XiuXianProject/GameClient/Packages/BestHTTP/Source/Connections/HTTP2/HTTP2Stream.cs

#if (!UNITY_WEBGL || UNITY_EDITOR) && !BESTHTTP_DISABLE_ALTERNATE_SSL && !BESTHTTP_DISABLE_HTTP2

using System;
using System.Collections.Generic;
using BestHTTP.Core;
using BestHTTP.PlatformSupport.Memory;
using BestHTTP.Logger;

#if !BESTHTTP_DISABLE_CACHING
using BestHTTP.Caching;
#endif

using BestHTTP.Timings;

namespace BestHTTP.Connections.HTTP2
{
    // https://httpwg.org/specs/rfc7540.html#StreamStates
    //
    //                                      Idle
    //                                       |
    //                                       V
    //                                      Open
    //                Receive END_STREAM  /  |   \  Send END_STREAM
    //                                   v   |R   V
    //                  Half Closed Remote   |S   Half Closed Locale
    //                                   \   |T  /
    //     Send END_STREAM | RST_STREAM   \  |  /    Receive END_STREAM | RST_STREAM
    //     Receive RST_STREAM              \ | /     Send RST_STREAM
    //                                       V
    //                                     Closed
    // 
    // IDLE -> send headers -> OPEN -> send data -> HALF CLOSED - LOCAL -> receive headers -> receive Data -> CLOSED
    //               |                                     ^                      |                             ^
    //               +-------------------------------------+                      +-----------------------------+
    //                      END_STREAM flag present?                                   END_STREAM flag present?
    //

    public enum HTTP2StreamStates
    {
        Idle,
        //ReservedLocale,
        //ReservedRemote,
        Open,
        HalfClosedLocal,
        HalfClosedRemote,
        Closed
    }

    public class HTTP2Stream
    {
        public UInt32 Id { get; private set; }

        public HTTP2StreamStates State {
            get { return this._state; }

            protected set {
                var oldState = this._state;

                this._state = value;

                if (oldState != this._state)
                {
                    //this.lastStateChangedAt = DateTime.Now;

                    HTTPManager.Logger.Information("HTTP2Stream", string.Format("[{0}] State changed from {1} to {2}", this.Id, oldState, this._state), this.Context, this.AssignedRequest.Context, this.parent.Context);
                }
            }
        }
        private HTTP2StreamStates _state;

        //protected DateTime lastStateChangedAt;
        //protected TimeSpan TimeSpentInCurrentState { get { return DateTime.Now - this.lastStateChangedAt; } }

        /// <summary>
        /// This flag is checked by the connection to decide whether to do a new processing-frame sending round before sleeping until new data arrives
        /// </summary>
        public virtual bool HasFrameToSend
        {
            get
            {
                // Don't let the connection sleep until
                return this.outgoing.Count > 0 || // we already booked at least one frame in advance
                       (this.State == HTTP2StreamStates.Open && this.remoteWindow > 0 && this.lastReadCount > 0); // we are in the middle of sending request data
            }
        }

        /// <summary>
        /// Next interaction scheduled by the stream relative to *now*. Its default is TimeSpan.MaxValue == no interaction.
        /// </summary>
        public virtual TimeSpan NextInteraction { get; } = TimeSpan.MaxValue;

        public HTTPRequest AssignedRequest { get; protected set; }

        public LoggingContext Context { get; protected set; }

        protected bool isStreamedDownload;
        protected uint downloaded;

        protected HTTPRequest.UploadStreamInfo uploadStreamInfo;

        protected HTTP2SettingsManager settings;
        protected HPACKEncoder encoder;

        // Outgoing frames. The stream will send one frame per Process call, but because one step might be able to
        // generate more than one frames, we use a list.
        protected Queue<HTTP2FrameHeaderAndPayload> outgoing = new Queue<HTTP2FrameHeaderAndPayload>();

        protected Queue<HTTP2FrameHeaderAndPayload> incomingFrames = new Queue<HTTP2FrameHeaderAndPayload>();

        protected FramesAsStreamView headerView;
        protected FramesAsStreamView dataView;

        protected UInt32 localWindow;
        protected Int64 remoteWindow;

        protected uint windowUpdateThreshold;

        protected UInt32 sentData;

        protected bool isRSTFrameSent;
        protected bool isEndSTRReceived;

        protected HTTP2Response response;

        protected HTTP2Handler parent;
        protected int lastReadCount;

