/*
    * Copyright 2013 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.spdy;
  
  import io.netty.channel.ChannelDuplexHandler;
  import io.netty.channel.ChannelFuture;
  import io.netty.channel.ChannelFutureListener;
  import io.netty.channel.ChannelHandlerContext;
  import io.netty.channel.ChannelPromise;
  import io.netty.util.internal.ObjectUtil;
  
  import java.util.concurrent.atomic.AtomicInteger;
  
  import static io.netty.handler.codec.spdy.SpdyCodecUtil.SPDY_SESSION_STREAM_ID;
  import static io.netty.handler.codec.spdy.SpdyCodecUtil.isServerId;
  import static io.netty.util.internal.ObjectUtil.checkPositive;
  import static io.netty.util.internal.ObjectUtil.checkPositiveOrZero;
  
  /**
   * Manages streams within a SPDY session.
   */
  public class SpdySessionHandler extends ChannelDuplexHandler {
  
      private static final SpdyProtocolException PROTOCOL_EXCEPTION =
              SpdyProtocolException.newStatic(null, SpdySessionHandler.class, "handleOutboundMessage(...)");
      private static final SpdyProtocolException STREAM_CLOSED =
              SpdyProtocolException.newStatic("Stream closed", SpdySessionHandler.class, "removeStream(...)");
  
      private static final int DEFAULT_WINDOW_SIZE = 64 * 1024; // 64 KB default initial window size
      private int initialSendWindowSize    = DEFAULT_WINDOW_SIZE;
      private int initialReceiveWindowSize = DEFAULT_WINDOW_SIZE;
      private volatile int initialSessionReceiveWindowSize = DEFAULT_WINDOW_SIZE;
  
      private final SpdySession spdySession = new SpdySession(initialSendWindowSize, initialReceiveWindowSize);
      private int lastGoodStreamId;
  
      // See https://datatracker.ietf.org/doc/html/rfc7540#section-6.5.2 for why 100 was chosen as a safe default.
      private static final int DEFAULT_MAX_CONCURRENT_STREAMS = 100;
      private int remoteConcurrentStreams = Integer.MAX_VALUE;
      private int localConcurrentStreams  = DEFAULT_MAX_CONCURRENT_STREAMS;
  
      private final AtomicInteger pings = new AtomicInteger();
  
      private boolean sentGoAwayFrame;
      private boolean receivedGoAwayFrame;
      private boolean sentInitialSettingsFrame;
  
      private ChannelFutureListener closeSessionFutureListener;
  
      private final boolean server;
      private final int minorVersion;
  
      /**
       * Creates a new session handler.
       * <p>
       * Remote-initiated streams are accepted up to {@value #DEFAULT_MAX_CONCURRENT_STREAMS}
       * concurrently (matching the HTTP/2 default, see
       * <a href="https://datatracker.ietf.org/doc/html/rfc7540#section-6.5.2">RFC 7540, Section 6.5.2</a>).
       * Use {@link #SpdySessionHandler(SpdyVersion, boolean, int)} to configure a different limit.
       *
       * @param version the protocol version
       * @param server  {@code true} if and only if this session handler should
       *                handle the server endpoint of the connection.
       *                {@code false} if and only if this session handler should
       *                handle the client endpoint of the connection.
       */
      public SpdySessionHandler(SpdyVersion version, boolean server) {
          this(version, server, DEFAULT_MAX_CONCURRENT_STREAMS);
      }
  
      /**
       * Creates a new session handler.
       *
       * @param version the protocol version
       * @param server  {@code true} if and only if this session handler should
       *                handle the server endpoint of the connection.
       *                {@code false} if and only if this session handler should
       *                handle the client endpoint of the connection.
       * @param maxLocalConcurrentStreams the maximum number of concurrent remote-initiated streams
       *                that will be accepted. This bounds the memory a remote peer can force this
       *                handler to allocate by opening streams. {@code SYN_STREAM} frames received
       *                once this limit is reached are rejected with a {@code RST_STREAM} carrying
       *                {@link SpdyStreamStatus#REFUSED_STREAM}. Must be positive.
       */
      public SpdySessionHandler(SpdyVersion version, boolean server, int maxLocalConcurrentStreams) {
          this.minorVersion = ObjectUtil.checkNotNull(version, "version").minorVersion();
         this.server = server;
         this.localConcurrentStreams = checkPositive(maxLocalConcurrentStreams, "maxLocalConcurrentStreams");
     }
 
     public void setSessionReceiveWindowSize(int sessionReceiveWindowSize) {
         checkPositiveOrZero(sessionReceiveWindowSize, "sessionReceiveWindowSize");
         // This will not send a window update frame immediately.
         // If this value increases the allowed receive window size,
         // a WINDOW_UPDATE frame will be sent when only half of the
         // session window size remains during data frame processing.
         // If this value decreases the allowed receive window size,
         // the window will be reduced as data frames are processed.
         initialSessionReceiveWindowSize = sessionReceiveWindowSize;
     }
 
