背景
我正在尝试使用preon库来编码/解码二进制数据。当我配置big endian的字节顺序时，我的1字节结构工作正常，但是对于little endian失败了。看来，endianess会影响preon中的字节内数据。似乎this问题涉及同一问题，但不解决小端方面问题。
我附上了一个简单的案例来证明这个问题。
PreonLittleEndianNumber.java中是否存在缺陷，或者在指定小端字节顺序时，preon是否无法正常工作？
PreonTest.java
package me;
import org.codehaus.preon.Codec;
import org.codehaus.preon.Codecs;
import org.codehaus.preon.DecodingException;
import org.junit.Test;
import java.io.IOException;
import org.junit.Assert;
public class PreonTest {
@Test
public void bigEndianDecodeEncodeTest() {
byte[] testByte = {(byte) 0xDE};
Codec<PreonBigEndianNumber> bigCodec = Codecs.create(PreonBigEndianNumber.class);
try {
// Big Endian Decode/Encode Test
PreonBigEndianNumber pben = Codecs.decode(bigCodec, testByte);
byte[] testByte1 = Codecs.encode(pben, bigCodec);
Assert.assertArrayEquals(testByte, testByte1);
} catch (IOException e) {
e.printStackTrace();
} catch (DecodingException e) {
e.printStackTrace();
}
}
@Test
public void bigEndianEncodeDecodeTest() {
PreonBigEndianNumber pben = new PreonBigEndianNumber((byte)0xDE);
Codec<PreonBigEndianNumber> bigCodec = Codecs.create(PreonBigEndianNumber.class);
try {
byte[] testByte1 = Codecs.encode(pben, bigCodec);
PreonBigEndianNumber pben2 = Codecs.decode(bigCodec, testByte1);
Assert.assertEquals(pben, pben2);
} catch (IOException e) {
e.printStackTrace();
} catch (DecodingException e) {
e.printStackTrace();
}
}
@Test
public void littleEndianDecodeEncodeTest() {
byte[] testByte = {(byte) 0xDE};
Codec<PreonLittleEndianNumber> littleCodec = Codecs.create(PreonLittleEndianNumber.class);
try {
// Big Endian Decode/Encode Test
PreonLittleEndianNumber plen = Codecs.decode(littleCodec, testByte);
byte[] testByte1 = Codecs.encode(plen, littleCodec);
Assert.assertArrayEquals(testByte, testByte1);
} catch (IOException e) {
e.printStackTrace();
} catch (DecodingException e) {
e.printStackTrace();
}
}
@Test
public void littleEndianEncodeDecodeTest() {
PreonLittleEndianNumber plen = new PreonLittleEndianNumber((byte)0xDE);
Codec<PreonLittleEndianNumber> littleCodec = Codecs.create(PreonLittleEndianNumber.class);
try {
byte[] testByte1 = Codecs.encode(plen, littleCodec);
PreonLittleEndianNumber plen2 = Codecs.decode(littleCodec, testByte1);
Assert.assertEquals(plen, plen2);
} catch (IOException e) {
e.printStackTrace();
} catch (DecodingException e) {
e.printStackTrace();
}
}
}
PreonBigEndianNumber.java
package me;
import org.codehaus.preon.annotation.BoundNumber;
import org.codehaus.preon.buffer.ByteOrder;
public class PreonBigEndianNumber {
@BoundNumber(size="1", byteOrder=ByteOrder.BigEndian) public byte bit7;
@BoundNumber(size="1", byteOrder=ByteOrder.BigEndian) public byte bit6;
@BoundNumber(size="1", byteOrder=ByteOrder.BigEndian) public byte bit5;
@BoundNumber(size="1", byteOrder=ByteOrder.BigEndian) public byte bit4;
@BoundNumber(size="1", byteOrder=ByteOrder.BigEndian) public byte bit3;
@BoundNumber(size="1", byteOrder=ByteOrder.BigEndian) public byte bit2;
@BoundNumber(size="1", byteOrder=ByteOrder.BigEndian) public byte bit1;
@BoundNumber(size="1", byteOrder=ByteOrder.BigEndian) public byte bit0;
/**
* Default constructor
*/
public PreonBigEndianNumber() {
}
public PreonBigEndianNumber(byte value) {
