Fixes for compression codecs

Motivation:

Fixed founded mistakes in compression codecs.

Modifications:

- Changed return type of ZlibUtil.inflaterException() from CompressionException to DecompressionException
- Updated @throws in javadoc of JZlibDecoder to throw DecompressionException instead of CompressionException
- Fixed JdkZlibDecoder to throw DecompressionException instead of CompressionException
- Removed unnecessary empty lines in JdkZlibEncoder and JZlibEncoder
- Removed public modifier from Snappy class
- Added MAX_UNCOMPRESSED_DATA_SIZE constant in SnappyFramedDecoder
- Used in.readableBytes() instead of (in.writerIndex() - in.readerIndex()) in SnappyFramedDecoder
- Added private modifier for enum ChunkType in SnappyFramedDecoder
- Fixed potential bug (sum overflow) in Bzip2HuffmanAllocator.first(). For more info, see http://googleresearch.blogspot.ru/2006/06/extra-extra-read-all-about-it-nearly.html

Result:

Fixed sum overflow in Bzip2HuffmanAllocator, improved exceptions in ZlibDecoder implementations, hid Snappy class

codec/src/main/java/io/netty/handler/codec/compression/Bzip2HuffmanAllocator.java

@@ -42,7 +42,7 @@ final class Bzip2HuffmanAllocator {
         i = Math.max(nodesToMove - 1, i);
 
         while (k > i + 1) {
-            int temp = i + k >> 1;
+            int temp = i + k >>> 1;
             if (array[temp] % length > limit) {
                 k = temp;
             } else {

codec/src/main/java/io/netty/handler/codec/compression/JZlibDecoder.java

@@ -31,7 +31,7 @@ public class JZlibDecoder extends ZlibDecoder {
     /**
      * Creates a new instance with the default wrapper ({@link ZlibWrapper#ZLIB}).
      *
-     * @throws CompressionException if failed to initialize zlib
+     * @throws DecompressionException if failed to initialize zlib
      */
     public JZlibDecoder() {
         this(ZlibWrapper.ZLIB);
@@ -40,7 +40,7 @@ public class JZlibDecoder extends ZlibDecoder {
     /**
      * Creates a new instance with the specified wrapper.
      *
-     * @throws CompressionException if failed to initialize zlib
+     * @throws DecompressionException if failed to initialize zlib
      */
     public JZlibDecoder(ZlibWrapper wrapper) {
         if (wrapper == null) {
@@ -58,7 +58,7 @@ public class JZlibDecoder extends ZlibDecoder {
      * is always {@link ZlibWrapper#ZLIB} because it is the only format that
      * supports the preset dictionary.
      *
-     * @throws CompressionException if failed to initialize zlib
+     * @throws DecompressionException if failed to initialize zlib
      */
     public JZlibDecoder(byte[] dictionary) {
         if (dictionary == null) {

codec/src/main/java/io/netty/handler/codec/compression/JZlibEncoder.java

@@ -29,7 +29,6 @@ import io.netty.util.internal.EmptyArrays;
 
 import java.util.concurrent.TimeUnit;
 
-
 /**
  * Compresses a {@link ByteBuf} using the deflate algorithm.
  */

codec/src/main/java/io/netty/handler/codec/compression/JdkZlibDecoder.java

@@ -24,7 +24,6 @@ import java.util.zip.DataFormatException;
 import java.util.zip.Deflater;
 import java.util.zip.Inflater;
 
-
 /**
  * Decompress a {@link ByteBuf} using the inflate algorithm.
  */
@@ -249,14 +248,14 @@ public class JdkZlibDecoder extends ZlibDecoder {
                 int magic1 = in.readByte();
 
                 if (magic0 != 31) {
-                    throw new CompressionException("Input is not in the GZIP format");
+                    throw new DecompressionException("Input is not in the GZIP format");
                 }
                 crc.update(magic0);
                 crc.update(magic1);
 
                 int method = in.readUnsignedByte();
                 if (method != Deflater.DEFLATED) {
-                    throw new CompressionException("Unsupported compression method "
+                    throw new DecompressionException("Unsupported compression method "
                             + method + " in the GZIP header");
                 }
                 crc.update(method);
@@ -265,7 +264,7 @@ public class JdkZlibDecoder extends ZlibDecoder {
                 crc.update(flags);
 
                 if ((flags & FRESERVED) != 0) {
-                    throw new CompressionException(
+                    throw new DecompressionException(
                             "Reserved flags are set in the GZIP header");
                 }
 