        /// <summary>
        /// Constructor to create a client stream.
        /// </summary>
        public HTTP2Stream(UInt32 id, HTTP2Handler parentHandler, HTTP2SettingsManager registry, HPACKEncoder hpackEncoder)
        {
            this.Id = id;
            this.parent = parentHandler;
            this.settings = registry;
            this.encoder = hpackEncoder;

            this.remoteWindow = this.settings.RemoteSettings[HTTP2Settings.INITIAL_WINDOW_SIZE];
            this.settings.RemoteSettings.OnSettingChangedEvent += OnRemoteSettingChanged;

            // Room for improvement: If INITIAL_WINDOW_SIZE is small (what we can consider a 'small' value?), threshold must be higher
            this.windowUpdateThreshold = (uint)(this.remoteWindow / 2);

            this.Context = new LoggingContext(this);
            this.Context.Add("id", id);
        }

        public virtual void Assign(HTTPRequest request)
        {
            if (request.IsRedirected)
                request.Timing.Add(TimingEventNames.Queued_For_Redirection);
            else
                request.Timing.Add(TimingEventNames.Queued);

            HTTPManager.Logger.Information("HTTP2Stream", string.Format("[{0}] Request assigned to stream. Remote Window: {1:N0}. Uri: {2}", this.Id, this.remoteWindow, request.CurrentUri.ToString()), this.Context, request.Context, this.parent.Context);
            this.AssignedRequest = request;
            this.isStreamedDownload = request.UseStreaming && request.OnStreamingData != null;
            this.downloaded = 0;
        }

        public void Process(List<HTTP2FrameHeaderAndPayload> outgoingFrames)
        {
            if (this.AssignedRequest.IsCancellationRequested && !this.isRSTFrameSent)
            {
                // These two are already set in HTTPRequest's Abort().
                //this.AssignedRequest.Response = null;
                //this.AssignedRequest.State = this.AssignedRequest.IsTimedOut ? HTTPRequestStates.TimedOut : HTTPRequestStates.Aborted;

                this.outgoing.Clear();
                if (this.State != HTTP2StreamStates.Idle)
                    this.outgoing.Enqueue(HTTP2FrameHelper.CreateRSTFrame(this.Id, HTTP2ErrorCodes.CANCEL));

                // We can close the stream if already received headers, or not even sent one
                if (this.State == HTTP2StreamStates.HalfClosedRemote || this.State == HTTP2StreamStates.Idle)
                    this.State = HTTP2StreamStates.Closed;

                this.isRSTFrameSent = true;
            }

            // 1.) Go through incoming frames
            ProcessIncomingFrames(outgoingFrames);

            // 2.) Create outgoing frames based on the stream's state and the request processing state.
            ProcessState(outgoingFrames);

            // 3.) Send one frame per Process call
            if (this.outgoing.Count > 0)
            {
                HTTP2FrameHeaderAndPayload frame = this.outgoing.Dequeue();

                outgoingFrames.Add(frame);

                // If END_Stream in header or data frame is present => half closed local
                if ((frame.Type == HTTP2FrameTypes.HEADERS && (frame.Flags & (byte)HTTP2HeadersFlags.END_STREAM) != 0) ||
                    (frame.Type == HTTP2FrameTypes.DATA && (frame.Flags & (byte)HTTP2DataFlags.END_STREAM) != 0))
                {
                    this.State = HTTP2StreamStates.HalfClosedLocal;
                }
            }
        }

        public void AddFrame(HTTP2FrameHeaderAndPayload frame, List<HTTP2FrameHeaderAndPayload> outgoingFrames)
        {
            // Room for improvement: error check for forbidden frames (like settings) and stream state

            this.incomingFrames.Enqueue(frame);

