Adapt unpaged cursors to paged requests.

Allow all client targeting Android O to assume paging
    support for any provider.
Adds a new PageViewCursor that adapts an unpaged cursor
    to a paged request.
Updates ContentProviderNative to perform wrapping on
    unpaged results.

Bug: 30927484
Change-Id: I4e225dc16761793c85ef8a195bf049113c79cd20
Test: Added for new class. Run info @ frameworks/base/core/tests/coretests/README

core/java/android/content/ContentProviderNative.java

@@ -24,6 +24,7 @@ import android.database.Cursor;
 import android.database.CursorToBulkCursorAdaptor;
 import android.database.DatabaseUtils;
 import android.database.IContentObserver;
+import android.database.PageViewCursor;
 import android.net.Uri;
 import android.os.Binder;
 import android.os.Bundle;
@@ -103,6 +104,7 @@ abstract public class ContentProviderNative extends Binder implements IContentPr
                     if (cursor != null) {
                         CursorToBulkCursorAdaptor adaptor = null;
 
+                        cursor = PageViewCursor.wrap(cursor, queryArgs);
                         try {
                             adaptor = new CursorToBulkCursorAdaptor(cursor, observer,
                                     getProviderName());

core/java/android/database/PageViewCursor.java

@@ -0,0 +1,245 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package android.database;
+
+import static com.android.internal.util.Preconditions.checkArgument;
+
+import android.annotation.Nullable;
+import android.content.ContentResolver;
+import android.os.Bundle;
+import android.util.Log;
+import android.util.MathUtils;
+
+import com.android.internal.annotations.VisibleForTesting;
+import com.android.internal.util.ArrayUtils;
+
+/**
+ * Cursor wrapper that provides visibility into a subset of a wrapped cursor.
+ *
+ * The window is specified by offset and limit.
+ *
+ * @hide
+ */
+public final class PageViewCursor extends CrossProcessCursorWrapper {
+
+    /**
+     * An extra added to results that are auto-paged using the wrapper.
+     */
+    public static final String EXTRA_AUTO_PAGED = "android.content.extra.AUTO_PAGED";
+
+    private static final String TAG = "PageViewCursor";
+    private static final boolean DEBUG = false;
+    private static final boolean VERBOSE = false;
+
+    private final int mOffset;  // aka first index
+    private final int mCount;
+    private final Bundle mExtras;
+
+    private int mPos = -1;
+
+    /**
+     * @see PageViewCursor#wrap(Cursor, Bundle)
+     */
+    @VisibleForTesting
+    public PageViewCursor(Cursor cursor, int offset, int limit) {
+        super(cursor);
+
+        checkArgument(offset > -1);
+        checkArgument(limit > -1);
+
+        mOffset = offset;
+
+        mExtras = new Bundle();
+        Bundle extras = cursor.getExtras();
+        if (extras != null) {
+            mExtras.putAll(extras);
+        }
+        mExtras.putBoolean(EXTRA_AUTO_PAGED, true);
+
+        // We need a mutable bundle so we can add QUERY_RESULT_SIZE.
+        // Direct equality check is correct here. Bundle.EMPTY is a specific instance
+        // of Bundle that is immutable by way of implementation.
+        // mExtras = (extras == Bundle.EMPTY) ? new Bundle() : extras;
+
+        // When we're wrapping another cursor, it should not already be "paged".
+        checkArgument(!mExtras.containsKey(ContentResolver.EXTRA_TOTAL_SIZE));
+
+        int count = mCursor.getCount();
+        mExtras.putInt(ContentResolver.EXTRA_TOTAL_SIZE, count);
+
+        mCount = MathUtils.constrain(count - offset, 0, limit);
+
+        if (DEBUG) Log.d(TAG, "Wrapped cursor"
+            + " offset: " + mOffset
+            + ", limit: " + limit
+            + ", delegate_size: " + count
+            + ", paged_count: " + mCount);
+    }
+
+    @Override
+    public Bundle getExtras() {
+        return mExtras;
+    }
+
+    @Override
+    public int getPosition() {
+        return mPos;
+    }
+
+    @Override
+    public boolean isBeforeFirst() {
+        if (mCount == 0) {
+            return true;
+        }
+        return mPos == -1;
