Java example source code file (Http2ConnectionHandler.java)

This example Java source code file (Http2ConnectionHandler.java) is included in the alvinalexander.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

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Java - Java tags/keywords

basedecoder, bytebuf, channelfuture, channelhandlercontext, channelpromise, closingchannelfuturelistener, exception, goaway, http/2, http2exception, http2stream, net, network, override, prefacedecoder, threading, threads, throwable, util

The Http2ConnectionHandler.java Java example source code

/*
 * Copyright 2014 The Netty Project
 *
 * The Netty Project licenses this file to you 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 io.netty.handler.codec.http2;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufUtil;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelOutboundHandler;
import io.netty.channel.ChannelPromise;
import io.netty.handler.codec.ByteToMessageDecoder;
import io.netty.handler.codec.http2.Http2Exception.CompositeStreamException;
import io.netty.handler.codec.http2.Http2Exception.StreamException;
import io.netty.util.concurrent.ScheduledFuture;
import io.netty.util.internal.UnstableApi;
import io.netty.util.internal.logging.InternalLogger;
import io.netty.util.internal.logging.InternalLoggerFactory;

import java.net.SocketAddress;
import java.util.List;
import java.util.concurrent.TimeUnit;

import static io.netty.buffer.ByteBufUtil.hexDump;
import static io.netty.buffer.Unpooled.EMPTY_BUFFER;
import static io.netty.handler.codec.http2.Http2CodecUtil.HTTP_UPGRADE_STREAM_ID;
import static io.netty.handler.codec.http2.Http2CodecUtil.connectionPrefaceBuf;
import static io.netty.handler.codec.http2.Http2CodecUtil.getEmbeddedHttp2Exception;
import static io.netty.handler.codec.http2.Http2Error.INTERNAL_ERROR;
import static io.netty.handler.codec.http2.Http2Error.NO_ERROR;
import static io.netty.handler.codec.http2.Http2Error.PROTOCOL_ERROR;
import static io.netty.handler.codec.http2.Http2Exception.connectionError;
import static io.netty.handler.codec.http2.Http2Exception.isStreamError;
import static io.netty.handler.codec.http2.Http2FrameTypes.SETTINGS;
import static io.netty.handler.codec.http2.Http2Stream.State.IDLE;
import static io.netty.util.CharsetUtil.UTF_8;
import static io.netty.util.internal.ObjectUtil.checkNotNull;
import static java.lang.Math.min;
import static java.util.concurrent.TimeUnit.MILLISECONDS;

/**
 * Provides the default implementation for processing inbound frame events and delegates to a
 * {@link Http2FrameListener}
 * <p>
 * This class will read HTTP/2 frames and delegate the events to a {@link Http2FrameListener}
 * <p>
 * This interface enforces inbound flow control functionality through
 * {@link Http2LocalFlowController}
 */
@UnstableApi
public class Http2ConnectionHandler extends ByteToMessageDecoder implements Http2LifecycleManager,
                                                                            ChannelOutboundHandler {

    private static final InternalLogger logger = InternalLoggerFactory.getInstance(Http2ConnectionHandler.class);

    private final Http2ConnectionDecoder decoder;
    private final Http2ConnectionEncoder encoder;
    private final Http2Settings initialSettings;
    private ChannelFutureListener closeListener;
    private BaseDecoder byteDecoder;
    private long gracefulShutdownTimeoutMillis;

    protected Http2ConnectionHandler(Http2ConnectionDecoder decoder, Http2ConnectionEncoder encoder,
                                     Http2Settings initialSettings) {
        this.initialSettings = checkNotNull(initialSettings, "initialSettings");
        this.decoder = checkNotNull(decoder, "decoder");
        this.encoder = checkNotNull(encoder, "encoder");
        if (encoder.connection() != decoder.connection()) {
            throw new IllegalArgumentException("Encoder and Decoder do not share the same connection object");
        }
    }

