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| 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.util; |
| 18 | + |
| 19 | +import android.os.FileUtils; |
| 20 | +import android.util.Log; |
| 21 | + |
| 22 | +import java.io.File; |
| 23 | +import java.io.FileInputStream; |
| 24 | +import java.io.FileNotFoundException; |
| 25 | +import java.io.FileOutputStream; |
| 26 | +import java.io.IOException; |
| 27 | + |
| 28 | +/** |
| 29 | + * Helper class for performing atomic operations on a file by creating a |
| 30 | + * backup file until a write has successfully completed. If you need this |
| 31 | + * on older versions of the platform you can use |
| 32 | + * {@link android.support.v4.util.AtomicFile} in the v4 support library. |
| 33 | + * <p> |
| 34 | + * Atomic file guarantees file integrity by ensuring that a file has |
| 35 | + * been completely written and sync'd to disk before removing its backup. |
| 36 | + * As long as the backup file exists, the original file is considered |
| 37 | + * to be invalid (left over from a previous attempt to write the file). |
| 38 | + * </p><p> |
| 39 | + * Atomic file does not confer any file locking semantics. |
| 40 | + * Do not use this class when the file may be accessed or modified concurrently |
| 41 | + * by multiple threads or processes. The caller is responsible for ensuring |
| 42 | + * appropriate mutual exclusion invariants whenever it accesses the file. |
| 43 | + * </p> |
| 44 | + */ |
| 45 | +public class AtomicFile { |
| 46 | + private final File mBaseName; |
| 47 | + private final File mBackupName; |
| 48 | + |
| 49 | + /** |
| 50 | + * Create a new AtomicFile for a file located at the given File path. |
| 51 | + * The secondary backup file will be the same file path with ".bak" appended. |
| 52 | + */ |
| 53 | + public AtomicFile(File baseName) { |
| 54 | + mBaseName = baseName; |
| 55 | + mBackupName = new File(baseName.getPath() + ".bak"); |
| 56 | + } |
| 57 | + |
| 58 | + /** |
| 59 | + * Return the path to the base file. You should not generally use this, |
| 60 | + * as the data at that path may not be valid. |
| 61 | + */ |
| 62 | + public File getBaseFile() { |
| 63 | + return mBaseName; |
| 64 | + } |
| 65 | + |
| 66 | + /** |
| 67 | + * Delete the atomic file. This deletes both the base and backup files. |
| 68 | + */ |
| 69 | + public void delete() { |
| 70 | + mBaseName.delete(); |
| 71 | + mBackupName.delete(); |
| 72 | + } |
| 73 | + |
| 74 | + /** |
| 75 | + * Start a new write operation on the file. This returns a FileOutputStream |
| 76 | + * to which you can write the new file data. The existing file is replaced |
| 77 | + * with the new data. You <em>must not</em> directly close the given |
| 78 | + * FileOutputStream; instead call either {@link #finishWrite(FileOutputStream)} |
| 79 | + * or {@link #failWrite(FileOutputStream)}. |
| 80 | + * |
| 81 | + * <p>Note that if another thread is currently performing |
| 82 | + * a write, this will simply replace whatever that thread is writing |
| 83 | + * with the new file being written by this thread, and when the other |
| 84 | + * thread finishes the write the new write operation will no longer be |
| 85 | + * safe (or will be lost). You must do your own threading protection for |
| 86 | + * access to AtomicFile. |
| 87 | + */ |
| 88 | + public FileOutputStream startWrite() throws IOException { |
| 89 | + // Rename the current file so it may be used as a backup during the next read |
| 90 | + if (mBaseName.exists()) { |
| 91 | + if (!mBackupName.exists()) { |
| 92 | + if (!mBaseName.renameTo(mBackupName)) { |
| 93 | + Log.w("AtomicFile", "Couldn't rename file " + mBaseName |
| 94 | + + " to backup file " + mBackupName); |
| 95 | + } |
| 96 | + } else { |
| 97 | + mBaseName.delete(); |
| 98 | + } |
| 99 | + } |
| 100 | + FileOutputStream str = null; |
| 101 | + try { |
| 102 | + str = new FileOutputStream(mBaseName); |
| 103 | + } catch (FileNotFoundException e) { |
| 104 | + File parent = mBaseName.getParentFile(); |
| 105 | + if (!parent.mkdir()) { |
| 106 | + throw new IOException("Couldn't create directory " + mBaseName); |
| 107 | + } |
| 108 | + FileUtils.setPermissions( |
| 109 | + parent.getPath(), |
| 110 | + FileUtils.S_IRWXU|FileUtils.S_IRWXG|FileUtils.S_IXOTH, |
| 111 | + -1, -1); |
| 112 | + try { |
| 113 | + str = new FileOutputStream(mBaseName); |
| 114 | + } catch (FileNotFoundException e2) { |
| 115 | + throw new IOException("Couldn't create " + mBaseName); |
