001/*
002 * Copyright (C) 2007 The Guava Authors
003 *
004 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
005 * in compliance with the License. You may obtain a copy of the License at
006 *
007 * http://www.apache.org/licenses/LICENSE-2.0
008 *
009 * Unless required by applicable law or agreed to in writing, software distributed under the License
010 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
011 * or implied. See the License for the specific language governing permissions and limitations under
012 * the License.
013 */
014
015package com.google.common.io;
016
017import com.google.common.annotations.Beta;
018import com.google.common.annotations.GwtIncompatible;
019import com.google.common.base.Preconditions;
020import com.google.common.primitives.Ints;
021import com.google.common.primitives.Longs;
022import com.google.errorprone.annotations.CanIgnoreReturnValue;
023import com.google.errorprone.annotations.DoNotCall;
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 for reading {@code
033 * short}, {@code int}, {@code float}, {@code double}, and {@code long} values.
034 *
035 * <p><b>Note:</b> This class intentionally violates the specification of its supertype {@code
036 * DataInput}, which explicitly requires big-endian byte order.
037 *
038 * @author Chris Nokleberg
039 * @author Keith Bottner
040 * @since 8.0
041 */
042@Beta
043@GwtIncompatible
044public final class LittleEndianDataInputStream extends FilterInputStream implements DataInput {
045
046  /**
047   * Creates a {@code LittleEndianDataInputStream} that wraps the given stream.
048   *
049   * @param in the stream to delegate to
050   */
051  public LittleEndianDataInputStream(InputStream in) {
052    super(Preconditions.checkNotNull(in));
053  }
054
055  /** This method will throw an {@link UnsupportedOperationException}. */
056  @CanIgnoreReturnValue // to skip a line
057  @Override
058  @DoNotCall("Always throws UnsupportedOperationException")
059  public String readLine() {
060    throw new UnsupportedOperationException("readLine is not supported");
061  }
062
063  @Override
064  public void readFully(byte[] b) throws IOException {
065    ByteStreams.readFully(this, b);
066  }
067
068  @Override
069  public void readFully(byte[] b, int off, int len) throws IOException {
070    ByteStreams.readFully(this, b, off, len);
071  }
072
073  @Override
074  public int skipBytes(int n) throws IOException {
075    return (int) in.skip(n);
076  }
077
078  @CanIgnoreReturnValue // to skip a byte
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 {@link DataInputStream#readUnsignedShort()},
091   * except using little-endian byte order.
092   *
093   * @return the next two bytes of the input stream, interpreted as an unsigned 16-bit integer in
094   *     little-endian byte order
095   * @throws IOException if an I/O error occurs
096   */
097  @CanIgnoreReturnValue // to skip some bytes
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 using little-endian
108   * byte order.
109   *
110   * @return the next four bytes of the input stream, interpreted as an {@code int} in little-endian
111   *     byte order
112   * @throws IOException if an I/O error occurs
113   */
114  @CanIgnoreReturnValue // to skip some bytes
115  @Override
116  public int readInt() throws IOException {
117    byte b1 = readAndCheckByte();
118    byte b2 = readAndCheckByte();
119    byte b3 = readAndCheckByte();
120    byte b4 = readAndCheckByte();
121
122    return Ints.fromBytes(b4, b3, b2, b1);
123  }
124
125  /**
126   * Reads a {@code long} as specified by {@link DataInputStream#readLong()}, except using
127   * little-endian byte order.
128   *
129   * @return the next eight bytes of the input stream, interpreted as a {@code long} in
130   *     little-endian byte order
131   * @throws IOException if an I/O error occurs
132   */
133  @CanIgnoreReturnValue // to skip some bytes
134  @Override
135  public long readLong() throws IOException {
136    byte b1 = readAndCheckByte();
137    byte b2 = readAndCheckByte();
138    byte b3 = readAndCheckByte();
139    byte b4 = readAndCheckByte();
140    byte b5 = readAndCheckByte();
141    byte b6 = readAndCheckByte();
142    byte b7 = readAndCheckByte();
143    byte b8 = readAndCheckByte();
144
145    return Longs.fromBytes(b8, b7, b6, b5, b4, b3, b2, b1);
146  }
147
148  /**
149   * Reads a {@code float} as specified by {@link DataInputStream#readFloat()}, except using
150   * little-endian byte order.
151   *
152   * @return the next four bytes of the input stream, interpreted as a {@code float} in
153   *     little-endian byte order
154   * @throws IOException if an I/O error occurs
155   */
156  @CanIgnoreReturnValue // to skip some bytes
157  @Override
158  public float readFloat() throws IOException {
159    return Float.intBitsToFloat(readInt());
160  }
161
162  /**
163   * Reads a {@code double} as specified by {@link DataInputStream#readDouble()}, except using
164   * little-endian byte order.
165   *
166   * @return the next eight bytes of the input stream, interpreted as a {@code double} in
167   *     little-endian byte order
168   * @throws IOException if an I/O error occurs
169   */
170  @CanIgnoreReturnValue // to skip some bytes
171  @Override
172  public double readDouble() throws IOException {
173    return Double.longBitsToDouble(readLong());
174  }
175
176  @CanIgnoreReturnValue // to skip a field
177  @Override
178  public String readUTF() throws IOException {
179    return new DataInputStream(in).readUTF();
180  }
181
182  /**
183   * Reads a {@code short} as specified by {@link DataInputStream#readShort()}, except using
184   * little-endian byte order.
185   *
186   * @return the next two bytes of the input stream, interpreted as a {@code short} in little-endian
187   *     byte order.
188   * @throws IOException if an I/O error occurs.
189   */
190  @CanIgnoreReturnValue // to skip some bytes
191  @Override
192  public short readShort() throws IOException {
193    return (short) readUnsignedShort();
194  }
195
196  /**
197   * Reads a char as specified by {@link DataInputStream#readChar()}, except using little-endian
198   * byte order.
199   *
200   * @return the next two bytes of the input stream, interpreted as a {@code char} in little-endian
201   *     byte order
202   * @throws IOException if an I/O error occurs
203   */
204  @CanIgnoreReturnValue // to skip some bytes
205  @Override
206  public char readChar() throws IOException {
207    return (char) readUnsignedShort();
208  }
209
210  @CanIgnoreReturnValue // to skip a byte
211  @Override
212  public byte readByte() throws IOException {
213    return (byte) readUnsignedByte();
214  }
215
216  @CanIgnoreReturnValue // to skip a byte
217  @Override
218  public boolean readBoolean() throws IOException {
219    return readUnsignedByte() != 0;
220  }
221
222  /**
223   * Reads a byte from the input stream checking that the end of file (EOF) has not been
224   * encountered.
225   *
226   * @return byte read from input
227   * @throws IOException if an error is encountered while reading
228   * @throws EOFException if the end of file (EOF) is encountered.
229   */
230  private byte readAndCheckByte() throws IOException, EOFException {
231    int b1 = in.read();
232
233    if (-1 == b1) {
234      throw new EOFException();
235    }
236
237    return (byte) b1;
238  }
239}