    /**
     * Get the amount of time (in milliseconds) this endpoint will wait for all streams to be closed before closing
     * the connection during the graceful shutdown process.
     */
    public long gracefulShutdownTimeoutMillis() {
        return gracefulShutdownTimeoutMillis;
    }

    /**
     * Set the amount of time (in milliseconds) this endpoint will wait for all streams to be closed before closing
     * the connection during the graceful shutdown process.
     * @param gracefulShutdownTimeoutMillis the amount of time (in milliseconds) this endpoint will wait for all
     * streams to be closed before closing the connection during the graceful shutdown process.
     */
    public void gracefulShutdownTimeoutMillis(long gracefulShutdownTimeoutMillis) {
        if (gracefulShutdownTimeoutMillis < 0) {
            throw new IllegalArgumentException("gracefulShutdownTimeoutMillis: " + gracefulShutdownTimeoutMillis +
                    " (expected: >= 0)");
        }
        this.gracefulShutdownTimeoutMillis = gracefulShutdownTimeoutMillis;
    }

    public Http2Connection connection() {
        return encoder.connection();
    }

    public Http2ConnectionDecoder decoder() {
        return decoder;
    }

    public Http2ConnectionEncoder encoder() {
        return encoder;
    }

    private boolean prefaceSent() {
        return byteDecoder != null && byteDecoder.prefaceSent();
    }

    /**
     * Handles the client-side (cleartext) upgrade from HTTP to HTTP/2.
     * Reserves local stream 1 for the HTTP/2 response.
     */
    public void onHttpClientUpgrade() throws Http2Exception {
        if (connection().isServer()) {
            throw connectionError(PROTOCOL_ERROR, "Client-side HTTP upgrade requested for a server");
        }
        if (prefaceSent() || decoder.prefaceReceived()) {
            throw connectionError(PROTOCOL_ERROR, "HTTP upgrade must occur before HTTP/2 preface is sent or received");
        }

        // Create a local stream used for the HTTP cleartext upgrade.
        connection().local().createStream(HTTP_UPGRADE_STREAM_ID, true);
    }

    /**
     * Handles the server-side (cleartext) upgrade from HTTP to HTTP/2.
     * @param settings the settings for the remote endpoint.
     */
    public void onHttpServerUpgrade(Http2Settings settings) throws Http2Exception {
        if (!connection().isServer()) {
            throw connectionError(PROTOCOL_ERROR, "Server-side HTTP upgrade requested for a client");
        }
        if (prefaceSent() || decoder.prefaceReceived()) {
            throw connectionError(PROTOCOL_ERROR, "HTTP upgrade must occur before HTTP/2 preface is sent or received");
        }

        // Apply the settings but no ACK is necessary.
        encoder.remoteSettings(settings);

        // Create a stream in the half-closed state.
        connection().remote().createStream(HTTP_UPGRADE_STREAM_ID, true);
    }

    @Override
    public void flush(ChannelHandlerContext ctx) throws Http2Exception {
        // Trigger pending writes in the remote flow controller.
        encoder.flowController().writePendingBytes();
        try {
            ctx.flush();
        } catch (Throwable t) {
            throw new Http2Exception(INTERNAL_ERROR, "Error flushing" , t);
        }
    }

    private abstract class BaseDecoder {
        public abstract void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception;
        public void handlerRemoved(ChannelHandlerContext ctx) throws Exception { }
        public void channelActive(ChannelHandlerContext ctx) throws Exception { }

        public void channelInactive(ChannelHandlerContext ctx) throws Exception {
            // Connection has terminated, close the encoder and decoder.
            encoder().close();
            decoder().close();

            // We need to remove all streams (not just the active ones).
            // See https://github.com/netty/netty/issues/4838.
            connection().close(ctx.voidPromise());
        }

