Added prefer ipv6 option

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

@@ -637,18 +637,9 @@ public class EmailService implements AutoCloseable {
             //    throw new MailConnectException(
             //            new SocketConnectException("Debug", new IOException("Test"), host, port, 0));
 
-            boolean prefer_ip4 = prefs.getBoolean("prefer_ip4", true);
-
             String key = "dns." + host;
             try {
                 main = DnsHelper.getByName(context, host, dnssec);
-                if (!prefer_ip4 && false)
-                    for (InetAddress iaddr : DnsHelper.getAllByName(context, host, dnssec))
-                        if (iaddr instanceof Inet6Address) {
-                            main = iaddr;
-                            break;
-                        }
-
                 EntityLog.log(context, EntityLog.Type.Network, "Main address=" + main);
                 prefs.edit().putString(key, main.getHostAddress()).apply();
             } catch (UnknownHostException ex) {
@@ -661,12 +652,14 @@ public class EmailService implements AutoCloseable {
                 }
             }
 
-            if (prefer_ip4 && main instanceof Inet6Address) {
+            boolean prefer_ip4 = prefs.getBoolean("prefer_ip4", true);
+            boolean prefer_ip6 = !prefer_ip4 && prefs.getBoolean("prefer_ip6", false);
+            if ((prefer_ip4 && main instanceof Inet6Address) || (prefer_ip6 && main instanceof Inet4Address)) {
                 boolean[] has46 = ConnectionHelper.has46(context);
-                if (has46[0])
+                if (prefer_ip4 ? has46[0] : has46[1])
                     try {
                         for (InetAddress iaddr : DnsHelper.getAllByName(context, host, dnssec))
-                            if (iaddr instanceof Inet4Address) {
+                            if ((prefer_ip4 && iaddr instanceof Inet4Address) || (prefer_ip6 && iaddr instanceof Inet6Address)) {
                                 main = iaddr;
                                 EntityLog.log(context, EntityLog.Type.Network, "Preferring=" + main);
                                 break;
@@ -761,17 +754,22 @@ public class EmailService implements AutoCloseable {
 
                     boolean[] has46 = ConnectionHelper.has46(context);
 
+                    boolean prefer_ip4 = prefs.getBoolean("prefer_ip4", true);
+                    boolean prefer_ip6 = !prefer_ip4 && prefs.getBoolean("prefer_ip6", false);
+
                     EntityLog.log(context, EntityLog.Type.Network, "Address main=" + main +
                             " count=" + iaddrs.length +
-                            " ip4=" + ip4 + " max4=" + MAX_IPV4 + " has4=" + has46[0] +
+                            " ip4=" + ip4 + " max4=" + MAX_IPV4 + " has4=" + has46[0] + " pref4=" + prefer_ip4 +
-                            " ip6=" + ip6 + " max6=" + MAX_IPV6 + " has6=" + has46[1]);
+                            " ip6=" + ip6 + " max6=" + MAX_IPV6 + " has6=" + has46[1] + " pref6=" + prefer_ip6);
 
-                    boolean prefer_ip4 = prefs.getBoolean("prefer_ip4", true);
+                    if (prefer_ip4 || prefer_ip6)
-                    if (prefer_ip4)
                         Arrays.sort(iaddrs, new Comparator<InetAddress>() {
                             @Override
                             public int compare(InetAddress a1, InetAddress a2) {
-                                return -Boolean.compare(a1 instanceof Inet4Address, a2 instanceof Inet4Address);
+                                int s = Boolean.compare(a1 instanceof Inet4Address, a2 instanceof Inet4Address);
+                                if (prefer_ip4)
+                                    s = -s;
+                                return s;
                             }
                         });
 

