/*
    * Copyright 2016 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:
    *
    *   https://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.channel.Channel;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelFutureListener;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelInboundHandler;
  import io.netty.channel.ChannelPromise;
  import io.netty.handler.codec.UnsupportedMessageTypeException;
  import io.netty.handler.codec.http.HttpServerUpgradeHandler.UpgradeEvent;
  import io.netty.handler.codec.http2.Http2Connection.PropertyKey;
  import io.netty.handler.codec.http2.Http2Stream.State;
  import io.netty.handler.codec.http2.StreamBufferingEncoder.Http2ChannelClosedException;
  import io.netty.handler.codec.http2.StreamBufferingEncoder.Http2GoAwayException;
  import io.netty.util.ReferenceCountUtil;
  import io.netty.util.ReferenceCounted;
  import io.netty.util.collection.IntObjectHashMap;
  import io.netty.util.collection.IntObjectMap;
  import io.netty.util.internal.logging.InternalLogger;
  import io.netty.util.internal.logging.InternalLoggerFactory;
  
  import static io.netty.buffer.ByteBufUtil.writeAscii;
  import static io.netty.handler.codec.http2.Http2CodecUtil.HTTP_UPGRADE_STREAM_ID;
  import static io.netty.handler.codec.http2.Http2CodecUtil.isStreamIdValid;
  import static io.netty.handler.codec.http2.Http2Error.NO_ERROR;
  import static io.netty.util.internal.logging.InternalLogLevel.DEBUG;
  
  /**
   * <p>An HTTP/2 handler that maps HTTP/2 frames to {@link Http2Frame} objects and vice versa. For every incoming HTTP/2
   * frame, an {@link Http2Frame} object is created and propagated via {@link #channelRead}. Outbound {@link Http2Frame}
   * objects received via {@link #write} are converted to the HTTP/2 wire format. HTTP/2 frames specific to a stream
   * implement the {@link Http2StreamFrame} interface. The {@link Http2FrameCodec} is instantiated using the
   * {@link Http2FrameCodecBuilder}. It's recommended for channel handlers to inherit from the
   * {@link Http2ChannelDuplexHandler}, as it provides additional functionality like iterating over all active streams or
   * creating outbound streams.
   *
   * <h3>Stream Lifecycle</h3>
   * <p>
   * The frame codec delivers and writes frames for active streams. An active stream is closed when either side sends a
   * {@code RST_STREAM} frame or both sides send a frame with the {@code END_STREAM} flag set. Each
   * {@link Http2StreamFrame} has a {@link Http2FrameStream} object attached that uniquely identifies a particular stream.
   *
   * <p>{@link Http2StreamFrame}s read from the channel always a {@link Http2FrameStream} object set, while when writing a
   * {@link Http2StreamFrame} the application code needs to set a {@link Http2FrameStream} object using
   * {@link Http2StreamFrame#stream(Http2FrameStream)}.
   *
   * <h3>Flow control</h3>
   * <p>
   * The frame codec automatically increments stream and connection flow control windows.
   *
   * <p>Incoming flow controlled frames need to be consumed by writing a {@link Http2WindowUpdateFrame} with the consumed
   * number of bytes and the corresponding stream identifier set to the frame codec.
   *
   * <p>The local stream-level flow control window can be changed by writing a {@link Http2SettingsFrame} with the
   * {@link Http2Settings#initialWindowSize()} set to the targeted value.
   *
   * <p>The connection-level flow control window can be changed by writing a {@link Http2WindowUpdateFrame} with the
   * desired window size <em>increment</em> in bytes and the stream identifier set to {@code 0}. By default the initial
   * connection-level flow control window is the same as initial stream-level flow control window.
   *
   * <h3>New inbound Streams</h3>
   * <p>
   * The first frame of an HTTP/2 stream must be an {@link Http2HeadersFrame}, which will have an {@link Http2FrameStream}
   * object attached.
   *
   * <h3>New outbound Streams</h3>
   * <p>
   * A outbound HTTP/2 stream can be created by first instantiating a new {@link Http2FrameStream} object via
   * {@link Http2ChannelDuplexHandler#newStream()}, and then writing a {@link Http2HeadersFrame} object with the stream
   * attached.
   *
   * <pre> {@code
   *     final Http2Stream2 stream = handler.newStream();
   *     ctx.write(headersFrame.stream(stream)).addListener(new ChannelFutureListener() {
   *
   *         @Override
   *         public void operationComplete(ChannelFuture f) {
   *             if (f.isSuccess()) {
   *                 // Stream is active and stream.id() returns a valid stream identifier.
   *                 System.out.println("New stream with id " + stream.id() + " created.");
   *             } else {
   *                 // Stream failed to become active. Handle error.
   *                 if (f.cause() instanceof Http2NoMoreStreamIdsException) {
  *
  *                 } else if (f.cause() instanceof Http2GoAwayException) {
  *
  *                 } else {
  *
  *                 }
  *             }
  *         }
  *     }
  *     }
  * </pre>
  *
  * <p>If a new stream cannot be created due to stream id exhaustion of the endpoint, the {@link ChannelPromise} of the
  * HEADERS frame will fail with a {@link Http2NoMoreStreamIdsException}.
  *
  * <p>The HTTP/2 standard allows for an endpoint to limit the maximum number of concurrently active streams via the
  * {@code SETTINGS_MAX_CONCURRENT_STREAMS} setting. When this limit is reached, no new streams can be created. However,
  * the {@link Http2FrameCodec} can be build with
  * {@link Http2FrameCodecBuilder#encoderEnforceMaxConcurrentStreams(boolean)} enabled, in which case a new stream and
  * its associated frames will be buffered until either the limit is increased or an active stream is closed. It's,
  * however, possible that a buffered stream will never become active. That is, the channel might
  * get closed or a GO_AWAY frame might be received. In the first case, all writes of buffered streams will fail with a
  * {@link Http2ChannelClosedException}. In the second case, all writes of buffered streams with an identifier less than
  * the last stream identifier of the GO_AWAY frame will fail with a {@link Http2GoAwayException}.
  *
  * <h3>Error Handling</h3>
  * <p>
  * Exceptions and errors are propagated via {@link ChannelInboundHandler#exceptionCaught}. Exceptions that apply to
  * a specific HTTP/2 stream are wrapped in a {@link Http2FrameStreamException} and have the corresponding
  * {@link Http2FrameStream} object attached.
  *
  * <h3>Reference Counting</h3>
  * <p>
  * Some {@link Http2StreamFrame}s implement the {@link ReferenceCounted} interface, as they carry
  * reference counted objects (e.g. {@link ByteBuf}s). The frame codec will call {@link ReferenceCounted#retain()} before
  * propagating a reference counted object through the pipeline, and thus an application handler needs to release such
  * an object after having consumed it. For more information on reference counting take a look at
  * <a href="https://netty.io/wiki/reference-counted-objects.html">Reference counted objects</a>
  *
  * <h3>HTTP Upgrade</h3>
  * <p>
  * Server-side HTTP to HTTP/2 upgrade is supported in conjunction with {@link Http2ServerUpgradeCodec}; the necessary
  * HTTP-to-HTTP/2 conversion is performed automatically.
  */
 public class Http2FrameCodec extends Http2ConnectionHandler {
 
