/core/java/android/content/ContentResolver.java

/*
 * Copyright (C) 2006 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.content;

import android.accounts.Account;
import android.app.ActivityManagerNative;
import android.app.ActivityThread;
import android.app.AppGlobals;
import android.content.pm.PackageManager.NameNotFoundException;
import android.content.res.AssetFileDescriptor;
import android.content.res.Resources;
import android.database.ContentObserver;
import android.database.CrossProcessCursorWrapper;
import android.database.Cursor;
import android.database.IContentObserver;
import android.graphics.Point;
import android.net.Uri;
import android.os.Bundle;
import android.os.CancellationSignal;
import android.os.DeadObjectException;
import android.os.IBinder;
import android.os.ICancellationSignal;
import android.os.OperationCanceledException;
import android.os.ParcelFileDescriptor;
import android.os.RemoteException;
import android.os.ServiceManager;
import android.os.SystemClock;
import android.os.UserHandle;
import android.text.TextUtils;
import android.util.EventLog;
import android.util.Log;

import dalvik.system.CloseGuard;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;

/**
 * This class provides applications access to the content model.
 *
 * <div class="special reference">
 * <h3>Developer Guides</h3>
 * <p>For more information about using a ContentResolver with content providers, read the
 * <a href="{@docRoot}guide/topics/providers/content-providers.html">Content Providers</a>
 * developer guide.</p>
 */
public abstract class ContentResolver {
    /**
     * @deprecated instead use
     * {@link #requestSync(android.accounts.Account, String, android.os.Bundle)}
     */
    @Deprecated
    public static final String SYNC_EXTRAS_ACCOUNT = "account";

    /**
     * If this extra is set to true, the sync request will be scheduled
     * at the front of the sync request queue and without any delay
     */
    public static final String SYNC_EXTRAS_EXPEDITED = "expedited";

    /**
     * @deprecated instead use
     * {@link #SYNC_EXTRAS_MANUAL}
     */
    @Deprecated
    public static final String SYNC_EXTRAS_FORCE = "force";

    /**
     * If this extra is set to true then the sync settings (like getSyncAutomatically())
     * are ignored by the sync scheduler.
     */
    public static final String SYNC_EXTRAS_IGNORE_SETTINGS = "ignore_settings";

    /**
     * If this extra is set to true then any backoffs for the initial attempt (e.g. due to retries)
     * are ignored by the sync scheduler. If this request fails and gets rescheduled then the
     * retries will still honor the backoff.
     */
    public static final String SYNC_EXTRAS_IGNORE_BACKOFF = "ignore_backoff";

    /**
     * If this extra is set to true then the request will not be retried if it fails.
     */
    public static final String SYNC_EXTRAS_DO_NOT_RETRY = "do_not_retry";

    /**
     * Setting this extra is the equivalent of setting both {@link #SYNC_EXTRAS_IGNORE_SETTINGS}
     * and {@link #SYNC_EXTRAS_IGNORE_BACKOFF}
     */
    public static final String SYNC_EXTRAS_MANUAL = "force";

    /**
     * Indicates that this sync is intended to only upload local changes to the server.
     * For example, this will be set to true if the sync is initiated by a call to
     * {@link ContentResolver#notifyChange(android.net.Uri, android.database.ContentObserver, boolean)}
     */
    public static final String SYNC_EXTRAS_UPLOAD = "upload";

    /**
     * Indicates that the sync adapter should proceed with the delete operations,
     * even if it determines that there are too many.
     * See {@link SyncResult#tooManyDeletions}
     */
    public static final String SYNC_EXTRAS_OVERRIDE_TOO_MANY_DELETIONS = "deletions_override";

    /**
     * Indicates that the sync adapter should not proceed with the delete operations,
     * if it determines that there are too many.
     * See {@link SyncResult#tooManyDeletions}
     */
    public static final String SYNC_EXTRAS_DISCARD_LOCAL_DELETIONS = "discard_deletions";

    /* Extensions to API. TODO: Not clear if we will keep these as public flags. */
    /** {@hide} User-specified flag for expected upload size. */
    public static final String SYNC_EXTRAS_EXPECTED_UPLOAD = "expected_upload";

    /** {@hide} User-specified flag for expected download size. */
    public static final String SYNC_EXTRAS_EXPECTED_DOWNLOAD = "expected_download";

    /** {@hide} Priority of this sync with respect to other syncs scheduled for this application. */
    public static final String SYNC_EXTRAS_PRIORITY = "sync_priority";

    /** {@hide} Flag to allow sync to occur on metered network. */
    public static final String SYNC_EXTRAS_DISALLOW_METERED = "allow_metered";

    /**
     * Set by the SyncManager to request that the SyncAdapter initialize itself for
     * the given account/authority pair. One required initialization step is to
     * ensure that {@link #setIsSyncable(android.accounts.Account, String, int)} has been
     * called with a >= 0 value. When this flag is set the SyncAdapter does not need to
     * do a full sync, though it is allowed to do so.
     */
    public static final String SYNC_EXTRAS_INITIALIZE = "initialize";

    /** @hide */
    public static final Intent ACTION_SYNC_CONN_STATUS_CHANGED =
            new Intent("com.android.sync.SYNC_CONN_STATUS_CHANGED");

    public static final String SCHEME_CONTENT = "content";
    public static final String SCHEME_ANDROID_RESOURCE = "android.resource";
    public static final String SCHEME_FILE = "file";

