io.servicetalk.transport.netty.internal

Class ByteToMessageDecoder

java.lang.Object

io.netty.channel.ChannelHandlerAdapter

io.netty.channel.ChannelInboundHandlerAdapter

io.servicetalk.transport.netty.internal.ByteToMessageDecoder

All Implemented Interfaces:

io.netty.channel.ChannelHandler, io.netty.channel.ChannelInboundHandler

public abstract class ByteToMessageDecoder
extends io.netty.channel.ChannelInboundHandlerAdapter

ChannelInboundHandlerAdapter which decodes bytes in a stream-like fashion from one ByteBuf to an other Message type. For example here is an implementation which reads all readable bytes from the input ByteBuf and create a new ByteBuf.

     public class SquareDecoder extends ByteToMessageDecoder {
          @Override
         public void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out)
                 throws Exception {
             out.add(in.readBytes(in.readableBytes()));
         }
     }
 

Frame detection

Generally frame detection should be handled earlier in the pipeline by adding a DelimiterBasedFrameDecoder, FixedLengthFrameDecoder, LengthFieldBasedFrameDecoder, or LineBasedFrameDecoder.

If a custom frame decoder is required, then one needs to be careful when implementing one with ByteToMessageDecoder. Ensure there are enough bytes in the buffer for a complete frame by checking ByteBuf.readableBytes(). If there are not enough bytes for a complete frame, return without modifying the reader index to allow more bytes to arrive.

To check for complete frames without modifying the reader index, use methods like ByteBuf.getInt(int). One MUST use the reader index when using methods like ByteBuf.getInt(int). For example calling in.getInt(0) is assuming the frame starts at the beginning of the buffer, which is not always the case. Use in.getInt(in.readerIndex()) instead.

Pitfalls

Be aware that sub-classes of ByteToMessageDecoder MUST NOT annotated with Sharable.

Some methods such as ByteBuf.readBytes(int) will cause a memory leak if the returned buffer is not released or added to the out List. Use derived buffers like ByteBuf.readSlice(int) to avoid leaking memory.

Nested Class Summary

Nested classes/interfaces inherited from interface io.netty.channel.ChannelHandler

io.netty.channel.ChannelHandler.Sharable

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	ByteToMessageDecoder() Create a new instance.

Method Summary

Modifier and Type	Method and Description
void	channelInactive(io.netty.channel.ChannelHandlerContext ctx)
void	channelRead(io.netty.channel.ChannelHandlerContext ctx, java.lang.Object msg)
void	channelReadComplete(io.netty.channel.ChannelHandlerContext ctx)
protected void	cumulationReset() Resets cumulation.
protected abstract void	decode(io.netty.channel.ChannelHandlerContext ctx, io.netty.buffer.ByteBuf in) Decode the from one ByteBuf to an other.
protected void	decodeLast(io.netty.channel.ChannelHandlerContext ctx, io.netty.buffer.ByteBuf in) Is called one last time when the ChannelHandlerContext goes in-active.
void	handlerRemoved(io.netty.channel.ChannelHandlerContext ctx)
protected void	handlerRemoved0(io.netty.channel.ChannelHandlerContext ctx) Gets called after the ByteToMessageDecoder was removed from the actual context and it doesn't handle events anymore.
void	setDiscardAfterReads(int discardAfterReads) Set the number of reads after which ByteBuf.discardSomeReadBytes() are called and so free up memory.
protected io.netty.buffer.ByteBuf	swapCumulation(io.netty.buffer.ByteBuf cumulation, io.netty.buffer.ByteBufAllocator allocator) Swap the existing cumulation ByteBuf for a new ByteBuf.
void	userEventTriggered(io.netty.channel.ChannelHandlerContext ctx, java.lang.Object evt)

Methods inherited from class io.netty.channel.ChannelInboundHandlerAdapter

channelActive, channelRegistered, channelUnregistered, channelWritabilityChanged, exceptionCaught

Methods inherited from class io.netty.channel.ChannelHandlerAdapter

ensureNotSharable, handlerAdded, isSharable

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Methods inherited from interface io.netty.channel.ChannelHandler

handlerAdded

Constructor Detail

ByteToMessageDecoder

protected ByteToMessageDecoder()

Create a new instance.

