Handle empty <cloud-backup> section in android:dataExtractionRules

Currently the <cloud-backup> section in android:dataExtractionRules is
ignored unless it contains rules. Instead, we should interpret it as
'everything other than cache and no-backup dirs is eligible for cloud
backup'.

Bug: 195095045
Test: 1. atest BackupEligibilityHostSideTest
      2. Use a test app with empty <cloud-backup> section to manually
      test:
          2.1. Empty section - everything is backed up
	  2.2. Empty section but "disableIfNoEncryptionCapabilitites"
	  set to "true" - data only backed up if the transport supports
	  encryption.
Change-Id: Ic8066721a46bda688f9211c51a0f2497e9caf93b

core/java/android/app/backup/FullBackup.java

@@ -116,7 +116,7 @@ public class FullBackup {
         ConfigSection.CLOUD_BACKUP,
         ConfigSection.DEVICE_TRANSFER
     })
-    private @interface ConfigSection {
+    @interface ConfigSection {
         String CLOUD_BACKUP = "cloud-backup";
         String DEVICE_TRANSFER = "device-transfer";
     }
@@ -528,7 +528,8 @@ public class FullBackup {
             return mExcludes;
         }
 
-        private synchronized int getRequiredTransportFlags()
+        @VisibleForTesting
+        public synchronized int getRequiredTransportFlags()
                 throws IOException, XmlPullParserException {
             if (mRequiredTransportFlags == null) {
                 maybeParseBackupSchemeLocked();
@@ -587,11 +588,13 @@ public class FullBackup {
             if (mDataExtractionRules != 0) {
                 // New config is present. Use it if it has configuration for this operation
                 // type.
+                boolean isSectionPresent;
                 try (XmlResourceParser parser = getParserForResource(mDataExtractionRules)) {
-                    parseNewBackupSchemeFromXmlLocked(parser, configSection, mExcludes, mIncludes);
+                    isSectionPresent = parseNewBackupSchemeFromXmlLocked(parser, configSection,
+                            mExcludes, mIncludes);
                 }
-                if (!mExcludes.isEmpty() || !mIncludes.isEmpty()) {
-                    // Found configuration in the new config, we will use it.
+                if (isSectionPresent) {
+                    // Found the relevant section in the new config, we will use it.
                     mIsUsingNewScheme = true;
                     return;
                 }
@@ -630,24 +633,31 @@ public class FullBackup {
                     .getXml(resourceId);
         }
 
-        private void parseNewBackupSchemeFromXmlLocked(XmlPullParser parser,
+        @VisibleForTesting
+        public boolean parseNewBackupSchemeFromXmlLocked(XmlPullParser parser,
                 @ConfigSection  String configSection,
                 Set<PathWithRequiredFlags> excludes,
                 Map<String, Set<PathWithRequiredFlags>> includes)
                 throws IOException, XmlPullParserException {
             verifyTopLevelTag(parser, "data-extraction-rules");
 
+            boolean isSectionPresent = false;
+
             int event;
             while ((event = parser.next()) != XmlPullParser.END_DOCUMENT) {
                 if (event != XmlPullParser.START_TAG || !configSection.equals(parser.getName())) {
                     continue;
                 }
 
+                isSectionPresent = true;
+
                 parseRequiredTransportFlags(parser, configSection);
                 parseRules(parser, excludes, includes, Optional.of(0), configSection);
             }
 
             logParsingResults(excludes, includes);
+
+            return isSectionPresent;
         }
 
         private void parseRequiredTransportFlags(XmlPullParser parser,

core/tests/coretests/src/android/app/backup/FullBackupTest.java

@@ -16,6 +16,8 @@
 
 package android.app.backup;
 
+import static android.app.backup.FullBackup.ConfigSection.CLOUD_BACKUP;
+
 import android.app.backup.FullBackup.BackupScheme.PathWithRequiredFlags;
 import android.content.Context;
 import android.test.AndroidTestCase;
@@ -414,6 +416,37 @@ public class FullBackupTest extends AndroidTestCase {
         assertNull("Didn't throw away invalid \"..\" path.", fileDomainIncludes);
     }
 
+    public void testParseNewBackupSchemeFromXml_emptyCloudSectionIsRespected() throws Exception {
+        mXpp.setInput(new StringReader(
+                "<data-extraction-rules>" +
+                        "<cloud-backup>" +
+                        "</cloud-backup>" +
+                        "</data-extraction-rules>"));
+
+        FullBackup.BackupScheme backupScheme = FullBackup.getBackupSchemeForTest(mContext);
+        boolean result = backupScheme.parseNewBackupSchemeFromXmlLocked(mXpp, CLOUD_BACKUP,
+                excludesSet, includeMap);
+
+        assertTrue(result);
+    }
+
+    public void testParseNewBackupSchemeFromXml_emptyCloudSectionWithEncryptionFlagIsRespected()
+            throws Exception {
+        mXpp.setInput(new StringReader(
+                "<data-extraction-rules>" +
+                        "<cloud-backup disableIfNoEncryptionCapabilities=\"true\">" +
+                        "</cloud-backup>" +
+                        "</data-extraction-rules>"));
+
+        FullBackup.BackupScheme backupScheme = FullBackup.getBackupSchemeForTest(mContext);
+        boolean result = backupScheme.parseNewBackupSchemeFromXmlLocked(mXpp, CLOUD_BACKUP,
+                excludesSet, includeMap);
+
+        assertTrue(result);
+        assertEquals(backupScheme.getRequiredTransportFlags(),
+                BackupAgent.FLAG_CLIENT_SIDE_ENCRYPTION_ENABLED);
+    }
+
     public void testDoubleDotInPath_isIgnored() throws Exception {
         mXpp.setInput(new StringReader(
                 "<full-backup-content>" +