1 /*
2 * Copyright (C) 2007 The Guava Authors
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
5 * in compliance with the License. You may obtain a copy of the License at
6 *
7 * http://www.apache.org/licenses/LICENSE-2.0
8 *
9 * Unless required by applicable law or agreed to in writing, software distributed under the License
10 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
11 * or implied. See the License for the specific language governing permissions and limitations under
12 * the License.
13 */
14
15 package com.google.common.io;
16
17 import com.google.common.annotations.Beta;
18 import com.google.common.annotations.GwtIncompatible;
19 import com.google.common.base.Preconditions;
20 import com.google.common.primitives.Ints;
21 import com.google.common.primitives.Longs;
22 import com.google.errorprone.annotations.CanIgnoreReturnValue;
23 import com.google.errorprone.annotations.DoNotCall;
24 import java.io.DataInput;
25 import java.io.DataInputStream;
26 import java.io.EOFException;
27 import java.io.FilterInputStream;
28 import java.io.IOException;
29 import java.io.InputStream;
30
31 /**
32 * An implementation of {@link DataInput} that uses little-endian byte ordering for reading {@code
33 * short}, {@code int}, {@code float}, {@code double}, and {@code long} values.
34 *
35 * <p><b>Note:</b> This class intentionally violates the specification of its supertype {@code
36 * DataInput}, which explicitly requires big-endian byte order.
37 *
38 * @author Chris Nokleberg
39 * @author Keith Bottner
40 * @since 8.0
41 */
42 @Beta
43 @GwtIncompatible
44 @ElementTypesAreNonnullByDefault
45 public final class LittleEndianDataInputStream extends FilterInputStream 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 /** This method will throw an {@link UnsupportedOperationException}. */
57 @CanIgnoreReturnValue // to skip a line
58 @Override
59 @DoNotCall("Always throws UnsupportedOperationException")
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 @CanIgnoreReturnValue // to skip a byte
80 @Override
81 public int readUnsignedByte() throws IOException {
82 int b1 = in.read();
83 if (0 > b1) {
84 throw new EOFException();
85 }
86
87 return b1;
88 }
89
90 /**
91 * Reads an unsigned {@code short} as specified by {@link DataInputStream#readUnsignedShort()},
92 * except using little-endian byte order.
93 *
94 * @return the next two bytes of the input stream, interpreted as an unsigned 16-bit integer in
95 * little-endian byte order
96 * @throws IOException if an I/O error occurs
97 */
98 @CanIgnoreReturnValue // to skip some bytes
99 @Override
100 public int readUnsignedShort() throws IOException {
101 byte b1 = readAndCheckByte();
102 byte b2 = readAndCheckByte();
103
104 return Ints.fromBytes((byte) 0, (byte) 0, b2, b1);
105 }
106
107 /**
108 * Reads an integer as specified by {@link DataInputStream#readInt()}, except using little-endian
109 * byte order.
110 *
111 * @return the next four bytes of the input stream, interpreted as an {@code int} in little-endian
112 * byte order
113 * @throws IOException if an I/O error occurs
114 */
115 @CanIgnoreReturnValue // to skip some bytes
116 @Override
117 public int readInt() throws IOException {
118 byte b1 = readAndCheckByte();
119 byte b2 = readAndCheckByte();
120 byte b3 = readAndCheckByte();
121 byte b4 = readAndCheckByte();
122
123 return Ints.fromBytes(b4, b3, b2, b1);
124 }
125
126 /**
127 * Reads a {@code long} as specified by {@link DataInputStream#readLong()}, except using
128 * little-endian byte order.
129 *
130 * @return the next eight bytes of the input stream, interpreted as a {@code long} in
131 * little-endian byte order
132 * @throws IOException if an I/O error occurs
133 */
134 @CanIgnoreReturnValue // to skip some bytes
135 @Override
136 public long readLong() throws IOException {
137 byte b1 = readAndCheckByte();
138 byte b2 = readAndCheckByte();
139 byte b3 = readAndCheckByte();
140 byte b4 = readAndCheckByte();
141 byte b5 = readAndCheckByte();
142 byte b6 = readAndCheckByte();
143 byte b7 = readAndCheckByte();
144 byte b8 = readAndCheckByte();
145
146 return Longs.fromBytes(b8, b7, b6, b5, b4, b3, b2, b1);
147 }
148
149 /**
150 * Reads a {@code float} as specified by {@link DataInputStream#readFloat()}, except using
151 * little-endian byte order.
152 *
153 * @return the next four bytes of the input stream, interpreted as a {@code float} in
154 * little-endian byte order
155 * @throws IOException if an I/O error occurs
156 */
157 @CanIgnoreReturnValue // to skip some bytes
158 @Override
159 public float readFloat() throws IOException {
160 return Float.intBitsToFloat(readInt());
161 }
162
163 /**
164 * Reads a {@code double} as specified by {@link DataInputStream#readDouble()}, except using
165 * little-endian byte order.
166 *
167 * @return the next eight bytes of the input stream, interpreted as a {@code double} in
168 * little-endian byte order
169 * @throws IOException if an I/O error occurs
170 */
171 @CanIgnoreReturnValue // to skip some bytes
172 @Override
173 public double readDouble() throws IOException {
174 return Double.longBitsToDouble(readLong());
175 }
176
177 @CanIgnoreReturnValue // to skip a field
178 @Override
179 public String readUTF() throws IOException {
180 return new DataInputStream(in).readUTF();
181 }
182
183 /**
184 * Reads a {@code short} as specified by {@link DataInputStream#readShort()}, except using
185 * little-endian byte order.
186 *
187 * @return the next two bytes of the input stream, interpreted as a {@code short} in little-endian
188 * byte order.
189 * @throws IOException if an I/O error occurs.
190 */
191 @CanIgnoreReturnValue // to skip some bytes
192 @Override
193 public short readShort() throws IOException {
194 return (short) readUnsignedShort();
195 }
196
197 /**
198 * Reads a char as specified by {@link DataInputStream#readChar()}, except using little-endian
199 * byte order.
200 *
201 * @return the next two bytes of the input stream, interpreted as a {@code char} in little-endian
202 * byte order
203 * @throws IOException if an I/O error occurs
204 */
205 @CanIgnoreReturnValue // to skip some bytes
206 @Override
207 public char readChar() throws IOException {
208 return (char) readUnsignedShort();
209 }
210
211 @CanIgnoreReturnValue // to skip a byte
212 @Override
213 public byte readByte() throws IOException {
214 return (byte) readUnsignedByte();
215 }
216
217 @CanIgnoreReturnValue // to skip a byte
218 @Override
219 public boolean readBoolean() throws IOException {
220 return readUnsignedByte() != 0;
221 }
222
223 /**
224 * Reads a byte from the input stream checking that the end of file (EOF) has not been
225 * encountered.
226 *
227 * @return byte read from input
228 * @throws IOException if an error is encountered while reading
229 * @throws EOFException if the end of file (EOF) is encountered.
230 */
231 private byte readAndCheckByte() throws IOException, EOFException {
232 int b1 = in.read();
233
234 if (-1 == b1) {
235 throw new EOFException();
236 }
237
238 return (byte) b1;
239 }
240 }