Remove unnecessary loop and indentation in decompressors

Motivation:

Decompression handlers contain heavy use of switch-case statements. We
use compact indentation style for 'case' so that we utilize our screen
real-estate more efficiently.

Also, the following decompression handlers do not need to run a loop,
because ByteToMessageDecoder already runs a loop for them:

- FastLzFrameDecoder
- Lz4FrameDecoder
- LzfDecoder

Modifications:

- Fix indentations
- Do not wrap the decoding logic with a for loop when unnecessary
- Handle the case where a FastLz/Lzf frame contains no data properly so
  that the buffer does not leak and less garbage is produced.

Result:

- Efficiency
- Compact source code
- No buffer leak

codec/src/main/java/io/netty/handler/codec/compression/Bzip2Decoder.java

@@ -81,6 +81,7 @@ public class Bzip2Decoder extends ByteToMessageDecoder {
         if (!in.isReadable()) {
             return;
         }
+
         final Bzip2BitReader reader = this.reader;
         reader.setByteBuf(in);
 

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

@@ -18,6 +18,7 @@ package io.netty.handler.codec.compression;
 import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.handler.codec.ByteToMessageDecoder;
+import io.netty.util.internal.EmptyArrays;
 
 import java.util.List;
 import java.util.zip.Adler32;
@@ -108,12 +109,11 @@ public class FastLzFrameDecoder extends ByteToMessageDecoder {
 
     @Override
     protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
-        for (;;) {
         try {
             switch (currentState) {
             case INIT_BLOCK:
                 if (in.readableBytes() < 4) {
-                            return;
+                    break;
                 }
 
                 final int magic = in.readUnsignedMedium();
@@ -128,7 +128,7 @@ public class FastLzFrameDecoder extends ByteToMessageDecoder {
                 currentState = State.INIT_BLOCK_PARAMS;
             case INIT_BLOCK_PARAMS:
                 if (in.readableBytes() < 2 + (isCompressed ? 2 : 0) + (hasChecksum ? 4 : 0)) {
-                            return;
+                    break;
                 }
                 currentChecksum = hasChecksum ? in.readInt() : 0;
                 chunkLength = in.readUnsignedShort();
@@ -138,15 +138,25 @@ public class FastLzFrameDecoder extends ByteToMessageDecoder {
             case DECOMPRESS_DATA:
                 final int chunkLength = this.chunkLength;
                 if (in.readableBytes() < chunkLength) {
-                            return;
+                    break;
                 }
 
                 final int idx = in.readerIndex();
                 final int originalLength = this.originalLength;
 
-                        ByteBuf uncompressed = ctx.alloc().heapBuffer(originalLength, originalLength);
+                final ByteBuf uncompressed;
-                        final byte[] output = uncompressed.array();
+                final byte[] output;
-                        final int outputPtr = uncompressed.arrayOffset() + uncompressed.writerIndex();
+                final int outputPtr;
+
+                if (originalLength != 0) {
+                    uncompressed = ctx.alloc().heapBuffer(originalLength, originalLength);
+                    output = uncompressed.array();
+                    outputPtr = uncompressed.arrayOffset() + uncompressed.writerIndex();
+                } else {
+                    uncompressed = null;
+                    output = EmptyArrays.EMPTY_BYTES;
+                    outputPtr = 0;
+                }
 
                 boolean success = false;
                 try {
@@ -184,8 +194,11 @@ public class FastLzFrameDecoder extends ByteToMessageDecoder {
                                     checksumResult, currentChecksum));
                         }
                     }
+
+                    if (uncompressed != null) {
                         uncompressed.writerIndex(uncompressed.writerIndex() + originalLength);
                         out.add(uncompressed);
+                    }
                     in.skipBytes(chunkLength);
 
                     currentState = State.INIT_BLOCK;
@@ -198,7 +211,7 @@ public class FastLzFrameDecoder extends ByteToMessageDecoder {
                 break;
             case CORRUPTED:
                 in.skipBytes(in.readableBytes());
-                        return;
+                break;
             default:
                 throw new IllegalStateException();
             }
@@ -207,5 +220,4 @@ public class FastLzFrameDecoder extends ByteToMessageDecoder {
             throw e;
         }
     }
-    }
 }

codec/src/main/java/io/netty/handler/codec/compression/Lz4FrameDecoder.java

@@ -148,12 +148,11 @@ public class Lz4FrameDecoder extends ByteToMessageDecoder {
 
     @Override
     protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
-        for (;;) {
         try {
             switch (currentState) {
             case INIT_BLOCK:
                 if (in.readableBytes() < HEADER_LENGTH) {
-                            return;
+                    break;
                 }
                 final long magic = in.readLong();
                 if (magic != MAGIC_NUMBER) {
@@ -210,7 +209,7 @@ public class Lz4FrameDecoder extends ByteToMessageDecoder {
                 currentChecksum = this.currentChecksum;
 
                 if (in.readableBytes() < compressedLength) {
-                            return;
+                    break;
                 }
 
                 final int idx = in.readerIndex();
@@ -283,7 +282,7 @@ public class Lz4FrameDecoder extends ByteToMessageDecoder {
             case FINISHED:
             case CORRUPTED:
                 in.skipBytes(in.readableBytes());
-                        return;
+                break;
             default:
                 throw new IllegalStateException();
             }
@@ -292,7 +291,6 @@ public class Lz4FrameDecoder extends ByteToMessageDecoder {
             throw e;
         }
     }
-    }
 
     /**
      * Returns {@code true} if and only if the end of the compressed stream

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

@@ -109,12 +109,11 @@ public class LzfDecoder extends ByteToMessageDecoder {
 
     @Override
     protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
-        for (;;) {
         try {
             switch (currentState) {
             case INIT_BLOCK:
                 if (in.readableBytes() < HEADER_LEN_NOT_COMPRESSED) {
-                            return;
+                    break;
                 }
                 final int magic = in.readUnsignedShort();
                 if (magic != MAGIC_NUMBER) {
@@ -143,7 +142,7 @@ public class LzfDecoder extends ByteToMessageDecoder {
                 }
             case INIT_ORIGINAL_LENGTH:
                 if (in.readableBytes() < 2) {
-                            return;
+                    break;
                 }
                 originalLength = in.readUnsignedShort();
 
@@ -151,7 +150,7 @@ public class LzfDecoder extends ByteToMessageDecoder {
             case DECOMPRESS_DATA:
                 final int chunkLength = this.chunkLength;
                 if (in.readableBytes() < chunkLength) {
-                            return;
+                    break;
                 }
                 final int originalLength = this.originalLength;
 
@@ -189,7 +188,7 @@ public class LzfDecoder extends ByteToMessageDecoder {
                     if (!in.hasArray()) {
                         recycler.releaseInputBuffer(inputArray);
                     }
-                        } else {
+                } else if (chunkLength > 0) {
                     out.add(in.readSlice(chunkLength).retain());
                 }
 
@@ -197,7 +196,7 @@ public class LzfDecoder extends ByteToMessageDecoder {
                 break;
             case CORRUPTED:
                 in.skipBytes(in.readableBytes());
-                        return;
+                break;
             default:
                 throw new IllegalStateException();
             }
@@ -208,5 +207,4 @@ public class LzfDecoder extends ByteToMessageDecoder {
             throw e;
         }
     }
-    }
 }