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    
017    package com.google.common.io;
018    
019    import com.google.common.annotations.Beta;
020    import com.google.common.base.Preconditions;
021    import com.google.common.primitives.Ints;
022    import com.google.common.primitives.Longs;
023    
024    import java.io.DataInput;
025    import java.io.DataInputStream;
026    import java.io.EOFException;
027    import java.io.FilterInputStream;
028    import java.io.IOException;
029    import 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
044    public 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    }