     @Override
     public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
         if (ctx.channel().isActive()) {
             sendInitialSettingsFrame(ctx);
         }
     }
 
     @Override
     public void channelActive(ChannelHandlerContext ctx) throws Exception {
         sendInitialSettingsFrame(ctx);
         super.channelActive(ctx);
     }
 
     private void sendInitialSettingsFrame(ChannelHandlerContext ctx) {
         if (sentInitialSettingsFrame) {
             return;
         }
         sentInitialSettingsFrame = true;
         // Advertise the accept limit to the remote peer. This is advisory only -- the limit is
         // enforced locally by acceptStream(...) regardless of whether the peer honors it.
         SpdySettingsFrame settingsFrame = new DefaultSpdySettingsFrame();
         settingsFrame.setValue(SpdySettingsFrame.SETTINGS_MAX_CONCURRENT_STREAMS, localConcurrentStreams);
         ctx.writeAndFlush(settingsFrame);
     }
 
     @Override
     public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
         if (msg instanceof SpdyDataFrame) {
 
             /*
              * SPDY Data frame processing requirements:
              *
              * If an endpoint receives a data frame for a Stream-ID which is not open
              * and the endpoint has not sent a GOAWAY frame, it must issue a stream error
              * with the error code INVALID_STREAM for the Stream-ID.
              *
              * If an endpoint which created the stream receives a data frame before receiving
              * a SYN_REPLY on that stream, it is a protocol error, and the recipient must
              * issue a stream error with the getStatus code PROTOCOL_ERROR for the Stream-ID.
              *
              * If an endpoint receives multiple data frames for invalid Stream-IDs,
              * it may close the session.
              *
              * If an endpoint refuses a stream it must ignore any data frames for that stream.
              *
              * If an endpoint receives a data frame after the stream is half-closed from the
              * sender, it must send a RST_STREAM frame with the getStatus STREAM_ALREADY_CLOSED.
              *
              * If an endpoint receives a data frame after the stream is closed, it must send
              * a RST_STREAM frame with the getStatus PROTOCOL_ERROR.
              */
             SpdyDataFrame spdyDataFrame = (SpdyDataFrame) msg;
             int streamId = spdyDataFrame.streamId();
 
             int deltaWindowSize = -1 * spdyDataFrame.content().readableBytes();
             int newSessionWindowSize =
                 spdySession.updateReceiveWindowSize(SPDY_SESSION_STREAM_ID, deltaWindowSize);
 
             // Check if session window size is reduced beyond allowable lower bound
             if (newSessionWindowSize < 0) {
                 spdyDataFrame.release();
                 issueSessionError(ctx, SpdySessionStatus.PROTOCOL_ERROR);
                 return;
             }
 
             // Send a WINDOW_UPDATE frame if less than half the session window size remains
             if (newSessionWindowSize <= initialSessionReceiveWindowSize / 2) {
                 int sessionDeltaWindowSize = initialSessionReceiveWindowSize - newSessionWindowSize;
                 spdySession.updateReceiveWindowSize(SPDY_SESSION_STREAM_ID, sessionDeltaWindowSize);
                 SpdyWindowUpdateFrame spdyWindowUpdateFrame =
                     new DefaultSpdyWindowUpdateFrame(SPDY_SESSION_STREAM_ID, sessionDeltaWindowSize);
                 ctx.writeAndFlush(spdyWindowUpdateFrame);
             }
 
             // Check if we received a data frame for a Stream-ID which is not open
 
             if (!spdySession.isActiveStream(streamId)) {
                 spdyDataFrame.release();
                 if (streamId <= lastGoodStreamId) {
                     issueStreamError(ctx, streamId, SpdyStreamStatus.PROTOCOL_ERROR);
                 } else if (!sentGoAwayFrame) {
                     issueStreamError(ctx, streamId, SpdyStreamStatus.INVALID_STREAM);
                 }
                 return;
             }
 
             // Check if we received a data frame for a stream which is half-closed
 
             if (spdySession.isRemoteSideClosed(streamId)) {
                 spdyDataFrame.release();
                 issueStreamError(ctx, streamId, SpdyStreamStatus.STREAM_ALREADY_CLOSED);
                 return;
             }
 
             // Check if we received a data frame before receiving a SYN_REPLY
             if (!isRemoteInitiatedId(streamId) && !spdySession.hasReceivedReply(streamId)) {
                 spdyDataFrame.release();
                 issueStreamError(ctx, streamId, SpdyStreamStatus.PROTOCOL_ERROR);
                 return;
             }
 
