README.adoc

Netty Incubator Buffer API

Note	The memory segment implementation has been merged into Netty 5: netty/netty#13028 Development now continue in the main Netty repository, and this incubator repository is no longer maintained.

This repository is incubating a new buffer API proposed for Netty 5.

See the RATIONALE document for more background.

Building and Testing

Short version: just run make if you want to build on Java 17, otherwise run mvn install if you want to build with Java 11, and without support for the java.lang.foreign APIs.

The project (specifically, the buffer-memseg module) currently relies on snapshot versions of the Panama Foreign fork of OpenJDK. This allows us to test out the most recent version of the java.lang.foreign APIs, but also make building, and local development more involved. To simplify things, we have a Docker based build, controlled via a Makefile with the following commands:

• image – build the docker image.This includes building a snapshot of OpenJDK, and download all relevant Maven dependencies.

• test – run all tests in a docker container.This implies image.The container is automatically deleted afterwards.

• dbg – drop into a shell in the build container, without running the build itself.The debugging container is not deleted afterwards.

• clean – remove the leftover containers created by dbg, test, and build.

• build – build binaries and run all tests in a container, and copy the target directory out of the container afterwards.This is the default build target.

Example: Echo Client and Server

Making use of this new buffer API on the client side is quite easy. Even though Netty 5 does not have native support for these buffers, it is able to convert them to the old ByteBuf API as needed. This means we are able to send incubator buffers through a Netty pipeline, and have it work as if we were sending ByteBuf instances.

public final class Client {
    public static void main(String[] args) throws Exception {
        EventLoopGroup group = new MultithreadEventLoopGroup(NioHandler.newFactory());
        try (BufferAllocator allocator = BufferAllocator.pooledDirect()) { // (1)
            Bootstrap b = new Bootstrap();
            b.group(group)
             .channel(NioSocketChannel.class)
             .option(ChannelOption.TCP_NODELAY, true)
             .handler(new ChannelInitializer<SocketChannel>() {
                 @Override
                 public void initChannel(SocketChannel ch) throws Exception {
                     ch.pipeline().addLast(new ChannelHandlerAdapter() {
                         @Override
                         public void channelActive(ChannelHandlerContext ctx) {
                             Buffer message = allocator.allocate(256); // (2)
                             for (int i = 0; i < message.capacity(); i++) {
                                 message.writeByte((byte) i);
                             }
                             ctx.writeAndFlush(message); // (3)
                         }
                     });
                 }
             });

            // Start the client.
            ChannelFuture f = b.connect("127.0.0.1", 8007).sync();

            // Wait until the connection is closed.
            f.channel().closeFuture().sync();
        } finally {
            // Shut down the event loop to terminate all threads.
            group.shutdownGracefully();
        }
    }
}

1. A life-cycled allocator is created to wrap the scope of our application.

2. Buffers are allocated with one of the allocate methods.

3. The buffer can then be sent down the pipeline, and will be written to the socket just like a ByteBuf would.

Note	The same is not the case for BufferHolder. It is not treated the same as a ByteBufHolder.

On the server side, things are more complicated because Netty itself will be allocating the buffers, and the ByteBufAllocator API is only capable of returning ByteBuf instances. The ByteBufAllocatorAdaptor will allocate ByteBuf instances that are backed by the new buffers. The buffers can then we extracted from the ByteBuf instances with the ByteBufAdaptor.extract method.

We can tell a Netty server how to allocate buffers by setting the ALLOCATOR child-channel option:

ByteBufAllocatorAdaptor allocator = new ByteBufAllocatorAdaptor(); // (1)
ServerBootstrap server = new ServerBootstrap();
server.group(bossGroup, workerGroup)
      .channel(NioServerSocketChannel.class)
      .childOption(ChannelOption.ALLOCATOR, allocator) // (2)
      .handler(new EchoServerHandler());

1. The ByteBufAllocatorAdaptor implements ByteBufAllocator, and directly allocates ByteBuf instances that are backed by buffers that use the new API.

2. To make Netty use a given allocator when allocating buffers for receiving data, we set the allocator as a child option.

With the above, we just changed how the buffers are allocated, but we haven’t changed the API we use for interacting with the buffers. The buffers are still allocated at ByteBuf instances, and flow through the pipeline as such. If we want to use the new buffer API in our server handlers, we have to extract the buffers from the ByteBuf instances that are passed down:

import io.netty.buffer.ByteBuf;
import io.netty.buffer.api.Buffer;
import io.netty.buffer.api.adaptor.ByteBufAdaptor;

@Sharable
public class EchoServerHandler implements ChannelHandler {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) { // (1)
        if (msg instanceof ByteBuf) { // (2)
            // For this example, we only echo back buffers that are using the new buffer API.
            Buffer buf = ByteBufAdaptor.extract((ByteBuf) msg); // (3)
            ctx.write(buf); // (4)
        }
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) {
        ctx.flush();
    }
}

1. Netty pipelines are defined as transferring Object instances as messages.

2. When we receive data directly from a socket, these messages will be ByteBuf instances with the received data.

3. Since we set the allocator to create ByteBuf instances that are backed by buffers with the new API, we will be able to extract the backing Buffer instances.

4. We can then operate on the extracted Buffer instances directly. The Buffer and ByteBuf instances mirror each other exactly. In this case, we just write them back to the client that sent the data to us.

The files in src/test/java/io/netty/buffer/api/examples/echo for the full source code to this example.