001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License");
005 * you may not use this file except in compliance with the License.
006 * You may obtain a copy of the License at
007 *
008 * http://www.apache.org/licenses/LICENSE-2.0
009 *
010 * Unless required by applicable law or agreed to in writing, software
011 * distributed under the License is distributed on an "AS IS" BASIS,
012 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
013 * See the License for the specific language governing permissions and
014 * limitations under the License.
015 */
016
017package com.google.common.io;
018
019import com.google.common.annotations.Beta;
020import com.google.common.base.Preconditions;
021import com.google.common.primitives.Ints;
022import com.google.common.primitives.Longs;
023
024import java.io.DataInput;
025import java.io.DataInputStream;
026import java.io.EOFException;
027import java.io.FilterInputStream;
028import java.io.IOException;
029import java.io.InputStream;
030
031/**
032 * An implementation of {@link DataInput} that uses little-endian byte ordering
033 * for reading {@code short}, {@code int}, {@code float}, {@code double}, and
034 * {@code long} values.
035 * <p>
036 * <b>Note:</b> This class intentionally violates the specification of its
037 * supertype {@code DataInput}, which explicitly requires big-endian byte order.
038 *
039 * @author Chris Nokleberg
040 * @author Keith Bottner
041 * @since 8.0
042 */
043@Beta
044public final class LittleEndianDataInputStream extends FilterInputStream
045    implements DataInput {
046
047  /**
048   * Creates a {@code LittleEndianDataInputStream} that wraps the given stream.
049   *
050   * @param in the stream to delegate to
051   */
052  public LittleEndianDataInputStream(InputStream in) {
053    super(Preconditions.checkNotNull(in));
054  }
055
056  /**
057   * This method will throw an {@link UnsupportedOperationException}.
058   */
059  @Override
060  public String readLine() {
061    throw new UnsupportedOperationException("readLine is not supported");
062  }
063
064  @Override
065  public void readFully(byte[] b) throws IOException {
066    ByteStreams.readFully(this, b);
067  }
068
069  @Override
070  public void readFully(byte[] b, int off, int len) throws IOException {
071    ByteStreams.readFully(this, b, off, len);
072  }
073
074  @Override
075  public int skipBytes(int n) throws IOException {
076    return (int) in.skip(n);
077  }
078
079  @Override
080  public int readUnsignedByte() throws IOException {
081    int b1 = in.read();
082    if (0 > b1) {
083      throw new EOFException();
084    }
085    
086    return b1;
087  }
088
089  /**
090   * Reads an unsigned {@code short} as specified by
091   * {@link DataInputStream#readUnsignedShort()}, except using little-endian
092   * byte order.
093   *
094   * @return the next two bytes of the input stream, interpreted as an 
095   *         unsigned 16-bit integer in little-endian byte order
096   * @throws IOException if an I/O error occurs
097   */
098  @Override
099  public int readUnsignedShort() throws IOException {
100    byte b1 = readAndCheckByte();
101    byte b2 = readAndCheckByte();
102
103    return Ints.fromBytes((byte) 0, (byte) 0, b2, b1);
104  }
105
106  /**
107   * Reads an integer as specified by {@link DataInputStream#readInt()}, except
108   * using little-endian byte order.
109   *
110   * @return the next four bytes of the input stream, interpreted as an 
111   *         {@code int} in little-endian byte order
112   * @throws IOException if an I/O error occurs
113   */
114  @Override
115  public int readInt() throws IOException {
116    byte b1 = readAndCheckByte();
117    byte b2 = readAndCheckByte();
118    byte b3 = readAndCheckByte();
119    byte b4 = readAndCheckByte();
120
121    return Ints.fromBytes( b4, b3, b2, b1);
122  }
123
124  /**
125   * Reads a {@code long} as specified by {@link DataInputStream#readLong()},
126   * except using little-endian byte order.
127   *
128   * @return the next eight bytes of the input stream, interpreted as a 
129   *         {@code long} in little-endian byte order
130   * @throws IOException if an I/O error occurs
131   */
132  @Override
133  public long readLong() throws IOException {
134    byte b1 = readAndCheckByte();
135    byte b2 = readAndCheckByte();
136    byte b3 = readAndCheckByte();
137    byte b4 = readAndCheckByte();
138    byte b5 = readAndCheckByte();
139    byte b6 = readAndCheckByte();
140    byte b7 = readAndCheckByte();
141    byte b8 = readAndCheckByte();
142
143    return Longs.fromBytes(b8, b7, b6, b5, b4, b3, b2, b1);
144  }
145
146  /**
147   * Reads a {@code float} as specified by {@link DataInputStream#readFloat()},
148   * except using little-endian byte order.
149   *
150   * @return the next four bytes of the input stream, interpreted as a
151   *         {@code float} in little-endian byte order
152   * @throws IOException if an I/O error occurs
153   */
154  @Override
155  public float readFloat() throws IOException {
156    return Float.intBitsToFloat(readInt());
157  }
158
159  /**
160   * Reads a {@code double} as specified by
161   * {@link DataInputStream#readDouble()}, except using little-endian byte
162   * order.
163   *
164   * @return the next eight bytes of the input stream, interpreted as a
165   *         {@code double} in little-endian byte order
166   * @throws IOException if an I/O error occurs
167   */
168  @Override
169  public double readDouble() throws IOException {
170    return Double.longBitsToDouble(readLong());
171  }
172
173  @Override
174  public String readUTF() throws IOException {
175    return new DataInputStream(in).readUTF();
176  }
177
178  /**
179   * Reads a {@code short} as specified by {@link DataInputStream#readShort()},
180   * except using little-endian byte order.
181   *
182   * @return the next two bytes of the input stream, interpreted as a
183   *         {@code short} in little-endian byte order.
184   * @throws IOException if an I/O error occurs.
185   */
186  @Override
187  public short readShort() throws IOException {
188    return (short) readUnsignedShort();
189  }
190
191  /**
192   * Reads a char as specified by {@link DataInputStream#readChar()}, except
193   * using little-endian byte order.
194   *
195   * @return the next two bytes of the input stream, interpreted as a 
196   *         {@code char} in little-endian byte order
197   * @throws IOException if an I/O error occurs
198   */
199  @Override
200  public char readChar() throws IOException {
201    return (char) readUnsignedShort();
202  }
203
204  @Override
205  public byte readByte() throws IOException {
206    return (byte) readUnsignedByte();
207  }
208
209  @Override
210  public boolean readBoolean() throws IOException {
211    return readUnsignedByte() != 0;
212  }
213
214  /**
215   * Reads a byte from the input stream checking that the end of file (EOF)
216   * has not been encountered.
217   *  
218   * @return byte read from input
219   * @throws IOException if an error is encountered while reading
220   * @throws EOFException if the end of file (EOF) is encountered.
221   */
222  private byte readAndCheckByte() throws IOException, EOFException {
223    int b1 = in.read();
224
225    if (-1 == b1) {
226      throw new EOFException();
227    }
228
229    return (byte) b1;
230  }
231
232}