     private static final InternalLogger LOG = InternalLoggerFactory.getInstance(Http2FrameCodec.class);
 
     private static final Class<?>[] SUPPORTED_MESSAGES = new Class[] {
             Http2DataFrame.class, Http2HeadersFrame.class, Http2WindowUpdateFrame.class, Http2ResetFrame.class,
             Http2PingFrame.class, Http2SettingsFrame.class, Http2SettingsAckFrame.class, Http2GoAwayFrame.class,
             Http2PushPromiseFrame.class, Http2PriorityFrame.class, Http2UnknownFrame.class };
 
     protected final PropertyKey streamKey;
     private final PropertyKey upgradeKey;
 
     private final Integer initialFlowControlWindowSize;
 
     ChannelHandlerContext ctx;
 
     /**
      * Number of buffered streams if the {@link StreamBufferingEncoder} is used.
      **/
     private int numBufferedStreams;
     private final IntObjectMap<DefaultHttp2FrameStream> frameStreamToInitializeMap =
             new IntObjectHashMap<DefaultHttp2FrameStream>(8);
 
     protected Http2FrameCodec(Http2ConnectionEncoder encoder, Http2ConnectionDecoder decoder,
                               Http2Settings initialSettings, boolean decoupleCloseAndGoAway, boolean flushPreface) {
         super(decoder, encoder, initialSettings, decoupleCloseAndGoAway, flushPreface);
 
         decoder.frameListener(new FrameListener());
         connection().addListener(new ConnectionListener());
         connection().remote().flowController().listener(new Http2RemoteFlowControllerListener());
         streamKey = connection().newKey();
         upgradeKey = connection().newKey();
         initialFlowControlWindowSize = initialSettings.initialWindowSize();
     }
 
