1 /* 2 * Copyright (C) 2009 The Android Open Source Project 3 * 4 * Licensed under the Apache License, Version 2.0 (the "License"); 5 * you may not use this file except in compliance with the License. 6 * You may obtain a copy of the License at 7 * 8 * http://www.apache.org/licenses/LICENSE-2.0 9 * 10 * Unless required by applicable law or agreed to in writing, software 11 * distributed under the License is distributed on an "AS IS" BASIS, 12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 13 * See the License for the specific language governing permissions and 14 * limitations under the License. 15 */ 16 17 package android.app.backup; 18 19 import android.annotation.SystemApi; 20 import android.os.ParcelFileDescriptor; 21 import java.io.FileDescriptor; 22 import java.io.IOException; 23 24 /** 25 * Provides the structured interface through which a {@link BackupAgent} commits 26 * information to the backup data set, via its {@link 27 * BackupAgent#onBackup(ParcelFileDescriptor,BackupDataOutput,ParcelFileDescriptor) 28 * onBackup()} method. Data written for backup is presented 29 * as a set of "entities," key/value pairs in which each binary data record "value" is 30 * named with a string "key." 31 * <p> 32 * To commit a data record to the backup transport, the agent's 33 * {@link BackupAgent#onBackup(ParcelFileDescriptor,BackupDataOutput,ParcelFileDescriptor) 34 * onBackup()} method first writes an "entity header" that supplies the key string for the record 35 * and the total size of the binary value for the record. After the header has been 36 * written, the agent then writes the binary entity value itself. The entity value can 37 * be written in multiple chunks if desired, as long as the total count of bytes written 38 * matches what was supplied to {@link #writeEntityHeader(String, int) writeEntityHeader()}. 39 * <p> 40 * Entity key strings are considered to be unique within a given application's backup 41 * data set. If a backup agent writes a new entity under an existing key string, its value will 42 * replace any previous value in the transport's remote data store. You can remove a record 43 * entirely from the remote data set by writing a new entity header using the 44 * existing record's key, but supplying a negative <code>dataSize</code> parameter. 45 * When you do so, the agent does not need to call {@link #writeEntityData(byte[], int)}. 46 * <h3>Example</h3> 47 * <p> 48 * Here is an example illustrating a way to back up the value of a String variable 49 * called <code>mStringToBackUp</code>: 50 * <pre> 51 * static final String MY_STRING_KEY = "storedstring"; 52 * 53 * public void {@link BackupAgent#onBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor) onBackup(ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)} 54 * throws IOException { 55 * ... 56 * byte[] stringBytes = mStringToBackUp.getBytes(); 57 * data.writeEntityHeader(MY_STRING_KEY, stringBytes.length); 58 * data.writeEntityData(stringBytes, stringBytes.length); 59 * ... 60 * }</pre> 61 * 62 * @see BackupAgent 63 */ 64 public class BackupDataOutput { 65 long mBackupWriter; 66 67 /** @hide */ 68 @SystemApi BackupDataOutput(FileDescriptor fd)69 public BackupDataOutput(FileDescriptor fd) { 70 if (fd == null) throw new NullPointerException(); 71 mBackupWriter = ctor(fd); 72 if (mBackupWriter == 0) { 73 throw new RuntimeException("Native initialization failed with fd=" + fd); 74 } 75 } 76 77 /** 78 * Mark the beginning of one record in the backup data stream. This must be called before 79 * {@link #writeEntityData}. 80 * @param key A string key that uniquely identifies the data record within the application. 81 * Keys whose first character is \uFF00 or higher are not valid. 82 * @param dataSize The size in bytes of this record's data. Passing a dataSize 83 * of -1 indicates that the record under this key should be deleted. 84 * @return The number of bytes written to the backup stream 85 * @throws IOException if the write failed 86 */ writeEntityHeader(String key, int dataSize)87 public int writeEntityHeader(String key, int dataSize) throws IOException { 88 int result = writeEntityHeader_native(mBackupWriter, key, dataSize); 89 if (result >= 0) { 90 return result; 91 } else { 92 throw new IOException("result=0x" + Integer.toHexString(result)); 93 } 94 } 95 96 /** 97 * Write a chunk of data under the current entity to the backup transport. 98 * @param data A raw data buffer to send 99 * @param size The number of bytes to be sent in this chunk 100 * @return the number of bytes written 101 * @throws IOException if the write failed 102 */ writeEntityData(byte[] data, int size)103 public int writeEntityData(byte[] data, int size) throws IOException { 104 int result = writeEntityData_native(mBackupWriter, data, size); 105 if (result >= 0) { 106 return result; 107 } else { 108 throw new IOException("result=0x" + Integer.toHexString(result)); 109 } 110 } 111 112 /** @hide */ setKeyPrefix(String keyPrefix)113 public void setKeyPrefix(String keyPrefix) { 114 setKeyPrefix_native(mBackupWriter, keyPrefix); 115 } 116 117 /** @hide */ 118 @Override finalize()119 protected void finalize() throws Throwable { 120 try { 121 dtor(mBackupWriter); 122 } finally { 123 super.finalize(); 124 } 125 } 126 ctor(FileDescriptor fd)127 private native static long ctor(FileDescriptor fd); dtor(long mBackupWriter)128 private native static void dtor(long mBackupWriter); 129 writeEntityHeader_native(long mBackupWriter, String key, int dataSize)130 private native static int writeEntityHeader_native(long mBackupWriter, String key, int dataSize); writeEntityData_native(long mBackupWriter, byte[] data, int size)131 private native static int writeEntityData_native(long mBackupWriter, byte[] data, int size); setKeyPrefix_native(long mBackupWriter, String keyPrefix)132 private native static void setKeyPrefix_native(long mBackupWriter, String keyPrefix); 133 } 134 135