xref: /frameworks/base/core/java/android/provider/DocumentsProvider.java

/*
 * Copyright (C) 2013 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.provider;

import static android.provider.DocumentsContract.EXTRA_THUMBNAIL_SIZE;
import static android.provider.DocumentsContract.METHOD_CREATE_DOCUMENT;
import static android.provider.DocumentsContract.METHOD_DELETE_DOCUMENT;
import static android.provider.DocumentsContract.getDocumentId;
import static android.provider.DocumentsContract.getRootId;
import static android.provider.DocumentsContract.getSearchDocumentsQuery;

import android.content.ContentProvider;
import android.content.ContentResolver;
import android.content.ContentValues;
import android.content.Context;
import android.content.Intent;
import android.content.UriMatcher;
import android.content.pm.PackageManager;
import android.content.pm.ProviderInfo;
import android.content.res.AssetFileDescriptor;
import android.database.Cursor;
import android.graphics.Point;
import android.net.Uri;
import android.os.Bundle;
import android.os.CancellationSignal;
import android.os.ParcelFileDescriptor;
import android.os.ParcelFileDescriptor.OnCloseListener;
import android.provider.DocumentsContract.Document;
import android.provider.DocumentsContract.Root;
import android.util.Log;

import libcore.io.IoUtils;

import java.io.FileNotFoundException;
import java.util.Objects;

/**
 * Base class for a document provider. A document provider offers read and write
 * access to durable files, such as files stored on a local disk, or files in a
 * cloud storage service. To create a document provider, extend this class,
 * implement the abstract methods, and add it to your manifest like this:
 *
 * <pre class="prettyprint">&lt;manifest&gt;
 *    ...
 *    &lt;application&gt;
 *        ...
 *        &lt;provider
 *            android:name="com.example.MyCloudProvider"
 *            android:authorities="com.example.mycloudprovider"
 *            android:exported="true"
 *            android:grantUriPermissions="true"
 *            android:permission="android.permission.MANAGE_DOCUMENTS"
 *            android:enabled="@bool/isAtLeastKitKat"&gt;
 *            &lt;intent-filter&gt;
 *                &lt;action android:name="android.content.action.DOCUMENTS_PROVIDER" /&gt;
 *            &lt;/intent-filter&gt;
 *        &lt;/provider&gt;
 *        ...
 *    &lt;/application&gt;
 *&lt;/manifest&gt;</pre>
 * <p>
 * When defining your provider, you must protect it with
 * {@link android.Manifest.permission#MANAGE_DOCUMENTS}, which is a permission
 * only the system can obtain. Applications cannot use a documents provider
 * directly; they must go through {@link Intent#ACTION_OPEN_DOCUMENT} or
 * {@link Intent#ACTION_CREATE_DOCUMENT} which requires a user to actively
 * navigate and select documents. When a user selects documents through that UI,
 * the system issues narrow URI permission grants to the requesting application.
 * </p>
 * <h3>Documents</h3>
 * <p>
 * A document can be either an openable stream (with a specific MIME type), or a
 * directory containing additional documents (with the
 * {@link Document#MIME_TYPE_DIR} MIME type). Each directory represents the top
 * of a subtree containing zero or more documents, which can recursively contain
 * even more documents and directories.
 * </p>
 * <p>
 * Each document can have different capabilities, as described by
 * {@link Document#COLUMN_FLAGS}. For example, if a document can be represented
 * as a thumbnail, your provider can set
 * {@link Document#FLAG_SUPPORTS_THUMBNAIL} and implement
 * {@link #openDocumentThumbnail(String, Point, CancellationSignal)} to return
 * that thumbnail.
 * </p>
 * <p>
 * Each document under a provider is uniquely referenced by its
 * {@link Document#COLUMN_DOCUMENT_ID}, which must not change once returned. A
 * single document can be included in multiple directories when responding to
 * {@link #queryChildDocuments(String, String[], String)}. For example, a
 * provider might surface a single photo in multiple locations: once in a
 * directory of geographic locations, and again in a directory of dates.
 * </p>
 * <h3>Roots</h3>
 * <p>
 * All documents are surfaced through one or more "roots." Each root represents
 * the top of a document tree that a user can navigate. For example, a root
 * could represent an account or a physical storage device. Similar to
 * documents, each root can have capabilities expressed through
 * {@link Root#COLUMN_FLAGS}.
 * </p>
 *
 * @see Intent#ACTION_OPEN_DOCUMENT
 * @see Intent#ACTION_CREATE_DOCUMENT
 */
public abstract class DocumentsProvider extends ContentProvider {
    private static final String TAG = "DocumentsProvider";

