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/*
* Copyright (C) 2009 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.app.backup;
import android.annotation.SystemApi;
import java.io.FileDescriptor;
import java.io.IOException;
/**
* Provides the structured interface through which a {@link BackupAgent} reads
* information from the backup data set, via its
* {@link BackupAgent#onRestore(BackupDataInput, int, android.os.ParcelFileDescriptor) onRestore()}
* method. The data is presented as a set of "entities," each
* representing one named record as previously stored by the agent's
* {@link BackupAgent#onBackup(ParcelFileDescriptor,BackupDataOutput,ParcelFileDescriptor)
* onBackup()} implementation. An entity is composed of a descriptive header plus a
* byte array that holds the raw data saved in the remote backup.
* <p>
* The agent must consume every entity in the data stream, otherwise the
* restored state of the application will be incomplete.
* <h3>Example</h3>
* <p>
* A typical
* {@link BackupAgent#onRestore(BackupDataInput,int,ParcelFileDescriptor)
* onRestore()} implementation might be structured something like this:
* <pre>
* public void onRestore(BackupDataInput data, int appVersionCode,
* ParcelFileDescriptor newState) {
* while (data.readNextHeader()) {
* String key = data.getKey();
* int dataSize = data.getDataSize();
*
* if (key.equals(MY_BACKUP_KEY_ONE)) {
* // process this kind of record here
* byte[] buffer = new byte[dataSize];
* data.readEntityData(buffer, 0, dataSize); // reads the entire entity at once
*
* // now 'buffer' holds the raw data and can be processed however
* // the agent wishes
* processBackupKeyOne(buffer);
* } else if (key.equals(MY_BACKUP_KEY_TO_IGNORE) {
* // a key we recognize but wish to discard
* data.skipEntityData();
* } // ... etc.
* }
* }</pre>
*/
public class BackupDataInput {
long mBackupReader;
private EntityHeader mHeader = new EntityHeader();
private boolean mHeaderReady;
private static class EntityHeader {
String key;
int dataSize;
}
/** @hide */
@SystemApi
public BackupDataInput(FileDescriptor fd) {
if (fd == null) throw new NullPointerException();
mBackupReader = ctor(fd);
if (mBackupReader == 0) {
throw new RuntimeException("Native initialization failed with fd=" + fd);
}
}
/** @hide */
@Override
protected void finalize() throws Throwable {
try {
dtor(mBackupReader);
} finally {
super.finalize();
}
}
/**
* Extract the next entity header from the restore stream. After this method
* return success, the {@link #getKey()} and {@link #getDataSize()} methods can
* be used to inspect the entity that is now available for processing.
*
* @return <code>true</code> when there is an entity ready for consumption from the
* restore stream, <code>false</code> if the restore stream has been fully consumed.
* @throws IOException if an error occurred while reading the restore stream
*/
public boolean readNextHeader() throws IOException {
int result = readNextHeader_native(mBackupReader, mHeader);
if (result == 0) {
// read successfully
mHeaderReady = true;
return true;
} else if (result > 0) {
// done
mHeaderReady = false;
return false;
} else {
// error
mHeaderReady = false;
throw new IOException("failed: 0x" + Integer.toHexString(result));
}
}
/**
* Report the key associated with the current entity in the restore stream
* @return the current entity's key string
* @throws IllegalStateException if the next record header has not yet been read
*/
public String getKey() {
if (mHeaderReady) {
return mHeader.key;
} else {
throw new IllegalStateException("Entity header not read");
}
}
/**
* Report the size in bytes of the data associated with the current entity in the
* restore stream.
*
* @return The size of the record's raw data, in bytes
* @throws IllegalStateException if the next record header has not yet been read
*/
public int getDataSize() {
if (mHeaderReady) {
return mHeader.dataSize;
} else {
throw new IllegalStateException("Entity header not read");
}
}
/**
* Read a record's raw data from the restore stream. The record's header must first
* have been processed by the {@link #readNextHeader()} method. Multiple calls to
* this method may be made in order to process the data in chunks; not all of it
* must be read in a single call. Once all of the raw data for the current entity
* has been read, further calls to this method will simply return zero.
*
* @param data An allocated byte array of at least 'size' bytes
* @param offset Offset within the 'data' array at which the data will be placed
* when read from the stream
* @param size The number of bytes to read in this pass
* @return The number of bytes of data read. Once all of the data for this entity
* has been read, further calls to this method will return zero.
* @throws IOException if an error occurred when trying to read the restore data stream
*/
public int readEntityData(byte[] data, int offset, int size) throws IOException {
if (mHeaderReady) {
int result = readEntityData_native(mBackupReader, data, offset, size);
if (result >= 0) {
return result;
} else {
throw new IOException("result=0x" + Integer.toHexString(result));
}
} else {
throw new IllegalStateException("Entity header not read");
}
}
/**
* Consume the current entity's data without extracting it into a buffer
* for further processing. This allows a {@link android.app.backup.BackupAgent} to
* efficiently discard obsolete or otherwise uninteresting records during the
* restore operation.
*
* @throws IOException if an error occurred when trying to read the restore data stream
*/
public void skipEntityData() throws IOException {
if (mHeaderReady) {
skipEntityData_native(mBackupReader);
} else {
throw new IllegalStateException("Entity header not read");
}
}
private native static long ctor(FileDescriptor fd);
private native static void dtor(long mBackupReader);
private native int readNextHeader_native(long mBackupReader, EntityHeader entity);
private native int readEntityData_native(long mBackupReader, byte[] data, int offset, int size);
private native int skipEntityData_native(long mBackupReader);
}
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