             /*
              * SPDY Data frame flow control processing requirements:
              *
              * Recipient should not send a WINDOW_UPDATE frame as it consumes the last data frame.
              */
 
             // Update receive window size
             int newWindowSize = spdySession.updateReceiveWindowSize(streamId, deltaWindowSize);
 
             // Window size can become negative if we sent a SETTINGS frame that reduces the
             // size of the transfer window after the peer has written data frames.
             // The value is bounded by the length that SETTINGS frame decrease the window.
             // This difference is stored for the session when writing the SETTINGS frame
             // and is cleared once we send a WINDOW_UPDATE frame.
             if (newWindowSize < spdySession.getReceiveWindowSizeLowerBound(streamId)) {
                 spdyDataFrame.release();
                 issueStreamError(ctx, streamId, SpdyStreamStatus.FLOW_CONTROL_ERROR);
                 return;
             }
 
             // Window size became negative due to sender writing frame before receiving SETTINGS
             // Send data frames upstream in initialReceiveWindowSize chunks
             if (newWindowSize < 0) {
                 while (spdyDataFrame.content().readableBytes() > initialReceiveWindowSize) {
                     SpdyDataFrame partialDataFrame = new DefaultSpdyDataFrame(
                             streamId, spdyDataFrame.content().readRetainedSlice(initialReceiveWindowSize));
                     ctx.writeAndFlush(partialDataFrame);
                 }
             }
 
             // Send a WINDOW_UPDATE frame if less than half the stream window size remains
             if (newWindowSize <= initialReceiveWindowSize / 2 && !spdyDataFrame.isLast()) {
                 int streamDeltaWindowSize = initialReceiveWindowSize - newWindowSize;
                 spdySession.updateReceiveWindowSize(streamId, streamDeltaWindowSize);
                 SpdyWindowUpdateFrame spdyWindowUpdateFrame =
                         new DefaultSpdyWindowUpdateFrame(streamId, streamDeltaWindowSize);
                 ctx.writeAndFlush(spdyWindowUpdateFrame);
             }
 
             // Close the remote side of the stream if this is the last frame
             if (spdyDataFrame.isLast()) {
                 halfCloseStream(streamId, true, ctx.newSucceededFuture());
             }
 
         } else if (msg instanceof SpdySynStreamFrame) {
 
             /*
              * SPDY SYN_STREAM frame processing requirements:
              *
              * If an endpoint receives a SYN_STREAM with a Stream-ID that is less than
              * any previously received SYN_STREAM, it must issue a session error with
              * the getStatus PROTOCOL_ERROR.
              *
              * If an endpoint receives multiple SYN_STREAM frames with the same active
              * Stream-ID, it must issue a stream error with the getStatus code PROTOCOL_ERROR.
              *
              * The recipient can reject a stream by sending a stream error with the
              * getStatus code REFUSED_STREAM.
              */
 
             SpdySynStreamFrame spdySynStreamFrame = (SpdySynStreamFrame) msg;
             int streamId = spdySynStreamFrame.streamId();
 
             // Check if we received a valid SYN_STREAM frame
             if (spdySynStreamFrame.isInvalid() ||
                 !isRemoteInitiatedId(streamId) ||
                 spdySession.isActiveStream(streamId)) {
                 issueStreamError(ctx, streamId, SpdyStreamStatus.PROTOCOL_ERROR);
                 return;
             }
 
             // Stream-IDs must be monotonically increasing
             if (streamId <= lastGoodStreamId) {
                 issueSessionError(ctx, SpdySessionStatus.PROTOCOL_ERROR);
                 return;
             }
 
             // Try to accept the stream
             byte priority = spdySynStreamFrame.priority();
             boolean remoteSideClosed = spdySynStreamFrame.isLast();
             boolean localSideClosed = spdySynStreamFrame.isUnidirectional();
             if (!acceptStream(streamId, priority, remoteSideClosed, localSideClosed)) {
                 issueStreamError(ctx, streamId, SpdyStreamStatus.REFUSED_STREAM);
                 return;
             }
 
         } else if (msg instanceof SpdySynReplyFrame) {
 
             /*
              * SPDY SYN_REPLY frame processing requirements:
              *
              * If an endpoint receives multiple SYN_REPLY frames for the same active Stream-ID
              * it must issue a stream error with the getStatus code STREAM_IN_USE.
              */
 
             SpdySynReplyFrame spdySynReplyFrame = (SpdySynReplyFrame) msg;
             int streamId = spdySynReplyFrame.streamId();
 
             // Check if we received a valid SYN_REPLY frame
             if (spdySynReplyFrame.isInvalid() ||
                 isRemoteInitiatedId(streamId) ||
                 spdySession.isRemoteSideClosed(streamId)) {
                 issueStreamError(ctx, streamId, SpdyStreamStatus.INVALID_STREAM);
                 return;
             }
 