    private static final int MATCH_ROOTS = 1;
    private static final int MATCH_ROOT = 2;
    private static final int MATCH_RECENT = 3;
    private static final int MATCH_SEARCH = 4;
    private static final int MATCH_DOCUMENT = 5;
    private static final int MATCH_CHILDREN = 6;
    private static final int MATCH_DOCUMENT_VIA = 7;
    private static final int MATCH_CHILDREN_VIA = 8;

    private String mAuthority;

    private UriMatcher mMatcher;

    /**
     * Implementation is provided by the parent class.
     */
    @Override
    public void attachInfo(Context context, ProviderInfo info) {
        mAuthority = info.authority;

        mMatcher = new UriMatcher(UriMatcher.NO_MATCH);
        mMatcher.addURI(mAuthority, "root", MATCH_ROOTS);
        mMatcher.addURI(mAuthority, "root/*", MATCH_ROOT);
        mMatcher.addURI(mAuthority, "root/*/recent", MATCH_RECENT);
        mMatcher.addURI(mAuthority, "root/*/search", MATCH_SEARCH);
        mMatcher.addURI(mAuthority, "document/*", MATCH_DOCUMENT);
        mMatcher.addURI(mAuthority, "document/*/children", MATCH_CHILDREN);
        mMatcher.addURI(mAuthority, "via/*/document/*", MATCH_DOCUMENT_VIA);
        mMatcher.addURI(mAuthority, "via/*/document/*/children", MATCH_CHILDREN_VIA);

        // Sanity check our setup
        if (!info.exported) {
            throw new SecurityException("Provider must be exported");
        }
        if (!info.grantUriPermissions) {
            throw new SecurityException("Provider must grantUriPermissions");
        }
        if (!android.Manifest.permission.MANAGE_DOCUMENTS.equals(info.readPermission)
                || !android.Manifest.permission.MANAGE_DOCUMENTS.equals(info.writePermission)) {
            throw new SecurityException("Provider must be protected by MANAGE_DOCUMENTS");
        }

        super.attachInfo(context, info);
    }

    /**
     * Test if a document is descendant (child, grandchild, etc) from the given
     * parent. Providers must override this to support directory selection. You
     * should avoid making network requests to keep this request fast.
     *
     * @param parentDocumentId parent to verify against.
     * @param documentId child to verify.
     * @return if given document is a descendant of the given parent.
     * @see DocumentsContract.Root#FLAG_SUPPORTS_DIR_SELECTION
     */
    public boolean isChildDocument(String parentDocumentId, String documentId) {
        return false;
    }

    /** {@hide} */
    private void enforceVia(Uri documentUri) {
        if (DocumentsContract.isViaUri(documentUri)) {
            final String parent = DocumentsContract.getViaDocumentId(documentUri);
            final String child = DocumentsContract.getDocumentId(documentUri);
            if (Objects.equals(parent, child)) {
                return;
            }
            if (!isChildDocument(parent, child)) {
                throw new SecurityException(
                        "Document " + child + " is not a descendant of " + parent);
            }
        }
    }