     /**
      * Creates a new outbound/local stream.
      */
     DefaultHttp2FrameStream newStream() {
         return new DefaultHttp2FrameStream();
     }
 
     /**
      * Iterates over all active HTTP/2 streams.
      *
      * <p>This method must not be called outside of the event loop.
      */
     final void forEachActiveStream(final Http2FrameStreamVisitor streamVisitor) throws Http2Exception {
         assert ctx.executor().inEventLoop();
         if (connection().numActiveStreams() > 0) {
             connection().forEachActiveStream(new Http2StreamVisitor() {
                 @Override
                 public boolean visit(Http2Stream stream) {
                     try {
                         return streamVisitor.visit((Http2FrameStream) stream.getProperty(streamKey));
                     } catch (Throwable cause) {
                         onError(ctx, false, cause);
                         return false;
                     }
                 }
             });
         }
     }
 
     /**
      * Retrieve the number of streams currently in the process of being initialized.
      * <p>
      * This is package-private for testing only.
      */
     int numInitializingStreams() {
         return frameStreamToInitializeMap.size();
     }
 
     @Override
     public final void handlerAdded(ChannelHandlerContext ctx) throws Exception {
         this.ctx = ctx;
         super.handlerAdded(ctx);
         handlerAdded0(ctx);
         // Must be after Http2ConnectionHandler does its initialization in handlerAdded above.
         // The server will not send a connection preface so we are good to send a window update.
         Http2Connection connection = connection();
         if (connection.isServer()) {
             tryExpandConnectionFlowControlWindow(connection);
         }
     }
 
     private void tryExpandConnectionFlowControlWindow(Http2Connection connection) throws Http2Exception {
         if (initialFlowControlWindowSize != null) {
             // The window size in the settings explicitly excludes the connection window. So we manually manipulate the
             // connection window to accommodate more concurrent data per connection.
             Http2Stream connectionStream = connection.connectionStream();
             Http2LocalFlowController localFlowController = connection.local().flowController();
             final int delta = initialFlowControlWindowSize - localFlowController.initialWindowSize(connectionStream);
             // Only increase the connection window, don't decrease it.
             if (delta > 0) {
                 // Double the delta just so a single stream can't exhaust the connection window.
                 localFlowController.incrementWindowSize(connectionStream, Math.max(delta << 1, delta));
                 flush(ctx);
             }
         }
     }
 
     void handlerAdded0(@SuppressWarnings("unsed") ChannelHandlerContext ctx) throws Exception {
         // sub-class can override this for extra steps that needs to be done when the handler is added.
     }
 
     /**
      * Handles the cleartext HTTP upgrade event. If an upgrade occurred, sends a simple response via
      * HTTP/2 on stream 1 (the stream specifically reserved for cleartext HTTP upgrade).
      */
     @Override
     public final void userEventTriggered(final ChannelHandlerContext ctx, final Object evt) throws Exception {
         if (evt == Http2ConnectionPrefaceAndSettingsFrameWrittenEvent.INSTANCE) {
             // The user event implies that we are on the client.
             tryExpandConnectionFlowControlWindow(connection());
 
             // We schedule this on the EventExecutor to allow to have any extra handlers added to the pipeline
             // before we pass the event to the next handler. This is needed as the event may be called from within
             // handlerAdded(...) which will be run before other handlers will be added to the pipeline.
             ctx.executor().execute(new Runnable() {
                 @Override
                 public void run() {
                     ctx.fireUserEventTriggered(evt);
                 }
             });
         } else if (evt instanceof UpgradeEvent) {
             UpgradeEvent upgrade = (UpgradeEvent) evt;
             try {
                 onUpgradeEvent(ctx, upgrade.retain());
                 Http2Stream stream = connection().stream(HTTP_UPGRADE_STREAM_ID);
                 if (stream.getProperty(streamKey) == null) {
                     // TODO: improve handler/stream lifecycle so that stream isn't active before handler added.
                     // The stream was already made active, but ctx may have been null so it wasn't initialized.
                     // https://github.com/netty/netty/issues/4942
                     onStreamActive0(stream);
                 }
                 upgrade.upgradeRequest().headers().setInt(
                         HttpConversionUtil.ExtensionHeaderNames.STREAM_ID.text(), HTTP_UPGRADE_STREAM_ID);
                 stream.setProperty(upgradeKey, true);
                 InboundHttpToHttp2Adapter.handle(
                         ctx, connection(), decoder().frameListener(), upgrade.upgradeRequest().retain());
             } finally {
                 upgrade.release();
             }
         } else {
             onUserEventTriggered(ctx, evt);
             ctx.fireUserEventTriggered(evt);
         }
     }
 
     void onUserEventTriggered(final ChannelHandlerContext ctx, final Object evt) throws Exception {
         // noop
     }
 