+    }
+
+    @Override
+    public boolean isAfterLast() {
+        if (mCount == 0) {
+            return true;
+        }
+        return mPos == mCount;
+    }
+
+    @Override
+    public boolean isFirst() {
+        return mPos == 0;
+    }
+
+    @Override
+    public boolean isLast() {
+        return mPos == mCount - 1;
+    }
+
+    @Override
+    public boolean moveToFirst() {
+        return moveToPosition(0);
+    }
+
+    @Override
+    public boolean moveToLast() {
+        return moveToPosition(mCount - 1);
+    }
+
+    @Override
+    public boolean moveToNext() {
+        return move(1);
+    }
+
+    @Override
+    public boolean moveToPrevious() {
+        return move(-1);
+    }
+
+    @Override
+    public boolean move(int offset) {
+        return moveToPosition(mPos + offset);
+    }
+
+    @Override
+    public boolean moveToPosition(int position) {
+        if (position >= mCount) {
+            if (VERBOSE) Log.v(TAG, "Invalid Positon: " + position + " >= count: " + mCount
+                    + ". Moving to last record.");
+            mPos = mCount;
+            super.moveToPosition(mOffset + mPos);  // move into "after last" state.
+            return false;
+        }
+
+        // Make sure position isn't before the beginning of the cursor
+        if (position < 0) {
+            if (VERBOSE) Log.v(TAG, "Ignoring invalid move to position: " + position);
+            mPos = -1;
+            super.moveToPosition(mPos);
+            return false;
+        }
+
+        if (position == mPos) {
+            if (VERBOSE) Log.v(TAG, "Ignoring no-op move to position: " + position);
+            return true;
+        }
+
+        int delegatePosition = position + mOffset;
+        if (VERBOSE) Log.v(TAG, "Moving delegate cursor to position: " + delegatePosition);
+        if (super.moveToPosition(delegatePosition)) {
+            mPos = position;
+            return true;
+        } else {
+            mPos = -1;
+            super.moveToPosition(-1);
+            return false;
+        }
+    }
+
+    @Override
+    public boolean onMove(int oldPosition, int newPosition) {
+        throw new UnsupportedOperationException("Not supported.");
+    }
+
+    @Override
+    public int getCount() {
+        return mCount;
+    }
+
+    /**
+     * Wraps the cursor such that it will honor paging args (if present), AND if the cursor
+     * does not report paging size.
+     *
+     * <p>No-op if cursor already contains paging or is less than specified page size.
+     */
+    public static Cursor wrap(Cursor cursor, @Nullable Bundle queryArgs) {
+
+        boolean hasPagingArgs =
+                queryArgs != null
+                && (queryArgs.containsKey(ContentResolver.QUERY_ARG_OFFSET)
+                || queryArgs.containsKey(ContentResolver.QUERY_ARG_LIMIT));
+
+        if (!hasPagingArgs) {
+            if (VERBOSE) Log.d(TAG, "No-wrap: No paging args in request.");
+            return cursor;
+        }
+
+        if (hasPagedResponseDetails(cursor.getExtras())) {
+            if (VERBOSE) Log.d(TAG, "No-wrap. Cursor has paging details.");
+            return cursor;
+        }
+
+        return new PageViewCursor(
+                cursor,
+                queryArgs.getInt(ContentResolver.QUERY_ARG_OFFSET, 0),
+                queryArgs.getInt(ContentResolver.QUERY_ARG_LIMIT, Integer.MAX_VALUE));
+    }
+
+    /**
+     * @return true if the extras contains information indicating the associated
+     * cursor is paged.
+     */
+    private static boolean hasPagedResponseDetails(@Nullable Bundle extras) {
+        if (extras != null && extras.containsKey(ContentResolver.EXTRA_TOTAL_SIZE)) {
+            return true;
+        }
+
+        String[] honoredArgs = extras.getStringArray(ContentResolver.EXTRA_HONORED_ARGS);
+        if (honoredArgs != null && (
+                ArrayUtils.contains(honoredArgs, ContentResolver.QUERY_ARG_OFFSET)
+                || ArrayUtils.contains(honoredArgs, ContentResolver.QUERY_ARG_LIMIT))) {
+            return true;
+        }
+
+        return false;
+    }
+}