a15597904019f68c02e6fd8f61fb6de0b13324.

If there is IPv6 available but the server doesn't listen to it, the connection will not be established

5 files changed, 369 insertions, 24 deletions

diff --git a/src/main/java/de/pixart/messenger/persistance/DatabaseBackend.java b/src/main/java/de/pixart/messenger/persistance/DatabaseBackend.java
index 243db470a..ba0f7927d 100644
--- a/src/main/java/de/pixart/messenger/persistance/DatabaseBackend.java
+++ b/src/main/java/de/pixart/messenger/persistance/DatabaseBackend.java
@@ -55,6 +55,7 @@ import de.pixart.messenger.entities.ServiceDiscoveryResult;
 import de.pixart.messenger.services.ShortcutService;
 import de.pixart.messenger.utils.CryptoHelper;
 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;
@@ -62,7 +63,7 @@ import rocks.xmpp.addr.Jid;
 public class DatabaseBackend extends SQLiteOpenHelper {
 
     public static final String DATABASE_NAME = "history";
-    public static final int DATABASE_VERSION = 47; // = Conversations DATABASE_VERSION + 3
+    public static final int DATABASE_VERSION = 48; // = Conversations DATABASE_VERSION + 4
     private static DatabaseBackend instance = null;
 
     private static String CREATE_CONTATCS_STATEMENT = "create table "
@@ -150,6 +151,17 @@ 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 + ")";
@@ -247,6 +259,7 @@ 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);
@@ -516,6 +529,10 @@ 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);
@@ -544,7 +561,14 @@ public class DatabaseBackend extends SQLiteOpenHelper {
                 db.execSQL("ALTER TABLE " + SQLiteAxolotlStore.IDENTITIES_TABLENAME + " ADD COLUMN " + SQLiteAxolotlStore.TRUSTED); // TODO - just to make old databases importable, column isn't needed at all
             }
         }
-	db.execSQL("DROP TABLE resolver_results");
+
+        if (oldVersion < 48 && newVersion >= 48) {
+            try {
+                db.execSQL(CREATE_RESOLVER_RESULTS_TABLE);
+            } catch (Exception e) {
+                //ignore
+            }
+        }
     }
 
     private boolean isColumnExisting(SQLiteDatabase db, String TableName, String ColumnName) {
@@ -681,6 +705,34 @@ 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
new file mode 100644
index 000000000..6097fcd03
--- /dev/null
+++ b/src/main/java/de/pixart/messenger/utils/AndroidUsingExecLowPriority.java
@@ -0,0 +1,92 @@
+/*
+ * 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
new file mode 100644
index 000000000..1c0fca8bb
--- /dev/null
+++ b/src/main/java/de/pixart/messenger/utils/AndroidUsingLinkProperties.java
@@ -0,0 +1,91 @@
+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;
+
+    protected 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() {
+        ConnectivityManager connectivityManager = (ConnectivityManager) context.getSystemService(Context.CONNECTIVITY_SERVICE);
+        Network[] networks = connectivityManager == null ? null : connectivityManager.getAllNetworks();
+        if (networks == null) {
+            return new String[0];
+        }
+        final Network activeNetwork = getActiveNetwork(connectivityManager);
+        List<String> servers = new ArrayList<>();
+        int vpnOffset = 0;
+        for (Network network : networks) {
+            LinkProperties linkProperties = connectivityManager.getLinkProperties(network);
+            if (linkProperties == null) {
+                continue;
+            }
+            NetworkInfo networkInfo = connectivityManager.getNetworkInfo(network);
+            final boolean isActiveNetwork = network.equals(activeNetwork);
+            if (isActiveNetwork) {
+                if (networkInfo != null && networkInfo.getType() == ConnectivityManager.TYPE_VPN) {
+                    final List<String> tmp = getIPv4First(linkProperties.getDnsServers());
+                    servers.addAll(0, tmp);
+                    vpnOffset += tmp.size();
+                } else {
+                    servers.addAll(vpnOffset, getIPv4First(linkProperties.getDnsServers()));
+                }
+            }
+        }
+        return servers.toArray(new String[servers.size()]);
+    }
+
+    @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 addr : in) {
+            if (addr instanceof Inet4Address) {
+                out.add(0, addr.getHostAddress());
+            } else {
+                out.add(addr.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 edde83088..2378c429e 100644
--- a/src/main/java/de/pixart/messenger/utils/Resolver.java
+++ b/src/main/java/de/pixart/messenger/utils/Resolver.java
@@ -7,6 +7,9 @@ import android.util.Log;
 