Method Detail

setDiscardAfterReads

public final void setDiscardAfterReads(int discardAfterReads)

Set the number of reads after which ByteBuf.discardSomeReadBytes() are called and so free up memory. The default is 16.

It is assumed this method is only called in the associated Channel's EventLoop thread, otherwise external synchronization must be provided.

Parameters:

discardAfterReads - The number of calls to ChannelHandlerContext.fireChannelRead(Object) before attempting to discard bytes from the buffer cumulator.

handlerRemoved

public final void handlerRemoved(io.netty.channel.ChannelHandlerContext ctx)

Specified by:

handlerRemoved in interface io.netty.channel.ChannelHandler

Overrides:

handlerRemoved in class io.netty.channel.ChannelHandlerAdapter

handlerRemoved0

protected void handlerRemoved0(io.netty.channel.ChannelHandlerContext ctx)

Gets called after the ByteToMessageDecoder was removed from the actual context and it doesn't handle events anymore.

Parameters:

ctx - the ChannelHandlerContext which this ByteToMessageDecoder belongs to

channelRead

public void channelRead(io.netty.channel.ChannelHandlerContext ctx,
                        java.lang.Object msg)

Specified by:

channelRead in interface io.netty.channel.ChannelInboundHandler

Overrides:

channelRead in class io.netty.channel.ChannelInboundHandlerAdapter

channelReadComplete

public void channelReadComplete(io.netty.channel.ChannelHandlerContext ctx)

Specified by:

channelReadComplete in interface io.netty.channel.ChannelInboundHandler

Overrides:

channelReadComplete in class io.netty.channel.ChannelInboundHandlerAdapter

swapCumulation

protected io.netty.buffer.ByteBuf swapCumulation(io.netty.buffer.ByteBuf cumulation,
                                                 io.netty.buffer.ByteBufAllocator allocator)

Swap the existing cumulation ByteBuf for a new ByteBuf. This method is called when a heuristic determines the amount of unused bytes is sufficiently high that a resize / defragmentation of the bytes from cumulation is beneficial.

ByteBuf.discardReadBytes() is generally avoided in this method because it changes the underlying data structure. If others have slices of this ByteBuf their view on the data will become corrupted. This is commonly a problem when processing data asynchronously to avoid blocking the EventLoop thread.

Parameters:

cumulation - The ByteBuf that accumulates across socket read operations.

allocator - Used to allocate a new ByteBuf if necessary.

Returns:

the ByteBuf that is responsible for accumulated socket reads.

cumulationReset

protected void cumulationReset()

Resets cumulation.

channelInactive

public void channelInactive(io.netty.channel.ChannelHandlerContext ctx)

Specified by:

channelInactive in interface io.netty.channel.ChannelInboundHandler

Overrides:

channelInactive in class io.netty.channel.ChannelInboundHandlerAdapter

userEventTriggered

public void userEventTriggered(io.netty.channel.ChannelHandlerContext ctx,
                               java.lang.Object evt)
                        throws java.lang.Exception

Specified by:

userEventTriggered in interface io.netty.channel.ChannelInboundHandler

Overrides:

userEventTriggered in class io.netty.channel.ChannelInboundHandlerAdapter

Throws:

java.lang.Exception

decode

protected abstract void decode(io.netty.channel.ChannelHandlerContext ctx,
                               io.netty.buffer.ByteBuf in)
                        throws java.lang.Exception

Decode the from one ByteBuf to an other. This method will be called till either the input ByteBuf has nothing to read when return from this method or till nothing was read from the input ByteBuf.

Parameters:

ctx - the ChannelHandlerContext which this ByteToMessageDecoder belongs to

in - the ByteBuf from which to read data

Throws:

java.lang.Exception - is thrown if an error occurs

decodeLast

protected void decodeLast(io.netty.channel.ChannelHandlerContext ctx,
                          io.netty.buffer.ByteBuf in)
                   throws java.lang.Exception

Is called one last time when the ChannelHandlerContext goes in-active. Which means the channelInactive(ChannelHandlerContext) was triggered. By default this will just call decode(ChannelHandlerContext, ByteBuf) but sub-classes may override this for some special cleanup operation.

Parameters:

ctx - the ChannelHandlerContext which this ByteToMessageDecoder belongs to

in - the ByteBuf from which to read data

Throws:

java.lang.Exception - is thrown if an error occurs