    /**
     * An extra {@link Point} describing the optimal size for a requested image
     * resource, in pixels. If a provider has multiple sizes of the image, it
     * should return the image closest to this size.
     *
     * @see #openTypedAssetFileDescriptor(Uri, String, Bundle)
     * @see #openTypedAssetFileDescriptor(Uri, String, Bundle,
     *      CancellationSignal)
     */
    public static final String EXTRA_SIZE = "android.content.extra.SIZE";

    /**
     * This is the Android platform's base MIME type for a content: URI
     * containing a Cursor of a single item.  Applications should use this
     * as the base type along with their own sub-type of their content: URIs
     * that represent a particular item.  For example, hypothetical IMAP email
     * client may have a URI
     * <code>content://com.company.provider.imap/inbox/1</code> for a particular
     * message in the inbox, whose MIME type would be reported as
     * <code>CURSOR_ITEM_BASE_TYPE + "/vnd.company.imap-msg"</code>
     *
     * <p>Compare with {@link #CURSOR_DIR_BASE_TYPE}.
     */
    public static final String CURSOR_ITEM_BASE_TYPE = "vnd.android.cursor.item";

    /**
     * This is the Android platform's base MIME type for a content: URI
     * containing a Cursor of zero or more items.  Applications should use this
     * as the base type along with their own sub-type of their content: URIs
     * that represent a directory of items.  For example, hypothetical IMAP email
     * client may have a URI
     * <code>content://com.company.provider.imap/inbox</code> for all of the
     * messages in its inbox, whose MIME type would be reported as
     * <code>CURSOR_DIR_BASE_TYPE + "/vnd.company.imap-msg"</code>
     *
     * <p>Note how the base MIME type varies between this and
     * {@link #CURSOR_ITEM_BASE_TYPE} depending on whether there is
     * one single item or multiple items in the data set, while the sub-type
     * remains the same because in either case the data structure contained
     * in the cursor is the same.
     */
    public static final String CURSOR_DIR_BASE_TYPE = "vnd.android.cursor.dir";

    /**
     * This is the Android platform's generic MIME type to match any MIME
     * type of the form "{@link #CURSOR_ITEM_BASE_TYPE}/{@code SUB_TYPE}".
     * {@code SUB_TYPE} is the sub-type of the application-dependent
     * content, e.g., "audio", "video", "playlist".
     */
    public static final String ANY_CURSOR_ITEM_TYPE = "vnd.android.cursor.item/*";

    /** @hide */
    public static final int SYNC_ERROR_SYNC_ALREADY_IN_PROGRESS = 1;
    /** @hide */
    public static final int SYNC_ERROR_AUTHENTICATION = 2;
    /** @hide */
    public static final int SYNC_ERROR_IO = 3;
    /** @hide */
    public static final int SYNC_ERROR_PARSE = 4;
    /** @hide */
    public static final int SYNC_ERROR_CONFLICT = 5;
    /** @hide */
    public static final int SYNC_ERROR_TOO_MANY_DELETIONS = 6;
    /** @hide */
    public static final int SYNC_ERROR_TOO_MANY_RETRIES = 7;
    /** @hide */
    public static final int SYNC_ERROR_INTERNAL = 8;

    private static final String[] SYNC_ERROR_NAMES = new String[] {
          "already-in-progress",
          "authentication-error",
          "io-error",
          "parse-error",
          "conflict",
          "too-many-deletions",
          "too-many-retries",
          "internal-error",
    };

    /** @hide */
    public static String syncErrorToString(int error) {
        if (error < 1 || error > SYNC_ERROR_NAMES.length) {
            return String.valueOf(error);
        }
        return SYNC_ERROR_NAMES[error - 1];
    }

    /** @hide */
    public static int syncErrorStringToInt(String error) {
        for (int i = 0, n = SYNC_ERROR_NAMES.length; i < n; i++) {
            if (SYNC_ERROR_NAMES[i].equals(error)) {
                return i + 1;
            }
        }
        if (error != null) {
            try {
                return Integer.parseInt(error);
            } catch (NumberFormatException e) {
                Log.d(TAG, "error parsing sync error: " + error);
            }
        }
        return 0;
    }

    public static final int SYNC_OBSERVER_TYPE_SETTINGS = 1<<0;
    public static final int SYNC_OBSERVER_TYPE_PENDING = 1<<1;
    public static final int SYNC_OBSERVER_TYPE_ACTIVE = 1<<2;
    /** @hide */
    public static final int SYNC_OBSERVER_TYPE_STATUS = 1<<3;
    /** @hide */
    public static final int SYNC_OBSERVER_TYPE_ALL = 0x7fffffff;

    // Always log queries which take 500ms+; shorter queries are
    // sampled accordingly.
    private static final boolean ENABLE_CONTENT_SAMPLE = false;
    private static final int SLOW_THRESHOLD_MILLIS = 500;
    private final Random mRandom = new Random();  // guarded by itself

    public ContentResolver(Context context) {
        mContext = context != null ? context : ActivityThread.currentApplication();
        mPackageName = mContext.getOpPackageName();
    }

    /** @hide */
    protected abstract IContentProvider acquireProvider(Context c, String name);

    /**
     * Providing a default implementation of this, to avoid having to change a
     * lot of other things, but implementations of ContentResolver should
     * implement it.
     *
     * @hide
     */
    protected IContentProvider acquireExistingProvider(Context c, String name) {
        return acquireProvider(c, name);
    }