        /**
         * Determine if the HTTP/2 connection preface been sent.
         */
        public boolean prefaceSent() {
            return true;
        }
    }

    private final class PrefaceDecoder extends BaseDecoder {
        private ByteBuf clientPrefaceString;
        private boolean prefaceSent;

        public PrefaceDecoder(ChannelHandlerContext ctx) {
            clientPrefaceString = clientPrefaceString(encoder.connection());
            // This handler was just added to the context. In case it was handled after
            // the connection became active, send the connection preface now.
            sendPreface(ctx);
        }

        @Override
        public boolean prefaceSent() {
            return prefaceSent;
        }

        @Override
        public void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
            try {
                if (ctx.channel().isActive() && readClientPrefaceString(in) && verifyFirstFrameIsSettings(in)) {
                    // After the preface is read, it is time to hand over control to the post initialized decoder.
                    byteDecoder = new FrameDecoder();
                    byteDecoder.decode(ctx, in, out);
                }
            } catch (Throwable e) {
                onError(ctx, e);
            }
        }

        @Override
        public void channelActive(ChannelHandlerContext ctx) throws Exception {
            // The channel just became active - send the connection preface to the remote endpoint.
            sendPreface(ctx);
        }

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

        /**
         * Releases the {@code clientPrefaceString}. Any active streams will be left in the open.
         */
        @Override
        public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
            cleanup();
        }

        /**
         * Releases the {@code clientPrefaceString}. Any active streams will be left in the open.
         */
        private void cleanup() {
            if (clientPrefaceString != null) {
                clientPrefaceString.release();
                clientPrefaceString = null;
            }
        }

        /**
         * Decodes the client connection preface string from the input buffer.
         *
         * @return {@code true} if processing of the client preface string is complete. Since client preface strings can
         *         only be received by servers, returns true immediately for client endpoints.
         */
        private boolean readClientPrefaceString(ByteBuf in) throws Http2Exception {
            if (clientPrefaceString == null) {
                return true;
            }

            int prefaceRemaining = clientPrefaceString.readableBytes();
            int bytesRead = min(in.readableBytes(), prefaceRemaining);

            // If the input so far doesn't match the preface, break the connection.
            if (bytesRead == 0 || !ByteBufUtil.equals(in, in.readerIndex(),
                    clientPrefaceString, clientPrefaceString.readerIndex(), bytesRead)) {
                String receivedBytes = hexDump(in, in.readerIndex(),
                        min(in.readableBytes(), clientPrefaceString.readableBytes()));
                throw connectionError(PROTOCOL_ERROR, "HTTP/2 client preface string missing or corrupt. " +
                        "Hex dump for received bytes: %s", receivedBytes);
            }
            in.skipBytes(bytesRead);
            clientPrefaceString.skipBytes(bytesRead);

            if (!clientPrefaceString.isReadable()) {
                // Entire preface has been read.
                clientPrefaceString.release();
                clientPrefaceString = null;
                return true;
            }
            return false;
        }

        /**
         * Peeks at that the next frame in the buffer and verifies that it is a non-ack {@code SETTINGS} frame.
         *
         * @param in the inbound buffer.
         * @return {@code} true if the next frame is a non-ack {@code SETTINGS} frame, {@code false} if more
         * data is required before we can determine the next frame type.
         * @throws Http2Exception thrown if the next frame is NOT a non-ack {@code SETTINGS} frame.
         */
        private boolean verifyFirstFrameIsSettings(ByteBuf in) throws Http2Exception {
            if (in.readableBytes() < 5) {
                // Need more data before we can see the frame type for the first frame.
                return false;
            }

            short frameType = in.getUnsignedByte(in.readerIndex() + 3);
            short flags = in.getUnsignedByte(in.readerIndex() + 4);
            if (frameType != SETTINGS || (flags & Http2Flags.ACK) != 0) {
                throw connectionError(PROTOCOL_ERROR, "First received frame was not SETTINGS. " +
                        "Hex dump for first 5 bytes: %s", hexDump(in, in.readerIndex(), 5));
            }
            return true;
        }