     /**
      * Processes all {@link Http2Frame}s. {@link Http2StreamFrame}s may only originate in child
      * streams.
      */
     @Override
     public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) {
         if (msg instanceof Http2DataFrame) {
             Http2DataFrame dataFrame = (Http2DataFrame) msg;
             encoder().writeData(ctx, dataFrame.stream().id(), dataFrame.content(),
                     dataFrame.padding(), dataFrame.isEndStream(), promise);
         } else if (msg instanceof Http2HeadersFrame) {
             writeHeadersFrame(ctx, (Http2HeadersFrame) msg, promise);
         } else if (msg instanceof Http2WindowUpdateFrame) {
             Http2WindowUpdateFrame frame = (Http2WindowUpdateFrame) msg;
             Http2FrameStream frameStream = frame.stream();
             // It is legit to send a WINDOW_UPDATE frame for the connection stream. The parent channel doesn't attempt
             // to set the Http2FrameStream so we assume if it is null the WINDOW_UPDATE is for the connection stream.
             try {
                 if (frameStream == null) {
                     increaseInitialConnectionWindow(frame.windowSizeIncrement());
                 } else {
                     consumeBytes(frameStream.id(), frame.windowSizeIncrement());
                 }
                 promise.setSuccess();
             } catch (Throwable t) {
                 promise.setFailure(t);
             }
         } else if (msg instanceof Http2ResetFrame) {
             Http2ResetFrame rstFrame = (Http2ResetFrame) msg;
             int id = rstFrame.stream().id();
             // Only ever send a reset frame if stream may have existed before as otherwise we may send a RST on a
             // stream in an invalid state and cause a connection error.
             if (connection().streamMayHaveExisted(id)) {
                 encoder().writeRstStream(ctx, rstFrame.stream().id(), rstFrame.errorCode(), promise);
             } else {
                 ReferenceCountUtil.release(rstFrame);
                 promise.setFailure(Http2Exception.streamError(
                         rstFrame.stream().id(), Http2Error.PROTOCOL_ERROR, "Stream never existed"));
             }
         } else if (msg instanceof Http2PingFrame) {
             Http2PingFrame frame = (Http2PingFrame) msg;
             encoder().writePing(ctx, frame.ack(), frame.content(), promise);
         } else if (msg instanceof Http2SettingsFrame) {
             encoder().writeSettings(ctx, ((Http2SettingsFrame) msg).settings(), promise);
         } else if (msg instanceof Http2SettingsAckFrame) {
             // In the event of manual SETTINGS ACK, it is assumed the encoder will apply the earliest received but not
             // yet ACKed settings.
             encoder().writeSettingsAck(ctx, promise);
         } else if (msg instanceof Http2GoAwayFrame) {
             writeGoAwayFrame(ctx, (Http2GoAwayFrame) msg, promise);
         } else if (msg instanceof Http2PushPromiseFrame) {
             Http2PushPromiseFrame pushPromiseFrame = (Http2PushPromiseFrame) msg;
             writePushPromise(ctx, pushPromiseFrame, promise);
         } else if (msg instanceof Http2PriorityFrame) {
             Http2PriorityFrame priorityFrame = (Http2PriorityFrame) msg;
             encoder().writePriority(ctx, priorityFrame.stream().id(), priorityFrame.streamDependency(),
                     priorityFrame.weight(), priorityFrame.exclusive(), promise);
         } else if (msg instanceof Http2UnknownFrame) {
             Http2UnknownFrame unknownFrame = (Http2UnknownFrame) msg;
             encoder().writeFrame(ctx, unknownFrame.frameType(), unknownFrame.stream().id(),
                     unknownFrame.flags(), unknownFrame.content(), promise);
         } else if (!(msg instanceof Http2Frame)) {
             ctx.write(msg, promise);
         } else {
             ReferenceCountUtil.release(msg);
             throw new UnsupportedMessageTypeException(msg, SUPPORTED_MESSAGES);
         }
     }
 
