Added support for standalone VPNs

Like https://github.com/Genymobile/gnirehtet

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

@@ -265,7 +265,10 @@ public class ConnectionHelper {
             return null;
         }
 
-        if (caps.hasCapability(NetworkCapabilities.NET_CAPABILITY_NOT_VPN)) {
+        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
+        boolean standalone_vpn = prefs.getBoolean("standalone_vpn", false);
+        if (standalone_vpn ||
+                caps.hasCapability(NetworkCapabilities.NET_CAPABILITY_NOT_VPN)) {
             // NET_CAPABILITY_NOT_METERED is unreliable on older Android versions
             boolean metered = cm.isActiveNetworkMetered();
             Log.i("isMetered: active not VPN metered=" + metered);

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

@@ -61,6 +61,7 @@ public class FragmentOptionsConnection extends FragmentBase implements SharedPre
     private SwitchCompat swRlah;
     private EditText etTimeout;
     private SwitchCompat swPreferIp4;
+    private SwitchCompat swStandaloneVpn;
     private SwitchCompat swTcpKeepAlive;
     private TextView tvTcpKeepAliveHint;
     private SwitchCompat swSslHarden;
@@ -70,7 +71,7 @@ public class FragmentOptionsConnection extends FragmentBase implements SharedPre
     private TextView tvNetworkInfo;
 
     private final static String[] RESET_OPTIONS = new String[]{
-            "metered", "download", "roaming", "rlah", "timeout", "prefer_ip4", "tcp_keep_alive", "ssl_harden"
+            "metered", "download", "roaming", "rlah", "timeout", "prefer_ip4", "standalone_vpn", "tcp_keep_alive", "ssl_harden"
     };
 
     @Override
@@ -89,6 +90,7 @@ public class FragmentOptionsConnection extends FragmentBase implements SharedPre
         swRlah = view.findViewById(R.id.swRlah);
         etTimeout = view.findViewById(R.id.etTimeout);
         swPreferIp4 = view.findViewById(R.id.swPreferIp4);
+        swStandaloneVpn = view.findViewById(R.id.swStandaloneVpn);
         swTcpKeepAlive = view.findViewById(R.id.swTcpKeepAlive);
         tvTcpKeepAliveHint = view.findViewById(R.id.tvTcpKeepAliveHint);
         swSslHarden = view.findViewById(R.id.swSslHarden);
@@ -103,6 +105,7 @@ public class FragmentOptionsConnection extends FragmentBase implements SharedPre
         // Wire controls
 
         final SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getContext());
+        boolean debug = prefs.getBoolean("debug", false);
 
         swMetered.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
             @Override
@@ -170,7 +173,15 @@ public class FragmentOptionsConnection extends FragmentBase implements SharedPre
             }
         });
 
-        boolean debug = prefs.getBoolean("debug", false);
+        swStandaloneVpn.setVisibility(debug || BuildConfig.DEBUG ? View.VISIBLE : View.GONE);
+
+        swStandaloneVpn.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
+            @Override
+            public void onCheckedChanged(CompoundButton compoundButton, boolean checked) {
+                prefs.edit().putBoolean("standalone_vpn", checked).apply();
+            }
+        });
+
         swTcpKeepAlive.setVisibility(debug || BuildConfig.DEBUG ? View.VISIBLE : View.GONE);
         tvTcpKeepAliveHint.setVisibility(debug || BuildConfig.DEBUG ? View.VISIBLE : View.GONE);
 
@@ -303,6 +314,7 @@ public class FragmentOptionsConnection extends FragmentBase implements SharedPre
         etTimeout.setHint(Integer.toString(EmailService.DEFAULT_CONNECT_TIMEOUT));
 
         swPreferIp4.setChecked(prefs.getBoolean("prefer_ip4", true));
+        swStandaloneVpn.setChecked(prefs.getBoolean("standalone_vpn", false));
         swTcpKeepAlive.setChecked(prefs.getBoolean("tcp_keep_alive", false));
         swSslHarden.setChecked(prefs.getBoolean("ssl_harden", false));
     }

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

@@ -146,7 +146,7 @@ public class ServiceSynchronize extends ServiceBase implements SharedPreferences
             "sync_kept",
             "sync_folders",
             "sync_shared_folders",
-            "prefer_ip4", "tcp_keep_alive", "ssl_harden", // force reconnect
+            "prefer_ip4", "standalone_vpn", "tcp_keep_alive", "ssl_harden", // force reconnect
             "badge", "unseen_ignored", // force update badge/widget
             "experiments", "debug", "protocol", // force reconnect
             "auth_plain",

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

@@ -196,6 +196,17 @@
             app:layout_constraintTop_toBottomOf="@id/etTimeout"
             app:switchPadding="12dp" />
 
+        <androidx.appcompat.widget.SwitchCompat
+            android:id="@+id/swStandaloneVpn"
+            android:layout_width="0dp"
+            android:layout_height="wrap_content"
+            android:layout_marginTop="12dp"
+            android:text="@string/title_advanced_standalone_vpn"
+            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/swTcpKeepAlive"
             android:layout_width="0dp"
@@ -204,7 +215,7 @@
             android:text="@string/title_advanced_tcp_keep_alive"
             app:layout_constraintEnd_toEndOf="parent"
             app:layout_constraintStart_toStartOf="parent"
-            app:layout_constraintTop_toBottomOf="@id/swPreferIp4"
+            app:layout_constraintTop_toBottomOf="@id/swStandaloneVpn"
             app:switchPadding="12dp" />
 
         <eu.faircode.email.FixedTextView

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

@@ -337,6 +337,7 @@
     <string name="title_advanced_rlah">Roam like at home</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_standalone_vpn" translatable="false">Standalone VPN</string>
     <string name="title_advanced_tcp_keep_alive" translatable="false">TCP keep alive</string>
     <string name="title_advanced_ssl_harden">Harden SSL connections</string>
     <string name="title_advanced_manage_connectivity">Manage connectivity</string>