             // Check if we have received multiple frames for the same Stream-ID
             if (spdySession.hasReceivedReply(streamId)) {
                 issueStreamError(ctx, streamId, SpdyStreamStatus.STREAM_IN_USE);
                 return;
             }
 
             spdySession.receivedReply(streamId);
 
             // Close the remote side of the stream if this is the last frame
             if (spdySynReplyFrame.isLast()) {
                 halfCloseStream(streamId, true, ctx.newSucceededFuture());
             }
 
         } else if (msg instanceof SpdyRstStreamFrame) {
 
             /*
              * SPDY RST_STREAM frame processing requirements:
              *
              * After receiving a RST_STREAM on a stream, the receiver must not send
              * additional frames on that stream.
              *
              * An endpoint must not send a RST_STREAM in response to a RST_STREAM.
              */
 
             SpdyRstStreamFrame spdyRstStreamFrame = (SpdyRstStreamFrame) msg;
             removeStream(spdyRstStreamFrame.streamId(), ctx.newSucceededFuture());
 
         } else if (msg instanceof SpdySettingsFrame) {
 
             SpdySettingsFrame spdySettingsFrame = (SpdySettingsFrame) msg;
 
             int settingsMinorVersion = spdySettingsFrame.getValue(SpdySettingsFrame.SETTINGS_MINOR_VERSION);
             if (settingsMinorVersion >= 0 && settingsMinorVersion != minorVersion) {
                 // Settings frame had the wrong minor version
                 issueSessionError(ctx, SpdySessionStatus.PROTOCOL_ERROR);
                 return;
             }
 
             int newConcurrentStreams =
                 spdySettingsFrame.getValue(SpdySettingsFrame.SETTINGS_MAX_CONCURRENT_STREAMS);
             if (newConcurrentStreams >= 0) {
                 remoteConcurrentStreams = newConcurrentStreams;
             }
 
             // Persistence flag are inconsistent with the use of SETTINGS to communicate
             // the initial window size. Remove flags from the sender requesting that the
             // value be persisted. Remove values that the sender indicates are persisted.
             if (spdySettingsFrame.isPersisted(SpdySettingsFrame.SETTINGS_INITIAL_WINDOW_SIZE)) {
                 spdySettingsFrame.removeValue(SpdySettingsFrame.SETTINGS_INITIAL_WINDOW_SIZE);
             }
             spdySettingsFrame.setPersistValue(SpdySettingsFrame.SETTINGS_INITIAL_WINDOW_SIZE, false);
 
             int newInitialWindowSize =
                 spdySettingsFrame.getValue(SpdySettingsFrame.SETTINGS_INITIAL_WINDOW_SIZE);
             if (newInitialWindowSize >= 0) {
                 updateInitialSendWindowSize(newInitialWindowSize);
             }
 
         } else if (msg instanceof SpdyPingFrame) {
 
             /*
              * SPDY PING frame processing requirements:
              *
              * Receivers of a PING frame should send an identical frame to the sender
              * as soon as possible.
              *
              * Receivers of a PING frame must ignore frames that it did not initiate
              */
 
             SpdyPingFrame spdyPingFrame = (SpdyPingFrame) msg;
 
             if (isRemoteInitiatedId(spdyPingFrame.id())) {
                 ctx.writeAndFlush(spdyPingFrame);
                 return;
             }
 
             // Note: only checks that there are outstanding pings since uniqueness is not enforced
             if (pings.get() == 0) {
                 return;
             }
             pings.getAndDecrement();
 
         } else if (msg instanceof SpdyGoAwayFrame) {
 
             receivedGoAwayFrame = true;
 
         } else if (msg instanceof SpdyHeadersFrame) {
 
             SpdyHeadersFrame spdyHeadersFrame = (SpdyHeadersFrame) msg;
             int streamId = spdyHeadersFrame.streamId();
 
             // Check if we received a valid HEADERS frame
             if (spdyHeadersFrame.isInvalid()) {
                 issueStreamError(ctx, streamId, SpdyStreamStatus.PROTOCOL_ERROR);
                 return;
             }
 
             if (spdySession.isRemoteSideClosed(streamId)) {
                 issueStreamError(ctx, streamId, SpdyStreamStatus.INVALID_STREAM);
                 return;
             }
 
             // Close the remote side of the stream if this is the last frame
             if (spdyHeadersFrame.isLast()) {
                 halfCloseStream(streamId, true, ctx.newSucceededFuture());
             }
 
         } else if (msg instanceof SpdyWindowUpdateFrame) {
 
             /*
              * SPDY WINDOW_UPDATE frame processing requirements:
              *
              * Receivers of a WINDOW_UPDATE that cause the window size to exceed 2^31
              * must send a RST_STREAM with the getStatus code FLOW_CONTROL_ERROR.
              *
              * Sender should ignore all WINDOW_UPDATE frames associated with a stream
              * after sending the last frame for the stream.
              */
 