     private void increaseInitialConnectionWindow(int deltaBytes) throws Http2Exception {
         // The LocalFlowController is responsible for detecting over/under flow.
         connection().local().flowController().incrementWindowSize(connection().connectionStream(), deltaBytes);
     }
 
     final boolean consumeBytes(int streamId, int bytes) throws Http2Exception {
         Http2Stream stream = connection().stream(streamId);
         // Upgraded requests are ineligible for stream control. We add the null check
         // in case the stream has been deregistered.
         if (stream != null && streamId == Http2CodecUtil.HTTP_UPGRADE_STREAM_ID) {
             Boolean upgraded = stream.getProperty(upgradeKey);
             if (Boolean.TRUE.equals(upgraded)) {
                 return false;
             }
         }
 
         return connection().local().flowController().consumeBytes(stream, bytes);
     }
 
     private void writeGoAwayFrame(ChannelHandlerContext ctx, Http2GoAwayFrame frame, ChannelPromise promise) {
         if (frame.lastStreamId() > -1) {
             frame.release();
             throw new IllegalArgumentException("Last stream id must not be set on GOAWAY frame");
         }
 
         int lastStreamCreated = connection().remote().lastStreamCreated();
         long lastStreamId = lastStreamCreated + ((long) frame.extraStreamIds()) * 2;
         // Check if the computation overflowed.
         if (lastStreamId > Integer.MAX_VALUE) {
             lastStreamId = Integer.MAX_VALUE;
         }
         goAway(ctx, (int) lastStreamId, frame.errorCode(), frame.content(), promise);
     }
 
     private void writeHeadersFrame(final ChannelHandlerContext ctx, Http2HeadersFrame headersFrame,
                                    ChannelPromise promise) {
 
         if (isStreamIdValid(headersFrame.stream().id())) {
             encoder().writeHeaders(ctx, headersFrame.stream().id(), headersFrame.headers(), headersFrame.padding(),
                     headersFrame.isEndStream(), promise);
         } else if (initializeNewStream(ctx, (DefaultHttp2FrameStream) headersFrame.stream(), promise)) {
             promise = promise.unvoid();
 
             final int streamId = headersFrame.stream().id();
 
             encoder().writeHeaders(ctx, streamId, headersFrame.headers(), headersFrame.padding(),
                     headersFrame.isEndStream(), promise);
 
             if (!promise.isDone()) {
                 numBufferedStreams++;
                 // Clean up the stream being initialized if writing the headers fails and also
                 // decrement the number of buffered streams.
                 promise.addListener(new ChannelFutureListener() {
                     @Override
                     public void operationComplete(ChannelFuture channelFuture) {
                         numBufferedStreams--;
                         handleHeaderFuture(channelFuture, streamId);
                     }
                 });
             } else {
                 handleHeaderFuture(promise, streamId);
             }
         }
     }
 
     private void writePushPromise(final ChannelHandlerContext ctx, Http2PushPromiseFrame pushPromiseFrame,
                                   final ChannelPromise promise) {
         if (isStreamIdValid(pushPromiseFrame.pushStream().id())) {
             encoder().writePushPromise(ctx, pushPromiseFrame.stream().id(), pushPromiseFrame.pushStream().id(),
                     pushPromiseFrame.http2Headers(), pushPromiseFrame.padding(), promise);
         } else if (initializeNewStream(ctx, (DefaultHttp2FrameStream) pushPromiseFrame.pushStream(), promise)) {
             final int streamId = pushPromiseFrame.stream().id();
             encoder().writePushPromise(ctx, streamId, pushPromiseFrame.pushStream().id(),
                     pushPromiseFrame.http2Headers(), pushPromiseFrame.padding(), promise);
 
             if (promise.isDone()) {
                 handleHeaderFuture(promise, streamId);
             } else {
                 numBufferedStreams++;
                 // Clean up the stream being initialized if writing the headers fails and also
                 // decrement the number of buffered streams.
                 promise.addListener(new ChannelFutureListener() {
                     @Override
                     public void operationComplete(ChannelFuture channelFuture) {
                         numBufferedStreams--;
                         handleHeaderFuture(channelFuture, streamId);
                     }
                 });
             }
         }
     }
 
     private boolean initializeNewStream(ChannelHandlerContext ctx, DefaultHttp2FrameStream http2FrameStream,
                                         ChannelPromise promise) {
         final Http2Connection connection = connection();
         final int streamId = connection.local().incrementAndGetNextStreamId();
         if (streamId < 0) {
             promise.setFailure(new Http2NoMoreStreamIdsException());
 