    /**
     * Create a new document and return its newly generated
     * {@link Document#COLUMN_DOCUMENT_ID}. You must allocate a new
     * {@link Document#COLUMN_DOCUMENT_ID} to represent the document, which must
     * not change once returned.
     *
     * @param parentDocumentId the parent directory to create the new document
     *            under.
     * @param mimeType the concrete MIME type associated with the new document.
     *            If the MIME type is not supported, the provider must throw.
     * @param displayName the display name of the new document. The provider may
     *            alter this name to meet any internal constraints, such as
     *            conflicting names.
     */
    @SuppressWarnings("unused")
    public String createDocument(String parentDocumentId, String mimeType, String displayName)
            throws FileNotFoundException {
        throw new UnsupportedOperationException("Create not supported");
    }

    /**
     * Delete the requested document. Upon returning, any URI permission grants
     * for the given document will be revoked. If additional documents were
     * deleted as a side effect of this call (such as documents inside a
     * directory) the implementor is responsible for revoking those permissions
     * using {@link #revokeDocumentPermission(String)}.
     *
     * @param documentId the document to delete.
     */
    @SuppressWarnings("unused")
    public void deleteDocument(String documentId) throws FileNotFoundException {
        throw new UnsupportedOperationException("Delete not supported");
    }

    /**
     * Return all roots currently provided. To display to users, you must define
     * at least one root. You should avoid making network requests to keep this
     * request fast.
     * <p>
     * Each root is defined by the metadata columns described in {@link Root},
     * including {@link Root#COLUMN_DOCUMENT_ID} which points to a directory
     * representing a tree of documents to display under that root.
     * <p>
     * If this set of roots changes, you must call {@link ContentResolver#notifyChange(Uri,
     * android.database.ContentObserver, boolean)} with
     * {@link DocumentsContract#buildRootsUri(String)} to notify the system.
     *
     * @param projection list of {@link Root} columns to put into the cursor. If
     *            {@code null} all supported columns should be included.
     */
    public abstract Cursor queryRoots(String[] projection) throws FileNotFoundException;

    /**
     * Return recently modified documents under the requested root. This will
     * only be called for roots that advertise
     * {@link Root#FLAG_SUPPORTS_RECENTS}. The returned documents should be
     * sorted by {@link Document#COLUMN_LAST_MODIFIED} in descending order, and
     * limited to only return the 64 most recently modified documents.
     * <p>
     * Recent documents do not support change notifications.
     *
     * @param projection list of {@link Document} columns to put into the
     *            cursor. If {@code null} all supported columns should be
     *            included.
     * @see DocumentsContract#EXTRA_LOADING
     */
    @SuppressWarnings("unused")
    public Cursor queryRecentDocuments(String rootId, String[] projection)
            throws FileNotFoundException {
        throw new UnsupportedOperationException("Recent not supported");
    }

    /**
     * Return metadata for the single requested document. You should avoid
     * making network requests to keep this request fast.
     *
     * @param documentId the document to return.
     * @param projection list of {@link Document} columns to put into the
     *            cursor. If {@code null} all supported columns should be
     *            included.
     */
    public abstract Cursor queryDocument(String documentId, String[] projection)
            throws FileNotFoundException;

    /**
     * Return the children documents contained in the requested directory. This
     * must only return immediate descendants, as additional queries will be
     * issued to recursively explore the tree.
     * <p>
     * If your provider is cloud-based, and you have some data cached or pinned
     * locally, you may return the local data immediately, setting
     * {@link DocumentsContract#EXTRA_LOADING} on the Cursor to indicate that
     * you are still fetching additional data. Then, when the network data is
     * available, you can send a change notification to trigger a requery and
     * return the complete contents. To return a Cursor with extras, you need to
     * extend and override {@link Cursor#getExtras()}.
     * <p>
     * To support change notifications, you must
     * {@link Cursor#setNotificationUri(ContentResolver, Uri)} with a relevant
     * Uri, such as
     * {@link DocumentsContract#buildChildDocumentsUri(String, String)}. Then
     * you can call {@link ContentResolver#notifyChange(Uri,
     * android.database.ContentObserver, boolean)} with that Uri to send change
     * notifications.
     *
     * @param parentDocumentId the directory to return children for.
     * @param projection list of {@link Document} columns to put into the
     *            cursor. If {@code null} all supported columns should be
     *            included.
     * @param sortOrder how to order the rows, formatted as an SQL
     *            {@code ORDER BY} clause (excluding the ORDER BY itself).
     *            Passing {@code null} will use the default sort order, which
     *            may be unordered. This ordering is a hint that can be used to
     *            prioritize how data is fetched from the network, but UI may
     *            always enforce a specific ordering.
     * @see DocumentsContract#EXTRA_LOADING
     * @see DocumentsContract#EXTRA_INFO
     * @see DocumentsContract#EXTRA_ERROR
     */
    public abstract Cursor queryChildDocuments(
            String parentDocumentId, String[] projection, String sortOrder)
            throws FileNotFoundException;