            ProcessIncomingFrames(outgoingFrames);
        }

        public void Abort(string msg)
        {
            if (this.AssignedRequest.State != HTTPRequestStates.Processing)
            {
                // do nothing, its state is already set.
            }
            else if (this.AssignedRequest.IsCancellationRequested)
            {
                // These two are already set in HTTPRequest's Abort().
                //this.AssignedRequest.Response = null;
                //this.AssignedRequest.State = this.AssignedRequest.IsTimedOut ? HTTPRequestStates.TimedOut : HTTPRequestStates.Aborted;

                this.State = HTTP2StreamStates.Closed;
            }
            else if (this.AssignedRequest.Retries >= this.AssignedRequest.MaxRetries)
            {
                this.AssignedRequest.Response = null;
                this.AssignedRequest.Exception = new Exception(msg);
                this.AssignedRequest.State = HTTPRequestStates.Error;

                this.State = HTTP2StreamStates.Closed;
            }
            else
            {
                this.AssignedRequest.Retries++;
                RequestEventHelper.EnqueueRequestEvent(new RequestEventInfo(this.AssignedRequest, RequestEvents.Resend));
            }

            this.Removed();
        }

        protected void ProcessIncomingFrames(List<HTTP2FrameHeaderAndPayload> outgoingFrames)
        {
            UInt32 windowUpdate = 0;

            while (this.incomingFrames.Count > 0)
            {
                HTTP2FrameHeaderAndPayload frame = this.incomingFrames.Dequeue();

                if ((this.isRSTFrameSent || this.AssignedRequest.IsCancellationRequested) && frame.Type != HTTP2FrameTypes.HEADERS && frame.Type != HTTP2FrameTypes.CONTINUATION)
                {
                    BufferPool.Release(frame.Payload);
                    continue;
                }

                if (/*HTTPManager.Logger.Level == Logger.Loglevels.All && */frame.Type != HTTP2FrameTypes.DATA && frame.Type != HTTP2FrameTypes.WINDOW_UPDATE)
                    HTTPManager.Logger.Information("HTTP2Stream", string.Format("[{0}] Process - processing frame: {1}", this.Id, frame.ToString()), this.Context, this.AssignedRequest.Context, this.parent.Context);

                switch (frame.Type)
                {
                    case HTTP2FrameTypes.HEADERS:
                    case HTTP2FrameTypes.CONTINUATION:
                        if (this.State != HTTP2StreamStates.HalfClosedLocal && this.State != HTTP2StreamStates.Open && this.State != HTTP2StreamStates.Idle)
                        {
                            // ERROR!
                            continue;
                        }

                        // payload will be released by the view
                        frame.DontUseMemPool = true;

                        if (this.headerView == null)
                        {
                            this.AssignedRequest.Timing.Add(TimingEventNames.Waiting_TTFB);
                            this.headerView = new FramesAsStreamView(new HeaderFrameView());
                        }

                        this.headerView.AddFrame(frame);

                        // END_STREAM may arrive sooner than an END_HEADERS, so we have to store that we already received it
                        if ((frame.Flags & (byte)HTTP2HeadersFlags.END_STREAM) != 0)
                            this.isEndSTRReceived = true;

                        if ((frame.Flags & (byte)HTTP2HeadersFlags.END_HEADERS) != 0)
                        {
                            List<KeyValuePair<string, string>> headers = new List<KeyValuePair<string, string>>();

                            try
                            {
                                this.encoder.Decode(this, this.headerView, headers);
                            }
                            catch(Exception ex)
                            {
                                HTTPManager.Logger.Exception("HTTP2Stream", string.Format("[{0}] ProcessIncomingFrames - Header Frames: {1}, Encoder: {2}", this.Id, this.headerView.ToString(), this.encoder.ToString()), ex, this.Context, this.AssignedRequest.Context, this.parent.Context);
                            }

                            this.headerView.Close();
                            this.headerView = null;

                            this.AssignedRequest.Timing.Add(TimingEventNames.Headers);

                            if (this.isRSTFrameSent)
                            {
                                this.State = HTTP2StreamStates.Closed;
                                break;
                            }

                            if (this.response == null)
                                this.AssignedRequest.Response = this.response = new HTTP2Response(this.AssignedRequest, false);

                            this.response.AddHeaders(headers);

