Added setting for internet connection validation

app/src/main/java/eu/faircode/netguard/ActivitySettings.java

@@ -62,6 +62,7 @@ import androidx.annotation.NonNull;
 import androidx.appcompat.app.AlertDialog;
 import androidx.appcompat.app.AppCompatActivity;
 import androidx.core.app.NavUtils;
+import androidx.core.util.PatternsCompat;
 import androidx.localbroadcastmanager.content.LocalBroadcastManager;
 
 import org.xml.sax.Attributes;
@@ -238,9 +239,11 @@ public class ActivitySettings extends AppCompatActivity implements SharedPrefere
         screen.findPreference("vpn6").setTitle(getString(R.string.setting_vpn6, prefs.getString("vpn6", "fd00:1:fd00:1:fd00:1:fd00:1")));
         EditTextPreference pref_dns1 = (EditTextPreference) screen.findPreference("dns");
         EditTextPreference pref_dns2 = (EditTextPreference) screen.findPreference("dns2");
+        EditTextPreference pref_validate = (EditTextPreference) screen.findPreference("validate");
         EditTextPreference pref_ttl = (EditTextPreference) screen.findPreference("ttl");
         pref_dns1.setTitle(getString(R.string.setting_dns, prefs.getString("dns", "-")));
         pref_dns2.setTitle(getString(R.string.setting_dns, prefs.getString("dns2", "-")));
+        pref_validate.setTitle(getString(R.string.setting_validate, prefs.getString("validate", "www.google.com")));
         pref_ttl.setTitle(getString(R.string.setting_ttl, prefs.getString("ttl", "259200")));
 
         // SOCKS5 parameters
@@ -669,6 +672,21 @@ public class ActivitySettings extends AppCompatActivity implements SharedPrefere
                     getString(R.string.setting_dns, prefs.getString(name, "-")));
             ServiceSinkhole.reload("changed " + name, this, false);
 
+        } else if ("validate".equals(name)) {
+            String host = prefs.getString(name, "www.google.com");
+            try {
+                checkDomain(host);
+                prefs.edit().putString(name, host.trim()).apply();
+            } catch (Throwable ex) {
+                prefs.edit().remove(name).apply();
+                ((EditTextPreference) getPreferenceScreen().findPreference(name)).setText(null);
+                if (!TextUtils.isEmpty(host))
+                    Toast.makeText(ActivitySettings.this, ex.toString(), Toast.LENGTH_LONG).show();
+            }
+            getPreferenceScreen().findPreference(name).setTitle(
+                    getString(R.string.setting_validate, prefs.getString(name, "www.google.com")));
+            ServiceSinkhole.reload("changed " + name, this, false);
+
         } else if ("ttl".equals(name))
             getPreferenceScreen().findPreference(name).setTitle(
                     getString(R.string.setting_ttl, prefs.getString(name, "259200")));
@@ -793,6 +811,17 @@ public class ActivitySettings extends AppCompatActivity implements SharedPrefere
         }
     }
 
+    private void checkDomain(String address) throws IllegalArgumentException, UnknownHostException {
+        if (address != null)
+            address = address.trim();
+        if (TextUtils.isEmpty(address))
+            throw new IllegalArgumentException("Bad address");
+        if (Util.isNumericAddress(address))
+            throw new IllegalArgumentException("Bad address");
+        if (!PatternsCompat.DOMAIN_NAME.matcher(address).matches())
+            throw new IllegalArgumentException("Bad address");
+    }
+
     private BroadcastReceiver interactiveStateReceiver = new BroadcastReceiver() {
         @Override
         public void onReceive(Context context, Intent intent) {

app/src/main/java/eu/faircode/netguard/ServiceSinkhole.java

@@ -2142,13 +2142,15 @@ public class ServiceSinkhole extends VpnService implements SharedPreferences.OnS
                     }
                 }
 
-                Log.i(TAG, "Validating " + network + " " + ni);
+                SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(ServiceSinkhole.this);
+                String host = prefs.getString("validate", "www.google.com");
+                Log.i(TAG, "Validating " + network + " " + ni + " host=" + host);
 
                 Socket socket = null;
                 try {
                     socket = network.getSocketFactory().createSocket();
-                    socket.connect(new InetSocketAddress("www.google.com", 443), 10000);
-                    Log.i(TAG, "Validated " + network + " " + ni);
+                    socket.connect(new InetSocketAddress(host, 443), 10000);
+                    Log.i(TAG, "Validated " + network + " " + ni + " host=" + host);
                     synchronized (validated) {
                         validated.put(network, new Date().getTime());
                     }

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

@@ -111,6 +111,7 @@
     <string name="setting_vpn4">VPN IPv4: %s</string>
     <string name="setting_vpn6">VPN IPv6: %s</string>
     <string name="setting_dns">VPN DNS: %s</string>
+    <string name="setting_validate">Validate at: %s</string>
     <string name="setting_ttl">Minimum DNS TTL: %s s</string>
     <string name="setting_socks5_enabled">Use SOCKS5 proxy</string>
     <string name="setting_socks5_addr">SOCKS5 address: %s</string>
@@ -165,6 +166,7 @@
     <string name="summary_track_usage">Track the number of bytes sent and received for each app and address. This might result in extra battery usage.</string>
     <string name="summary_block_domains">Respond with the configured DNS response code for blocked domain names. This switch is disabled when no hosts file is available.</string>
     <string name="summary_rcode">The default value is 3 (NXDOMAIN), which means \'non-existent domain\'.</string>
+    <string name="summary_validate">Domain name used to validate the internet connection at port 443 (https).</string>
     <string name="summary_socks5_enabled">Only TCP traffic will be sent to the proxy server</string>
     <string name="summary_watchdog">Periodically check if NetGuard is still running (enter zero to disable this option). This might result in extra battery usage.</string>
 

app/src/main/res/xml-v14/preferences.xml

@@ -228,6 +228,11 @@
                 android:dependency="filter"
                 android:inputType="text"
                 android:key="dns2" />
+            <EditTextPreference
+                android:hint="www.google.com"
+                android:inputType="text"
+                android:key="validate"
+                android:summary="@string/summary_validate" />
             <EditTextPreference
                 android:dependency="filter"
                 android:inputType="number"

app/src/main/res/xml-v21/preferences.xml

@@ -228,6 +228,11 @@
                 android:dependency="filter"
                 android:inputType="text"
                 android:key="dns2" />
+            <EditTextPreference
+                android:hint="www.google.com"
+                android:inputType="text"
+                android:key="validate"
+                android:summary="@string/summary_validate" />
             <EditTextPreference
                 android:dependency="filter"
                 android:inputType="number"