    /** {@hide} */
    @SuppressWarnings("unused")
    public Cursor queryChildDocumentsForManage(
            String parentDocumentId, String[] projection, String sortOrder)
            throws FileNotFoundException {
        throw new UnsupportedOperationException("Manage not supported");
    }

    /**
     * Return documents that that match the given query under the requested
     * root. The returned documents should be sorted by relevance in descending
     * order. How documents are matched against the query string is an
     * implementation detail left to each provider, but it's suggested that at
     * least {@link Document#COLUMN_DISPLAY_NAME} be matched in a
     * case-insensitive fashion.
     * <p>
     * Only documents may be returned; directories are not supported in search
     * results.
     * <p>
     * If your provider is cloud-based, and you have some data cached or pinned
     * locally, you may return the local data immediately, setting
     * {@link DocumentsContract#EXTRA_LOADING} on the Cursor to indicate that
     * you are still fetching additional data. Then, when the network data is
     * available, you can send a change notification to trigger a requery and
     * return the complete contents.
     * <p>
     * To support change notifications, you must
     * {@link Cursor#setNotificationUri(ContentResolver, Uri)} with a relevant
     * Uri, such as {@link DocumentsContract#buildSearchDocumentsUri(String,
     * String, String)}. Then you can call {@link ContentResolver#notifyChange(Uri,
     * android.database.ContentObserver, boolean)} with that Uri to send change
     * notifications.
     *
     * @param rootId the root to search under.
     * @param query string to match documents against.
     * @param projection list of {@link Document} columns to put into the
     *            cursor. If {@code null} all supported columns should be
     *            included.
     * @see DocumentsContract#EXTRA_LOADING
     * @see DocumentsContract#EXTRA_INFO
     * @see DocumentsContract#EXTRA_ERROR
     */
    @SuppressWarnings("unused")
    public Cursor querySearchDocuments(String rootId, String query, String[] projection)
            throws FileNotFoundException {
        throw new UnsupportedOperationException("Search not supported");
    }

    /**
     * Return concrete MIME type of the requested document. Must match the value
     * of {@link Document#COLUMN_MIME_TYPE} for this document. The default
     * implementation queries {@link #queryDocument(String, String[])}, so
     * providers may choose to override this as an optimization.
     */
    public String getDocumentType(String documentId) throws FileNotFoundException {
        final Cursor cursor = queryDocument(documentId, null);
        try {
            if (cursor.moveToFirst()) {
                return cursor.getString(cursor.getColumnIndexOrThrow(Document.COLUMN_MIME_TYPE));
            } else {
                return null;
            }
        } finally {
            IoUtils.closeQuietly(cursor);
        }
    }

    /**
     * Open and return the requested document.
     * <p>
     * Your provider should return a reliable {@link ParcelFileDescriptor} to
     * detect when the remote caller has finished reading or writing the
     * document. You may return a pipe or socket pair if the mode is exclusively
     * "r" or "w", but complex modes like "rw" imply a normal file on disk that
     * supports seeking.
     * <p>
     * If you block while downloading content, you should periodically check
     * {@link CancellationSignal#isCanceled()} to abort abandoned open requests.
     *
     * @param documentId the document to return.
     * @param mode the mode to open with, such as 'r', 'w', or 'rw'.
     * @param signal used by the caller to signal if the request should be
     *            cancelled. May be null.
     * @see ParcelFileDescriptor#open(java.io.File, int, android.os.Handler,
     *      OnCloseListener)
     * @see ParcelFileDescriptor#createReliablePipe()
     * @see ParcelFileDescriptor#createReliableSocketPair()
     * @see ParcelFileDescriptor#parseMode(String)
     */
    public abstract ParcelFileDescriptor openDocument(
            String documentId, String mode, CancellationSignal signal) throws FileNotFoundException;