bit7 = (byte) ((0b10000000 & value) >>> 7);
bit6 = (byte) ((0b01000000 & value) >>> 6);
bit5 = (byte) ((0b00100000 & value) >>> 5);
bit4 = (byte) ((0b00010000 & value) >>> 4);
bit3 = (byte) ((0b00001000 & value) >>> 3);
bit2 = (byte) ((0b00000100 & value) >>> 2);
bit1 = (byte) ((0b00000010 & value) >>> 1);
bit0 = (byte) ((0b00000001 & value) >>> 0);
}
public byte getByte() {
// Pack bits back into an int
int b = 0;
int shift = 0;
for (int i=7;i>=0;i--) {
b = (b << shift);
if (i==0) {b += bit0;}
else if (i==1) {b += bit1;}
else if (i==2) {b += bit2;}
else if (i==3) {b += bit3;}
else if (i==4) {b += bit4;}
else if (i==5) {b += bit5;}
else if (i==6) {b += bit6;}
else if (i==7) {b += bit7;}
shift = 1;
}
return (byte) b;
}
@Override
public String toString() {
return bit7 +
bit6 +
bit5 +
bit4 +
" " +
bit3 +
bit2 +
bit1 +
bit0;
}
@Override
public boolean equals(Object o) {
if (this == o) {return true;}
if (o == null || getClass() != o.getClass()) {return false;}
PreonBigEndianNumber preonBits = (PreonBigEndianNumber) o;
if (bit7 != preonBits.bit7) {return false;}
if (bit6 != preonBits.bit6) {return false;}
if (bit5 != preonBits.bit5) {return false;}
if (bit4 != preonBits.bit4) {return false;}
if (bit3 != preonBits.bit3) {return false;}
if (bit2 != preonBits.bit2) {return false;}
if (bit1 != preonBits.bit1) {return false;}
return bit0 == preonBits.bit0;
}
@Override
public int hashCode() {
int result = (int) bit7;
result = 31 * result + (int) bit6;
result = 31 * result + (int) bit5;
result = 31 * result + (int) bit4;
result = 31 * result + (int) bit3;
result = 31 * result + (int) bit2;
result = 31 * result + (int) bit1;
result = 31 * result + (int) bit0;
return result;
}
}
PreonLittleEndianNumber.java
package me;
import org.codehaus.preon.annotation.BoundNumber;
import org.codehaus.preon.buffer.ByteOrder;
public class PreonLittleEndianNumber {
@BoundNumber(size="1", byteOrder=ByteOrder.LittleEndian) public byte bit7;
@BoundNumber(size="1", byteOrder=ByteOrder.LittleEndian) public byte bit6;
@BoundNumber(size="1", byteOrder=ByteOrder.LittleEndian) public byte bit5;
@BoundNumber(size="1", byteOrder=ByteOrder.LittleEndian) public byte bit4;
@BoundNumber(size="1", byteOrder=ByteOrder.LittleEndian) public byte bit3;
@BoundNumber(size="1", byteOrder=ByteOrder.LittleEndian) public byte bit2;
@BoundNumber(size="1", byteOrder=ByteOrder.LittleEndian) public byte bit1;
@BoundNumber(size="1", byteOrder=ByteOrder.LittleEndian) public byte bit0;
/**
* Default constructor
*/
public PreonLittleEndianNumber() {
}
public PreonLittleEndianNumber(byte value) {
bit7 = (byte) ((0b10000000 & value) >>> 7);
bit6 = (byte) ((0b01000000 & value) >>> 6);
bit5 = (byte) ((0b00100000 & value) >>> 5);
bit4 = (byte) ((0b00010000 & value) >>> 4);
bit3 = (byte) ((0b00001000 & value) >>> 3);
bit2 = (byte) ((0b00000100 & value) >>> 2);
bit1 = (byte) ((0b00000010 & value) >>> 1);
bit0 = (byte) ((0b00000001 & value) >>> 0);
}
public byte getByte() {
// Pack bits back into an int
int b = 0;
int shift = 0;
for (int i=7;i>=0;i--) {
b = (b << shift);
if (i==0) {b += bit0;}
else if (i==1) {b += bit1;}
else if (i==2) {b += bit2;}
else if (i==3) {b += bit3;}
else if (i==4) {b += bit4;}
else if (i==5) {b += bit5;}