@@ -360,7 +359,7 @@ public class JdkZlibDecoder extends ZlibDecoder {
         }
         int readLength = inflater.getTotalOut();
         if (dataLength != readLength) {
-            throw new CompressionException(
+            throw new DecompressionException(
                     "Number of bytes mismatch. Expected: " + dataLength + ", Got: " + readLength);
         }
         return true;
@@ -373,7 +372,7 @@ public class JdkZlibDecoder extends ZlibDecoder {
         }
         long readCrc = crc.getValue();
         if (crcValue != readCrc) {
-            throw new CompressionException(
+            throw new DecompressionException(
                     "CRC value missmatch. Expected: " + crcValue + ", Got: " + readCrc);
         }
     }

codec/src/main/java/io/netty/handler/codec/compression/JdkZlibEncoder.java

@@ -27,7 +27,6 @@ import java.util.concurrent.TimeUnit;
 import java.util.zip.CRC32;
 import java.util.zip.Deflater;
 
-
 /**
  * Compresses a {@link ByteBuf} using the deflate algorithm.
  */

codec/src/main/java/io/netty/handler/codec/compression/Snappy.java

@@ -24,7 +24,7 @@ import io.netty.buffer.ByteBufUtil;
  *
  * See http://code.google.com/p/snappy/source/browse/trunk/format_description.txt
  */
-public class Snappy {
+class Snappy {
 
     private static final int MAX_HT_SIZE = 1 << 14;
     private static final int MIN_COMPRESSIBLE_BYTES = 15;

codec/src/main/java/io/netty/handler/codec/compression/SnappyFramedDecoder.java

@@ -36,7 +36,8 @@ import java.util.List;
  * set to {@code true}.
  */
 public class SnappyFramedDecoder extends ByteToMessageDecoder {
-    enum ChunkType {
+
+    private enum ChunkType {
         STREAM_IDENTIFIER,
         COMPRESSED_DATA,
         UNCOMPRESSED_DATA,
@@ -45,6 +46,7 @@ public class SnappyFramedDecoder extends ByteToMessageDecoder {
     }
 
     private static final byte[] SNAPPY = { 's', 'N', 'a', 'P', 'p', 'Y' };
+    private static final int MAX_UNCOMPRESSED_DATA_SIZE = 65536 + 4;
 
     private final Snappy snappy = new Snappy();
     private final boolean validateChecksums;
@@ -83,7 +85,7 @@ public class SnappyFramedDecoder extends ByteToMessageDecoder {
 
         try {
             int idx = in.readerIndex();
-            final int inSize = in.writerIndex() - idx;
+            final int inSize = in.readableBytes();
             if (inSize < 4) {
                 // We need to be at least able to read the chunk type identifier (one byte),
                 // and the length of the chunk (3 bytes) in order to proceed
@@ -136,7 +138,7 @@ public class SnappyFramedDecoder extends ByteToMessageDecoder {
                     if (!started) {
                         throw new DecompressionException("Received UNCOMPRESSED_DATA tag before STREAM_IDENTIFIER");
                     }
-                    if (chunkLength > 65536 + 4) {
+                    if (chunkLength > MAX_UNCOMPRESSED_DATA_SIZE) {
                         throw new DecompressionException("Received UNCOMPRESSED_DATA larger than 65540 bytes");
                     }
 
@@ -193,7 +195,7 @@ public class SnappyFramedDecoder extends ByteToMessageDecoder {
      * @param type The tag byte extracted from the stream
      * @return The appropriate {@link ChunkType}, defaulting to {@link ChunkType#RESERVED_UNSKIPPABLE}
      */
-    static ChunkType mapChunkType(byte type) {
+    private static ChunkType mapChunkType(byte type) {
         if (type == 0) {
             return ChunkType.COMPRESSED_DATA;
         } else if (type == 1) {

codec/src/main/java/io/netty/handler/codec/compression/ZlibUtil.java

@@ -32,8 +32,8 @@ final class ZlibUtil {
         throw deflaterException(z, message, resultCode);
     }
 
-    static CompressionException inflaterException(Inflater z, String message, int resultCode) {
+    static DecompressionException inflaterException(Inflater z, String message, int resultCode) {
-        return new CompressionException(message + " (" + resultCode + ')' + (z.msg != null? ": " + z.msg : ""));
+        return new DecompressionException(message + " (" + resultCode + ')' + (z.msg != null? ": " + z.msg : ""));
     }
 
     static CompressionException deflaterException(Deflater z, String message, int resultCode) {