             SpdyWindowUpdateFrame spdyWindowUpdateFrame = (SpdyWindowUpdateFrame) msg;
             int streamId = spdyWindowUpdateFrame.streamId();
             int deltaWindowSize = spdyWindowUpdateFrame.deltaWindowSize();
 
             // Ignore frames for half-closed streams
             if (streamId != SPDY_SESSION_STREAM_ID && spdySession.isLocalSideClosed(streamId)) {
                 return;
             }
 
             // Check for numerical overflow
             if (spdySession.getSendWindowSize(streamId) > Integer.MAX_VALUE - deltaWindowSize) {
                 if (streamId == SPDY_SESSION_STREAM_ID) {
                     issueSessionError(ctx, SpdySessionStatus.PROTOCOL_ERROR);
                 } else {
                     issueStreamError(ctx, streamId, SpdyStreamStatus.FLOW_CONTROL_ERROR);
                 }
                 return;
             }
 
             updateSendWindowSize(ctx, streamId, deltaWindowSize);
         }
 
         ctx.fireChannelRead(msg);
     }
 
     @Override
     public void channelInactive(ChannelHandlerContext ctx) throws Exception {
         for (Integer streamId: spdySession.activeStreams().keySet()) {
             removeStream(streamId, ctx.newSucceededFuture());
         }
         ctx.fireChannelInactive();
     }
 
     @Override
     public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
         if (cause instanceof SpdyProtocolException) {
             issueSessionError(ctx, SpdySessionStatus.PROTOCOL_ERROR);
         }
 
         ctx.fireExceptionCaught(cause);
     }
 
     @Override
     public void close(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
         sendGoAwayFrame(ctx, promise);
     }
 
     @Override
     public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
         if (msg instanceof SpdyDataFrame ||
             msg instanceof SpdySynStreamFrame ||
             msg instanceof SpdySynReplyFrame ||
             msg instanceof SpdyRstStreamFrame ||
             msg instanceof SpdySettingsFrame ||
             msg instanceof SpdyPingFrame ||
             msg instanceof SpdyGoAwayFrame ||
             msg instanceof SpdyHeadersFrame ||
             msg instanceof SpdyWindowUpdateFrame) {
 
             handleOutboundMessage(ctx, msg, promise);
         } else {
             ctx.write(msg, promise);
         }
     }
 
     private void handleOutboundMessage(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
         if (msg instanceof SpdyDataFrame) {
 
             SpdyDataFrame spdyDataFrame = (SpdyDataFrame) msg;
             int streamId = spdyDataFrame.streamId();
 
             // Frames must not be sent on half-closed streams
             if (spdySession.isLocalSideClosed(streamId)) {
                 spdyDataFrame.release();
                 promise.setFailure(PROTOCOL_EXCEPTION);
                 return;
             }
 
             /*
              * SPDY Data frame flow control processing requirements:
              *
              * Sender must not send a data frame with data length greater
              * than the transfer window size.
              *
              * After sending each data frame, the sender decrements its
              * transfer window size by the amount of data transmitted.
              *
              * When the window size becomes less than or equal to 0, the
              * sender must pause transmitting data frames.
              */
 
             int dataLength = spdyDataFrame.content().readableBytes();
             int sendWindowSize = spdySession.getSendWindowSize(streamId);
             int sessionSendWindowSize = spdySession.getSendWindowSize(SPDY_SESSION_STREAM_ID);
             sendWindowSize = Math.min(sendWindowSize, sessionSendWindowSize);
 
             if (sendWindowSize <= 0) {
                 // Stream is stalled -- enqueue Data frame and return
                 spdySession.putPendingWrite(streamId, new SpdySession.PendingWrite(spdyDataFrame, promise));
                 return;
             } else if (sendWindowSize < dataLength) {
                 // Stream is not stalled but we cannot send the entire frame
                 spdySession.updateSendWindowSize(streamId, -1 * sendWindowSize);
                 spdySession.updateSendWindowSize(SPDY_SESSION_STREAM_ID, -1 * sendWindowSize);
 
                 // Create a partial data frame whose length is the current window size
                 SpdyDataFrame partialDataFrame = new DefaultSpdyDataFrame(
                         streamId, spdyDataFrame.content().readRetainedSlice(sendWindowSize));
 
                 // Enqueue the remaining data (will be the first frame queued)
                 spdySession.putPendingWrite(streamId, new SpdySession.PendingWrite(spdyDataFrame, promise));
 
