1 files changed, 153 insertions, 0 deletions
diff --git a/core/java/com/android/internal/os/AtomicFile.java b/core/java/com/android/internal/os/AtomicFile.java
new file mode 100644
index 0000000..ca0345f
--- /dev/null
+++ b/core/java/com/android/internal/os/AtomicFile.java
@@ -0,0 +1,153 @@
+/*
+ * 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 com.android.internal.os;
+
+import android.os.FileUtils;
+import android.util.Log;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileNotFoundException;
+import java.io.FileOutputStream;
+import java.io.IOException;
+
+/**
+ * Helper class for performing atomic operations on a file, by creating a
+ * backup file until a write has successfully completed.
+ */
+public class AtomicFile {
+    private final File mBaseName;
+    private final File mBackupName;
+    
+    public AtomicFile(File baseName) {
+        mBaseName = baseName;
+        mBackupName = new File(baseName.getPath() + ".bak");
+    }
+    
+    public File getBaseFile() {
+        return mBaseName;
+    }
+    
+    public FileOutputStream startWrite() throws IOException {
+        // Rename the current file so it may be used as a backup during the next read
+        if (mBaseName.exists()) {
+            if (!mBaseName.renameTo(mBackupName)) {
+                mBackupName.delete();
+                if (!mBaseName.renameTo(mBackupName)) {
+                    Log.w("AtomicFile", "Couldn't rename file " + mBaseName
+                            + " to backup file " + mBackupName);
+                }
+            }
+        }
+        FileOutputStream str = null;
+        try {
+            str = new FileOutputStream(mBaseName);
+        } catch (FileNotFoundException e) {
+            File parent = mBaseName.getParentFile();
+            if (!parent.mkdir()) {
+                throw new IOException("Couldn't create directory " + mBaseName);
+            }
+            FileUtils.setPermissions(
+                parent.getPath(),
+                FileUtils.S_IRWXU|FileUtils.S_IRWXG|FileUtils.S_IXOTH,
+                -1, -1);
+            try {
+                str = new FileOutputStream(mBaseName);
+            } catch (FileNotFoundException e2) {
+                throw new IOException("Couldn't create " + mBaseName);
+            }
+        }
+        return str;
+    }
+    
+    public void finishWrite(FileOutputStream str) {
+        if (str != null) {
+            try {
+                str.close();
+                mBackupName.delete();
+            } catch (IOException e) {
+                Log.w("AtomicFile", "finishWrite: Got exception:", e);
+            }
+        }
+    }
+    
+    public void failWrite(FileOutputStream str) {
+        if (str != null) {
+            try {
+                str.close();
+                mBaseName.delete();
+                mBackupName.renameTo(mBaseName);
+            } catch (IOException e) {
+                Log.w("AtomicFile", "failWrite: Got exception:", e);
+            }
+        }
+    }
+    
+    public FileOutputStream openAppend() throws IOException {
+        try {
+            return new FileOutputStream(mBaseName, true);
+        } catch (FileNotFoundException e) {
+            throw new IOException("Couldn't append " + mBaseName);
+        }
+    }
+    
+    public void truncate() throws IOException {
+        try {
+            FileOutputStream fos = new FileOutputStream(mBaseName);
+            fos.close();
+        } catch (FileNotFoundException e) {
+            throw new IOException("Couldn't append " + mBaseName);
+        } catch (IOException e) {
+        }
+    }
+    
+    public FileInputStream openRead() throws FileNotFoundException {
+        if (mBackupName.exists()) {
+            mBaseName.delete();
+            mBackupName.renameTo(mBaseName);
+        }
+        return new FileInputStream(mBaseName);
+    }
+    
+    public byte[] readFully() throws IOException {
+        FileInputStream stream = openRead();
+        try {
+            int pos = 0;
+            int avail = stream.available();
+            byte[] data = new byte[avail];
+            while (true) {
+                int amt = stream.read(data, pos, data.length-pos);
+                //Log.i("foo", "Read " + amt + " bytes at " + pos
+                //        + " of avail " + data.length);
+                if (amt <= 0) {
+                    //Log.i("foo", "**** FINISHED READING: pos=" + pos
+                    //        + " len=" + data.length);
+                    return data;
+                }
+                pos += amt;
+                avail = stream.available();
+                if (avail > data.length-pos) {
+                    byte[] newData = new byte[pos+avail];
+                    System.arraycopy(data, 0, newData, 0, pos);
+                    data = newData;
+                }
+            }
+        } finally {
+            stream.close();
+        }
+    }
+}