else if (i==6) {b += bit6;}
else if (i==7) {b += bit7;}
shift = 1;
}
return (byte) b;
}
@Override
public String toString() {
return bit7 +
bit6 +
bit5 +
bit4 +
" " +
bit3 +
bit2 +
bit1 +
bit0;
}
@Override
public boolean equals(Object o) {
if (this == o) {return true;}
if (o == null || getClass() != o.getClass()) {return false;}
PreonLittleEndianNumber preonBits = (PreonLittleEndianNumber) o;
if (bit7 != preonBits.bit7) {return false;}
if (bit6 != preonBits.bit6) {return false;}
if (bit5 != preonBits.bit5) {return false;}
if (bit4 != preonBits.bit4) {return false;}
if (bit3 != preonBits.bit3) {return false;}
if (bit2 != preonBits.bit2) {return false;}
if (bit1 != preonBits.bit1) {return false;}
return bit0 == preonBits.bit0;
}
@Override
public int hashCode() {
int result = (int) bit7;
result = 31 * result + (int) bit6;
result = 31 * result + (int) bit5;
result = 31 * result + (int) bit4;
result = 31 * result + (int) bit3;
result = 31 * result + (int) bit2;
result = 31 * result + (int) bit1;
result = 31 * result + (int) bit0;
return result;
}
}
的pom.xml
<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
<modelVersion>4.0.0</modelVersion>
<groupId>me</groupId>
<artifactId>parser</artifactId>
<version>1.0</version>
<repositories>
<repository>
<id>atlassian-repo</id>
<name>Atlassian Repository</name>
<url>https://maven.atlassian.com/repository/public</url>
</repository>
<repository>
<id>limbo-repository</id>
<url>http://limbo.sourceforge.net/repository</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
<releases>
<enabled>true</enabled>
</releases>
</repository>
<repository>
<id>pecia-repository</id>
<url>http://pecia.sourceforge.net/repository</url>
<snapshots>
<enabled>false</enabled>
</snapshots>
<releases>
<enabled>true</enabled>
</releases>
</repository>
</repositories>
<dependencies>
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
<dependency>
<groupId>org.codehaus.preon</groupId>
<artifactId>preon-binding</artifactId>
<version>1.1-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>org.codehaus.preon</groupId>
<artifactId>preon-el</artifactId>
<version>1.1-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>org.codehaus.preon</groupId>
<artifactId>preon-emitter</artifactId>
<version>1.1-SNAPSHOT</version>
</dependency>
<dependency>
<groupId>org.codehaus.preon</groupId>
<artifactId>preon-io</artifactId>
<version>1.1-SNAPSHOT</version>
</dependency>
</dependencies>
答案 0 :(得分：2)
我遇到了同样的问题。似乎ByteOrder.BigEndian和ByteOrder.LittleEndian的解码不同。但是，编码是相同的。这意味着当您使用ByteOrder.LittleEndian时，编码和解码之间的往返将是不正确的。
ByteOrder.BigEndian的解码使用MSB 0比特编号，ByteOrder.LittleEndian的解码使用LSB 0比特编号解码。考虑到这一点，我认为ByteOrder.LittleEndian的编码器已被破坏。
我分叉了preon（https://github.com/jdl17/preon/）的当前存储库并进行了必要的更改。随着这些变化，我发现我需要在拉取请求（https://github.com/preon/preon/pull/25）中加入最初由mrumpf提交的刷新修复。我进一步扩展它以允许关于刷新的字节顺序的规范。
除了上述更改之外，fork还包括实现ListCodecFactory的编码和解码方法以及SelectFromCode的编码方法的更改。最后，我将ANTLR从3.3更新到3.5.2，因此它适用于Java 8。
所有这些都已作为拉取请求提交回preon（https://github.com/preon/preon/pull/35）。
我还应该评论我添加了例程来正确编码小端和大端的布尔值。但是，Bound的当前实现不允许byteOrder注释当前硬编码为ByteOrder.BigEndian。这超出了我的工作范围，我也不需要使用布尔值进行解码和编码。但是，如果您计划在ByteOrder.LittleEndian编码中使用布尔值，请注意这一点。
希望这可以解决您的问题。
除此之外，pull请求实现了ListCodecFactory的编码和解码方法以及SelectFromCode的编码方法。