             // Simulate a GOAWAY being received due to stream exhaustion on this connection. We use the maximum
             // valid stream ID for the current peer.
             onHttp2Frame(ctx, new DefaultHttp2GoAwayFrame(connection.isServer() ? Integer.MAX_VALUE :
                     Integer.MAX_VALUE - 1, NO_ERROR.code(),
                     writeAscii(ctx.alloc(), "Stream IDs exhausted on local stream creation")));
 
             return false;
         }
         http2FrameStream.id = streamId;
 
         // Use a Map to store all pending streams as we may have multiple. This is needed as if we would store the
         // stream in a field directly we may override the stored field before onStreamAdded(...) was called
         // and so not correctly set the property for the buffered stream.
         //
         // See https://github.com/netty/netty/issues/8692
         Object old = frameStreamToInitializeMap.put(streamId, http2FrameStream);
 
         // We should not re-use ids.
         assert old == null;
         return true;
     }
 
     private void handleHeaderFuture(ChannelFuture channelFuture, int streamId) {
         if (!channelFuture.isSuccess()) {
             frameStreamToInitializeMap.remove(streamId);
         }
     }
 
     private void onStreamActive0(Http2Stream stream) {
         if (stream.id() != Http2CodecUtil.HTTP_UPGRADE_STREAM_ID &&
                 connection().local().isValidStreamId(stream.id())) {
             return;
         }
 
         DefaultHttp2FrameStream stream2 = newStream().setStreamAndProperty(streamKey, stream);
         onHttp2StreamStateChanged(ctx, stream2);
     }
 
     private final class ConnectionListener extends Http2ConnectionAdapter {
         @Override
         public void onStreamAdded(Http2Stream stream) {
             DefaultHttp2FrameStream frameStream = frameStreamToInitializeMap.remove(stream.id());
 
             if (frameStream != null) {
                 frameStream.setStreamAndProperty(streamKey, stream);
             }
         }
 
         @Override
         public void onStreamActive(Http2Stream stream) {
             onStreamActive0(stream);
         }
 
         @Override
         public void onStreamClosed(Http2Stream stream) {
             onHttp2StreamStateChanged0(stream);
         }
 
         @Override
         public void onStreamHalfClosed(Http2Stream stream) {
             onHttp2StreamStateChanged0(stream);
         }
 
         private void onHttp2StreamStateChanged0(Http2Stream stream) {
             DefaultHttp2FrameStream stream2 = stream.getProperty(streamKey);
             if (stream2 != null) {
                 onHttp2StreamStateChanged(ctx, stream2);
             }
         }
     }
 
     @Override
     protected void onConnectionError(
             ChannelHandlerContext ctx, boolean outbound, Throwable cause, Http2Exception http2Ex) {
         if (!outbound) {
             // allow the user to handle it first in the pipeline, and then automatically clean up.
             // If this is not desired behavior the user can override this method.
             //
             // We only forward non outbound errors as outbound errors will already be reflected by failing the promise.
             ctx.fireExceptionCaught(cause);
         }
         super.onConnectionError(ctx, outbound, cause, http2Ex);
     }
 
     /**
      * Exceptions for unknown streams, that is streams that have no {@link Http2FrameStream} object attached
      * are simply logged and replied to by sending a RST_STREAM frame.
      */
     @Override
     protected final void onStreamError(ChannelHandlerContext ctx, boolean outbound, Throwable cause,
                                        Http2Exception.StreamException streamException) {
         int streamId = streamException.streamId();
         Http2Stream connectionStream = connection().stream(streamId);
         if (connectionStream == null) {
             onHttp2UnknownStreamError(ctx, cause, streamException);
             // Write a RST_STREAM
             super.onStreamError(ctx, outbound, cause, streamException);
             return;
         }
 