 import java.io.IOException;
 import java.lang.reflect.Field;
+import java.net.Inet4Address;
+import java.net.InetAddress;
+import java.net.UnknownHostException;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
@@ -17,12 +20,16 @@ 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;
 import de.measite.minidns.iterative.ReliableDNSClient;
+import de.measite.minidns.record.A;
+import de.measite.minidns.record.AAAA;
 import de.measite.minidns.record.CNAME;
 import de.measite.minidns.record.Data;
+import de.measite.minidns.record.InternetAddressRR;
 import de.measite.minidns.record.SRV;
 import de.pixart.messenger.Config;
 import de.pixart.messenger.R;
@@ -32,13 +39,16 @@ 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_SERVICE = "_xmpp-client";
+    private static final String STARTTLS_SERICE = "_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);
@@ -138,41 +148,91 @@ public class Resolver {
         if (!IP.matches(domain)) {
             return Collections.emptyList();
         }
-        return Collections.singletonList(Result.createDefault(DNSName.from(domain)));
+        try {
+            Result result = new Result();
+            result.ip = InetAddress.getByName(domain);
+            result.port = DEFAULT_PORT_XMPP;
+            return Collections.singletonList(result);
+        } catch (UnknownHostException e) {
+            return Collections.emptyList();
+        }
     }
 
     private static List<Result> resolveSrv(String domain, final boolean directTls) throws IOException {
-        DNSName dnsName = DNSName.from((directTls ? DIRECT_TLS_SERVICE : STARTTLS_SERVICE) + "._tcp." + domain);
+        DNSName dnsName = DNSName.from((directTls ? DIRECT_TLS_SERVICE : STARTTLS_SERICE) + "._tcp." + domain);
         ResolverResult<SRV> result = resolveWithFallback(dnsName, SRV.class);
         final List<Result> results = new ArrayList<>();
+        final List<Thread> threads = new ArrayList<>();
         for (SRV record : result.getAnswersOrEmptySet()) {
             if (record.name.length() == 0 && record.priority == 0) {
                 continue;
             }
-            Result resolverResult = Result.fromRecord(record, directTls);
-            resolverResult.authenticated = result.isAuthenticData();
-            results.add(resolverResult);
-        }
+            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);
+                }
+                synchronized (results) {
+                    results.addAll(ipv4s);
+                }
 
+            }));
+            threads.add(new Thread(() -> {
+                final List<Result> ipv6s = resolveIp(record, AAAA.class, result.isAuthenticData(), directTls);
+                synchronized (results) {
+                    results.addAll(ipv6s);
+                }
+            }));
+        }
+        for (Thread thread : threads) {
+            thread.start();
+        }
+        for (Thread thread : threads) {
+            try {
+                thread.join();
+            } catch (InterruptedException e) {
+                return Collections.emptyList();
+            }
+        }
         return results;
     }
 
+    private static <D extends InternetAddressRR> List<Result> resolveIp(SRV srv, Class<D> type, boolean authenticated, boolean directTls) {
+        List<Result> list = new ArrayList<>();
+        try {
+            ResolverResult<D> results = resolveWithFallback(srv.name, type, authenticated);
+            for (D record : results.getAnswersOrEmptySet()) {
+                Result resolverResult = Result.fromRecord(srv, directTls);
+                resolverResult.authenticated = results.isAuthenticData() && authenticated;
+                resolverResult.ip = record.getInetAddress();
+                list.add(resolverResult);
+            }
+        } catch (Throwable t) {
+            Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + ": error resolving " + type.getSimpleName() + " " + t.getMessage());
+        }
+        return list;
+    }
+
     private static List<Result> resolveNoSrvRecords(DNSName dnsName, boolean withCnames) {
         List<Result> results = new ArrayList<>();
-        Boolean resolveCNAME = false;
         try {
-            if (withCnames) {
+            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()));
+            }
+            if (results.size() == 0 && withCnames) {
                 for (CNAME cname : resolveWithFallback(dnsName, CNAME.class, false).getAnswersOrEmptySet()) {
                     results.addAll(resolveNoSrvRecords(cname.name, false));
-                    resolveCNAME = true;
                 }
             }
         } catch (Throwable throwable) {
             Log.d(Config.LOGTAG, Resolver.class.getSimpleName() + "error resolving fallback records", throwable);
         }
-        if(!resolveCNAME) {
-            results.add(Result.createDefault(dnsName));
-        }
+        results.add(Result.createDefault(dnsName));
         return results;
     }
 
