Improved connect fallback

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

@@ -12,7 +12,6 @@ import androidx.preference.PreferenceManager;
 import com.sun.mail.imap.IMAPFolder;
 import com.sun.mail.imap.IMAPStore;
 import com.sun.mail.smtp.SMTPTransport;
-import com.sun.mail.util.MailConnectException;
 
 import net.openid.appauth.AuthState;
 import net.openid.appauth.AuthorizationException;
@@ -219,7 +218,10 @@ public class MailService implements AutoCloseable {
         }
     }
 
-    public String connect(String host, int port, int auth, String provider, String user, String password, String fingerprint) throws MessagingException {
+    public String connect(
+            String host, int port,
+            int auth, String provider, String user, String password,
+            String fingerprint) throws MessagingException {
         SSLSocketFactoryService factory = null;
         try {
             factory = new SSLSocketFactoryService(host, insecure, fingerprint);
@@ -237,16 +239,12 @@ public class MailService implements AutoCloseable {
             if (auth == AUTH_TYPE_GMAIL || auth == AUTH_TYPE_OAUTH)
                 properties.put("mail." + protocol + ".auth.mechanisms", "XOAUTH2");
 
-            //if (BuildConfig.DEBUG)
-            //    throw new MailConnectException(
-            //            new SocketConnectException("Debug", new Exception("Test"), host, port, 0));
-
             if (auth == AUTH_TYPE_OAUTH) {
                 AuthState authState = OAuthRefresh(context, provider, password);
-                _connect(context, host, port, user, authState.getAccessToken(), factory);
+                connect(host, port, user, authState.getAccessToken(), factory);
                 return authState.jsonSerializeString();
             } else {
-                _connect(context, host, port, user, password, factory);
+                connect(host, port, user, password, factory);
                 return null;
             }
         } catch (AuthenticationFailedException ex) {
@@ -264,7 +262,7 @@ public class MailService implements AutoCloseable {
                             if (token == null)
                                 throw new IllegalArgumentException("No token on refresh");
 
-                            _connect(context, host, port, user, token, factory);
+                            connect(host, port, user, token, factory);
                             return token;
                         }
 
@@ -275,11 +273,34 @@ public class MailService implements AutoCloseable {
                 }
             else if (auth == AUTH_TYPE_OAUTH) {
                 AuthState authState = OAuthRefresh(context, provider, password);
-                _connect(context, host, port, user, authState.getAccessToken(), factory);
+                connect(host, port, user, authState.getAccessToken(), factory);
                 return authState.jsonSerializeString();
             } else
                 throw ex;
-        } catch (MailConnectException ex) {
+        }
+    }
+
+    private void connect(
+            String host, int port, String user, String password,
+            SSLSocketFactoryService factory) throws MessagingException {
+        try {
+            //if (BuildConfig.DEBUG)
+            //    throw new MailConnectException(
+            //            new SocketConnectException("Debug", new IOException("Test"), host, port, 0));
+
+            _connect(host, port, user, password, factory);
+        } catch (MessagingException ex) {
+            boolean ioError = false;
+            Throwable ce = ex;
+            while (ce != null) {
+                if (factory != null && ce instanceof CertificateException)
+                    throw new UntrustedException(factory.getFingerPrint(), ex);
+                if (ce instanceof IOException)
+                    ioError = true;
+                ce = ce.getCause();
+            }
+
+            if (ioError) {
                 try {
                     // Some devices resolve IPv6 addresses while not having IPv6 connectivity
                     InetAddress[] iaddrs = InetAddress.getAllByName(host);
@@ -288,24 +309,23 @@ public class MailService implements AutoCloseable {
                         for (InetAddress iaddr : iaddrs)
                             try {
                                 Log.i("Falling back to " + iaddr.getHostAddress());
-                            _connect(context, iaddr.getHostAddress(), port, user, password, factory);
+                                _connect(iaddr.getHostAddress(), port, user, password, factory);
-                            return null;
+                                return;
                             } catch (MessagingException ex1) {
                                 Log.w(ex1);
                             }
                 } catch (Throwable ex1) {
                     Log.w(ex1);
                 }
+            }
 
             throw ex;
         }
     }
 
     private void _connect(
-            Context context,
             String host, int port, String user, String password,
             SSLSocketFactoryService factory) throws MessagingException {
-        try {
         isession = Session.getInstance(properties, null);
         isession.setDebug(debug);
         //System.setProperty("mail.socket.debug", Boolean.toString(debug));
@@ -377,17 +397,6 @@ public class MailService implements AutoCloseable {
             }
         } else
             throw new NoSuchProviderException(protocol);
-        } catch (MessagingException ex) {
-            if (factory != null) {
-                Throwable ce = ex;
-                while (ce != null) {
-                    if (ce instanceof CertificateException)
-                        throw new UntrustedException(factory.getFingerPrint(), ex);
-                    ce = ce.getCause();
-                }
-            }
-            throw ex;
-        }
     }
 
     private static class ErrorHolder {