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

@@ -94,6 +94,7 @@ public class FragmentOptionsConnection extends FragmentBase implements SharedPre
     private SwitchCompat swVpnOnly;
     private EditText etTimeout;
     private SwitchCompat swPreferIp4;
+    private SwitchCompat swPreferIp6;
     private SwitchCompat swBindSocket;
     private SwitchCompat swStandaloneVpn;
     private SwitchCompat swDnsCustom;
@@ -133,7 +134,7 @@ public class FragmentOptionsConnection extends FragmentBase implements SharedPre
             "metered", "download", "download_limited", "roaming", "rlah",
             "download_headers", "download_eml", "download_plain",
             "require_validated", "require_validated_captive", "vpn_only",
-            "timeout", "prefer_ip4", "bind_socket", "standalone_vpn",
+            "timeout", "prefer_ip4", "prefer_ip6", "bind_socket", "standalone_vpn",
             "dns_extra", "dns_custom", "dns_clear",
             "tcp_keep_alive",
             "ssl_update", "ssl_harden", "ssl_harden_strict", "cert_strict", "cert_transparency", "check_names",
@@ -165,6 +166,7 @@ public class FragmentOptionsConnection extends FragmentBase implements SharedPre
         swVpnOnly = view.findViewById(R.id.swVpnOnly);
         etTimeout = view.findViewById(R.id.etTimeout);
         swPreferIp4 = view.findViewById(R.id.swPreferIp4);
+        swPreferIp6 = view.findViewById(R.id.swPreferIp6);
         swBindSocket = view.findViewById(R.id.swBindSocket);
         swStandaloneVpn = view.findViewById(R.id.swStandaloneVpn);
         swDnsCustom = view.findViewById(R.id.swDnsCustom);
@@ -330,6 +332,14 @@ public class FragmentOptionsConnection extends FragmentBase implements SharedPre
             @Override
             public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
                 prefs.edit().putBoolean("prefer_ip4", checked).apply();
+                swPreferIp6.setEnabled(!checked);
+            }
+        });
+
+        swPreferIp6.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
+            @Override
+            public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
+                prefs.edit().putBoolean("prefer_ip6", checked).apply();
             }
         });
 
@@ -769,6 +779,8 @@ public class FragmentOptionsConnection extends FragmentBase implements SharedPre
             etTimeout.setHint(Integer.toString(EmailService.DEFAULT_CONNECT_TIMEOUT));
 
             swPreferIp4.setChecked(prefs.getBoolean("prefer_ip4", true));
+            swPreferIp6.setChecked(prefs.getBoolean("prefer_ip6", false));
+            swPreferIp6.setEnabled(!swPreferIp4.isChecked());
             swBindSocket.setChecked(prefs.getBoolean("bind_socket", false));
             swStandaloneVpn.setChecked(prefs.getBoolean("standalone_vpn", false));
             swDnsCustom.setChecked(prefs.getBoolean("dns_custom", false));

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

@@ -176,7 +176,7 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
             "sync_folders",
             "sync_shared_folders",
             "download_headers", "download_eml",
-            "prefer_ip4", "bind_socket", "standalone_vpn", // force reconnect
+            "prefer_ip4", "prefer_ip6", "bind_socket", "standalone_vpn", // force reconnect
             "dns_extra", "dns_custom", // force reconnect
             "tcp_keep_alive", // force reconnect
             "ssl_harden", "ssl_harden_strict", "cert_strict", "cert_transparency", "check_names", "bouncy_castle", "bc_fips", // force reconnect

app/src/main/res/layout/fragment_options_connection.xml

@@ -413,6 +413,19 @@
                     app:layout_constraintTop_toBottomOf="@id/etTimeout"
                     app:switchPadding="12dp" />
 
+                <androidx.appcompat.widget.SwitchCompat
+                    android:id="@+id/swPreferIp6"
+                    android:layout_width="0dp"
+                    android:layout_height="wrap_content"
+                    android:layout_marginStart="12dp"
+                    android:layout_marginTop="12dp"
+                    android:checked="true"
+                    android:text="@string/title_advanced_prefer_ip6"
+                    app:layout_constraintEnd_toEndOf="parent"
+                    app:layout_constraintStart_toStartOf="parent"
+                    app:layout_constraintTop_toBottomOf="@id/swPreferIp4"
+                    app:switchPadding="12dp" />
+
                 <androidx.appcompat.widget.SwitchCompat
                     android:id="@+id/swBindSocket"
                     android:layout_width="0dp"
@@ -422,7 +435,7 @@
                     android:text="@string/title_advanced_bind_socket"
                     app:layout_constraintEnd_toEndOf="parent"
                     app:layout_constraintStart_toStartOf="parent"
-                    app:layout_constraintTop_toBottomOf="@id/swPreferIp4"
+                    app:layout_constraintTop_toBottomOf="@id/swPreferIp6"
                     app:switchPadding="12dp" />
 
                 <androidx.appcompat.widget.SwitchCompat

app/src/main/res/values/strings.xml

@@ -541,6 +541,7 @@
     <string name="title_advanced_vpn_only">Connect only via a VPN</string>
     <string name="title_advanced_timeout">Connection timeout (seconds)</string>
     <string name="title_advanced_prefer_ip4">Prefer IPv4 over IPv6</string>
+    <string name="title_advanced_prefer_ip6">Prefer IPv6 over IPv4</string>
     <string name="title_advanced_bind_socket" translatable="false">Bind sockets to the active network</string>
     <string name="title_advanced_standalone_vpn" translatable="false">Standalone VPN</string>
     <string name="title_advanced_dns">Preferred DNS server addresses (comma separated)</string>