         Http2FrameStream stream = connectionStream.getProperty(streamKey);
         if (stream == null) {
             LOG.warn("{} Stream exception thrown without stream object attached.", ctx.channel(), cause);
             // Write a RST_STREAM
             super.onStreamError(ctx, outbound, cause, streamException);
             return;
         }
 
         if (!outbound) {
             // We only forward non outbound errors as outbound errors will already be reflected by failing the promise.
             onHttp2FrameStreamException(ctx, new Http2FrameStreamException(stream, streamException.error(), cause));
         }
     }
 
     private static void onHttp2UnknownStreamError(@SuppressWarnings("unused") ChannelHandlerContext ctx,
             Throwable cause, Http2Exception.StreamException streamException) {
         // We log here for debugging purposes. This exception will be propagated to the upper layers through other ways:
         // - fireExceptionCaught
         // - fireUserEventTriggered(Http2ResetFrame), see Http2MultiplexHandler#channelRead(...)
         // - by failing write promise
         // Receiver of the error is responsible for correct handling of this exception.
         LOG.log(DEBUG, "{} Stream exception thrown for unknown stream {}.",
                 ctx.channel(), streamException.streamId(), cause);
     }
 
     @Override
     protected final boolean isGracefulShutdownComplete() {
         return super.isGracefulShutdownComplete() && numBufferedStreams == 0;
     }
 
     private final class FrameListener implements Http2FrameListener {
 
         @Override
         public void onUnknownFrame(
                 ChannelHandlerContext ctx, byte frameType, int streamId, Http2Flags flags, ByteBuf payload) {
             if (streamId == 0) {
                 // Ignore unknown frames on connection stream, for example: HTTP/2 GREASE testing
                 return;
             }
             Http2FrameStream stream = requireStream(streamId);
             onHttp2Frame(ctx, newHttp2UnknownFrame(frameType, streamId, flags, payload.retain()).stream(stream));
         }
 
         @Override
         public void onSettingsRead(ChannelHandlerContext ctx, Http2Settings settings) {
             onHttp2Frame(ctx, new DefaultHttp2SettingsFrame(settings));
         }
 
         @Override
         public void onPingRead(ChannelHandlerContext ctx, long data) {
             onHttp2Frame(ctx, new DefaultHttp2PingFrame(data, false));
         }
 
         @Override
         public void onPingAckRead(ChannelHandlerContext ctx, long data) {
             onHttp2Frame(ctx, new DefaultHttp2PingFrame(data, true));
         }
 
         @Override
         public void onRstStreamRead(ChannelHandlerContext ctx, int streamId, long errorCode) {
             Http2FrameStream stream = requireStream(streamId);
             onHttp2Frame(ctx, new DefaultHttp2ResetFrame(errorCode).stream(stream));
         }
 
         @Override
         public void onWindowUpdateRead(ChannelHandlerContext ctx, int streamId, int windowSizeIncrement) {
             if (streamId == 0) {
                 // Ignore connection window updates.
                 return;
             }
             Http2FrameStream stream = requireStream(streamId);
             onHttp2Frame(ctx, new DefaultHttp2WindowUpdateFrame(windowSizeIncrement).stream(stream));
         }
 
         @Override
         public void onHeadersRead(ChannelHandlerContext ctx, int streamId,
                                   Http2Headers headers, int streamDependency, short weight, boolean
                                           exclusive, int padding, boolean endStream) {
             onHeadersRead(ctx, streamId, headers, padding, endStream);
         }
 
         @Override
         public void onHeadersRead(ChannelHandlerContext ctx, int streamId, Http2Headers headers,
                                   int padding, boolean endOfStream) {
             Http2FrameStream stream = requireStream(streamId);
             onHttp2Frame(ctx, new DefaultHttp2HeadersFrame(headers, endOfStream, padding).stream(stream));
         }
 
         @Override
         public int onDataRead(ChannelHandlerContext ctx, int streamId, ByteBuf data, int padding,
                               boolean endOfStream) {
             Http2FrameStream stream = requireStream(streamId);
             final Http2DataFrame dataframe;
             try {
                 dataframe = new DefaultHttp2DataFrame(data.retain(), endOfStream, padding);
             } catch (IllegalArgumentException e) {
                 // Might be thrown in case of invalid padding / length.
                 data.release();
                 throw e;
             }
             dataframe.stream(stream);
             onHttp2Frame(ctx, dataframe);
             // We return the bytes in consumeBytes() once the stream channel consumed the bytes.
             return 0;
         }
 
         @Override
         public void onGoAwayRead(ChannelHandlerContext ctx, int lastStreamId, long errorCode, ByteBuf debugData) {
             onHttp2Frame(ctx, new DefaultHttp2GoAwayFrame(lastStreamId, errorCode, debugData.retain()));
         }
 