    /** @hide */
    public abstract boolean releaseProvider(IContentProvider icp);
    /** @hide */
    protected abstract IContentProvider acquireUnstableProvider(Context c, String name);
    /** @hide */
    public abstract boolean releaseUnstableProvider(IContentProvider icp);
    /** @hide */
    public abstract void unstableProviderDied(IContentProvider icp);

    /** @hide */
    public void appNotRespondingViaProvider(IContentProvider icp) {
        throw new UnsupportedOperationException("appNotRespondingViaProvider");
    }

    /**
     * Return the MIME type of the given content URL.
     *
     * @param url A Uri identifying content (either a list or specific type),
     * using the content:// scheme.
     * @return A MIME type for the content, or null if the URL is invalid or the type is unknown
     */
    public final String getType(Uri url) {
        // XXX would like to have an acquireExistingUnstableProvider for this.
        IContentProvider provider = acquireExistingProvider(url);
        if (provider != null) {
            try {
                return provider.getType(url);
            } catch (RemoteException e) {
                return null;
            } catch (java.lang.Exception e) {
                Log.w(TAG, "Failed to get type for: " + url + " (" + e.getMessage() + ")");
                return null;
            } finally {
                releaseProvider(provider);
            }
        }

        if (!SCHEME_CONTENT.equals(url.getScheme())) {
            return null;
        }

        try {
            String type = ActivityManagerNative.getDefault().getProviderMimeType(
                    ContentProvider.getUriWithoutUserId(url), resolveUserId(url));
            return type;
        } catch (RemoteException e) {
            // Arbitrary and not worth documenting, as Activity
            // Manager will kill this process shortly anyway.
            return null;
        } catch (java.lang.Exception e) {
            Log.w(TAG, "Failed to get type for: " + url + " (" + e.getMessage() + ")");
            return null;
        }
    }

    /**
     * Query for the possible MIME types for the representations the given
     * content URL can be returned when opened as as stream with
     * {@link #openTypedAssetFileDescriptor}.  Note that the types here are
     * not necessarily a superset of the type returned by {@link #getType} --
     * many content providers cannot return a raw stream for the structured
     * data that they contain.
     *
     * @param url A Uri identifying content (either a list or specific type),
     * using the content:// scheme.
     * @param mimeTypeFilter The desired MIME type.  This may be a pattern,
     * such as *&#47;*, to query for all available MIME types that match the
     * pattern.
     * @return Returns an array of MIME type strings for all available
     * data streams that match the given mimeTypeFilter.  If there are none,
     * null is returned.
     */
    public String[] getStreamTypes(Uri url, String mimeTypeFilter) {
        IContentProvider provider = acquireProvider(url);
        if (provider == null) {
            return null;
        }

        try {
            return provider.getStreamTypes(url, mimeTypeFilter);
        } catch (RemoteException e) {
            // Arbitrary and not worth documenting, as Activity
            // Manager will kill this process shortly anyway.
            return null;
        } finally {
            releaseProvider(provider);
        }
    }

    /**
     * Query the given URI, returning a {@link Cursor} over the result set.
     * <p>
     * For best performance, the caller should follow these guidelines:
     * <ul>
     * <li>Provide an explicit projection, to prevent
     * reading data from storage that aren't going to be used.</li>
     * <li>Use question mark parameter markers such as 'phone=?' instead of
     * explicit values in the {@code selection} parameter, so that queries
     * that differ only by those values will be recognized as the same
     * for caching purposes.</li>
     * </ul>
     * </p>
     *
     * @param uri The URI, using the content:// scheme, for the content to
     *         retrieve.
     * @param projection A list of which columns to return. Passing null will
     *         return all columns, which is inefficient.
     * @param selection A filter declaring which rows to return, formatted as an
     *         SQL WHERE clause (excluding the WHERE itself). Passing null will
     *         return all rows for the given URI.
     * @param selectionArgs You may include ?s in selection, which will be
     *         replaced by the values from selectionArgs, in the order that they
     *         appear in the selection. The values will be bound as Strings.
     * @param sortOrder How to order the rows, formatted as an SQL ORDER BY
     *         clause (excluding the ORDER BY itself). Passing null will use the
     *         default sort order, which may be unordered.
     * @return A Cursor object, which is positioned before the first entry, or null
     * @see Cursor
     */
    public final Cursor query(Uri uri, String[] projection,
            String selection, String[] selectionArgs, String sortOrder) {
        return query(uri, projection, selection, selectionArgs, sortOrder, null);
    }

    /**
     * Query the given URI, returning a {@link Cursor} over the result set
     * with optional support for cancellation.
     * <p>
     * For best performance, the caller should follow these guidelines:
     * <ul>
     * <li>Provide an explicit projection, to prevent
     * reading data from storage that aren't going to be used.</li>
     * <li>Use question mark parameter markers such as 'phone=?' instead of
     * explicit values in the {@code selection} parameter, so that queries
     * that differ only by those values will be recognized as the same
     * for caching purposes.</li>
     * </ul>
     * </p>
     *
     * @param uri The URI, using the content:// scheme, for the content to
     *         retrieve.
     * @param projection A list of which columns to return. Passing null will
     *         return all columns, which is inefficient.
     * @param selection A filter declaring which rows to return, formatted as an
     *         SQL WHERE clause (excluding the WHERE itself). Passing null will
     *         return all rows for the given URI.
     * @param selectionArgs You may include ?s in selection, which will be
     *         replaced by the values from selectionArgs, in the order that they
     *         appear in the selection. The values will be bound as Strings.
     * @param sortOrder How to order the rows, formatted as an SQL ORDER BY
     *         clause (excluding the ORDER BY itself). Passing null will use the
     *         default sort order, which may be unordered.
     * @param cancellationSignal A signal to cancel the operation in progress, or null if none.
     * If the operation is canceled, then {@link OperationCanceledException} will be thrown
     * when the query is executed.
     * @return A Cursor object, which is positioned before the first entry, or null
     * @see Cursor
     */
    public final Cursor query(final Uri uri, String[] projection,
            String selection, String[] selectionArgs, String sortOrder,
            CancellationSignal cancellationSignal) {
        IContentProvider unstableProvider = acquireUnstableProvider(uri);
        if (unstableProvider == null) {
            return null;
        }
        IContentProvider stableProvider = null;
        Cursor qCursor = null;
        try {
            long startTime = SystemClock.uptimeMillis();

