/*
    * Copyright 2012 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 org.jboss.netty.handler.codec.spdy;
  
  import static org.jboss.netty.handler.codec.spdy.SpdyCodecUtil.*;
  
  import java.net.SocketAddress;
  import java.nio.channels.ClosedChannelException;
  import java.util.concurrent.atomic.AtomicInteger;
  
  import org.jboss.netty.channel.Channel;
  import org.jboss.netty.channel.ChannelDownstreamHandler;
  import org.jboss.netty.channel.ChannelEvent;
  import org.jboss.netty.channel.ChannelFuture;
  import org.jboss.netty.channel.ChannelFutureListener;
  import org.jboss.netty.channel.ChannelHandlerContext;
  import org.jboss.netty.channel.ChannelStateEvent;
  import org.jboss.netty.channel.Channels;
  import org.jboss.netty.channel.ExceptionEvent;
  import org.jboss.netty.channel.MessageEvent;
  import org.jboss.netty.channel.SimpleChannelUpstreamHandler;
  
  /**
   * Manages streams within a SPDY session.
   */
  public class SpdySessionHandler extends SimpleChannelUpstreamHandler
          implements ChannelDownstreamHandler {
  
      private static final SpdyProtocolException PROTOCOL_EXCEPTION = new SpdyProtocolException();
  
      private final SpdySession spdySession = new SpdySession();
      private volatile int lastGoodStreamID;
  
      private volatile int remoteConcurrentStreams;
      private volatile int localConcurrentStreams;
      private volatile int maxConcurrentStreams;
  
      private static final int DEFAULT_WINDOW_SIZE = 64 * 1024; // 64 KB default initial window size
      private volatile int initialSendWindowSize = DEFAULT_WINDOW_SIZE;
      private volatile int initialReceiveWindowSize = DEFAULT_WINDOW_SIZE;
  
      private final Object flowControlLock = new Object();
  
      private final AtomicInteger pings = new AtomicInteger();
  
      private volatile boolean sentGoAwayFrame;
      private volatile boolean receivedGoAwayFrame;
  
      private volatile ChannelFuture closeSessionFuture;
  
      private final boolean server;
      private final boolean flowControl;
  
      /**
       * Creates a new SPDY/2 session handler.
       *
       * @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.
       */
      @Deprecated
      public SpdySessionHandler(boolean server) {
          this(2, server);
      }
  
      /**
       * 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.
       */
      public SpdySessionHandler(int version, boolean server) {
          if (version < SPDY_MIN_VERSION || version > SPDY_MAX_VERSION) {
              throw new IllegalArgumentException(
                      "unsupported version: " + version);
          }
          this.server = server;
          flowControl = version >= 3;
      }
  
      @Override
      public void messageReceived(ChannelHandlerContext ctx, MessageEvent e)
             throws Exception {
 
         Object msg = e.getMessage();
         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 status 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 status STREAM_ALREADY_CLOSED.
              *
              * If an endpoint receives a data frame after the stream is closed, it must send
              * a RST_STREAM frame with the status PROTOCOL_ERROR.
              */
 
             SpdyDataFrame spdyDataFrame = (SpdyDataFrame) msg;
             int streamID = spdyDataFrame.getStreamId();
 
             // Check if we received a data frame for a Stream-ID which is not open
             if (!spdySession.isActiveStream(streamID)) {
                 if (streamID <= lastGoodStreamID) {
                     issueStreamError(ctx, e.getRemoteAddress(), streamID, SpdyStreamStatus.PROTOCOL_ERROR);
                 } else if (!sentGoAwayFrame) {
                     issueStreamError(ctx, e.getRemoteAddress(), streamID, SpdyStreamStatus.INVALID_STREAM);
                 }
                 return;
             }
 
             // Check if we received a data frame for a stream which is half-closed
             if (spdySession.isRemoteSideClosed(streamID)) {
                 issueStreamError(ctx, e.getRemoteAddress(), streamID, SpdyStreamStatus.STREAM_ALREADY_CLOSED);
                 return;
             }
 
