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
17package android.app.backup;
18
19import android.annotation.SystemApi;
20import android.os.ParcelFileDescriptor;
21import android.os.Process;
22
23import java.io.FileDescriptor;
24import java.io.IOException;
25
26/**
27 * Provides the structured interface through which a {@link BackupAgent} commits
28 * information to the backup data set, via its {@link
29 * BackupAgent#onBackup(ParcelFileDescriptor,BackupDataOutput,ParcelFileDescriptor)
30 * onBackup()} method.  Data written for backup is presented
31 * as a set of "entities," key/value pairs in which each binary data record "value" is
32 * named with a string "key."
33 * <p>
34 * To commit a data record to the backup transport, the agent's
35 * {@link BackupAgent#onBackup(ParcelFileDescriptor,BackupDataOutput,ParcelFileDescriptor)
36 * onBackup()} method first writes an "entity header" that supplies the key string for the record
37 * and the total size of the binary value for the record.  After the header has been
38 * written, the agent then writes the binary entity value itself.  The entity value can
39 * be written in multiple chunks if desired, as long as the total count of bytes written
40 * matches what was supplied to {@link #writeEntityHeader(String, int) writeEntityHeader()}.
41 * <p>
42 * Entity key strings are considered to be unique within a given application's backup
43 * data set. If a backup agent writes a new entity under an existing key string, its value will
44 * replace any previous value in the transport's remote data store.  You can remove a record
45 * entirely from the remote data set by writing a new entity header using the
46 * existing record's key, but supplying a negative <code>dataSize</code> parameter.
47 * When you do so, the agent does not need to call {@link #writeEntityData(byte[], int)}.
48 * <h3>Example</h3>
49 * <p>
50 * Here is an example illustrating a way to back up the value of a String variable
51 * called <code>mStringToBackUp</code>:
52 * <pre>
53 * static final String MY_STRING_KEY = "storedstring";
54 *
55 * public void {@link BackupAgent#onBackup(ParcelFileDescriptor, BackupDataOutput, ParcelFileDescriptor) onBackup(ParcelFileDescriptor oldState, BackupDataOutput data, ParcelFileDescriptor newState)}
56 *         throws IOException {
57 *     ...
58 *     byte[] stringBytes = mStringToBackUp.getBytes();
59 *     data.writeEntityHeader(MY_STRING_KEY, stringBytes.length);
60 *     data.writeEntityData(stringBytes, stringBytes.length);
61 *     ...
62 * }</pre>
63 *
64 * @see BackupAgent
65 */
66public class BackupDataOutput {
67    long mBackupWriter;
68
69    /** @hide */
70    @SystemApi
71    public BackupDataOutput(FileDescriptor fd) {
72        if (fd == null) throw new NullPointerException();
73        mBackupWriter = ctor(fd);
74        if (mBackupWriter == 0) {
75            throw new RuntimeException("Native initialization failed with fd=" + fd);
76        }
77    }
78
79    /**
80     * Mark the beginning of one record in the backup data stream. This must be called before
81     * {@link #writeEntityData}.
82     * @param key A string key that uniquely identifies the data record within the application.
83     *    Keys whose first character is \uFF00 or higher are not valid.
84     * @param dataSize The size in bytes of this record's data.  Passing a dataSize
85     *    of -1 indicates that the record under this key should be deleted.
86     * @return The number of bytes written to the backup stream
87     * @throws IOException if the write failed
88     */
89    public int writeEntityHeader(String key, int dataSize) throws IOException {
90        int result = writeEntityHeader_native(mBackupWriter, key, dataSize);
91        if (result >= 0) {
92            return result;
93        } else {
94            throw new IOException("result=0x" + Integer.toHexString(result));
95        }
96    }
97
98    /**
99     * Write a chunk of data under the current entity to the backup transport.
100     * @param data A raw data buffer to send
101     * @param size The number of bytes to be sent in this chunk
102     * @return the number of bytes written
103     * @throws IOException if the write failed
104     */
105    public int writeEntityData(byte[] data, int size) throws IOException {
106        int result = writeEntityData_native(mBackupWriter, data, size);
107        if (result >= 0) {
108            return result;
109        } else {
110            throw new IOException("result=0x" + Integer.toHexString(result));
111        }
112    }
113
114    /** @hide */
115    public void setKeyPrefix(String keyPrefix) {
116        setKeyPrefix_native(mBackupWriter, keyPrefix);
117    }
118
119    /** @hide */
120    @Override
121    protected void finalize() throws Throwable {
122        try {
123            dtor(mBackupWriter);
124        } finally {
125            super.finalize();
126        }
127    }
128
129    private native static long ctor(FileDescriptor fd);
130    private native static void dtor(long mBackupWriter);
131
132    private native static int writeEntityHeader_native(long mBackupWriter, String key, int dataSize);
133    private native static int writeEntityData_native(long mBackupWriter, byte[] data, int size);
134    private native static void setKeyPrefix_native(long mBackupWriter, String keyPrefix);
135}
136
137