            ICancellationSignal remoteCancellationSignal = null;
            if (cancellationSignal != null) {
                cancellationSignal.throwIfCanceled();
                remoteCancellationSignal = unstableProvider.createCancellationSignal();
                cancellationSignal.setRemote(remoteCancellationSignal);
            }
            try {
                qCursor = unstableProvider.query(mPackageName, uri, projection,
                        selection, selectionArgs, sortOrder, remoteCancellationSignal);
            } catch (DeadObjectException e) {
                // The remote process has died...  but we only hold an unstable
                // reference though, so we might recover!!!  Let's try!!!!
                // This is exciting!!1!!1!!!!1
                unstableProviderDied(unstableProvider);
                stableProvider = acquireProvider(uri);
                if (stableProvider == null) {
                    return null;
                }
                qCursor = stableProvider.query(mPackageName, uri, projection,
                        selection, selectionArgs, sortOrder, remoteCancellationSignal);
            }
            if (qCursor == null) {
                return null;
            }

            // Force query execution.  Might fail and throw a runtime exception here.
            qCursor.getCount();
            long durationMillis = SystemClock.uptimeMillis() - startTime;
            maybeLogQueryToEventLog(durationMillis, uri, projection, selection, sortOrder);

            // Wrap the cursor object into CursorWrapperInner object.
            CursorWrapperInner wrapper = new CursorWrapperInner(qCursor,
                    stableProvider != null ? stableProvider : acquireProvider(uri));
            stableProvider = null;
            qCursor = null;
            return wrapper;
        } catch (RemoteException e) {
            // Arbitrary and not worth documenting, as Activity
            // Manager will kill this process shortly anyway.
            return null;
        } finally {
            if (qCursor != null) {
                qCursor.close();
            }
            if (cancellationSignal != null) {
                cancellationSignal.setRemote(null);
            }
            if (unstableProvider != null) {
                releaseUnstableProvider(unstableProvider);
            }
            if (stableProvider != null) {
                releaseProvider(stableProvider);
            }
        }
    }

    /**
     * Transform the given <var>url</var> to a canonical representation of
     * its referenced resource, which can be used across devices, persisted,
     * backed up and restored, etc.  The returned Uri is still a fully capable
     * Uri for use with its content provider, allowing you to do all of the
     * same content provider operations as with the original Uri --
     * {@link #query}, {@link #openInputStream(android.net.Uri)}, etc.  The
     * only difference in behavior between the original and new Uris is that
     * the content provider may need to do some additional work at each call
     * using it to resolve it to the correct resource, especially if the
     * canonical Uri has been moved to a different environment.
     *
     * <p>If you are moving a canonical Uri between environments, you should
     * perform another call to {@link #canonicalize} with that original Uri to
     * re-canonicalize it for the current environment.  Alternatively, you may
     * want to use {@link #uncanonicalize} to transform it to a non-canonical
     * Uri that works only in the current environment but potentially more
     * efficiently than the canonical representation.</p>
     *
     * @param url The {@link Uri} that is to be transformed to a canonical
     * representation.  Like all resolver calls, the input can be either
     * a non-canonical or canonical Uri.
     *
     * @return Returns the official canonical representation of <var>url</var>,
     * or null if the content provider does not support a canonical representation
     * of the given Uri.  Many providers may not support canonicalization of some
     * or all of their Uris.
     *
     * @see #uncanonicalize
     */
    public final Uri canonicalize(Uri url) {
        IContentProvider provider = acquireProvider(url);
        if (provider == null) {
            return null;
        }

        try {
            return provider.canonicalize(mPackageName, url);
        } catch (RemoteException e) {
            // Arbitrary and not worth documenting, as Activity
            // Manager will kill this process shortly anyway.
            return null;
        } finally {
            releaseProvider(provider);
        }
    }

    /**
     * Given a canonical Uri previously generated by {@link #canonicalize}, convert
     * it to its local non-canonical form.  This can be useful in some cases where
     * you know that you will only be using the Uri in the current environment and
     * want to avoid any possible overhead when using it with the content
     * provider or want to verify that the referenced data exists at all in the
     * new environment.
     *
     * @param url The canonical {@link Uri} that is to be convered back to its
     * non-canonical form.
     *
     * @return Returns the non-canonical representation of <var>url</var>.  This will
     * return null if data identified by the canonical Uri can not be found in
     * the current environment; callers must always check for null and deal with
     * that by appropriately falling back to an alternative.
     *
     * @see #canonicalize
     */
    public final Uri uncanonicalize(Uri url) {
        IContentProvider provider = acquireProvider(url);
        if (provider == null) {
            return null;
        }

        try {
            return provider.uncanonicalize(mPackageName, url);
        } catch (RemoteException e) {
            // Arbitrary and not worth documenting, as Activity
            // Manager will kill this process shortly anyway.
            return null;
        } finally {
            releaseProvider(provider);
        }
    }