                 // The transfer window size is pre-decremented when sending a data frame downstream.
                 // Close the session on write failures that leave the transfer window in a corrupt state.
                 final ChannelHandlerContext context = ctx;
                 ctx.write(partialDataFrame).addListener(future -> {
                     if (!future.isSuccess()) {
                         issueSessionError(context, SpdySessionStatus.INTERNAL_ERROR);
                     }
                 });
                 return;
             } else {
                 // Window size is large enough to send entire data frame
                 spdySession.updateSendWindowSize(streamId, -1 * dataLength);
                 spdySession.updateSendWindowSize(SPDY_SESSION_STREAM_ID, -1 * dataLength);
 
                 // The transfer window size is pre-decremented when sending a data frame downstream.
                 // Close the session on write failures that leave the transfer window in a corrupt state.
                 final ChannelHandlerContext context = ctx;
                 promise.addListener(future -> {
                     if (!future.isSuccess()) {
                         issueSessionError(context, SpdySessionStatus.INTERNAL_ERROR);
                     }
                 });
             }
 
             // Close the local side of the stream if this is the last frame
             if (spdyDataFrame.isLast()) {
                 halfCloseStream(streamId, false, promise);
             }
 
         } else if (msg instanceof SpdySynStreamFrame) {
 
             SpdySynStreamFrame spdySynStreamFrame = (SpdySynStreamFrame) msg;
             int streamId = spdySynStreamFrame.streamId();
 
             if (isRemoteInitiatedId(streamId)) {
                 promise.setFailure(PROTOCOL_EXCEPTION);
                 return;
             }
 
             byte priority = spdySynStreamFrame.priority();
             boolean remoteSideClosed = spdySynStreamFrame.isUnidirectional();
             boolean localSideClosed = spdySynStreamFrame.isLast();
             if (!acceptStream(streamId, priority, remoteSideClosed, localSideClosed)) {
                 promise.setFailure(PROTOCOL_EXCEPTION);
                 return;
             }
 
         } else if (msg instanceof SpdySynReplyFrame) {
 
             SpdySynReplyFrame spdySynReplyFrame = (SpdySynReplyFrame) msg;
             int streamId = spdySynReplyFrame.streamId();
 
             // Frames must not be sent on half-closed streams
             if (!isRemoteInitiatedId(streamId) || spdySession.isLocalSideClosed(streamId)) {
                 promise.setFailure(PROTOCOL_EXCEPTION);
                 return;
             }
 
             // Close the local side of the stream if this is the last frame
             if (spdySynReplyFrame.isLast()) {
                 halfCloseStream(streamId, false, promise);
             }
 
         } else if (msg instanceof SpdyRstStreamFrame) {
 
             SpdyRstStreamFrame spdyRstStreamFrame = (SpdyRstStreamFrame) msg;
             removeStream(spdyRstStreamFrame.streamId(), promise);
 
         } else if (msg instanceof SpdySettingsFrame) {
 
             SpdySettingsFrame spdySettingsFrame = (SpdySettingsFrame) msg;
 
             int settingsMinorVersion = spdySettingsFrame.getValue(SpdySettingsFrame.SETTINGS_MINOR_VERSION);
             if (settingsMinorVersion >= 0 && settingsMinorVersion != minorVersion) {
                 // Settings frame had the wrong minor version
                 promise.setFailure(PROTOCOL_EXCEPTION);
                 return;
             }
 
             int newConcurrentStreams =
                     spdySettingsFrame.getValue(SpdySettingsFrame.SETTINGS_MAX_CONCURRENT_STREAMS);
             if (newConcurrentStreams >= 0) {
                 localConcurrentStreams = newConcurrentStreams;
             }
 
             // Persistence flag are inconsistent with the use of SETTINGS to communicate
             // the initial window size. Remove flags from the sender requesting that the
             // value be persisted. Remove values that the sender indicates are persisted.
             if (spdySettingsFrame.isPersisted(SpdySettingsFrame.SETTINGS_INITIAL_WINDOW_SIZE)) {
                 spdySettingsFrame.removeValue(SpdySettingsFrame.SETTINGS_INITIAL_WINDOW_SIZE);
             }
             spdySettingsFrame.setPersistValue(SpdySettingsFrame.SETTINGS_INITIAL_WINDOW_SIZE, false);
 
             int newInitialWindowSize =
                     spdySettingsFrame.getValue(SpdySettingsFrame.SETTINGS_INITIAL_WINDOW_SIZE);
             if (newInitialWindowSize >= 0) {
                 updateInitialReceiveWindowSize(newInitialWindowSize);
             }
 
         } else if (msg instanceof SpdyPingFrame) {
 
             SpdyPingFrame spdyPingFrame = (SpdyPingFrame) msg;
             if (isRemoteInitiatedId(spdyPingFrame.id())) {
                 ctx.fireExceptionCaught(new IllegalArgumentException(
                             "invalid PING ID: " + spdyPingFrame.id()));
                 return;
             }
             pings.getAndIncrement();
 