                            if (this.isEndSTRReceived)
                            {
                                // If there's any trailing header, no data frame has an END_STREAM flag
                                if (this.isStreamedDownload)
                                    this.response.FinishProcessData();

                                PlatformSupport.Threading.ThreadedRunner.RunShortLiving<HTTP2Stream, FramesAsStreamView>(FinishRequest, this, this.dataView);

                                this.dataView = null;

                                if (this.State == HTTP2StreamStates.HalfClosedLocal)
                                    this.State = HTTP2StreamStates.Closed;
                                else
                                    this.State = HTTP2StreamStates.HalfClosedRemote;
                            }
                        }
                        break;

                    case HTTP2FrameTypes.DATA:
                        ProcessIncomingDATAFrame(ref frame, ref windowUpdate);
                        break;

                    case HTTP2FrameTypes.WINDOW_UPDATE:
                        HTTP2WindowUpdateFrame windowUpdateFrame = HTTP2FrameHelper.ReadWindowUpdateFrame(frame);

                        if (HTTPManager.Logger.Level == Logger.Loglevels.All)
                            HTTPManager.Logger.Information("HTTP2Stream", string.Format("[{0}] Received Window Update: {1:N0}, new remoteWindow: {2:N0}, initial remote window: {3:N0}, total data sent: {4:N0}", this.Id, windowUpdateFrame.WindowSizeIncrement, this.remoteWindow + windowUpdateFrame.WindowSizeIncrement, this.settings.RemoteSettings[HTTP2Settings.INITIAL_WINDOW_SIZE], this.sentData), this.Context, this.AssignedRequest.Context, this.parent.Context);

                        this.remoteWindow += windowUpdateFrame.WindowSizeIncrement;
                        break;

                    case HTTP2FrameTypes.RST_STREAM:
                        // https://httpwg.org/specs/rfc7540.html#RST_STREAM

                        // It's possible to receive an RST_STREAM on a closed stream. In this case, we have to ignore it.
                        if (this.State == HTTP2StreamStates.Closed)
                            break;

                        var rstStreamFrame = HTTP2FrameHelper.ReadRST_StreamFrame(frame);

                        //HTTPManager.Logger.Error("HTTP2Stream", string.Format("[{0}] RST Stream frame ({1}) received in state {2}!", this.Id, rstStreamFrame, this.State), this.Context, this.AssignedRequest.Context, this.parent.Context);

                        Abort(string.Format("RST_STREAM frame received! Error code: {0}({1})", rstStreamFrame.Error.ToString(), rstStreamFrame.ErrorCode));
                        break;

                    default:
                        HTTPManager.Logger.Warning("HTTP2Stream", string.Format("[{0}] Unexpected frame ({1}, Payload: {2}) in state {3}!", this.Id, frame, frame.PayloadAsHex(), this.State), this.Context, this.AssignedRequest.Context, this.parent.Context);
                        break;
                }

                if (!frame.DontUseMemPool)
                    BufferPool.Release(frame.Payload);
            }

            // 2023.07.08: Even if State is Closed, we should send back a window update.
            // Not because of this stream, but for the global window update.
            if (windowUpdate > 0 /*&& this.State != HTTP2StreamStates.Closed*/)
            {
                if (HTTPManager.Logger.Level <= Logger.Loglevels.All)
                    HTTPManager.Logger.Information("HTTP2Stream", string.Format("[{0}] Sending window update: {1:N0}, current window: {2:N0}, initial window size: {3:N0}", this.Id, windowUpdate, this.localWindow, this.settings.MySettings[HTTP2Settings.INITIAL_WINDOW_SIZE]), this.Context, this.AssignedRequest.Context, this.parent.Context);

                this.localWindow += windowUpdate;

                outgoingFrames.Add(HTTP2FrameHelper.CreateWindowUpdateFrame(this.Id, windowUpdate));
            }
        }

        protected virtual void ProcessIncomingDATAFrame(ref HTTP2FrameHeaderAndPayload frame, ref uint windowUpdate)
        {
            if (this.State != HTTP2StreamStates.HalfClosedLocal && this.State != HTTP2StreamStates.Open)
            {
                // ERROR!
                return;
            }

            this.downloaded += frame.PayloadLength;

            if (this.isStreamedDownload && frame.Payload != null && frame.PayloadLength > 0)
                this.response.ProcessData(frame.Payload, (int)frame.PayloadLength);