    /**
     * Open a stream on to the content associated with a content URI.  If there
     * is no data associated with the URI, FileNotFoundException is thrown.
     *
     * <h5>Accepts the following URI schemes:</h5>
     * <ul>
     * <li>content ({@link #SCHEME_CONTENT})</li>
     * <li>android.resource ({@link #SCHEME_ANDROID_RESOURCE})</li>
     * <li>file ({@link #SCHEME_FILE})</li>
     * </ul>
     *
     * <p>See {@link #openAssetFileDescriptor(Uri, String)} for more information
     * on these schemes.
     *
     * @param uri The desired URI.
     * @return InputStream
     * @throws FileNotFoundException if the provided URI could not be opened.
     * @see #openAssetFileDescriptor(Uri, String)
     */
    public final InputStream openInputStream(Uri uri)
            throws FileNotFoundException {
        String scheme = uri.getScheme();
        if (SCHEME_ANDROID_RESOURCE.equals(scheme)) {
            // Note: left here to avoid breaking compatibility.  May be removed
            // with sufficient testing.
            OpenResourceIdResult r = getResourceId(uri);
            try {
                InputStream stream = r.r.openRawResource(r.id);
                return stream;
            } catch (Resources.NotFoundException ex) {
                throw new FileNotFoundException("Resource does not exist: " + uri);
            }
        } else if (SCHEME_FILE.equals(scheme)) {
            // Note: left here to avoid breaking compatibility.  May be removed
            // with sufficient testing.
            return new FileInputStream(uri.getPath());
        } else {
            AssetFileDescriptor fd = openAssetFileDescriptor(uri, "r", null);
            try {
                return fd != null ? fd.createInputStream() : null;
            } catch (IOException e) {
                throw new FileNotFoundException("Unable to create stream");
            }
        }
    }

    /**
     * Synonym for {@link #openOutputStream(Uri, String)
     * openOutputStream(uri, "w")}.
     * @throws FileNotFoundException if the provided URI could not be opened.
     */
    public final OutputStream openOutputStream(Uri uri)
            throws FileNotFoundException {
        return openOutputStream(uri, "w");
    }

    /**
     * Open a stream on to the content associated with a content URI.  If there
     * is no data associated with the URI, FileNotFoundException is thrown.
     *
     * <h5>Accepts the following URI schemes:</h5>
     * <ul>
     * <li>content ({@link #SCHEME_CONTENT})</li>
     * <li>file ({@link #SCHEME_FILE})</li>
     * </ul>
     *
     * <p>See {@link #openAssetFileDescriptor(Uri, String)} for more information
     * on these schemes.
     *
     * @param uri The desired URI.
     * @param mode May be "w", "wa", "rw", or "rwt".
     * @return OutputStream
     * @throws FileNotFoundException if the provided URI could not be opened.
     * @see #openAssetFileDescriptor(Uri, String)
     */
    public final OutputStream openOutputStream(Uri uri, String mode)
            throws FileNotFoundException {
        AssetFileDescriptor fd = openAssetFileDescriptor(uri, mode, null);
        try {
            return fd != null ? fd.createOutputStream() : null;
        } catch (IOException e) {
            throw new FileNotFoundException("Unable to create stream");
        }
    }

    /**
     * Open a raw file descriptor to access data under a URI.  This
     * is like {@link #openAssetFileDescriptor(Uri, String)}, but uses the
     * underlying {@link ContentProvider#openFile}
     * ContentProvider.openFile()} method, so will <em>not</em> work with
     * providers that return sub-sections of files.  If at all possible,
     * you should use {@link #openAssetFileDescriptor(Uri, String)}.  You
     * will receive a FileNotFoundException exception if the provider returns a
     * sub-section of a file.
     *
     * <h5>Accepts the following URI schemes:</h5>
     * <ul>
     * <li>content ({@link #SCHEME_CONTENT})</li>
     * <li>file ({@link #SCHEME_FILE})</li>
     * </ul>
     *
     * <p>See {@link #openAssetFileDescriptor(Uri, String)} for more information
     * on these schemes.
     * <p>
     * If opening with the exclusive "r" or "w" modes, the returned
     * ParcelFileDescriptor could be a pipe or socket pair to enable streaming
     * of data. Opening with the "rw" mode implies a file on disk that supports
     * seeking. If possible, always use an exclusive mode to give the underlying
     * {@link ContentProvider} the most flexibility.
     * <p>
     * If you are writing a file, and need to communicate an error to the
     * provider, use {@link ParcelFileDescriptor#closeWithError(String)}.
     *
     * @param uri The desired URI to open.
     * @param mode The file mode to use, as per {@link ContentProvider#openFile
     * ContentProvider.openFile}.
     * @return Returns a new ParcelFileDescriptor pointing to the file.  You
     * own this descriptor and are responsible for closing it when done.
     * @throws FileNotFoundException Throws FileNotFoundException if no
     * file exists under the URI or the mode is invalid.
     * @see #openAssetFileDescriptor(Uri, String)
     */
    public final ParcelFileDescriptor openFileDescriptor(Uri uri, String mode)
            throws FileNotFoundException {
        return openFileDescriptor(uri, mode, null);
    }

