content: /*
   * 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.server;
  
  import android.util.Slog;
  
  import java.io.Closeable;
  import java.io.DataOutput;
  import java.io.EOFException;
  import java.io.FileInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.RandomAccessFile;
  
  /**
   * A block of 512 random {@code byte}s.
   */
  class RandomBlock {
  
      private static final String TAG = "RandomBlock";
      private static final boolean DEBUG = false;
      private static final int BLOCK_SIZE = 512;
      private byte[] block = new byte[BLOCK_SIZE];
  
      private RandomBlock() { }
  
      static RandomBlock fromFile(String filename) throws IOException {
          if (DEBUG) Slog.v(TAG, "reading from file " + filename);
          InputStream stream = null;
          try {
              stream = new FileInputStream(filename);
              return fromStream(stream);
          } finally {
              close(stream);
          }
      }
  
      private static RandomBlock fromStream(InputStream in) throws IOException {
          RandomBlock retval = new RandomBlock();
          int total = 0;
          while(total < BLOCK_SIZE) {
              int result = in.read(retval.block, total, BLOCK_SIZE - total);
              if (result == -1) {
                  throw new EOFException();
              }
              total += result;
          }
          return retval;
      }
  
      void toFile(String filename, boolean sync) throws IOException {
          if (DEBUG) Slog.v(TAG, "writing to file " + filename);
          RandomAccessFile out = null;
          try {
              out = new RandomAccessFile(filename, sync ? "rws" : "rw");
              toDataOut(out);
              truncateIfPossible(out);
          } finally {
              close(out);
          }
      }
  
      private static void truncateIfPossible(RandomAccessFile f) {
          try {
              f.setLength(BLOCK_SIZE);
          } catch (IOException e) {
              // ignore this exception.  Sometimes, the file we're trying to
              // write is a character device, such as /dev/urandom, and
              // these character devices do not support setting the length.
          }
      }
  
      private void toDataOut(DataOutput out) throws IOException {
          out.write(block);
      }
  
      private static void close(Closeable c) {
          try {
              if (c == null) {
                  return;
              }
              c.close();
          } catch (IOException e) {
              Slog.w(TAG, "IOException thrown while closing Closeable", e);
          }
      }
  }
  