            // frame's buffer will be released by the frames view
            frame.DontUseMemPool = !this.isStreamedDownload;

            if (this.dataView == null && !this.isStreamedDownload)
                this.dataView = new FramesAsStreamView(new DataFrameView());

            if (!this.isStreamedDownload)
                this.dataView.AddFrame(frame);

            // Track received data, and if necessary(local window getting too low), send a window update frame
            if (this.localWindow < frame.PayloadLength)
            {
                HTTPManager.Logger.Error("HTTP2Stream", string.Format("[{0}] Frame's PayloadLength ({1:N0}) is larger then local window ({2:N0}). Frame: {3}", this.Id, frame.PayloadLength, this.localWindow, frame), this.Context, this.AssignedRequest.Context, this.parent.Context);
            }
            else
                this.localWindow -= frame.PayloadLength;

            if ((frame.Flags & (byte)HTTP2DataFlags.END_STREAM) != 0)
                this.isEndSTRReceived = true;

            // Window update logic.
            //  1.) We could use a logic to only send window update(s) after a threshold is reached.
            //      When the initial window size is high enough to contain the whole or most of the result,
            //      sending back two window updates (connection and stream) after every data frame is pointless.
            //  2.) On the other hand, window updates are cheap and works even when initial window size is low.
            //          (
            if (this.isEndSTRReceived || this.localWindow <= this.windowUpdateThreshold)
                windowUpdate += this.settings.MySettings[HTTP2Settings.INITIAL_WINDOW_SIZE] - this.localWindow - windowUpdate;

            if (this.isEndSTRReceived)
            {
                if (this.isStreamedDownload)
                    this.response.FinishProcessData();

                HTTPManager.Logger.Information("HTTP2Stream", string.Format("[{0}] All data arrived, data length: {1:N0}", this.Id, this.downloaded), this.Context, this.AssignedRequest.Context, this.parent.Context);

                // create a short living thread to process the downloaded data:
                PlatformSupport.Threading.ThreadedRunner.RunShortLiving<HTTP2Stream, FramesAsStreamView>(FinishRequest, this, this.dataView);

                this.dataView = null;

                if (this.State == HTTP2StreamStates.HalfClosedLocal)
                    this.State = HTTP2StreamStates.Closed;
                else
                    this.State = HTTP2StreamStates.HalfClosedRemote;
            }
            else if (this.AssignedRequest.OnDownloadProgress != null)
                RequestEventHelper.EnqueueRequestEvent(new RequestEventInfo(this.AssignedRequest,
                                                                     RequestEvents.DownloadProgress,
                                                                     downloaded,
                                                                     this.response.ExpectedContentLength));
        }

        protected void ProcessState(List<HTTP2FrameHeaderAndPayload> outgoingFrames)
        {
            switch (this.State)
            {
                case HTTP2StreamStates.Idle:

                    UInt32 initiatedInitialWindowSize = this.settings.InitiatedMySettings[HTTP2Settings.INITIAL_WINDOW_SIZE];
                    this.localWindow = initiatedInitialWindowSize;
                    // window update with a zero increment would be an error (https://httpwg.org/specs/rfc7540.html#WINDOW_UPDATE)
                    //if (HTTP2Connection.MaxValueFor31Bits > initiatedInitialWindowSize)
                    //    this.outgoing.Enqueue(HTTP2FrameHelper.CreateWindowUpdateFrame(this.Id, HTTP2Connection.MaxValueFor31Bits - initiatedInitialWindowSize));
                    //this.localWindow = HTTP2Connection.MaxValueFor31Bits;

#if !BESTHTTP_DISABLE_CACHING
                    // Setup cache control headers before we send out the request
                    if (!this.AssignedRequest.DisableCache)
                        HTTPCacheService.SetHeaders(this.AssignedRequest);
#endif

                    // hpack encode the request's headers
                    this.encoder.Encode(this, this.AssignedRequest, this.outgoing, this.Id);