    /**
     * Open and return a thumbnail of the requested document.
     * <p>
     * A provider should return a thumbnail closely matching the hinted size,
     * attempting to serve from a local cache if possible. A provider should
     * never return images more than double the hinted size.
     * <p>
     * If you perform expensive operations to download or generate a thumbnail,
     * you should periodically check {@link CancellationSignal#isCanceled()} to
     * abort abandoned thumbnail requests.
     *
     * @param documentId the document to return.
     * @param sizeHint hint of the optimal thumbnail dimensions.
     * @param signal used by the caller to signal if the request should be
     *            cancelled. May be null.
     * @see Document#FLAG_SUPPORTS_THUMBNAIL
     */
    @SuppressWarnings("unused")
    public AssetFileDescriptor openDocumentThumbnail(
            String documentId, Point sizeHint, CancellationSignal signal)
            throws FileNotFoundException {
        throw new UnsupportedOperationException("Thumbnails not supported");
    }

    /**
     * Implementation is provided by the parent class. Cannot be overriden.
     *
     * @see #queryRoots(String[])
     * @see #queryRecentDocuments(String, String[])
     * @see #queryDocument(String, String[])
     * @see #queryChildDocuments(String, String[], String)
     * @see #querySearchDocuments(String, String, String[])
     */
    @Override
    public final Cursor query(Uri uri, String[] projection, String selection,
            String[] selectionArgs, String sortOrder) {
        try {
            switch (mMatcher.match(uri)) {
                case MATCH_ROOTS:
                    return queryRoots(projection);
                case MATCH_RECENT:
                    return queryRecentDocuments(getRootId(uri), projection);
                case MATCH_SEARCH:
                    return querySearchDocuments(
                            getRootId(uri), getSearchDocumentsQuery(uri), projection);
                case MATCH_DOCUMENT:
                case MATCH_DOCUMENT_VIA:
                    enforceVia(uri);
                    return queryDocument(getDocumentId(uri), projection);
                case MATCH_CHILDREN:
                case MATCH_CHILDREN_VIA:
                    enforceVia(uri);
                    if (DocumentsContract.isManageMode(uri)) {
                        return queryChildDocumentsForManage(
                                getDocumentId(uri), projection, sortOrder);
                    } else {
                        return queryChildDocuments(getDocumentId(uri), projection, sortOrder);
                    }
                default:
                    throw new UnsupportedOperationException("Unsupported Uri " + uri);
            }
        } catch (FileNotFoundException e) {
            Log.w(TAG, "Failed during query", e);
            return null;
        }
    }

    /**
     * Implementation is provided by the parent class. Cannot be overriden.
     *
     * @see #getDocumentType(String)
     */
    @Override
    public final String getType(Uri uri) {
        try {
            switch (mMatcher.match(uri)) {
                case MATCH_ROOT:
                    return DocumentsContract.Root.MIME_TYPE_ITEM;
                case MATCH_DOCUMENT:
                case MATCH_DOCUMENT_VIA:
                    enforceVia(uri);
                    return getDocumentType(getDocumentId(uri));
                default:
                    return null;
            }
        } catch (FileNotFoundException e) {
            Log.w(TAG, "Failed during getType", e);
            return null;
        }
    }

    /**
     * Implementation is provided by the parent class. Can be overridden to
     * provide additional functionality, but subclasses <em>must</em> always
     * call the superclass. If the superclass returns {@code null}, the subclass
     * may implement custom behavior.
     * <p>
     * This is typically used to resolve a "via" URI into a concrete document
     * reference, issuing a narrower single-document URI permission grant along
     * the way.
     *
     * @see DocumentsContract#buildDocumentViaUri(Uri, String)
     */
    @Override
    public Uri canonicalize(Uri uri) {
        final Context context = getContext();
        switch (mMatcher.match(uri)) {
            case MATCH_DOCUMENT_VIA:
                enforceVia(uri);

                final Uri narrowUri = DocumentsContract.buildDocumentUri(uri.getAuthority(),
                        DocumentsContract.getDocumentId(uri));