             // Check if we received a data frame before receiving a SYN_REPLY
             if (!isRemoteInitiatedID(streamID) && !spdySession.hasReceivedReply(streamID)) {
                 issueStreamError(ctx, e.getRemoteAddress(), 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.
             */
 
             if (flowControl) {
                 // Update receive window size
                 int deltaWindowSize = -1 * spdyDataFrame.getData().readableBytes();
                 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)) {
                     issueStreamError(ctx, e.getRemoteAddress(), 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.getData().readableBytes() > initialReceiveWindowSize) {
                         SpdyDataFrame partialDataFrame = new DefaultSpdyDataFrame(streamID);
                         partialDataFrame.setData(spdyDataFrame.getData().readSlice(initialReceiveWindowSize));
                         Channels.fireMessageReceived(ctx, partialDataFrame, e.getRemoteAddress());
                     }
                 }
 
                 // Send a WINDOW_UPDATE frame if less than half the window size remains
                 if (newWindowSize <= initialReceiveWindowSize / 2 && !spdyDataFrame.isLast()) {
                     deltaWindowSize = initialReceiveWindowSize - newWindowSize;
                     spdySession.updateReceiveWindowSize(streamID, deltaWindowSize);
                     SpdyWindowUpdateFrame spdyWindowUpdateFrame =
                             new DefaultSpdyWindowUpdateFrame(streamID, deltaWindowSize);
                     Channels.write(
                             ctx, Channels.future(e.getChannel()), spdyWindowUpdateFrame, e.getRemoteAddress());
                 }
             }
 
             // Close the remote side of the stream if this is the last frame
             if (spdyDataFrame.isLast()) {
                 halfCloseStream(streamID, true);
             }
 
         } 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 status PROTOCOL_ERROR.
              *
              * If an endpoint receives multiple SYN_STREAM frames with the same active
              * Stream-ID, it must issue a stream error with the status code PROTOCOL_ERROR.
              *
              * The recipient can reject a stream by sending a stream error with the
              * status code REFUSED_STREAM.
              */
 
             SpdySynStreamFrame spdySynStreamFrame = (SpdySynStreamFrame) msg;
             int streamID = spdySynStreamFrame.getStreamId();
 
             // Check if we received a valid SYN_STREAM frame
             if (spdySynStreamFrame.isInvalid() ||
                 !isRemoteInitiatedID(streamID) ||
                 spdySession.isActiveStream(streamID)) {
                 issueStreamError(ctx, e.getRemoteAddress(), streamID, SpdyStreamStatus.PROTOCOL_ERROR);
                 return;
             }
 
             // Stream-IDs must be monotonically increasing
             if (streamID <= lastGoodStreamID) {
                 issueSessionError(ctx, e.getChannel(), e.getRemoteAddress(), SpdySessionStatus.PROTOCOL_ERROR);
                 return;
             }
 
             // Try to accept the stream
             byte priority = spdySynStreamFrame.getPriority();
             boolean remoteSideClosed = spdySynStreamFrame.isLast();
             boolean localSideClosed = spdySynStreamFrame.isUnidirectional();
             if (!acceptStream(streamID, priority, remoteSideClosed, localSideClosed)) {
                 issueStreamError(ctx, e.getRemoteAddress(), 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 status code STREAM_IN_USE.
              */
 
             SpdySynReplyFrame spdySynReplyFrame = (SpdySynReplyFrame) msg;
             int streamID = spdySynReplyFrame.getStreamId();
 
             // Check if we received a valid SYN_REPLY frame
             if (spdySynReplyFrame.isInvalid() ||
                 isRemoteInitiatedID(streamID) ||
                 spdySession.isRemoteSideClosed(streamID)) {
                 issueStreamError(ctx, e.getRemoteAddress(), streamID, SpdyStreamStatus.INVALID_STREAM);
                 return;
             }
 
             // Check if we have received multiple frames for the same Stream-ID
             if (spdySession.hasReceivedReply(streamID)) {
                 issueStreamError(ctx, e.getRemoteAddress(), 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);
             }
 
         } 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.getStreamId());
 
         } else if (msg instanceof SpdySettingsFrame) {
 
             SpdySettingsFrame spdySettingsFrame = (SpdySettingsFrame) msg;
 
             int newConcurrentStreams =
                 spdySettingsFrame.getValue(SpdySettingsFrame.SETTINGS_MAX_CONCURRENT_STREAMS);
             if (newConcurrentStreams >= 0) {
                 updateConcurrentStreams(newConcurrentStreams, true);
             }
 
             // 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);
 
             if (flowControl) {
                 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.getId())) {
                 Channels.write(ctx, Channels.future(e.getChannel()), spdyPingFrame, e.getRemoteAddress());
                 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.getStreamId();
 