                    // HTTP/2 uses DATA frames to carry message payloads.
                    // The chunked transfer encoding defined in Section 4.1 of [RFC7230] MUST NOT be used in HTTP/2.
                    this.uploadStreamInfo = this.AssignedRequest.GetUpStream();

                    //this.State = HTTP2StreamStates.Open;

                    if (this.uploadStreamInfo.Stream == null)
                    {
                        this.State = HTTP2StreamStates.HalfClosedLocal;
                        this.AssignedRequest.Timing.Add(TimingEventNames.Request_Sent);
                    }
                    else
                    {
                        this.State = HTTP2StreamStates.Open;
                        this.lastReadCount = 1;
                    }
                    break;

                case HTTP2StreamStates.Open:
                    ProcessOpenState(outgoingFrames);
                    //HTTPManager.Logger.Information("HTTP2Stream", string.Format("[{0}] New DATA frame created! remoteWindow: {1:N0}", this.Id, this.remoteWindow), this.Context, this.AssignedRequest.Context, this.parent.Context);
                    break;

                case HTTP2StreamStates.HalfClosedLocal:
                    break;

                case HTTP2StreamStates.HalfClosedRemote:
                    break;

                case HTTP2StreamStates.Closed:
                    break;
            }
        }

        protected virtual void ProcessOpenState(List<HTTP2FrameHeaderAndPayload> outgoingFrames)
        {
            // remote Window can be negative! See https://httpwg.org/specs/rfc7540.html#InitialWindowSize
            if (this.remoteWindow <= 0)
            {
                HTTPManager.Logger.Information("HTTP2Stream", string.Format("[{0}] Skipping data sending as remote Window is {1}!", this.Id, this.remoteWindow), this.Context, this.AssignedRequest.Context, this.parent.Context);
                return;
            }

            // This step will send one frame per OpenState call.

            Int64 maxFrameSize = Math.Min(HTTPRequest.UploadChunkSize, Math.Min(this.remoteWindow, this.settings.RemoteSettings[HTTP2Settings.MAX_FRAME_SIZE]));

            HTTP2FrameHeaderAndPayload frame = new HTTP2FrameHeaderAndPayload();
            frame.Type = HTTP2FrameTypes.DATA;
            frame.StreamId = this.Id;

            frame.Payload = BufferPool.Get(maxFrameSize, true);

            // Expect a readCount of zero if it's end of the stream. But, to enable non-blocking scenario to wait for data, going to treat a negative value as no data.
            this.lastReadCount = this.uploadStreamInfo.Stream.Read(frame.Payload, 0, (int)Math.Min(maxFrameSize, int.MaxValue));
            if (this.lastReadCount <= 0)
            {
                BufferPool.Release(frame.Payload);
                frame.Payload = null;
                frame.PayloadLength = 0;

                if (this.lastReadCount < 0)
                    return;
            }
            else
                frame.PayloadLength = (UInt32)this.lastReadCount;

            frame.PayloadOffset = 0;
            frame.DontUseMemPool = false;

            if (this.lastReadCount <= 0)
            {
                this.uploadStreamInfo.Stream.Dispose();
                this.uploadStreamInfo = new HTTPRequest.UploadStreamInfo();

                frame.Flags = (byte)(HTTP2DataFlags.END_STREAM);

                this.State = HTTP2StreamStates.HalfClosedLocal;

                this.AssignedRequest.Timing.Add(TimingEventNames.Request_Sent);
            }

            this.outgoing.Enqueue(frame);

            this.remoteWindow -= frame.PayloadLength;

            this.sentData += frame.PayloadLength;

            if (this.AssignedRequest.OnUploadProgress != null)
                RequestEventHelper.EnqueueRequestEvent(new RequestEventInfo(this.AssignedRequest, RequestEvents.UploadProgress, this.sentData, this.uploadStreamInfo.Length));
        }

        protected void OnRemoteSettingChanged(HTTP2SettingsRegistry registry, HTTP2Settings setting, uint oldValue, uint newValue)
        {
            switch (setting)
            {
                case HTTP2Settings.INITIAL_WINDOW_SIZE:
                    // https://httpwg.org/specs/rfc7540.html#InitialWindowSize
                    // "Prior to receiving a SETTINGS frame that sets a value for SETTINGS_INITIAL_WINDOW_SIZE,
                    // an endpoint can only use the default initial window size when sending flow-controlled frames."
                    // "In addition to changing the flow-control window for streams that are not yet active,
                    // a SETTINGS frame can alter the initial flow-control window size for streams with active flow-control windows
                    // (that is, streams in the "open" or "half-closed (remote)" state). When the value of SETTINGS_INITIAL_WINDOW_SIZE changes,
                    // a receiver MUST adjust the size of all stream flow-control windows that it maintains by the difference between the new value and the old value."