                // Caller may only have prefix grant, so extend them a grant to
                // the narrow Uri. Caller already holds read grant to get here,
                // so check for any other modes we should extend.
                int modeFlags = Intent.FLAG_GRANT_READ_URI_PERMISSION;
                if (context.checkCallingOrSelfUriPermission(uri,
                        Intent.FLAG_GRANT_WRITE_URI_PERMISSION)
                        == PackageManager.PERMISSION_GRANTED) {
                    modeFlags |= Intent.FLAG_GRANT_WRITE_URI_PERMISSION;
                }
                if (context.checkCallingOrSelfUriPermission(uri,
                        Intent.FLAG_GRANT_READ_URI_PERMISSION
                        | Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION)
                        == PackageManager.PERMISSION_GRANTED) {
                    modeFlags |= Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION;
                }
                context.grantUriPermission(getCallingPackage(), narrowUri, modeFlags);
                return narrowUri;
        }
        return null;
    }

    /**
     * Implementation is provided by the parent class. Throws by default, and
     * cannot be overriden.
     *
     * @see #createDocument(String, String, String)
     */
    @Override
    public final Uri insert(Uri uri, ContentValues values) {
        throw new UnsupportedOperationException("Insert not supported");
    }

    /**
     * Implementation is provided by the parent class. Throws by default, and
     * cannot be overriden.
     *
     * @see #deleteDocument(String)
     */
    @Override
    public final int delete(Uri uri, String selection, String[] selectionArgs) {
        throw new UnsupportedOperationException("Delete not supported");
    }

    /**
     * Implementation is provided by the parent class. Throws by default, and
     * cannot be overriden.
     */
    @Override
    public final int update(
            Uri uri, ContentValues values, String selection, String[] selectionArgs) {
        throw new UnsupportedOperationException("Update not supported");
    }

    /**
     * Implementation is provided by the parent class. Can be overridden to
     * provide additional functionality, but subclasses <em>must</em> always
     * call the superclass. If the superclass returns {@code null}, the subclass
     * may implement custom behavior.
     */
    @Override
    public Bundle call(String method, String arg, Bundle extras) {
        if (!method.startsWith("android:")) {
            // Ignore non-platform methods
            return super.call(method, arg, extras);
        }

        final Uri documentUri = extras.getParcelable(DocumentsContract.EXTRA_URI);
        final String authority = documentUri.getAuthority();
        final String documentId = DocumentsContract.getDocumentId(documentUri);

        if (!mAuthority.equals(authority)) {
            throw new SecurityException(
                    "Requested authority " + authority + " doesn't match provider " + mAuthority);
        }
        enforceVia(documentUri);

        final Bundle out = new Bundle();
        try {
            if (METHOD_CREATE_DOCUMENT.equals(method)) {
                enforceWritePermissionInner(documentUri);

                final String mimeType = extras.getString(Document.COLUMN_MIME_TYPE);
                final String displayName = extras.getString(Document.COLUMN_DISPLAY_NAME);

                final String newDocumentId = createDocument(documentId, mimeType, displayName);

                // No need to issue new grants here, since caller either has
                // manage permission or a prefix grant. We might generate a
                // "via" style URI if that's how they called us.
                final Uri newDocumentUri = DocumentsContract.buildDocumentMaybeViaUri(documentUri,
                        newDocumentId);
                out.putParcelable(DocumentsContract.EXTRA_URI, newDocumentUri);

            } else if (METHOD_DELETE_DOCUMENT.equals(method)) {
                enforceWritePermissionInner(documentUri);
                deleteDocument(documentId);

                // Document no longer exists, clean up any grants
                revokeDocumentPermission(documentId);