         @Override
         public void onPriorityRead(ChannelHandlerContext ctx, int streamId, int streamDependency,
                                    short weight, boolean exclusive) {
 
             Http2Stream stream = connection().stream(streamId);
             if (stream == null) {
                 // The stream was not opened yet, let's just ignore this for now.
                 return;
             }
             Http2FrameStream frameStream = requireStream(streamId);
             onHttp2Frame(ctx, new DefaultHttp2PriorityFrame(streamDependency, weight, exclusive)
                     .stream(frameStream));
         }
 
         @Override
         public void onSettingsAckRead(ChannelHandlerContext ctx) {
             onHttp2Frame(ctx, Http2SettingsAckFrame.INSTANCE);
         }
 
         @Override
         public void onPushPromiseRead(ChannelHandlerContext ctx, int streamId, int promisedStreamId,
                                       Http2Headers headers, int padding) {
             Http2FrameStream stream = requireStream(streamId);
             onHttp2Frame(ctx, new DefaultHttp2PushPromiseFrame(headers, padding, promisedStreamId)
                     .pushStream(new DefaultHttp2FrameStream()
                             .setStreamAndProperty(streamKey, connection().stream(promisedStreamId)))
                     .stream(stream));
         }
 
         private Http2FrameStream requireStream(int streamId) {
             Http2FrameStream stream = connection().stream(streamId).getProperty(streamKey);
             if (stream == null) {
                 throw new IllegalStateException("Stream object required for identifier: " + streamId);
             }
             return stream;
         }
     }
 
     private void onUpgradeEvent(ChannelHandlerContext ctx, UpgradeEvent evt) {
         ctx.fireUserEventTriggered(evt);
     }
 
     private void onHttp2StreamWritabilityChanged(ChannelHandlerContext ctx, DefaultHttp2FrameStream stream,
                                                  @SuppressWarnings("unused") boolean writable) {
         ctx.fireUserEventTriggered(stream.writabilityChanged);
     }
 
     void onHttp2StreamStateChanged(ChannelHandlerContext ctx, DefaultHttp2FrameStream stream) {
         ctx.fireUserEventTriggered(stream.stateChanged);
     }
 
     void onHttp2Frame(ChannelHandlerContext ctx, Http2Frame frame) {
         ctx.fireChannelRead(frame);
     }
 
     /**
      * Create a Http2UnknownFrame. The ownership of the {@link ByteBuf} is transferred.
      * */
     protected Http2StreamFrame newHttp2UnknownFrame(byte frameType, int streamId, Http2Flags flags, ByteBuf payload) {
         return new DefaultHttp2UnknownFrame(frameType, flags, payload);
     }
 
     void onHttp2FrameStreamException(ChannelHandlerContext ctx, Http2FrameStreamException cause) {
         ctx.fireExceptionCaught(cause);
     }
 
     private final class Http2RemoteFlowControllerListener implements Http2RemoteFlowController.Listener {
         @Override
         public void writabilityChanged(Http2Stream stream) {
             DefaultHttp2FrameStream frameStream = stream.getProperty(streamKey);
             if (frameStream == null) {
                 return;
             }
             onHttp2StreamWritabilityChanged(
                     ctx, frameStream, connection().remote().flowController().isWritable(stream));
         }
     }
 
     /**
      * {@link Http2FrameStream} implementation.
      */
     // TODO(buchgr): Merge Http2FrameStream and Http2Stream.
     static class DefaultHttp2FrameStream implements Http2FrameStream {
 
         private volatile int id = -1;
         private volatile Http2Stream stream;
 
         final Http2FrameStreamEvent stateChanged = Http2FrameStreamEvent.stateChanged(this);
         final Http2FrameStreamEvent writabilityChanged = Http2FrameStreamEvent.writabilityChanged(this);
 
         Channel attachment;
 
         DefaultHttp2FrameStream setStreamAndProperty(PropertyKey streamKey, Http2Stream stream) {
             assert id == -1 || stream.id() == id;
             this.stream = stream;
             this.id = stream.id();
             stream.setProperty(streamKey, this);
             return this;
         }
 
         @Override
         public int id() {
             Http2Stream stream = this.stream;
             return stream == null ? id : stream.id();
         }
 
         @Override
         public State state() {
             Http2Stream stream = this.stream;
             return stream == null ? State.IDLE : stream.state();
         }
 
         @Override
         public String toString() {
             return String.valueOf(id());
         }
     }
 }