        /**
         * Sends the HTTP/2 connection preface upon establishment of the connection, if not already sent.
         */
        private void sendPreface(ChannelHandlerContext ctx) {
            if (prefaceSent || !ctx.channel().isActive()) {
                return;
            }

            prefaceSent = true;

            if (!connection().isServer()) {
                // Clients must send the preface string as the first bytes on the connection.
                ctx.write(connectionPrefaceBuf()).addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
            }

            // Both client and server must send their initial settings.
            encoder.writeSettings(ctx, initialSettings, ctx.newPromise()).addListener(
                    ChannelFutureListener.CLOSE_ON_FAILURE);
        }
    }

    private final class FrameDecoder extends BaseDecoder {
        @Override
        public void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
            try {
                decoder.decodeFrame(ctx, in, out);
            } catch (Throwable e) {
                onError(ctx, e);
            }
        }
    }

    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        // Initialize the encoder, decoder, flow controllers, and internal state.
        encoder.lifecycleManager(this);
        decoder.lifecycleManager(this);
        encoder.flowController().channelHandlerContext(ctx);
        decoder.flowController().channelHandlerContext(ctx);
        byteDecoder = new PrefaceDecoder(ctx);
    }

    @Override
    protected void handlerRemoved0(ChannelHandlerContext ctx) throws Exception {
        if (byteDecoder != null) {
            byteDecoder.handlerRemoved(ctx);
            byteDecoder = null;
        }
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        if (byteDecoder == null) {
            byteDecoder = new PrefaceDecoder(ctx);
        }
        byteDecoder.channelActive(ctx);
        super.channelActive(ctx);
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        // Call super class first, as this may result in decode being called.
        super.channelInactive(ctx);
        if (byteDecoder != null) {
            byteDecoder.channelInactive(ctx);
            byteDecoder = null;
        }
    }

    @Override
    public void channelWritabilityChanged(ChannelHandlerContext ctx) throws Exception {
        // Writability is expected to change while we are writing. We cannot allow this event to trigger reentering
        // the allocation and write loop. Reentering the event loop will lead to over or illegal allocation.
        try {
            if (ctx.channel().isWritable()) {
                flush(ctx);
            }
            encoder.flowController().channelWritabilityChanged();
        } finally {
            super.channelWritabilityChanged(ctx);
        }
    }

    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        byteDecoder.decode(ctx, in, out);
    }

    @Override
    public void bind(ChannelHandlerContext ctx, SocketAddress localAddress, ChannelPromise promise) throws Exception {
        ctx.bind(localAddress, promise);
    }

    @Override
    public void connect(ChannelHandlerContext ctx, SocketAddress remoteAddress, SocketAddress localAddress,
                        ChannelPromise promise) throws Exception {
        ctx.connect(remoteAddress, localAddress, promise);
    }

    @Override
    public void disconnect(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
        ctx.disconnect(promise);
    }

    @Override
    public void close(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
        // Avoid NotYetConnectedException
        if (!ctx.channel().isActive()) {
            ctx.close(promise);
            return;
        }

        // If the user has already sent a GO_AWAY frame they may be attempting to do a graceful shutdown which requires
        // sending multiple GO_AWAY frames. We should only send a GO_AWAY here if one has not already been sent. If
        // a GO_AWAY has been sent we send a empty buffer just so we can wait to close until all other data has been
        // flushed to the OS.
        // https://github.com/netty/netty/issues/5307
        final ChannelFuture future = connection().goAwaySent() ? ctx.write(EMPTY_BUFFER) : goAway(ctx, null);
        ctx.flush();
        doGracefulShutdown(ctx, future, promise);
    }

    private void doGracefulShutdown(ChannelHandlerContext ctx, ChannelFuture future, ChannelPromise promise) {
        if (isGracefulShutdownComplete()) {
            // If there are no active streams, close immediately after the GO_AWAY write completes.
            future.addListener(new ClosingChannelFutureListener(ctx, promise));
        } else {
            // If there are active streams we should wait until they are all closed before closing the connection.
            closeListener = new ClosingChannelFutureListener(ctx, promise,
                                        gracefulShutdownTimeoutMillis, MILLISECONDS);
        }
    }

