Check if ip4 on prefer ip4

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

@@ -536,18 +536,20 @@ public class EmailService implements AutoCloseable {
             }
 
             boolean prefer_ip4 = prefs.getBoolean("prefer_ip4", true);
-            if (prefer_ip4 &&
-                    main instanceof Inet6Address)
-                try {
-                    for (InetAddress iaddr : InetAddress.getAllByName(host))
-                        if (iaddr instanceof Inet4Address) {
-                            main = iaddr;
-                            EntityLog.log(context, "Preferring=" + main);
-                            break;
-                        }
-                } catch (UnknownHostException ex) {
-                    Log.w(ex);
-                }
+            if (prefer_ip4 && main instanceof Inet6Address) {
+                boolean[] has46 = has46(context);
+                if (has46[0])
+                    try {
+                        for (InetAddress iaddr : InetAddress.getAllByName(host))
+                            if (iaddr instanceof Inet4Address) {
+                                main = iaddr;
+                                EntityLog.log(context, "Preferring=" + main);
+                                break;
+                            }
+                    } catch (UnknownHostException ex) {
+                        Log.w(ex);
+                    }
+            }
 
             _connect(main, port, require_id, user, factory);
         } catch (UnknownHostException ex) {
@@ -618,36 +620,12 @@ public class EmailService implements AutoCloseable {
                     int ip4 = (main instanceof Inet4Address ? 1 : 0);
                     int ip6 = (main instanceof Inet6Address ? 1 : 0);
 
-                    boolean has4 = false;
-                    boolean has6 = false;
-                    try {
-                        Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
-                        while (interfaces != null && interfaces.hasMoreElements()) {
-                            NetworkInterface ni = interfaces.nextElement();
-                            for (InterfaceAddress iaddr : ni.getInterfaceAddresses()) {
-                                InetAddress addr = iaddr.getAddress();
-                                boolean local = (addr.isLoopbackAddress() || addr.isLinkLocalAddress());
-                                EntityLog.log(context, "Interface=" + ni + " addr=" + addr + " local=" + local);
-                                if (!local)
-                                    if (addr instanceof Inet4Address)
-                                        has4 = true;
-                                    else if (addr instanceof Inet6Address)
-                                        has6 = true;
-                            }
-                        }
-                    } catch (Throwable ex2) {
-                        Log.e(ex2);
-                        /*
-                            java.lang.NullPointerException: Attempt to read from field 'java.util.List java.net.NetworkInterface.childs' on a null object reference
-                                at java.net.NetworkInterface.getAll(NetworkInterface.java:498)
-                                at java.net.NetworkInterface.getNetworkInterfaces(NetworkInterface.java:398)
-                         */
-                    }
+                    boolean[] has46 = has46(context);
 
                     EntityLog.log(context, "Address main=" + main +
                             " count=" + iaddrs.length +
-                            " ip4=" + ip4 + " max4=" + MAX_IPV4 + " has4=" + has4 +
-                            " ip6=" + ip6 + " max6=" + MAX_IPV6 + " has6=" + has6);
+                            " ip4=" + ip4 + " max4=" + MAX_IPV4 + " has4=" + has46[0] +
+                            " ip6=" + ip6 + " max6=" + MAX_IPV6 + " has6=" + has46[1]);
 
                     for (InetAddress iaddr : iaddrs) {
                         EntityLog.log(context, "Address resolved=" + iaddr);
@@ -656,13 +634,13 @@ public class EmailService implements AutoCloseable {
                             continue;
 
                         if (iaddr instanceof Inet4Address) {
-                            if (!has4 || ip4 >= MAX_IPV4)
+                            if (!has46[0] || ip4 >= MAX_IPV4)
                                 continue;
                             ip4++;
                         }
 
                         if (iaddr instanceof Inet6Address) {
-                            if (!has6 || ip6 >= MAX_IPV6)
+                            if (!has46[1] || ip6 >= MAX_IPV6)
                                 continue;
                             ip6++;
                         }
@@ -797,6 +775,36 @@ public class EmailService implements AutoCloseable {
             throw new NoSuchProviderException(protocol);
     }
 
+    static boolean[] has46(Context context) {
+        boolean has4 = false;
+        boolean has6 = false;
+        try {
+            Enumeration<NetworkInterface> interfaces = NetworkInterface.getNetworkInterfaces();
+            while (interfaces != null && interfaces.hasMoreElements()) {
+                NetworkInterface ni = interfaces.nextElement();
+                for (InterfaceAddress iaddr : ni.getInterfaceAddresses()) {
+                    InetAddress addr = iaddr.getAddress();
+                    boolean local = (addr.isLoopbackAddress() || addr.isLinkLocalAddress());
+                    EntityLog.log(context, "Interface=" + ni + " addr=" + addr + " local=" + local);
+                    if (!local)
+                        if (addr instanceof Inet4Address)
+                            has4 = true;
+                        else if (addr instanceof Inet6Address)
+                            has6 = true;
+                }
+            }
+        } catch (Throwable ex) {
+            Log.e(ex);
+            /*
+                java.lang.NullPointerException: Attempt to read from field 'java.util.List java.net.NetworkInterface.childs' on a null object reference
+                    at java.net.NetworkInterface.getAll(NetworkInterface.java:498)
+                    at java.net.NetworkInterface.getNetworkInterfaces(NetworkInterface.java:398)
+             */
+        }
+
+        return new boolean[]{has4, has6};
+    }
+
     static Map<String, String> getId(Context context) {
         Map<String, String> id = new LinkedHashMap<>();
         id.put("name", context.getString(R.string.app_name));