             // Check if we received a valid HEADERS frame
             if (spdyHeadersFrame.isInvalid()) {
                 issueStreamError(ctx, e.getRemoteAddress(), streamID, SpdyStreamStatus.PROTOCOL_ERROR);
                 return;
             }
 
             if (spdySession.isRemoteSideClosed(streamID)) {
                 issueStreamError(ctx, e.getRemoteAddress(), streamID, SpdyStreamStatus.INVALID_STREAM);
                 return;
             }
 
             // Close the remote side of the stream if this is the last frame
             if (spdyHeadersFrame.isLast()) {
                 halfCloseStream(streamID, true);
             }
 
         } 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 status code FLOW_CONTROL_ERROR.
              *
              * Sender should ignore all WINDOW_UPDATE frames associated with a stream
              * after sending the last frame for the stream.
              */
 
             if (flowControl) {
                 SpdyWindowUpdateFrame spdyWindowUpdateFrame = (SpdyWindowUpdateFrame) msg;
                 int streamID = spdyWindowUpdateFrame.getStreamId();
                 int deltaWindowSize = spdyWindowUpdateFrame.getDeltaWindowSize();
 
                 // Ignore frames for half-closed streams
                 if (spdySession.isLocalSideClosed(streamID)) {
                     return;
                 }
 
                 // Check for numerical overflow
                 if (spdySession.getSendWindowSize(streamID) > Integer.MAX_VALUE - deltaWindowSize) {
                     issueStreamError(ctx, e.getRemoteAddress(), streamID, SpdyStreamStatus.FLOW_CONTROL_ERROR);
                     return;
                 }
 
                 updateSendWindowSize(ctx, streamID, deltaWindowSize);
             }
             return;
         }
 
         super.messageReceived(ctx, e);
     }
 
     @Override
     public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e)
             throws Exception {
 
         Throwable cause = e.getCause();
         if (cause instanceof SpdyProtocolException) {
             issueSessionError(ctx, e.getChannel(), null, SpdySessionStatus.PROTOCOL_ERROR);
         }
 
         super.exceptionCaught(ctx, e);
     }
 
     public void handleDownstream(ChannelHandlerContext ctx, ChannelEvent evt)
             throws Exception {
         if (evt instanceof ChannelStateEvent) {
             ChannelStateEvent e = (ChannelStateEvent) evt;
             switch (e.getState()) {
             case OPEN:
             case CONNECTED:
             case BOUND:
 
                 /*
                  * SPDY connection requirements:
                  *
                  * When either endpoint closes the transport-level connection,
                  * it must first send a GOAWAY frame.
                  */
                 if (Boolean.FALSE.equals(e.getValue()) || e.getValue() == null) {
                     sendGoAwayFrame(ctx, e);
                     return;
                 }
             }
         }
         if (!(evt instanceof MessageEvent)) {
             ctx.sendDownstream(evt);
             return;
         }
 
         MessageEvent e = (MessageEvent) evt;
         Object msg = e.getMessage();
 
         if (msg instanceof SpdyDataFrame) {
 
             SpdyDataFrame spdyDataFrame = (SpdyDataFrame) msg;
             final int streamID = spdyDataFrame.getStreamId();
 
             // Frames must not be sent on half-closed streams
             if (spdySession.isLocalSideClosed(streamID)) {
                 e.getFuture().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.
              */
 
             if (flowControl) {
                 synchronized (flowControlLock) {
                     int dataLength = spdyDataFrame.getData().readableBytes();
                     int sendWindowSize = spdySession.getSendWindowSize(streamID);
 
                     if (sendWindowSize >= dataLength) {
                         // Window size is large enough to send entire data frame
                         spdySession.updateSendWindowSize(streamID, -1 * dataLength);
 
                         // The transfer window size is pre-decremented when sending a data frame downstream.
                         // Close the stream on write failures that leaves the transfer window in a corrupt state.
                         final SocketAddress remoteAddress = e.getRemoteAddress();
                         final ChannelHandlerContext context = ctx;
                         e.getFuture().addListener(new ChannelFutureListener() {
                             public void operationComplete(ChannelFuture future) throws Exception {
                                 if (!future.isSuccess()) {
                                     issueStreamError(
                                             context, remoteAddress, streamID, SpdyStreamStatus.INTERNAL_ERROR);
                                 }
                             }
                         });
 
                     } else if (sendWindowSize > 0) {
                         // Stream is not stalled but we cannot send the entire frame
                         spdySession.updateSendWindowSize(streamID, -1 * sendWindowSize);
 
