Retry to connect using interface addresses

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

@@ -7,13 +7,19 @@ import com.bugsnag.android.Bugsnag;
 import com.sun.mail.imap.IMAPStore;
 import com.sun.mail.smtp.SMTPTransport;
 import com.sun.mail.util.MailConnectException;
+import com.sun.mail.util.SocketConnectException;
 
 import java.net.Inet4Address;
 import java.net.Inet6Address;
 import java.net.InetAddress;
+import java.net.InterfaceAddress;
+import java.net.NetworkInterface;
 import java.net.UnknownHostException;
+import java.util.Collections;
+import java.util.Enumeration;
 import java.util.HashMap;
 import java.util.LinkedHashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.Properties;
 
@@ -30,8 +36,6 @@ public class MailService implements AutoCloseable {
     private Session isession;
     private Service iservice;
 
-    private static final String any4 = "0.0.0.0";
-
     private MailService() {
     }
 
@@ -76,22 +80,50 @@ public class MailService implements AutoCloseable {
 
     public void connect(String host, int port, String user, String password) throws MessagingException {
         try {
+            if (BuildConfig.DEBUG)
+                throw new MailConnectException(new SocketConnectException("Debug", new Exception(), host, port, 0));
             _connect(context, host, port, user, password);
         } catch (MailConnectException ex) {
-            if (!hasIPv6(host))
-                throw ex;
-
             try {
-                Log.i("Binding to " + any4);
-                properties.put("mail.imap.localaddress", any4);
-                properties.put("mail.imaps.localaddress", any4);
-                properties.put("mail.smtp.localaddress", any4);
-                properties.put("mail.smtps.localaddress", any4);
-                _connect(context, host, port, user, password);
+                // Addresses
+                InetAddress[] iaddrs = InetAddress.getAllByName(host);
+                if (iaddrs.length == 1 && !BuildConfig.DEBUG)
+                    throw ex;
+
+                // Interfaces
+                Enumeration<NetworkInterface> _nis = NetworkInterface.getNetworkInterfaces();
+                if (_nis == null)
+                    throw ex;
+                List<NetworkInterface> nis = Collections.list(_nis);
+
+                // Match address/interfaces
+                for (InetAddress iaddr : iaddrs) {
+                    Log.i("Evaluating " + iaddr);
+                    for (NetworkInterface ni : nis)
+                        if (ni.isUp() && !ni.isLoopback()) {
+                            Log.i("Evaluating " + ni);
+                            List<InterfaceAddress> ias = ni.getInterfaceAddresses();
+                            if (ias != null)
+                                for (InterfaceAddress ia : ias) {
+                                    InetAddress a = ia.getAddress();
+                                    if (a != null && a.getClass().equals(iaddr.getClass())) {
+                                        Log.i("Binding to " + ia + " for " + iaddr);
+                                        properties.put("mail." + this.protocol + ".localaddress", a.getHostAddress());
+                                        try {
+                                            _connect(context, host, port, user, password);
+                                            return;
+                                        } catch (MessagingException ex1) {
+                                            Log.w(ex1);
+                                        }
+                                    }
+                                }
+                        }
+                }
             } catch (Throwable ex1) {
                 Log.w(ex1);
-                throw ex;
             }
+
+            throw ex;
         }
     }
 
@@ -130,19 +162,6 @@ public class MailService implements AutoCloseable {
             throw new NoSuchProviderException(protocol);
     }
 
-    private static boolean hasIPv6(String host) {
-        boolean has = false;
-        try {
-            for (InetAddress iaddr : InetAddress.getAllByName(host)) {
-                Log.i(host + " resolves to " + iaddr);
-                if (iaddr instanceof Inet6Address)
-                    has = true;
-            }
-        } catch (UnknownHostException ignored) {
-        }
-        return has;
-    }
-
     IMAPStore getStore() {
         return (IMAPStore) this.iservice;
     }