    @Override
    public void deregister(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
        ctx.deregister(promise);
    }

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

    @Override
    public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
        ctx.write(msg, promise);
    }

    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        // Trigger flush after read on the assumption that flush is cheap if there is nothing to write and that
        // for flow-control the read may release window that causes data to be written that can now be flushed.
        try {
            flush(ctx);
        } finally {
            super.channelReadComplete(ctx);
        }
    }

    /**
     * Handles {@link Http2Exception} objects that were thrown from other handlers. Ignores all other exceptions.
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        if (getEmbeddedHttp2Exception(cause) != null) {
            // Some exception in the causality chain is an Http2Exception - handle it.
            onError(ctx, cause);
        } else {
            super.exceptionCaught(ctx, cause);
        }
    }

    /**
     * Closes the local side of the given stream. If this causes the stream to be closed, adds a
     * hook to close the channel after the given future completes.
     *
     * @param stream the stream to be half closed.
     * @param future If closing, the future after which to close the channel.
     */
    @Override
    public void closeStreamLocal(Http2Stream stream, ChannelFuture future) {
        switch (stream.state()) {
            case HALF_CLOSED_LOCAL:
            case OPEN:
                stream.closeLocalSide();
                break;
            default:
                closeStream(stream, future);
                break;
        }
    }

    /**
     * Closes the remote side of the given stream. If this causes the stream to be closed, adds a
     * hook to close the channel after the given future completes.
     *
     * @param stream the stream to be half closed.
     * @param future If closing, the future after which to close the channel.
     */
    @Override
    public void closeStreamRemote(Http2Stream stream, ChannelFuture future) {
        switch (stream.state()) {
            case HALF_CLOSED_REMOTE:
            case OPEN:
                stream.closeRemoteSide();
                break;
            default:
                closeStream(stream, future);
                break;
        }
    }

    @Override
    public void closeStream(final Http2Stream stream, ChannelFuture future) {
        stream.close();

        if (future.isDone()) {
            checkCloseConnection(future);
        } else {
            future.addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture future) throws Exception {
                    checkCloseConnection(future);
                }
            });
        }
    }

    /**
     * Central handler for all exceptions caught during HTTP/2 processing.
     */
    @Override
    public void onError(ChannelHandlerContext ctx, Throwable cause) {
        Http2Exception embedded = getEmbeddedHttp2Exception(cause);
        if (isStreamError(embedded)) {
            onStreamError(ctx, cause, (StreamException) embedded);
        } else if (embedded instanceof CompositeStreamException) {
            CompositeStreamException compositException = (CompositeStreamException) embedded;
            for (StreamException streamException : compositException) {
                onStreamError(ctx, cause, streamException);
            }
        } else {
            onConnectionError(ctx, cause, embedded);
        }
        ctx.flush();
    }

    /**
     * Called by the graceful shutdown logic to determine when it is safe to close the connection. Returns {@code true}
     * if the graceful shutdown has completed and the connection can be safely closed. This implementation just
     * guarantees that there are no active streams. Subclasses may override to provide additional checks.
     */
    protected boolean isGracefulShutdownComplete() {
        return connection().numActiveStreams() == 0;
    }

    /**
     * Handler for a connection error. Sends a GO_AWAY frame to the remote endpoint. Once all
     * streams are closed, the connection is shut down.
     *
     * @param ctx the channel context
     * @param cause the exception that was caught
     * @param http2Ex the {@link Http2Exception} that is embedded in the causality chain. This may
     *            be {@code null} if it's an unknown exception.
     */
    protected void onConnectionError(ChannelHandlerContext ctx, Throwable cause, Http2Exception http2Ex) {
        if (http2Ex == null) {
            http2Ex = new Http2Exception(INTERNAL_ERROR, cause.getMessage(), cause);
        }

