Validate transport before selecting in UserBackupManagerService.

Make sure transport is registered before changing current transport in UserBackupManagerService.
If the input transport is not registered, throw an error to user.

Fixes: 163539637

Test: 1. atest -v BackupFrameworksServicesRoboTests
	2. Manual test on device.
		- bmgr list transports # which lists registered transports
		- Verify selecting transport succeeds on registered transports
		- Verify selecting transport throws an error on non-registered transports
Change-Id: I7e3572a13df07b2dee34e295ea07f1ccff5ca505

services/backup/java/com/android/server/backup/UserBackupManagerService.java

@@ -160,7 +160,6 @@ import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashSet;
-import java.util.LinkedList;
 import java.util.List;
 import java.util.Objects;
 import java.util.Queue;
@@ -3401,7 +3400,8 @@ public class UserBackupManagerService {
     }
 
     /**
-     * Selects transport {@code transportName} and returns previously selected transport.
+     * Selects transport {@code transportName}, if it is already registered, and returns previously
+     * selected transport. Returns {@code null} if the transport is not registered.
      *
      * @deprecated Use {@link #selectBackupTransportAsync(ComponentName,
      * ISelectBackupTransportCallback)} instead.
@@ -3414,6 +3414,17 @@ public class UserBackupManagerService {
 
         final long oldId = Binder.clearCallingIdentity();
         try {
+            if (!mTransportManager.isTransportRegistered(transportName)) {
+                Slog.v(
+                        TAG,
+                        addUserIdToLogMessage(
+                                mUserId,
+                                "Could not select transport "
+                                        + transportName
+                                        + ", as the transport is not registered."));
+                return null;
+            }
+
             String previousTransportName = mTransportManager.selectTransport(transportName);
             updateStateForTransport(transportName);
             Slog.v(

services/robotests/backup/src/com/android/server/backup/UserBackupManagerServiceTest.java

@@ -61,8 +61,8 @@ import com.android.server.backup.testing.BackupManagerServiceTestUtils;
 import com.android.server.backup.testing.TransportData;
 import com.android.server.backup.testing.TransportTestUtils.TransportMock;
 import com.android.server.backup.transport.TransportNotRegisteredException;
-import com.android.server.testing.shadows.ShadowBackupEligibilityRules;
 import com.android.server.testing.shadows.ShadowApplicationPackageManager;
+import com.android.server.testing.shadows.ShadowBackupEligibilityRules;
 import com.android.server.testing.shadows.ShadowBinder;
 import com.android.server.testing.shadows.ShadowKeyValueBackupJob;
 import com.android.server.testing.shadows.ShadowKeyValueBackupTask;
@@ -360,6 +360,26 @@ public class UserBackupManagerServiceTest {
                 .disposeOfTransportClient(eq(mNewTransportMock.mTransportConnection), any());
     }
 
+    /**
+     * Test verifying that {@link UserBackupManagerService#selectBackupTransport(String)} does not
+     * switch the current transport to the inputted transport, when the inputted transport is not
+     * registered.
+     */
+    @Test
+    public void testSelectBackupTransport_nonRegisteredTransport() throws Exception {
+        setUpForSelectTransport();
+        mShadowContext.grantPermissions(android.Manifest.permission.BACKUP);
+        when(mTransportManager.isTransportRegistered(eq(mNewTransport.transportName)))
+                .thenReturn(false);
+        UserBackupManagerService backupManagerService = createUserBackupManagerServiceAndRunTasks();
+
+        String oldTransport = backupManagerService.selectBackupTransport(
+                mNewTransport.transportName);
+
+        assertThat(getSettingsTransport()).isNotEqualTo(mNewTransport.transportName);
+        assertThat(oldTransport).isEqualTo(null);
+    }
+
     /**
      * Test verifying that {@link UserBackupManagerService#selectBackupTransport(String)} throws a
      * {@link SecurityException} if the caller does not have backup permission.