Have a new API to get private DNS mode

- Expose PRIVATE_DNS_MODE_OFF, PRIVATE_DNS_MODE_OPPORTUNISTIC and
PRIVATE_DNS_MODE_PROVIDER_HOSTNAME for external users.
- Since PRIVATE_DNS_DEFAULT_MODE_FALLBACK might be changed from
release to release, so it cannot be exposed as a system API.
Remove PRIVATE_DNS_DEFAULT_MODE_FALLBACK and have a new API -
getPrivateDnsMode() for users to get the private DNS mode instead.

Bug: 172183305
Test: atest FrameworksNetTests CtsNetTestCases
Change-Id: I02a1e91b4eafb5f5df3eada1c07b99849a050c3c
Merged-In: I02a1e91b4eafb5f5df3eada1c07b99849a050c3c

framework/api/module-lib-current.txt

@@ -8,9 +8,13 @@ package android.net {
   public class ConnectivityManager {
     method @NonNull @RequiresPermission(anyOf={android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK, android.Manifest.permission.NETWORK_STACK, android.Manifest.permission.NETWORK_SETTINGS}) public java.util.List<android.net.NetworkStateSnapshot> getAllNetworkStateSnapshot();
     method @NonNull public static android.util.Range<java.lang.Integer> getIpSecNetIdRange();
+    method @NonNull public static String getPrivateDnsMode(@NonNull android.content.ContentResolver);
     method @RequiresPermission(anyOf={android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK, android.Manifest.permission.NETWORK_SETTINGS}) public void registerSystemDefaultNetworkCallback(@NonNull android.net.ConnectivityManager.NetworkCallback, @NonNull android.os.Handler);
     method @RequiresPermission(anyOf={android.Manifest.permission.NETWORK_SETTINGS, android.Manifest.permission.NETWORK_STACK, android.net.NetworkStack.PERMISSION_MAINLINE_NETWORK_STACK}) public void requestBackgroundNetwork(@NonNull android.net.NetworkRequest, @NonNull android.os.Handler, @NonNull android.net.ConnectivityManager.NetworkCallback);
     method @RequiresPermission(anyOf={android.Manifest.permission.MANAGE_TEST_NETWORKS, android.Manifest.permission.NETWORK_STACK}) public void simulateDataStall(int, long, @NonNull android.net.Network, @NonNull android.os.PersistableBundle);
+    field public static final String PRIVATE_DNS_MODE_OFF = "off";
+    field public static final String PRIVATE_DNS_MODE_OPPORTUNISTIC = "opportunistic";
+    field public static final String PRIVATE_DNS_MODE_PROVIDER_HOSTNAME = "hostname";
   }
 
   public final class NetworkAgentConfig implements android.os.Parcelable {

framework/src/android/net/ConnectivityManager.java

@@ -24,6 +24,8 @@ import static android.net.NetworkRequest.Type.TRACK_BEST;
 import static android.net.NetworkRequest.Type.TRACK_DEFAULT;
 import static android.net.NetworkRequest.Type.TRACK_SYSTEM_DEFAULT;
 import static android.net.QosCallback.QosCallbackRegistrationException;
+import static android.provider.Settings.Global.PRIVATE_DNS_DEFAULT_MODE;
+import static android.provider.Settings.Global.PRIVATE_DNS_MODE;
 
 import android.annotation.CallbackExecutor;
 import android.annotation.IntDef;
@@ -32,11 +34,13 @@ import android.annotation.Nullable;
 import android.annotation.RequiresPermission;
 import android.annotation.SdkConstant;
 import android.annotation.SdkConstant.SdkConstantType;
+import android.annotation.StringDef;
 import android.annotation.SuppressLint;
 import android.annotation.SystemApi;
 import android.annotation.SystemService;
 import android.app.PendingIntent;
 import android.compat.annotation.UnsupportedAppUsage;
+import android.content.ContentResolver;
 import android.content.Context;
 import android.content.Intent;
 import android.net.IpSecManager.UdpEncapsulationSocket;
@@ -64,6 +68,7 @@ import android.os.ServiceSpecificException;
 import android.provider.Settings;
 import android.telephony.SubscriptionManager;
 import android.telephony.TelephonyManager;
+import android.text.TextUtils;
 import android.util.ArrayMap;
 import android.util.Log;
 import android.util.Range;
@@ -803,24 +808,27 @@ public class ConnectivityManager {
     /**
      * @hide
      */
+    @SystemApi(client = MODULE_LIBRARIES)
     public static final String PRIVATE_DNS_MODE_OFF = "off";
     /**
      * @hide
      */
+    @SystemApi(client = MODULE_LIBRARIES)
     public static final String PRIVATE_DNS_MODE_OPPORTUNISTIC = "opportunistic";
     /**
      * @hide
      */
+    @SystemApi(client = MODULE_LIBRARIES)
     public static final String PRIVATE_DNS_MODE_PROVIDER_HOSTNAME = "hostname";
-    /**
+
-     * The default Private DNS mode.
+    /** @hide */
-     *
+    @Retention(RetentionPolicy.SOURCE)
-     * This may change from release to release or may become dependent upon
+    @StringDef(value = {
-     * the capabilities of the underlying platform.
+            PRIVATE_DNS_MODE_OFF,
-     *
+            PRIVATE_DNS_MODE_OPPORTUNISTIC,
-     * @hide
+            PRIVATE_DNS_MODE_PROVIDER_HOSTNAME,
-     */
+    })
-    public static final String PRIVATE_DNS_DEFAULT_MODE_FALLBACK = PRIVATE_DNS_MODE_OPPORTUNISTIC;
+    public @interface PrivateDnsMode {}
 
     @UnsupportedAppUsage(maxTargetSdk = Build.VERSION_CODES.P, trackingBug = 130143562)
     private final IConnectivityManager mService;
@@ -5129,4 +5137,24 @@ public class ConnectivityManager {
     public static Range<Integer> getIpSecNetIdRange() {
         return new Range(TUN_INTF_NETID_START, TUN_INTF_NETID_START + TUN_INTF_NETID_RANGE - 1);
     }
+
+    /**
+     * Get private DNS mode from settings.
+     *
+     * @param cr The ContentResolver to query private DNS mode from settings.
+     * @return A string of private DNS mode as one of the PRIVATE_DNS_MODE_* constants.
+     *
+     * @hide
+     */
+    @SystemApi(client = MODULE_LIBRARIES)
+    @NonNull
+    @PrivateDnsMode
+    public static String getPrivateDnsMode(@NonNull ContentResolver cr) {
+        String mode = Settings.Global.getString(cr, PRIVATE_DNS_MODE);
+        if (TextUtils.isEmpty(mode)) mode = Settings.Global.getString(cr, PRIVATE_DNS_DEFAULT_MODE);
+        // If both PRIVATE_DNS_MODE and PRIVATE_DNS_DEFAULT_MODE are not set, choose
+        // PRIVATE_DNS_MODE_OPPORTUNISTIC as default mode.
+        if (TextUtils.isEmpty(mode)) mode = PRIVATE_DNS_MODE_OPPORTUNISTIC;
+        return mode;
+    }
 }