@@ -203,11 +263,13 @@ public class Resolver {
 
     public static class Result implements Comparable<Result> {
         public static final String DOMAIN = "domain";
+        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;
@@ -223,15 +285,25 @@ public class Resolver {
             return result;
         }
 
-        static Result createDefault(DNSName hostname) {
+        static Result createDefault(DNSName hostname, InetAddress ip) {
             Result result = new Result();
             result.port = DEFAULT_PORT_XMPP;
             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));
@@ -252,12 +324,14 @@ public class Resolver {
             if (directTls != result.directTls) return false;
             if (authenticated != result.authenticated) return false;
             if (priority != result.priority) return false;
+            if (ip != null ? !ip.equals(result.ip) : result.ip != null) return false;
             return hostname != null ? hostname.equals(result.hostname) : result.hostname == null;
         }
 
         @Override
         public int hashCode() {
-            int result = hostname != null ? hostname.hashCode() : 0;
+            int result = ip != null ? ip.hashCode() : 0;
+            result = 31 * result + (hostname != null ? hostname.hashCode() : 0);
             result = 31 * result + port;
             result = 31 * result + (directTls ? 1 : 0);
             result = 31 * result + (authenticated ? 1 : 0);
@@ -265,6 +339,10 @@ public class Resolver {
             return result;
         }
 
+        public InetAddress getIp() {
+            return ip;
+        }
+
         public int getPort() {
             return port;
         }
@@ -284,6 +362,7 @@ public class Resolver {
         @Override
         public String toString() {
             return "Result{" +
+                    "ip='" + (ip == null ? null : ip.getHostAddress()) + '\'' +
                     ", hostame='" + hostname.toString() + '\'' +
                     ", port=" + port +
                     ", directTls=" + directTls +
@@ -296,7 +375,17 @@ public class Resolver {
         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;
+                    }
                 } else {
                     return directTls ? -1 : 1;
                 }
@@ -307,6 +396,7 @@ public class Resolver {
 
         public ContentValues toContentValues() {
             final ContentValues contentValues = new ContentValues();
+            contentValues.put(IP, ip == null ? null : ip.getAddress());
             contentValues.put(HOSTNAME, hostname == null ? null : hostname.toString());
             contentValues.put(PORT, port);
             contentValues.put(PRIORITY, priority);
@@ -315,5 +405,4 @@ 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 9a72203b7..3a7e41c9a 100644
--- a/src/main/java/de/pixart/messenger/xmpp/XmppConnection.java
+++ b/src/main/java/de/pixart/messenger/xmpp/XmppConnection.java
@@ -320,6 +320,16 @@ public class XmppConnection implements Runnable {
                     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()) {
@@ -331,10 +341,18 @@ public class XmppConnection implements Runnable {
                         features.encryptionEnabled = result.isDirectTls();
                         verifiedHostname = result.isAuthenticated() ? result.getHostname().toString() : null;
                         Log.d(Config.LOGTAG, "verified hostname " + verifiedHostname);
-                        final InetSocketAddress 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);
+                        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);
+                        }
 
                         if (!features.encryptionEnabled) {
                             localSocket = new Socket();
@@ -362,6 +380,9 @@ public class XmppConnection implements Runnable {
                         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);
@@ -1969,4 +1990,4 @@ public class XmppConnection implements Runnable {
             return hasDiscoFeature(account.getJid().asBareJid(), Namespace.STANZA_IDS);
         }
     }
-}
+}
\ No newline at end of file