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 com.android.server; 18 19import android.util.Slog; 20 21import java.io.Closeable; 22import java.io.DataOutput; 23import java.io.EOFException; 24import java.io.FileInputStream; 25import java.io.IOException; 26import java.io.InputStream; 27import java.io.RandomAccessFile; 28 29/** 30 * A 4k block of random {@code byte}s. 31 */ 32class RandomBlock { 33 34 private static final String TAG = "RandomBlock"; 35 private static final boolean DEBUG = false; 36 private static final int BLOCK_SIZE = 4096; 37 private byte[] block = new byte[BLOCK_SIZE]; 38 39 private RandomBlock() { } 40 41 static RandomBlock fromFile(String filename) throws IOException { 42 if (DEBUG) Slog.v(TAG, "reading from file " + filename); 43 InputStream stream = null; 44 try { 45 stream = new FileInputStream(filename); 46 return fromStream(stream); 47 } finally { 48 close(stream); 49 } 50 } 51 52 private static RandomBlock fromStream(InputStream in) throws IOException { 53 RandomBlock retval = new RandomBlock(); 54 int total = 0; 55 while(total < BLOCK_SIZE) { 56 int result = in.read(retval.block, total, BLOCK_SIZE - total); 57 if (result == -1) { 58 throw new EOFException(); 59 } 60 total += result; 61 } 62 return retval; 63 } 64 65 void toFile(String filename, boolean sync) throws IOException { 66 if (DEBUG) Slog.v(TAG, "writing to file " + filename); 67 RandomAccessFile out = null; 68 try { 69 out = new RandomAccessFile(filename, sync ? "rws" : "rw"); 70 toDataOut(out); 71 truncateIfPossible(out); 72 } finally { 73 close(out); 74 } 75 } 76 77 private static void truncateIfPossible(RandomAccessFile f) { 78 try { 79 f.setLength(BLOCK_SIZE); 80 } catch (IOException e) { 81 // ignore this exception. Sometimes, the file we're trying to 82 // write is a character device, such as /dev/urandom, and 83 // these character devices do not support setting the length. 84 } 85 } 86 87 private void toDataOut(DataOutput out) throws IOException { 88 out.write(block); 89 } 90 91 private static void close(Closeable c) { 92 try { 93 if (c == null) { 94 return; 95 } 96 c.close(); 97 } catch (IOException e) { 98 Slog.w(TAG, "IOException thrown while closing Closeable", e); 99 } 100 } 101} 102