                         // Create a partial data frame whose length is the current window size
                         SpdyDataFrame partialDataFrame = new DefaultSpdyDataFrame(streamID);
                         partialDataFrame.setData(spdyDataFrame.getData().readSlice(sendWindowSize));
 
                         // Enqueue the remaining data (will be the first frame queued)
                         spdySession.putPendingWrite(streamID, e);
 
                         ChannelFuture writeFuture = Channels.future(e.getChannel());
 
                         // The transfer window size is pre-decremented when sending a data frame downstream.
                         // Close the stream on write failures that leaves the transfer window in a corrupt state.
                         final SocketAddress remoteAddress = e.getRemoteAddress();
                         final ChannelHandlerContext context = ctx;
                         e.getFuture().addListener(new ChannelFutureListener() {
                             public void operationComplete(ChannelFuture future) throws Exception {
                                 if (!future.isSuccess()) {
                                     issueStreamError(
                                             context, remoteAddress, streamID, SpdyStreamStatus.INTERNAL_ERROR);
                                 }
                             }
                         });
 
                         Channels.write(ctx, writeFuture, partialDataFrame, remoteAddress);
                         return;
 
                     } else {
                         // Stream is stalled -- enqueue Data frame and return
                         spdySession.putPendingWrite(streamID, e);
                         return;
                     }
                 }
             }
 
             // Close the local side of the stream if this is the last frame
             if (spdyDataFrame.isLast()) {
                 halfCloseStream(streamID, false);
             }
 
         } else if (msg instanceof SpdySynStreamFrame) {
 
             SpdySynStreamFrame spdySynStreamFrame = (SpdySynStreamFrame) msg;
             int streamID = spdySynStreamFrame.getStreamId();
 
             if (isRemoteInitiatedID(streamID)) {
                 e.getFuture().setFailure(PROTOCOL_EXCEPTION);
                 return;
             }
 
             byte priority = spdySynStreamFrame.getPriority();
             boolean remoteSideClosed = spdySynStreamFrame.isUnidirectional();
             boolean localSideClosed = spdySynStreamFrame.isLast();
             if (!acceptStream(streamID, priority, remoteSideClosed, localSideClosed)) {
                 e.getFuture().setFailure(PROTOCOL_EXCEPTION);
                 return;
             }
 
         } else if (msg instanceof SpdySynReplyFrame) {
 
             SpdySynReplyFrame spdySynReplyFrame = (SpdySynReplyFrame) msg;
             int streamID = spdySynReplyFrame.getStreamId();
 
             // Frames must not be sent on half-closed streams
             if (!isRemoteInitiatedID(streamID) || spdySession.isLocalSideClosed(streamID)) {
                 e.getFuture().setFailure(PROTOCOL_EXCEPTION);
                 return;
             }
 
             // Close the local side of the stream if this is the last frame
             if (spdySynReplyFrame.isLast()) {
                 halfCloseStream(streamID, false);
             }
 
         } else if (msg instanceof SpdyRstStreamFrame) {
 
             SpdyRstStreamFrame spdyRstStreamFrame = (SpdyRstStreamFrame) msg;
             removeStream(spdyRstStreamFrame.getStreamId());
 
         } else if (msg instanceof SpdySettingsFrame) {
 
             SpdySettingsFrame spdySettingsFrame = (SpdySettingsFrame) msg;
 
             int newConcurrentStreams =
                     spdySettingsFrame.getValue(SpdySettingsFrame.SETTINGS_MAX_CONCURRENT_STREAMS);
             if (newConcurrentStreams >= 0) {
                 updateConcurrentStreams(newConcurrentStreams, false);
             }
 
             // 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);
 
             if (flowControl) {
                 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.getId())) {
                 e.getFuture().setFailure(new IllegalArgumentException(
                             "invalid PING ID: " + spdyPingFrame.getId()));
                 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
             e.getFuture().setFailure(PROTOCOL_EXCEPTION);
             return;
 
         } else if (msg instanceof SpdyHeadersFrame) {
 
             SpdyHeadersFrame spdyHeadersFrame = (SpdyHeadersFrame) msg;
             int streamID = spdyHeadersFrame.getStreamId();
 
             // Frames must not be sent on half-closed streams
             if (spdySession.isLocalSideClosed(streamID)) {
                 e.getFuture().setFailure(PROTOCOL_EXCEPTION);
                 return;
             }
 
