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The Async Http Client (AHC) classes.
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/*
 *    Copyright (c) 2014-2024 AsyncHttpClient Project. All rights reserved.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.asynchttpclient.netty.handler;

import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.handler.codec.PrematureChannelClosureException;
import io.netty.handler.codec.http.LastHttpContent;
import io.netty.util.ReferenceCountUtil;
import org.asynchttpclient.AsyncHttpClientConfig;
import org.asynchttpclient.exception.ChannelClosedException;
import org.asynchttpclient.netty.DiscardEvent;
import org.asynchttpclient.netty.NettyResponseFuture;
import org.asynchttpclient.netty.OnLastHttpContentCallback;
import org.asynchttpclient.netty.channel.ChannelManager;
import org.asynchttpclient.netty.channel.Channels;
import org.asynchttpclient.netty.future.StackTraceInspector;
import org.asynchttpclient.netty.handler.intercept.Interceptors;
import org.asynchttpclient.netty.request.NettyRequestSender;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.nio.channels.ClosedChannelException;

import static org.asynchttpclient.util.MiscUtils.getCause;

public abstract class AsyncHttpClientHandler extends ChannelInboundHandlerAdapter {

    protected final Logger logger = LoggerFactory.getLogger(getClass());

    protected final AsyncHttpClientConfig config;
    protected final ChannelManager channelManager;
    protected final NettyRequestSender requestSender;
    final Interceptors interceptors;
    final boolean hasIOExceptionFilters;

    AsyncHttpClientHandler(AsyncHttpClientConfig config,
                           ChannelManager channelManager,
                           NettyRequestSender requestSender) {
        this.config = config;
        this.channelManager = channelManager;
        this.requestSender = requestSender;
        interceptors = new Interceptors(config, channelManager, requestSender);
        hasIOExceptionFilters = !config.getIoExceptionFilters().isEmpty();
    }

    @Override
    public void channelRead(final ChannelHandlerContext ctx, Object msg) throws Exception {
        Channel channel = ctx.channel();
        Object attribute = Channels.getAttribute(channel);

        try {
            if (attribute instanceof OnLastHttpContentCallback) {
                if (msg instanceof LastHttpContent) {
                    ((OnLastHttpContentCallback) attribute).call();
                }
            } else if (attribute instanceof NettyResponseFuture) {
                NettyResponseFuture future = (NettyResponseFuture) attribute;
                future.touch();
                handleRead(channel, future, msg);
            } else if (attribute != DiscardEvent.DISCARD) {
                // unhandled message
                logger.debug("Orphan channel {} with attribute {} received message {}, closing", channel, attribute, msg);
                Channels.silentlyCloseChannel(channel);
            }
        } finally {
            ReferenceCountUtil.release(msg);
        }
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        if (requestSender.isClosed()) {
            return;
        }

        Channel channel = ctx.channel();
        channelManager.removeAll(channel);

        Object attribute = Channels.getAttribute(channel);
        logger.debug("Channel Closed: {} with attribute {}", channel, attribute);
        if (attribute instanceof OnLastHttpContentCallback) {
            OnLastHttpContentCallback callback = (OnLastHttpContentCallback) attribute;
            Channels.setAttribute(channel, callback.future());
            callback.call();

        } else if (attribute instanceof NettyResponseFuture) {
            NettyResponseFuture future = (NettyResponseFuture) attribute;
            future.touch();

            if (hasIOExceptionFilters && requestSender.applyIoExceptionFiltersAndReplayRequest(future, ChannelClosedException.INSTANCE, channel)) {
                return;
            }

            handleChannelInactive(future);
            requestSender.handleUnexpectedClosedChannel(channel, future);
        }
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable e) {
        Throwable cause = getCause(e);

        if (cause instanceof PrematureChannelClosureException || cause instanceof ClosedChannelException) {
            return;
        }

        Channel channel = ctx.channel();
        NettyResponseFuture future = null;

        logger.debug("Unexpected I/O exception on channel {}", channel, cause);

        try {
            Object attribute = Channels.getAttribute(channel);
            if (attribute instanceof NettyResponseFuture) {
                future = (NettyResponseFuture) attribute;
                future.attachChannel(null, false);
                future.touch();

                if (cause instanceof IOException) {
                    // FIXME why drop the original exception and throw a new one?
                    if (hasIOExceptionFilters) {
                        if (!requestSender.applyIoExceptionFiltersAndReplayRequest(future, ChannelClosedException.INSTANCE, channel)) {
                            // Close the channel so the recovering can occurs.
                            Channels.silentlyCloseChannel(channel);
                        }
                        return;
                    }
                }

                if (StackTraceInspector.recoverOnReadOrWriteException(cause)) {
                    logger.debug("Trying to recover from dead Channel: {}", channel);
                    future.pendingException = cause;
                    return;
                }
            } else if (attribute instanceof OnLastHttpContentCallback) {
                future = ((OnLastHttpContentCallback) attribute).future();
            }
        } catch (Throwable t) {
            cause = t;
        }

        if (future != null) {
            try {
                logger.debug("Was unable to recover Future: {}", future);
                requestSender.abort(channel, future, cause);
                handleException(future, e);
            } catch (Throwable t) {
                logger.error(t.getMessage(), t);
            }
        }

        channelManager.closeChannel(channel);
        // FIXME not really sure
        // ctx.fireChannelRead(e);
        Channels.silentlyCloseChannel(channel);
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) {
        ctx.read();
    }

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

    void finishUpdate(NettyResponseFuture future, Channel channel, boolean close) {
        future.cancelTimeouts();

        if (close) {
            channelManager.closeChannel(channel);
        } else {
            channelManager.tryToOfferChannelToPool(channel, future.getAsyncHandler(), true, future.getPartitionKey());
        }

        try {
            future.done();
        } catch (Exception t) {
            // Never propagate exception once we know we are done.
            logger.debug(t.getMessage(), t);
        }
    }

    public abstract void handleRead(Channel channel, NettyResponseFuture future, Object message) throws Exception;

    public abstract void handleException(NettyResponseFuture future, Throwable error);

    public abstract void handleChannelInactive(NettyResponseFuture future);
}