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The nio transport.
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/*
 * 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.http.nio;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelHandler;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOutboundHandlerAdapter;
import io.netty.channel.ChannelPromise;
import io.netty.channel.embedded.EmbeddedChannel;

import org.elasticsearch.ExceptionsHelper;
import org.elasticsearch.nio.FlushOperation;
import org.elasticsearch.nio.Page;
import org.elasticsearch.nio.WriteOperation;

import java.nio.ByteBuffer;
import java.util.LinkedList;
import java.util.function.BiConsumer;

class NettyAdaptor {

    private final EmbeddedChannel nettyChannel;
    private final LinkedList flushOperations = new LinkedList<>();

    NettyAdaptor(ChannelHandler... handlers) {
        nettyChannel = new EmbeddedChannel();
        nettyChannel.pipeline().addLast("write_captor", new ChannelOutboundHandlerAdapter() {

            @Override
            public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) {
                // This is a little tricky. The embedded channel will complete the promise once it writes the message
                // to its outbound buffer. We do not want to complete the promise until the message is sent. So we
                // intercept the promise and pass a different promise back to the rest of the pipeline.

                try {
                    ByteBuf message = (ByteBuf) msg;
                    promise.addListener((f) -> message.release());
                    NettyListener listener = NettyListener.fromChannelPromise(promise);
                    flushOperations.add(new FlushOperation(message.nioBuffers(), listener));
                } catch (Exception e) {
                    promise.setFailure(e);
                }
            }
        });
        nettyChannel.pipeline().addLast(handlers);
    }

    public void close() throws Exception {
        assert flushOperations.isEmpty() : "Should close outbound operations before calling close";

        ChannelFuture closeFuture = nettyChannel.close();
        // This should be safe as we are not a real network channel
        closeFuture.await();
        if (closeFuture.isSuccess() == false) {
            Throwable cause = closeFuture.cause();
            ExceptionsHelper.maybeDieOnAnotherThread(cause);
            throw (Exception) cause;
        }
    }

    public void addCloseListener(BiConsumer listener) {
        nettyChannel.closeFuture().addListener(f -> {
            if (f.isSuccess()) {
                listener.accept(null, null);
            } else {
                final Throwable cause = f.cause();
                ExceptionsHelper.maybeDieOnAnotherThread(cause);
                assert cause instanceof Exception;
                listener.accept(null, (Exception) cause);
            }
        });
    }

    public int read(ByteBuffer[] buffers) {
        ByteBuf byteBuf = Unpooled.wrappedBuffer(buffers);
        int initialReaderIndex = byteBuf.readerIndex();
        nettyChannel.writeInbound(byteBuf);
        return byteBuf.readerIndex() - initialReaderIndex;
    }

    public int read(Page[] pages) {
        ByteBuf byteBuf = PagedByteBuf.byteBufFromPages(pages);
        int readableBytes = byteBuf.readableBytes();
        nettyChannel.writeInbound(byteBuf);
        return readableBytes;
    }

    public Object pollInboundMessage() {
        return nettyChannel.readInbound();
    }

    public void write(WriteOperation writeOperation) {
        nettyChannel.writeAndFlush(writeOperation.getObject(), NettyListener.fromBiConsumer(writeOperation.getListener(), nettyChannel));
    }

    public FlushOperation pollOutboundOperation() {
        return flushOperations.pollFirst();
    }

    public int getOutboundCount() {
        return flushOperations.size();
    }
}