             // Close the local side of the stream if this is the last frame
             if (spdyHeadersFrame.isLast()) {
                 halfCloseStream(streamID, false);
             }
 
         } else if (msg instanceof SpdyWindowUpdateFrame) {
 
             // Why is this being sent? Intercept it and fail the write.
             e.getFuture().setFailure(PROTOCOL_EXCEPTION);
             return;
         }
 
         ctx.sendDownstream(evt);
     }
 
     /*
      * 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, Channel channel, SocketAddress remoteAddress, SpdySessionStatus status) {
 
         ChannelFuture future = sendGoAwayFrame(ctx, channel, remoteAddress, status);
         future.addListener(ChannelFutureListener.CLOSE);
     }
 
     /*
      * 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 status 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, SocketAddress remoteAddress, int streamID, SpdyStreamStatus status) {
 
         boolean fireMessageReceived = !spdySession.isRemoteSideClosed(streamID);
         removeStream(streamID);
 
         SpdyRstStreamFrame spdyRstStreamFrame = new DefaultSpdyRstStreamFrame(streamID, status);
         Channels.write(ctx, Channels.future(ctx.getChannel()), spdyRstStreamFrame, remoteAddress);
         if (fireMessageReceived) {
             Channels.fireMessageReceived(ctx, spdyRstStreamFrame, remoteAddress);
         }
     }
 
     /*
      * Helper functions
      */
 
     private boolean isRemoteInitiatedID(int id) {
         boolean serverID = isServerId(id);
         return server && !serverID || !server && serverID;
     }
 
     private void updateConcurrentStreams(int newConcurrentStreams, boolean remote) {
         if (remote) {
             remoteConcurrentStreams = newConcurrentStreams;
         } else {
             localConcurrentStreams = newConcurrentStreams;
         }
         if (localConcurrentStreams == remoteConcurrentStreams) {
             maxConcurrentStreams = localConcurrentStreams;
             return;
         }
         if (localConcurrentStreams == 0) {
             maxConcurrentStreams = remoteConcurrentStreams;
             return;
         }
         if (remoteConcurrentStreams == 0) {
             maxConcurrentStreams = localConcurrentStreams;
             return;
         }
         if (localConcurrentStreams > remoteConcurrentStreams) {
             maxConcurrentStreams = remoteConcurrentStreams;
         } else {
             maxConcurrentStreams = localConcurrentStreams;
         }
     }
 
     // need to synchronize to prevent new streams from being created while updating active streams
     private synchronized void updateInitialSendWindowSize(int newInitialWindowSize) {
         int deltaWindowSize = newInitialWindowSize - initialSendWindowSize;
         initialSendWindowSize = newInitialWindowSize;
         for (Integer StreamID: spdySession.getActiveStreams()) {
             spdySession.updateSendWindowSize(StreamID.intValue(), deltaWindowSize);
         }
     }
 
     // need to synchronize to prevent new streams from being created while updating active streams
     private synchronized 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 synchronized 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;
         }
 
         int maxConcurrentStreams = this.maxConcurrentStreams; // read volatile once
         if (maxConcurrentStreams != 0 &&
            spdySession.numActiveStreams() >= maxConcurrentStreams) {
             return false;
         }
         spdySession.acceptStream(
                 streamID, priority, remoteSideClosed, localSideClosed,
                 initialSendWindowSize, initialReceiveWindowSize);
         if (isRemoteInitiatedID(streamID)) {
             lastGoodStreamID = streamID;
         }
         return true;
     }
 
     private void halfCloseStream(int streamID, boolean remote) {
         if (remote) {
             spdySession.closeRemoteSide(streamID);
         } else {
             spdySession.closeLocalSide(streamID);
         }
         if (closeSessionFuture != null && spdySession.noActiveStreams()) {
             closeSessionFuture.setSuccess();
         }
     }
 
     private void removeStream(int streamID) {
         spdySession.removeStream(streamID);
         if (closeSessionFuture != null && spdySession.noActiveStreams()) {
             closeSessionFuture.setSuccess();
         }
     }
 
     private void updateSendWindowSize(ChannelHandlerContext ctx, final int streamID, int deltaWindowSize) {
         synchronized (flowControlLock) {
             int newWindowSize = spdySession.updateSendWindowSize(streamID, deltaWindowSize);
 
             while (newWindowSize > 0) {
                 // Check if we have unblocked a stalled stream
                 MessageEvent e = spdySession.getPendingWrite(streamID);
                 if (e == null) {
                     break;
                 }
 