    /**
     * Open a raw file descriptor to access data under a URI.  This
     * is like {@link #openAssetFileDescriptor(Uri, String)}, but uses the
     * underlying {@link ContentProvider#openFile}
     * ContentProvider.openFile()} method, so will <em>not</em> work with
     * providers that return sub-sections of files.  If at all possible,
     * you should use {@link #openAssetFileDescriptor(Uri, String)}.  You
     * will receive a FileNotFoundException exception if the provider returns a
     * sub-section of a file.
     *
     * <h5>Accepts the following URI schemes:</h5>
     * <ul>
     * <li>content ({@link #SCHEME_CONTENT})</li>
     * <li>file ({@link #SCHEME_FILE})</li>
     * </ul>
     *
     * <p>See {@link #openAssetFileDescriptor(Uri, String)} for more information
     * on these schemes.
     * <p>
     * If opening with the exclusive "r" or "w" modes, the returned
     * ParcelFileDescriptor could be a pipe or socket pair to enable streaming
     * of data. Opening with the "rw" mode implies a file on disk that supports
     * seeking. If possible, always use an exclusive mode to give the underlying
     * {@link ContentProvider} the most flexibility.
     * <p>
     * If you are writing a file, and need to communicate an error to the
     * provider, use {@link ParcelFileDescriptor#closeWithError(String)}.
     *
     * @param uri The desired URI to open.
     * @param mode The file mode to use, as per {@link ContentProvider#openFile
     * ContentProvider.openFile}.
     * @param cancellationSignal A signal to cancel the operation in progress,
     *         or null if none. If the operation is canceled, then
     *         {@link OperationCanceledException} will be thrown.
     * @return Returns a new ParcelFileDescriptor pointing to the file.  You
     * own this descriptor and are responsible for closing it when done.
     * @throws FileNotFoundException Throws FileNotFoundException if no
     * file exists under the URI or the mode is invalid.
     * @see #openAssetFileDescriptor(Uri, String)
     */
    public final ParcelFileDescriptor openFileDescriptor(Uri uri,
            String mode, CancellationSignal cancellationSignal) throws FileNotFoundException {
        AssetFileDescriptor afd = openAssetFileDescriptor(uri, mode, cancellationSignal);
        if (afd == null) {
            return null;
        }

        if (afd.getDeclaredLength() < 0) {
            // This is a full file!
            return afd.getParcelFileDescriptor();
        }

        // Client can't handle a sub-section of a file, so close what
        // we got and bail with an exception.
        try {
            afd.close();
        } catch (IOException e) {
        }

        throw new FileNotFoundException("Not a whole file");
    }

    /**
     * Open a raw file descriptor to access data under a URI.  This
     * interacts with the underlying {@link ContentProvider#openAssetFile}
     * method of the provider associated with the given URI, to retrieve any file stored there.
     *
     * <h5>Accepts the following URI schemes:</h5>
     * <ul>
     * <li>content ({@link #SCHEME_CONTENT})</li>
     * <li>android.resource ({@link #SCHEME_ANDROID_RESOURCE})</li>
     * <li>file ({@link #SCHEME_FILE})</li>
     * </ul>
     * <h5>The android.resource ({@link #SCHEME_ANDROID_RESOURCE}) Scheme</h5>
     * <p>
     * A Uri object can be used to reference a resource in an APK file.  The
     * Uri should be one of the following formats:
     * <ul>
     * <li><code>android.resource://package_name/id_number</code><br/>
     * <code>package_name</code> is your package name as listed in your AndroidManifest.xml.
     * For example <code>com.example.myapp</code><br/>
     * <code>id_number</code> is the int form of the ID.<br/>
     * The easiest way to construct this form is
     * <pre>Uri uri = Uri.parse("android.resource://com.example.myapp/" + R.raw.my_resource");</pre>
     * </li>
     * <li><code>android.resource://package_name/type/name</code><br/>
     * <code>package_name</code> is your package name as listed in your AndroidManifest.xml.
     * For example <code>com.example.myapp</code><br/>
     * <code>type</code> is the string form of the resource type.  For example, <code>raw</code>
     * or <code>drawable</code>.
     * <code>name</code> is the string form of the resource name.  That is, whatever the file
     * name was in your res directory, without the type extension.
     * The easiest way to construct this form is
     * <pre>Uri uri = Uri.parse("android.resource://com.example.myapp/raw/my_resource");</pre>
     * </li>
     * </ul>
     *
     * <p>Note that if this function is called for read-only input (mode is "r")
     * on a content: URI, it will instead call {@link #openTypedAssetFileDescriptor}
     * for you with a MIME type of "*&#47;*".  This allows such callers to benefit
     * from any built-in data conversion that a provider implements.
     *
     * @param uri The desired URI to open.
     * @param mode The file mode to use, as per {@link ContentProvider#openAssetFile
     * ContentProvider.openAssetFile}.
     * @return Returns a new ParcelFileDescriptor pointing to the file.  You
     * own this descriptor and are responsible for closing it when done.
     * @throws FileNotFoundException Throws FileNotFoundException of no
     * file exists under the URI or the mode is invalid.
     */
    public final AssetFileDescriptor openAssetFileDescriptor(Uri uri, String mode)
            throws FileNotFoundException {
        return openAssetFileDescriptor(uri, mode, null);
    }

