1/*
2 * Copyright (C) 2007 The Guava Authors
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.google.common.io;
18
19import com.google.common.annotations.Beta;
20import com.google.common.base.Preconditions;
21import com.google.common.primitives.Ints;
22import com.google.common.primitives.Longs;
23
24import java.io.DataInput;
25import java.io.DataInputStream;
26import java.io.EOFException;
27import java.io.FilterInputStream;
28import java.io.IOException;
29import java.io.InputStream;
30
31/**
32 * An implementation of {@link DataInput} that uses little-endian byte ordering
33 * for reading {@code short}, {@code int}, {@code float}, {@code double}, and
34 * {@code long} values.
35 * <p>
36 * <b>Note:</b> This class intentionally violates the specification of its
37 * supertype {@code DataInput}, which explicitly requires big-endian byte order.
38 *
39 * @author Chris Nokleberg
40 * @author Keith Bottner
41 * @since 8.0
42 */
43@Beta
44public final class LittleEndianDataInputStream extends FilterInputStream
45    implements DataInput {
46
47  /**
48   * Creates a {@code LittleEndianDataInputStream} that wraps the given stream.
49   *
50   * @param in the stream to delegate to
51   */
52  public LittleEndianDataInputStream(InputStream in) {
53    super(Preconditions.checkNotNull(in));
54  }
55
56  /**
57   * This method will throw an {@link UnsupportedOperationException}.
58   */
59  @Override
60  public String readLine() {
61    throw new UnsupportedOperationException("readLine is not supported");
62  }
63
64  @Override
65  public void readFully(byte[] b) throws IOException {
66    ByteStreams.readFully(this, b);
67  }
68
69  @Override
70  public void readFully(byte[] b, int off, int len) throws IOException {
71    ByteStreams.readFully(this, b, off, len);
72  }
73
74  @Override
75  public int skipBytes(int n) throws IOException {
76    return (int) in.skip(n);
77  }
78
79  @Override
80  public int readUnsignedByte() throws IOException {
81    int b1 = in.read();
82    if (0 > b1) {
83      throw new EOFException();
84    }
85
86    return b1;
87  }
88
89  /**
90   * Reads an unsigned {@code short} as specified by
91   * {@link DataInputStream#readUnsignedShort()}, except using little-endian
92   * byte order.
93   *
94   * @return the next two bytes of the input stream, interpreted as an
95   *         unsigned 16-bit integer in little-endian byte order
96   * @throws IOException if an I/O error occurs
97   */
98  @Override
99  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}
233