                 SpdyDataFrame spdyDataFrame = (SpdyDataFrame) e.getMessage();
                 int dataFrameSize = spdyDataFrame.getData().readableBytes();
 
                 if (newWindowSize >= dataFrameSize) {
                     // Window size is large enough to send entire data frame
                     spdySession.removePendingWrite(streamID);
                     newWindowSize = spdySession.updateSendWindowSize(streamID, -1 * dataFrameSize);
 
                     // The transfer window size is pre-decremented when sending a data frame downstream.
                     // Close the stream on write failures that leaves the transfer window in a corrupt state.
                     final SocketAddress remoteAddress = e.getRemoteAddress();
                     final ChannelHandlerContext context = ctx;
                     e.getFuture().addListener(new ChannelFutureListener() {
                         public void operationComplete(ChannelFuture future) throws Exception {
                             if (!future.isSuccess()) {
                                 issueStreamError(context, remoteAddress, streamID, SpdyStreamStatus.INTERNAL_ERROR);
                             }
                         }
                     });
 
                     // Close the local side of the stream if this is the last frame
                     if (spdyDataFrame.isLast()) {
                         halfCloseStream(streamID, false);
                     }
 
                     Channels.write(ctx, e.getFuture(), spdyDataFrame, e.getRemoteAddress());
 
                 } else {
                     // We can send a partial frame
                     spdySession.updateSendWindowSize(streamID, -1 * newWindowSize);
 
                     // Create a partial data frame whose length is the current window size
                     SpdyDataFrame partialDataFrame = new DefaultSpdyDataFrame(streamID);
                     partialDataFrame.setData(spdyDataFrame.getData().readSlice(newWindowSize));
 
                     ChannelFuture writeFuture = Channels.future(e.getChannel());
 
                     // The transfer window size is pre-decremented when sending a data frame downstream.
                     // Close the stream on write failures that leaves the transfer window in a corrupt state.
                     final SocketAddress remoteAddress = e.getRemoteAddress();
                     final ChannelHandlerContext context = ctx;
                     e.getFuture().addListener(new ChannelFutureListener() {
                         public void operationComplete(ChannelFuture future) throws Exception {
                             if (!future.isSuccess()) {
                                 issueStreamError(context, remoteAddress, streamID, SpdyStreamStatus.INTERNAL_ERROR);
                             }
                         }
                     });
 
                     Channels.write(ctx, writeFuture, partialDataFrame, remoteAddress);
 
                     newWindowSize = 0;
                 }
             }
         }
     }
 
     private void sendGoAwayFrame(ChannelHandlerContext ctx, ChannelStateEvent e) {
         // Avoid NotYetConnectedException
         if (!e.getChannel().isConnected()) {
             ctx.sendDownstream(e);
             return;
         }
 
         ChannelFuture future = sendGoAwayFrame(ctx, e.getChannel(), null, SpdySessionStatus.OK);
         if (spdySession.noActiveStreams()) {
             future.addListener(new ClosingChannelFutureListener(ctx, e));
         } else {
             closeSessionFuture = Channels.future(e.getChannel());
             closeSessionFuture.addListener(new ClosingChannelFutureListener(ctx, e));
         }
     }
 
     private synchronized ChannelFuture sendGoAwayFrame(
             ChannelHandlerContext ctx, Channel channel, SocketAddress remoteAddress, SpdySessionStatus status) {
         if (!sentGoAwayFrame) {
             sentGoAwayFrame = true;
             SpdyGoAwayFrame spdyGoAwayFrame = new DefaultSpdyGoAwayFrame(lastGoodStreamID, status);
             ChannelFuture future = Channels.future(channel);
             Channels.write(ctx, future, spdyGoAwayFrame, remoteAddress);
             return future;
         }
         return Channels.succeededFuture(channel);
     }
 
     private static final class ClosingChannelFutureListener implements ChannelFutureListener {
         private final ChannelHandlerContext ctx;
         private final ChannelStateEvent e;
 
         ClosingChannelFutureListener(ChannelHandlerContext ctx, ChannelStateEvent e) {
             this.ctx = ctx;
             this.e = e;
         }
 
         public void operationComplete(ChannelFuture sentGoAwayFuture) throws Exception {
             if (!(sentGoAwayFuture.getCause() instanceof ClosedChannelException)) {
                 Channels.close(ctx, e.getFuture());
             } else {
                 e.getFuture().setSuccess();
             }
         }
     }
 }