    /**
     * Open a raw file descriptor to access data under a URI.  This
     * interacts with the underlying {@link ContentProvider#openAssetFile}
     * method of the provider associated with the given URI, to retrieve any file stored there.
     *
     * <h5>Accepts the following URI schemes:</h5>
     * <ul>
     * <li>content ({@link #SCHEME_CONTENT})</li>
     * <li>android.resource ({@link #SCHEME_ANDROID_RESOURCE})</li>
     * <li>file ({@link #SCHEME_FILE})</li>
     * </ul>
     * <h5>The android.resource ({@link #SCHEME_ANDROID_RESOURCE}) Scheme</h5>
     * <p>
     * A Uri object can be used to reference a resource in an APK file.  The
     * Uri should be one of the following formats:
     * <ul>
     * <li><code>android.resource://package_name/id_number</code><br/>
     * <code>package_name</code> is your package name as listed in your AndroidManifest.xml.
     * For example <code>com.example.myapp</code><br/>
     * <code>id_number</code> is the int form of the ID.<br/>
     * The easiest way to construct this form is
     * <pre>Uri uri = Uri.parse("android.resource://com.example.myapp/" + R.raw.my_resource");</pre>
     * </li>
     * <li><code>android.resource://package_name/type/name</code><br/>
     * <code>package_name</code> is your package name as listed in your AndroidManifest.xml.
     * For example <code>com.example.myapp</code><br/>
     * <code>type</code> is the string form of the resource type.  For example, <code>raw</code>
     * or <code>drawable</code>.
     * <code>name</code> is the string form of the resource name.  That is, whatever the file
     * name was in your res directory, without the type extension.
     * The easiest way to construct this form is
     * <pre>Uri uri = Uri.parse("android.resource://com.example.myapp/raw/my_resource");</pre>
     * </li>
     * </ul>
     *
     * <p>Note that if this function is called for read-only input (mode is "r")
     * on a content: URI, it will instead call {@link #openTypedAssetFileDescriptor}
     * for you with a MIME type of "*&#47;*".  This allows such callers to benefit
     * from any built-in data conversion that a provider implements.
     *
     * @param uri The desired URI to open.
     * @param mode The file mode to use, as per {@link ContentProvider#openAssetFile
     * ContentProvider.openAssetFile}.
     * @param cancellationSignal A signal to cancel the operation in progress, or null if
     *            none. If the operation is canceled, then
     *            {@link OperationCanceledException} will be thrown.
     * @return Returns a new ParcelFileDescriptor pointing to the file.  You
     * own this descriptor and are responsible for closing it when done.
     * @throws FileNotFoundException Throws FileNotFoundException of no
     * file exists under the URI or the mode is invalid.
     */
    public final AssetFileDescriptor openAssetFileDescriptor(Uri uri,
            String mode, CancellationSignal cancellationSignal) throws FileNotFoundException {
        String scheme = uri.getScheme();
        if (SCHEME_ANDROID_RESOURCE.equals(scheme)) {
            if (!"r".equals(mode)) {
                throw new FileNotFoundException("Can't write resources: " + uri);
            }
            OpenResourceIdResult r = getResourceId(uri);
            try {
                return r.r.openRawResourceFd(r.id);
            } catch (Resources.NotFoundException ex) {
                throw new FileNotFoundException("Resource does not exist: " + uri);
            }
        } else if (SCHEME_FILE.equals(scheme)) {
            ParcelFileDescriptor pfd = ParcelFileDescriptor.open(
                    new File(uri.getPath()), ParcelFileDescriptor.parseMode(mode));
            return new AssetFileDescriptor(pfd, 0, -1);
        } else {
            if ("r".equals(mode)) {
                return openTypedAssetFileDescriptor(uri, "*/*", null, cancellationSignal);
            } else {
                IContentProvider unstableProvider = acquireUnstableProvider(uri);
                if (unstableProvider == null) {
                    throw new FileNotFoundException("No content provider: " + uri);
                }
                IContentProvider stableProvider = null;
                AssetFileDescriptor fd = null;

                try {
                    ICancellationSignal remoteCancellationSignal = null;
                    if (cancellationSignal != null) {
                        cancellationSignal.throwIfCanceled();
                        remoteCancellationSignal = unstableProvider.createCancellationSignal();
                        cancellationSignal.setRemote(remoteCancellationSignal);
                    }

                    try {
                        fd = unstableProvider.openAssetFile(
                                mPackageName, uri, mode, remoteCancellationSignal);
                        if (fd == null) {
                            // The provider will be released by the finally{} clause
                            return null;
                        }
                    } catch (DeadObjectException e) {
                        // The remote process has died...  but we only hold an unstable
                        // reference though, so we might recover!!!  Let's try!!!!
                        // This is exciting!!1!!1!!!!1
                        unstableProviderDied(unstableProvider);
                        stableProvider = acquireProvider(uri);
                        if (stableProvider == null) {
                            throw new FileNotFoundException("No content provider: " + uri);
                        }
                        fd = stableProvider.openAssetFile(
                                mPackageName, uri, mode, remoteCancellationSignal);
                        if (fd == null) {
                            // The provider will be released by the finally{} clause
                            return null;
                        }
                    }

                    if (stableProvider == null) {
                        stableProvider = acquireProvider(uri);
                    }
                    releaseUnstableProvider(unstableProvider);
                    ParcelFileDescriptor pfd = new ParcelFileDescriptorInner(
                            fd.getParcelFileDescriptor(), stableProvider);

                    // Success!  Don't release the provider when exiting, let
                    // ParcelFileDescriptorInner do that when it is closed.
                    stableProvider = null;

                    return new AssetFileDescriptor(pfd, fd.getStartOffset(),
                            fd.getDeclaredLength());