| 116 | + } |
| 117 | + } |
| 118 | + return str; |
| 119 | + } |
| 120 | + |
| 121 | + /** |
| 122 | + * Call when you have successfully finished writing to the stream |
| 123 | + * returned by {@link #startWrite()}. This will close, sync, and |
| 124 | + * commit the new data. The next attempt to read the atomic file |
| 125 | + * will return the new file stream. |
| 126 | + */ |
| 127 | + public void finishWrite(FileOutputStream str) { |
| 128 | + if (str != null) { |
| 129 | + FileUtils.sync(str); |
| 130 | + try { |
| 131 | + str.close(); |
| 132 | + mBackupName.delete(); |
| 133 | + } catch (IOException e) { |
| 134 | + Log.w("AtomicFile", "finishWrite: Got exception:", e); |
| 135 | + } |
| 136 | + } |
| 137 | + } |
| 138 | + |
| 139 | + /** |
| 140 | + * Call when you have failed for some reason at writing to the stream |
| 141 | + * returned by {@link #startWrite()}. This will close the current |
| 142 | + * write stream, and roll back to the previous state of the file. |
| 143 | + */ |
| 144 | + public void failWrite(FileOutputStream str) { |
| 145 | + if (str != null) { |
| 146 | + FileUtils.sync(str); |
| 147 | + try { |
| 148 | + str.close(); |
| 149 | + mBaseName.delete(); |
| 150 | + mBackupName.renameTo(mBaseName); |
| 151 | + } catch (IOException e) { |
| 152 | + Log.w("AtomicFile", "failWrite: Got exception:", e); |
| 153 | + } |
| 154 | + } |
| 155 | + } |
| 156 | + |
| 157 | + /** @hide |
| 158 | + * @deprecated This is not safe. |
| 159 | + */ |
| 160 | + @Deprecated public void truncate() throws IOException { |
| 161 | + try { |
| 162 | + FileOutputStream fos = new FileOutputStream(mBaseName); |
| 163 | + FileUtils.sync(fos); |
| 164 | + fos.close(); |
| 165 | + } catch (FileNotFoundException e) { |
| 166 | + throw new IOException("Couldn't append " + mBaseName); |
| 167 | + } catch (IOException e) { |
| 168 | + } |
| 169 | + } |
| 170 | + |
| 171 | + /** @hide |
| 172 | + * @deprecated This is not safe. |
| 173 | + */ |
| 174 | + @Deprecated public FileOutputStream openAppend() throws IOException { |
| 175 | + try { |
| 176 | + return new FileOutputStream(mBaseName, true); |
| 177 | + } catch (FileNotFoundException e) { |
| 178 | + throw new IOException("Couldn't append " + mBaseName); |
| 179 | + } |
| 180 | + } |
| 181 | + |
| 182 | + /** |
| 183 | + * Open the atomic file for reading. If there previously was an |
| 184 | + * incomplete write, this will roll back to the last good data before |
| 185 | + * opening for read. You should call close() on the FileInputStream when |
| 186 | + * you are done reading from it. |
| 187 | + * |
| 188 | + * <p>Note that if another thread is currently performing |
| 189 | + * a write, this will incorrectly consider it to be in the state of a bad |
| 190 | + * write and roll back, causing the new data currently being written to |
| 191 | + * be dropped. You must do your own threading protection for access to |
| 192 | + * AtomicFile. |
| 193 | + */ |
| 194 | + public FileInputStream openRead() throws FileNotFoundException { |
| 195 | + if (mBackupName.exists()) { |
| 196 | + mBaseName.delete(); |
| 197 | + mBackupName.renameTo(mBaseName); |
| 198 | + } |
| 199 | + return new FileInputStream(mBaseName); |
| 200 | + } |
| 201 | + |
| 202 | + /** |
| 203 | + * A convenience for {@link #openRead()} that also reads all of the |
| 204 | + * file contents into a byte array which is returned. |
| 205 | + */ |
| 206 | + public byte[] readFully() throws IOException { |
| 207 | + FileInputStream stream = openRead(); |
| 208 | + try { |
| 209 | + int pos = 0; |
| 210 | + int avail = stream.available(); |
| 211 | + byte[] data = new byte[avail]; |
| 212 | + while (true) { |
| 213 | + int amt = stream.read(data, pos, data.length-pos); |
| 214 | + //Log.i("foo", "Read " + amt + " bytes at " + pos |
| 215 | + // + " of avail " + data.length); |
| 216 | + if (amt <= 0) { |
| 217 | + //Log.i("foo", "**** FINISHED READING: pos=" + pos |
| 218 | + // + " len=" + data.length); |
| 219 | + return data; |
| 220 | + } |
| 221 | + pos += amt; |
| 222 | + avail = stream.available(); |
| 223 | + if (avail > data.length-pos) { |
| 224 | + byte[] newData = new byte[pos+avail]; |
| 225 | + System.arraycopy(data, 0, newData, 0, pos); |
| 226 | + data = newData; |
| 227 | + } |
| 228 | + } |
| 229 | + } finally { |
| 230 | + stream.close(); |
| 231 | + } |
| 232 | + } |
| 233 | +} |
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