        ChannelPromise promise = ctx.newPromise();
        ChannelFuture future = goAway(ctx, http2Ex);
        switch (http2Ex.shutdownHint()) {
        case GRACEFUL_SHUTDOWN:
            doGracefulShutdown(ctx, future, promise);
            break;
        default:
            future.addListener(new ClosingChannelFutureListener(ctx, promise));
            break;
        }
    }

    /**
     * Handler for a stream error. Sends a {@code RST_STREAM} frame to the remote endpoint and closes the
     * stream.
     *
     * @param ctx the channel context
     * @param cause the exception that was caught
     * @param http2Ex the {@link StreamException} that is embedded in the causality chain.
     */
    protected void onStreamError(ChannelHandlerContext ctx, @SuppressWarnings("unused") Throwable cause,
                                 StreamException http2Ex) {
        resetStream(ctx, http2Ex.streamId(), http2Ex.error().code(), ctx.newPromise());
    }

    protected Http2FrameWriter frameWriter() {
        return encoder().frameWriter();
    }

    @Override
    public ChannelFuture resetStream(final ChannelHandlerContext ctx, int streamId, long errorCode,
            final ChannelPromise promise) {
        final Http2Stream stream = connection().stream(streamId);
        if (stream == null || stream.isResetSent()) {
            // Don't write a RST_STREAM frame if we are not aware of the stream, or if we have already written one.
            return promise.setSuccess();
        }

        final ChannelFuture future;
        if (stream.state() == IDLE) {
            // We cannot write RST_STREAM frames on IDLE streams https://tools.ietf.org/html/rfc7540#section-6.4.
            future = promise.setSuccess();
        } else {
            future = frameWriter().writeRstStream(ctx, streamId, errorCode, promise);
        }

        // Synchronously set the resetSent flag to prevent any subsequent calls
        // from resulting in multiple reset frames being sent.
        stream.resetSent();

        if (future.isDone()) {
            processRstStreamWriteResult(ctx, stream, future);
        } else {
            future.addListener(new ChannelFutureListener() {
                @Override
                public void operationComplete(ChannelFuture future) throws Exception {
                    processRstStreamWriteResult(ctx, stream, future);
                }
            });
        }

        return future;
    }

    @Override
    public ChannelFuture goAway(final ChannelHandlerContext ctx, final int lastStreamId, final long errorCode,
                                final ByteBuf debugData, ChannelPromise promise) {
        try {
            final Http2Connection connection = connection();
            if (connection.goAwaySent() && lastStreamId > connection.remote().lastStreamKnownByPeer()) {
                throw connectionError(PROTOCOL_ERROR, "Last stream identifier must not increase between " +
                                                      "sending multiple GOAWAY frames (was '%d', is '%d').",
                                                      connection.remote().lastStreamKnownByPeer(),
                                                      lastStreamId);
            }
            connection.goAwaySent(lastStreamId, errorCode, debugData);

            // Need to retain before we write the buffer because if we do it after the refCnt could already be 0 and
            // result in an IllegalRefCountException.
            debugData.retain();
            ChannelFuture future = frameWriter().writeGoAway(ctx, lastStreamId, errorCode, debugData, promise);

            if (future.isDone()) {
                processGoAwayWriteResult(ctx, lastStreamId, errorCode, debugData, future);
            } else {
                future.addListener(new ChannelFutureListener() {
                    @Override
                    public void operationComplete(ChannelFuture future) throws Exception {
                        processGoAwayWriteResult(ctx, lastStreamId, errorCode, debugData, future);
                    }
                });
            }

            return future;
        } catch (Throwable cause) { // Make sure to catch Throwable because we are doing a retain() in this method.
            debugData.release();
            return promise.setFailure(cause);
        }
    }

