Add isChildDocument to MtpDocumentsProvider.

Bug: 32687127
Test: adb shell am instrument -w -e class com.android.mtp.MtpDocumentsProviderTest#testIsChildDocument com.android.mtp.tests/com.android.mtp.TestResultInstrumentation
Change-Id: I44ded3c73443735229a8b3465122f7e10c4da178

packages/MtpDocumentsProvider/src/com/android/mtp/MtpDocumentsProvider.java

@@ -414,6 +414,24 @@ public class MtpDocumentsProvider extends DocumentsProvider {
         }
     }
 
+    @Override
+    public boolean isChildDocument(String parentDocumentId, String documentId) {
+        try {
+            Identifier identifier = mDatabase.createIdentifier(documentId);
+            while (true) {
+                if (parentDocumentId.equals(identifier.mDocumentId)) {
+                    return true;
+                }
+                if (identifier.mDocumentType == MtpDatabaseConstants.DOCUMENT_TYPE_DEVICE) {
+                    return false;
+                }
+                identifier = mDatabase.getParentIdentifier(identifier.mDocumentId);
+            }
+        } catch (FileNotFoundException error) {
+            return false;
+        }
+    }
+
     void openDevice(int deviceId) throws IOException {
         synchronized (mDeviceListLock) {
             if (mDeviceToolkits.containsKey(deviceId)) {

packages/MtpDocumentsProvider/tests/src/com/android/mtp/MtpDocumentsProviderTest.java

@@ -34,6 +34,8 @@ import android.test.suitebuilder.annotation.MediumTest;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.util.Arrays;
+import java.util.LinkedList;
+import java.util.Queue;
 import java.util.concurrent.TimeoutException;
 
 import static com.android.mtp.MtpDatabase.strings;
@@ -769,6 +771,18 @@ public class MtpDocumentsProviderTest extends AndroidTestCase {
         assertEquals(0x400000000L, cursor.getLong(0));
     }
 
+    public void testIsChildDocument() throws Exception {
+        setupProvider(MtpDatabaseConstants.FLAG_DATABASE_IN_MEMORY);
+        setupRoots(0, new MtpRoot[] { new MtpRoot(0, 0, "Storage", 1000, 1000, "") });
+        setupHierarchyDocuments("1");
+        assertTrue(mProvider.isChildDocument("1", "1"));
+        assertTrue(mProvider.isChildDocument("1", "14"));
+        assertTrue(mProvider.isChildDocument("2", "14"));
+        assertTrue(mProvider.isChildDocument("5", "14"));
+        assertFalse(mProvider.isChildDocument("3", "14"));
+        assertFalse(mProvider.isChildDocument("6", "14"));
+    }
+
     private void setupProvider(int flag) {
         mDatabase = new MtpDatabase(getContext(), flag);
         mProvider = new MtpDocumentsProvider();
@@ -822,4 +836,63 @@ public class MtpDocumentsProviderTest extends AndroidTestCase {
         return getStrings(mProvider.queryChildDocuments(
                 parentDocumentId, strings(DocumentsContract.Document.COLUMN_DOCUMENT_ID), null));
     }
+
+    static class HierarchyDocument {
+        int depth;
+        String documentId;
+        int objectHandle;
+        int parentHandle;
+
+        HierarchyDocument createChildDocument(int newHandle) {
+            final HierarchyDocument doc = new HierarchyDocument();
+            doc.depth = depth - 1;
+            doc.objectHandle = newHandle;
+            doc.parentHandle = objectHandle;
+            return doc;
+        }
+
+        MtpObjectInfo toObjectInfo() {
+            return new MtpObjectInfo.Builder()
+                    .setName("doc_" + documentId)
+                    .setFormat(depth > 0 ?
+                            MtpConstants.FORMAT_ASSOCIATION : MtpConstants.FORMAT_TEXT)
+                    .setObjectHandle(objectHandle)
+                    .setParent(parentHandle)
+                    .build();
+        }
+    }
+
+    private void setupHierarchyDocuments(String documentId) throws Exception {
+        final Queue<HierarchyDocument> ids = new LinkedList<>();
+        final HierarchyDocument firstDocument = new HierarchyDocument();
+        firstDocument.depth = 3;
+        firstDocument.documentId = documentId;
+        firstDocument.objectHandle = MtpManager.OBJECT_HANDLE_ROOT_CHILDREN;
+        ids.add(firstDocument);
+
+        int objectHandle = 100;
+        while (!ids.isEmpty()) {
+            final HierarchyDocument document = ids.remove();
+            final HierarchyDocument[] children = new HierarchyDocument[] {
+                    document.createChildDocument(objectHandle++),
+                    document.createChildDocument(objectHandle++),
+                    document.createChildDocument(objectHandle++),
+            };
+            final String[] childDocIds = setupDocuments(
+                    0, 0, document.objectHandle, document.documentId, new MtpObjectInfo[] {
+                            children[0].toObjectInfo(),
+                            children[1].toObjectInfo(),
+                            children[2].toObjectInfo(),
+                    });
+            children[0].documentId = childDocIds[0];
+            children[1].documentId = childDocIds[1];
+            children[2].documentId = childDocIds[2];
+
+            if (children[0].depth > 0) {
+                ids.add(children[0]);
+                ids.add(children[1]);
+                ids.add(children[2]);
+            }
+        }
+    }
 }