                } catch (RemoteException e) {
                    // Whatever, whatever, we'll go away.
                    throw new FileNotFoundException(
                            "Failed opening content provider: " + uri);
                } catch (FileNotFoundException e) {
                    throw e;
                } finally {
                    if (cancellationSignal != null) {
                        cancellationSignal.setRemote(null);
                    }
                    if (stableProvider != null) {
                        releaseProvider(stableProvider);
                    }
                    if (unstableProvider != null) {
                        releaseUnstableProvider(unstableProvider);
                    }
                }
            }
        }
    }

    /**
     * Open a raw file descriptor to access (potentially type transformed)
     * data from a "content:" URI.  This interacts with the underlying
     * {@link ContentProvider#openTypedAssetFile} method of the provider
     * associated with the given URI, to retrieve retrieve any appropriate
     * data stream for the data stored there.
     *
     * <p>Unlike {@link #openAssetFileDescriptor}, this function only works
     * with "content:" URIs, because content providers are the only facility
     * with an associated MIME type to ensure that the returned data stream
     * is of the desired type.
     *
     * <p>All text/* streams are encoded in UTF-8.
     *
     * @param uri The desired URI to open.
     * @param mimeType The desired MIME type of the returned data.  This can
     * be a pattern such as *&#47;*, which will allow the content provider to
     * select a type, though there is no way for you to determine what type
     * it is returning.
     * @param opts Additional provider-dependent options.
     * @return Returns a new ParcelFileDescriptor from which you can read the
     * data stream from the provider.  Note that this may be a pipe, meaning
     * you can't seek in it.  The only seek you should do is if the
     * AssetFileDescriptor contains an offset, to move to that offset before
     * reading.  You own this descriptor and are responsible for closing it when done.
     * @throws FileNotFoundException Throws FileNotFoundException of no
     * data of the desired type exists under the URI.
     */
    public final AssetFileDescriptor openTypedAssetFileDescriptor(
            Uri uri, String mimeType, Bundle opts) throws FileNotFoundException {
        return openTypedAssetFileDescriptor(uri, mimeType, opts, null);
    }

    /**
     * Open a raw file descriptor to access (potentially type transformed)
     * data from a "content:" URI.  This interacts with the underlying
     * {@link ContentProvider#openTypedAssetFile} method of the provider
     * associated with the given URI, to retrieve retrieve any appropriate
     * data stream for the data stored there.
     *
     * <p>Unlike {@link #openAssetFileDescriptor}, this function only works
     * with "content:" URIs, because content providers are the only facility
     * with an associated MIME type to ensure that the returned data stream
     * is of the desired type.
     *
     * <p>All text/* streams are encoded in UTF-8.
     *
     * @param uri The desired URI to open.
     * @param mimeType The desired MIME type of the returned data.  This can
     * be a pattern such as *&#47;*, which will allow the content provider to
     * select a type, though there is no way for you to determine what type
     * it is returning.
     * @param opts Additional provider-dependent options.
     * @param cancellationSignal A signal to cancel the operation in progress,
     *         or null if none. If the operation is canceled, then
     *         {@link OperationCanceledException} will be thrown.
     * @return Returns a new ParcelFileDescriptor from which you can read the
     * data stream from the provider.  Note that this may be a pipe, meaning
     * you can't seek in it.  The only seek you should do is if the
     * AssetFileDescriptor contains an offset, to move to that offset before
     * reading.  You own this descriptor and are responsible for closing it when done.
     * @throws FileNotFoundException Throws FileNotFoundException of no
     * data of the desired type exists under the URI.
     */
    public final AssetFileDescriptor openTypedAssetFileDescriptor(Uri uri,
            String mimeType, Bundle opts, CancellationSignal cancellationSignal)
            throws FileNotFoundException {
        IContentProvider unstableProvider = acquireUnstableProvider(uri);
        if (unstableProvider == null) {
            throw new FileNotFoundException("No content provider: " + uri);
        }
        IContentProvider stableProvider = null;
        AssetFileDescriptor fd = null;

        try {
            ICancellationSignal remoteCancellationSignal = null;
            if (cancellationSignal != null) {
                cancellationSignal.throwIfCanceled();
                remoteCancellationSignal = unstableProvider.createCancellationSignal();
                cancellationSignal.setRemote(remoteCancellationSignal);
            }

            try {
                fd = unstableProvider.openTypedAssetFile(
                        mPackageName, uri, mimeType, opts, remoteCancellationSignal);
                if (fd == null) {
                    // The provider will be released by the finally{} clause
                    return null;
                }
            } catch (DeadObjectException e) {
                // The remote process has died...  but we only hold an unstable
                // reference though, so we might recover!!!  Let's try!!!!
                // This is exciting!!1!!1!!!!1
                unstableProviderDied(unstableProvider);
                stableProvider = acquireProvider(uri);
                if (stableProvider == null) {
                    throw new FileNotFoundException("No content provider: " + uri);
                }
                fd = stableProvider.openTypedAssetFile(
                        mPackageName, uri, mimeType, opts, remoteCancellationSignal);
                if (fd == null) {
                    // The provider will be released by the finally{} clause
                    return null;
                }
            }

            if (stableProvider == null) {
                stableProvider = acquireProvider(uri);
            }
            releaseUnstableProvider(unstableProvider);
            ParcelFileDescriptor pfd = new ParcelFileDescriptorInner(
                    fd.getParcelFileDescriptor(), stableProvider);

            // Success!  Don't release the provider when exiting, let
            // ParcelFileDescriptorInner do that