    /**
     * Closes the connection if the graceful shutdown process has completed.
     * @param future Represents the status that will be passed to the {@link #closeListener}.
     */
    private void checkCloseConnection(ChannelFuture future) {
        // If this connection is closing and the graceful shutdown has completed, close the connection
        // once this operation completes.
        if (closeListener != null && isGracefulShutdownComplete()) {
            ChannelFutureListener closeListener = this.closeListener;
            // This method could be called multiple times
            // and we don't want to notify the closeListener multiple times.
            this.closeListener = null;
            try {
                closeListener.operationComplete(future);
            } catch (Exception e) {
                throw new IllegalStateException("Close listener threw an unexpected exception", e);
            }
        }
    }

    /**
     * Close the remote endpoint with with a {@code GO_AWAY} frame. Does <strong>not flush
     * immediately, this is the responsibility of the caller.
     */
    private ChannelFuture goAway(ChannelHandlerContext ctx, Http2Exception cause) {
        long errorCode = cause != null ? cause.error().code() : NO_ERROR.code();
        int lastKnownStream = connection().remote().lastStreamCreated();
        return goAway(ctx, lastKnownStream, errorCode, Http2CodecUtil.toByteBuf(ctx, cause), ctx.newPromise());
    }

    private void processRstStreamWriteResult(ChannelHandlerContext ctx, Http2Stream stream, ChannelFuture future) {
        if (future.isSuccess()) {
            closeStream(stream, future);
        } else {
            // The connection will be closed and so no need to change the resetSent flag to false.
            onConnectionError(ctx, future.cause(), null);
        }
    }

    /**
     * Returns the client preface string if this is a client connection, otherwise returns {@code null}.
     */
    private static ByteBuf clientPrefaceString(Http2Connection connection) {
        return connection.isServer() ? connectionPrefaceBuf() : null;
    }

    private static void processGoAwayWriteResult(final ChannelHandlerContext ctx, final int lastStreamId,
            final long errorCode, final ByteBuf debugData, ChannelFuture future) {
        try {
            if (future.isSuccess()) {
                if (errorCode != NO_ERROR.code()) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("{} Sent GOAWAY: lastStreamId '{}', errorCode '{}', " +
                                     "debugData '{}'. Forcing shutdown of the connection.",
                                     ctx.channel(), lastStreamId, errorCode, debugData.toString(UTF_8), future.cause());
                    }
                    ctx.close();
                }
            } else {
                if (logger.isDebugEnabled()) {
                    logger.debug("{} Sending GOAWAY failed: lastStreamId '{}', errorCode '{}', " +
                                 "debugData '{}'. Forcing shutdown of the connection.",
                                 ctx.channel(), lastStreamId, errorCode, debugData.toString(UTF_8), future.cause());
                }
                ctx.close();
            }
        } finally {
            // We're done with the debug data now.
            debugData.release();
        }
    }

    /**
     * Closes the channel when the future completes.
     */
    private static final class ClosingChannelFutureListener implements ChannelFutureListener {
        private final ChannelHandlerContext ctx;
        private final ChannelPromise promise;
        private final ScheduledFuture<?> timeoutTask;

        ClosingChannelFutureListener(ChannelHandlerContext ctx, ChannelPromise promise) {
            this.ctx = ctx;
            this.promise = promise;
            timeoutTask = null;
        }

        ClosingChannelFutureListener(final ChannelHandlerContext ctx, final ChannelPromise promise,
                                     long timeout, TimeUnit unit) {
            this.ctx = ctx;
            this.promise = promise;
            timeoutTask = ctx.executor().schedule(new Runnable() {
                @Override
                public void run() {
                    ctx.close(promise);
                }
            }, timeout, unit);
        }

        @Override
        public void operationComplete(ChannelFuture sentGoAwayFuture) throws Exception {
            if (timeoutTask != null) {
                timeoutTask.cancel(false);
            }
            ctx.close(promise);
        }
    }
}