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Netty 4 based transport implementation
There is a newer version: 8.17.0
/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */
package org.elasticsearch.transport.netty4;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;

import org.apache.lucene.util.BytesRef;
import org.elasticsearch.ElasticsearchException;
import org.elasticsearch.ExceptionsHelper;
import org.elasticsearch.common.bytes.BytesReference;
import org.elasticsearch.common.bytes.ReleasableBytesReference;
import org.elasticsearch.common.recycler.Recycler;
import org.elasticsearch.core.RefCounted;
import org.elasticsearch.core.Releasables;
import org.elasticsearch.threadpool.ThreadPool;
import org.elasticsearch.transport.InboundPipeline;
import org.elasticsearch.transport.Transport;
import org.elasticsearch.transport.Transports;

/**
 * A handler (must be the last one!) that does size based frame decoding and forwards the actual message
 * to the relevant action.
 */
public class Netty4MessageInboundHandler extends ChannelInboundHandlerAdapter {

    private final Netty4Transport transport;

    private final InboundPipeline pipeline;

    public Netty4MessageInboundHandler(Netty4Transport transport, Recycler recycler) {
        this.transport = transport;
        final ThreadPool threadPool = transport.getThreadPool();
        final Transport.RequestHandlers requestHandlers = transport.getRequestHandlers();
        this.pipeline = new InboundPipeline(
            transport.getVersion(),
            transport.getStatsTracker(),
            recycler,
            threadPool::relativeTimeInMillis,
            transport.getInflightBreaker(),
            requestHandlers::getHandler,
            transport::inboundMessage,
            transport.ignoreDeserializationErrors()
        );
    }

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        assert Transports.assertDefaultThreadContext(transport.getThreadPool().getThreadContext());
        assert Transports.assertTransportThread();
        assert msg instanceof ByteBuf : "Expected message type ByteBuf, found: " + msg.getClass();

        final ByteBuf buffer = (ByteBuf) msg;
        Netty4TcpChannel channel = ctx.channel().attr(Netty4Transport.CHANNEL_KEY).get();
        final BytesReference wrapped = Netty4Utils.toBytesReference(buffer);
        try (ReleasableBytesReference reference = new ReleasableBytesReference(wrapped, new ByteBufRefCounted(buffer))) {
            pipeline.handleBytes(channel, reference);
        }
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) {
        assert Transports.assertDefaultThreadContext(transport.getThreadPool().getThreadContext());
        ExceptionsHelper.maybeDieOnAnotherThread(cause);
        final Throwable unwrapped = ExceptionsHelper.unwrap(cause, ElasticsearchException.class);
        final Throwable newCause = unwrapped != null ? unwrapped : cause;
        Netty4TcpChannel tcpChannel = ctx.channel().attr(Netty4Transport.CHANNEL_KEY).get();
        if (newCause instanceof Error) {
            transport.onException(tcpChannel, new Exception(newCause));
        } else {
            transport.onException(tcpChannel, (Exception) newCause);
        }
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        Releasables.closeExpectNoException(pipeline);
        super.channelInactive(ctx);
    }

    private record ByteBufRefCounted(ByteBuf buffer) implements RefCounted {

        @Override
        public void incRef() {
            buffer.retain();
        }

        @Override
        public boolean tryIncRef() {
            if (hasReferences() == false) {
                return false;
            }
            try {
                buffer.retain();
            } catch (RuntimeException e) {
                assert hasReferences() == false;
                return false;
            }
            return true;
        }

        @Override
        public boolean decRef() {
            return buffer.release();
        }

        @Override
        public boolean hasReferences() {
            return buffer.refCnt() > 0;
        }
    }
}