         } else if (msg instanceof SpdyGoAwayFrame) {
 
             // Why is this being sent? Intercept it and fail the write.
             // Should have sent a CLOSE ChannelStateEvent
             promise.setFailure(PROTOCOL_EXCEPTION);
             return;
 
         } else if (msg instanceof SpdyHeadersFrame) {
 
             SpdyHeadersFrame spdyHeadersFrame = (SpdyHeadersFrame) msg;
             int streamId = spdyHeadersFrame.streamId();
 
             // Frames must not be sent on half-closed streams
             if (spdySession.isLocalSideClosed(streamId)) {
                 promise.setFailure(PROTOCOL_EXCEPTION);
                 return;
             }
 
             // Close the local side of the stream if this is the last frame
             if (spdyHeadersFrame.isLast()) {
                 halfCloseStream(streamId, false, promise);
             }
 
         } else if (msg instanceof SpdyWindowUpdateFrame) {
 
             // Why is this being sent? Intercept it and fail the write.
             promise.setFailure(PROTOCOL_EXCEPTION);
             return;
         }
 
         ctx.write(msg, promise);
     }
 
     /*
      * SPDY Session Error Handling:
      *
      * When a session error occurs, the endpoint encountering the error must first
      * send a GOAWAY frame with the Stream-ID of the most recently received stream
      * from the remote endpoint, and the error code for why the session is terminating.
      *
      * After sending the GOAWAY frame, the endpoint must close the TCP connection.
      */
     private void issueSessionError(
             ChannelHandlerContext ctx, SpdySessionStatus status) {
 
         sendGoAwayFrame(ctx, status).addListener(new ClosingChannelFutureListener(ctx, ctx.newPromise()));
     }
 
     /*
      * SPDY Stream Error Handling:
      *
      * Upon a stream error, the endpoint must send a RST_STREAM frame which contains
      * the Stream-ID for the stream where the error occurred and the error getStatus which
      * caused the error.
      *
      * After sending the RST_STREAM, the stream is closed to the sending endpoint.
      *
      * Note: this is only called by the worker thread
      */
     private void issueStreamError(ChannelHandlerContext ctx, int streamId, SpdyStreamStatus status) {
         boolean fireChannelRead = !spdySession.isRemoteSideClosed(streamId);
         ChannelPromise promise = ctx.newPromise();
         removeStream(streamId, promise);
 
         SpdyRstStreamFrame spdyRstStreamFrame = new DefaultSpdyRstStreamFrame(streamId, status);
         ctx.writeAndFlush(spdyRstStreamFrame, promise);
         if (fireChannelRead) {
             ctx.fireChannelRead(spdyRstStreamFrame);
         }
     }
 
     /*
      * Helper functions
      */
 
     private boolean isRemoteInitiatedId(int id) {
         boolean serverId = isServerId(id);
         return server && !serverId || !server && serverId;
     }
 
     // need to synchronize to prevent new streams from being created while updating active streams
     private void updateInitialSendWindowSize(int newInitialWindowSize) {
         int deltaWindowSize = newInitialWindowSize - initialSendWindowSize;
         initialSendWindowSize = newInitialWindowSize;
         spdySession.updateAllSendWindowSizes(deltaWindowSize);
     }
 
     // need to synchronize to prevent new streams from being created while updating active streams
     private void updateInitialReceiveWindowSize(int newInitialWindowSize) {
         int deltaWindowSize = newInitialWindowSize - initialReceiveWindowSize;
         initialReceiveWindowSize = newInitialWindowSize;
         spdySession.updateAllReceiveWindowSizes(deltaWindowSize);
     }
 
     // need to synchronize accesses to sentGoAwayFrame, lastGoodStreamId, and initial window sizes
     private boolean acceptStream(
             int streamId, byte priority, boolean remoteSideClosed, boolean localSideClosed) {
         // Cannot initiate any new streams after receiving or sending GOAWAY
         if (receivedGoAwayFrame || sentGoAwayFrame) {
             return false;
         }
 
         boolean remote = isRemoteInitiatedId(streamId);
         int maxConcurrentStreams = remote ? localConcurrentStreams : remoteConcurrentStreams;
         if (spdySession.numActiveStreams(remote) >= maxConcurrentStreams) {
             return false;
         }
         spdySession.acceptStream(
                 streamId, priority, remoteSideClosed, localSideClosed,
                 initialSendWindowSize, initialReceiveWindowSize, remote);
         if (remote) {
             lastGoodStreamId = streamId;
         }
         return true;
     }
 
     private void halfCloseStream(int streamId, boolean remote, ChannelFuture future) {
         if (remote) {
             spdySession.closeRemoteSide(streamId, isRemoteInitiatedId(streamId));
         } else {
             spdySession.closeLocalSide(streamId, isRemoteInitiatedId(streamId));
         }
         if (closeSessionFutureListener != null && spdySession.noActiveStreams()) {
             future.addListener(closeSessionFutureListener);
         }
     }
 