            } else {
                throw new UnsupportedOperationException("Method not supported " + method);
            }
        } catch (FileNotFoundException e) {
            throw new IllegalStateException("Failed call " + method, e);
        }
        return out;
    }

    /**
     * Revoke any active permission grants for the given
     * {@link Document#COLUMN_DOCUMENT_ID}, usually called when a document
     * becomes invalid. Follows the same semantics as
     * {@link Context#revokeUriPermission(Uri, int)}.
     */
    public final void revokeDocumentPermission(String documentId) {
        final Context context = getContext();
        context.revokeUriPermission(DocumentsContract.buildDocumentUri(mAuthority, documentId), ~0);
        context.revokeUriPermission(DocumentsContract.buildViaUri(mAuthority, documentId), ~0);
    }

    /**
     * Implementation is provided by the parent class. Cannot be overriden.
     *
     * @see #openDocument(String, String, CancellationSignal)
     */
    @Override
    public final ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException {
        enforceVia(uri);
        return openDocument(getDocumentId(uri), mode, null);
    }

    /**
     * Implementation is provided by the parent class. Cannot be overriden.
     *
     * @see #openDocument(String, String, CancellationSignal)
     */
    @Override
    public final ParcelFileDescriptor openFile(Uri uri, String mode, CancellationSignal signal)
            throws FileNotFoundException {
        enforceVia(uri);
        return openDocument(getDocumentId(uri), mode, signal);
    }

    /**
     * Implementation is provided by the parent class. Cannot be overriden.
     *
     * @see #openDocument(String, String, CancellationSignal)
     */
    @Override
    @SuppressWarnings("resource")
    public final AssetFileDescriptor openAssetFile(Uri uri, String mode)
            throws FileNotFoundException {
        enforceVia(uri);
        final ParcelFileDescriptor fd = openDocument(getDocumentId(uri), mode, null);
        return fd != null ? new AssetFileDescriptor(fd, 0, -1) : null;
    }

    /**
     * Implementation is provided by the parent class. Cannot be overriden.
     *
     * @see #openDocument(String, String, CancellationSignal)
     */
    @Override
    @SuppressWarnings("resource")
    public final AssetFileDescriptor openAssetFile(Uri uri, String mode, CancellationSignal signal)
            throws FileNotFoundException {
        enforceVia(uri);
        final ParcelFileDescriptor fd = openDocument(getDocumentId(uri), mode, signal);
        return fd != null ? new AssetFileDescriptor(fd, 0, -1) : null;
    }

    /**
     * Implementation is provided by the parent class. Cannot be overriden.
     *
     * @see #openDocumentThumbnail(String, Point, CancellationSignal)
     */
    @Override
    public final AssetFileDescriptor openTypedAssetFile(Uri uri, String mimeTypeFilter, Bundle opts)
            throws FileNotFoundException {
        enforceVia(uri);
        if (opts != null && opts.containsKey(EXTRA_THUMBNAIL_SIZE)) {
            final Point sizeHint = opts.getParcelable(EXTRA_THUMBNAIL_SIZE);
            return openDocumentThumbnail(getDocumentId(uri), sizeHint, null);
        } else {
            return super.openTypedAssetFile(uri, mimeTypeFilter, opts);
        }
    }

    /**
     * Implementation is provided by the parent class. Cannot be overriden.
     *
     * @see #openDocumentThumbnail(String, Point, CancellationSignal)
     */
    @Override
    public final AssetFileDescriptor openTypedAssetFile(
            Uri uri, String mimeTypeFilter, Bundle opts, CancellationSignal signal)
            throws FileNotFoundException {
        enforceVia(uri);
        if (opts != null && opts.containsKey(EXTRA_THUMBNAIL_SIZE)) {
            final Point sizeHint = opts.getParcelable(EXTRA_THUMBNAIL_SIZE);
            return openDocumentThumbnail(getDocumentId(uri), sizeHint, signal);
        } else {
            return super.openTypedAssetFile(uri, mimeTypeFilter, opts, signal);
        }
    }
}