     private void removeStream(int streamId, ChannelFuture future) {
         spdySession.removeStream(streamId, STREAM_CLOSED, isRemoteInitiatedId(streamId));
 
         if (closeSessionFutureListener != null && spdySession.noActiveStreams()) {
             future.addListener(closeSessionFutureListener);
         }
     }
 
     private void updateSendWindowSize(final ChannelHandlerContext ctx, int streamId, int deltaWindowSize) {
         spdySession.updateSendWindowSize(streamId, deltaWindowSize);
 
         while (true) {
             // Check if we have unblocked a stalled stream
             SpdySession.PendingWrite pendingWrite = spdySession.getPendingWrite(streamId);
             if (pendingWrite == null) {
                 return;
             }
 
             SpdyDataFrame spdyDataFrame = pendingWrite.spdyDataFrame;
             int dataFrameSize = spdyDataFrame.content().readableBytes();
             int writeStreamId = spdyDataFrame.streamId();
             int sendWindowSize = spdySession.getSendWindowSize(writeStreamId);
             int sessionSendWindowSize = spdySession.getSendWindowSize(SPDY_SESSION_STREAM_ID);
             sendWindowSize = Math.min(sendWindowSize, sessionSendWindowSize);
 
             if (sendWindowSize <= 0) {
                 return;
             } else if (sendWindowSize < dataFrameSize) {
                 // We can send a partial frame
                 spdySession.updateSendWindowSize(writeStreamId, -1 * sendWindowSize);
                 spdySession.updateSendWindowSize(SPDY_SESSION_STREAM_ID, -1 * sendWindowSize);
 
                 // Create a partial data frame whose length is the current window size
                 SpdyDataFrame partialDataFrame = new DefaultSpdyDataFrame(
                         writeStreamId, spdyDataFrame.content().readRetainedSlice(sendWindowSize));
 
                 // The transfer window size is pre-decremented when sending a data frame downstream.
                 ctx.writeAndFlush(partialDataFrame).addListener(future -> {
                     if (!future.isSuccess()) {
                         issueSessionError(ctx, SpdySessionStatus.INTERNAL_ERROR);
                     }
                 });
             } else {
                 // Window size is large enough to send entire data frame
                 spdySession.removePendingWrite(writeStreamId);
                 spdySession.updateSendWindowSize(writeStreamId, -1 * dataFrameSize);
                 spdySession.updateSendWindowSize(SPDY_SESSION_STREAM_ID, -1 * dataFrameSize);
 
                 // Close the local side of the stream if this is the last frame
                 if (spdyDataFrame.isLast()) {
                     halfCloseStream(writeStreamId, false, pendingWrite.promise);
                 }
 
                 // The transfer window size is pre-decremented when sending a data frame downstream.
                 // Close the session on write failures that leave the transfer window in a corrupt state.
                 ctx.writeAndFlush(spdyDataFrame, pendingWrite.promise).addListener(future -> {
                     if (!future.isSuccess()) {
                         issueSessionError(ctx, SpdySessionStatus.INTERNAL_ERROR);
                     }
                 });
             }
         }
     }
 
     private void sendGoAwayFrame(ChannelHandlerContext ctx, ChannelPromise future) {
         // Avoid NotYetConnectedException
         if (!ctx.channel().isActive()) {
             ctx.close(future);
             return;
         }
 
         ChannelFuture f = sendGoAwayFrame(ctx, SpdySessionStatus.OK);
         if (spdySession.noActiveStreams()) {
             f.addListener(new ClosingChannelFutureListener(ctx, future));
         } else {
             closeSessionFutureListener = new ClosingChannelFutureListener(ctx, future);
         }
         // FIXME: Close the connection forcibly after timeout.
     }
 
     private ChannelFuture sendGoAwayFrame(
             ChannelHandlerContext ctx, SpdySessionStatus status) {
         if (!sentGoAwayFrame) {
             sentGoAwayFrame = true;
             SpdyGoAwayFrame spdyGoAwayFrame = new DefaultSpdyGoAwayFrame(lastGoodStreamId, status);
             return ctx.writeAndFlush(spdyGoAwayFrame);
         } else {
             return ctx.newSucceededFuture();
         }
     }
 
     private static final class ClosingChannelFutureListener implements ChannelFutureListener {
         private final ChannelHandlerContext ctx;
         private final ChannelPromise promise;
 
         ClosingChannelFutureListener(ChannelHandlerContext ctx, ChannelPromise promise) {
             this.ctx = ctx;
             this.promise = promise;
         }
 
         @Override
         public void operationComplete(ChannelFuture sentGoAwayFuture) throws Exception {
             ctx.close(promise);
         }
     }
 }