                    // So, if we created a stream before the remote peer's initial settings frame is received, we
                    // will adjust the window size. For example: initial window size by default is 65535, if we later
                    // receive a change to 1048576 (1 MB) we will increase the current remoteWindow by (1 048 576 - 65 535 =) 983 041

                    // But because initial window size in a setting frame can be smaller then the default 65535 bytes,
                    // the difference can be negative:
                    // "A change to SETTINGS_INITIAL_WINDOW_SIZE can cause the available space in a flow-control window to become negative.
                    // A sender MUST track the negative flow-control window and MUST NOT send new flow-controlled frames
                    // until it receives WINDOW_UPDATE frames that cause the flow-control window to become positive.

                    // For example, if the client sends 60 KB immediately on connection establishment
                    // and the server sets the initial window size to be 16 KB, the client will recalculate
                    // the available flow - control window to be - 44 KB on receipt of the SETTINGS frame.
                    // The client retains a negative flow-control window until WINDOW_UPDATE frames restore the
                    // window to being positive, after which the client can resume sending."

                    this.remoteWindow += newValue - oldValue;

                    HTTPManager.Logger.Information("HTTP2Stream", string.Format("[{0}] Remote Setting's Initial Window Updated from {1:N0} to {2:N0}, diff: {3:N0}, new remoteWindow: {4:N0}, total data sent: {5:N0}", this.Id, oldValue, newValue, newValue - oldValue, this.remoteWindow, this.sentData), this.Context, this.AssignedRequest.Context, this.parent.Context);
                    break;
            }
        }

        protected static void FinishRequest(HTTP2Stream stream, FramesAsStreamView dataStream)
        {
            try
            {
                if (dataStream != null)
                {
                    try
                    {
                        stream.response.AddData(dataStream);
                    }
                    finally
                    {
                        dataStream.Close();
                    }
                }

                stream.AssignedRequest.Timing.Add(TimingEventNames.Response_Received);

                bool resendRequest;
                HTTPConnectionStates proposedConnectionStates; // ignored
                KeepAliveHeader keepAliveHeader = null; // ignored

                ConnectionHelper.HandleResponse("HTTP2Stream", stream.AssignedRequest, out resendRequest, out proposedConnectionStates, ref keepAliveHeader, stream.Context, stream.AssignedRequest.Context);

                if (resendRequest && !stream.AssignedRequest.IsCancellationRequested)
                    RequestEventHelper.EnqueueRequestEvent(new RequestEventInfo(stream.AssignedRequest, RequestEvents.Resend));
                else if (stream.AssignedRequest.State == HTTPRequestStates.Processing && !stream.AssignedRequest.IsCancellationRequested)
                    stream.AssignedRequest.State = HTTPRequestStates.Finished;
                else
                {
                    // Already set in HTTPRequest's Abort().
                    //if (stream.AssignedRequest.State == HTTPRequestStates.Processing && stream.AssignedRequest.IsCancellationRequested)
                    //    stream.AssignedRequest.State = stream.AssignedRequest.IsTimedOut ? HTTPRequestStates.TimedOut : HTTPRequestStates.Aborted;
                }
            }
            catch(Exception ex)
            {
                HTTPManager.Logger.Exception("HTTP2Stream", "FinishRequest", ex, stream.AssignedRequest.Context);
            }
        }

        public void Removed()
        {
            if (this.uploadStreamInfo.Stream != null)
            {
                this.uploadStreamInfo.Stream.Dispose();
                this.uploadStreamInfo = new HTTPRequest.UploadStreamInfo();
            }

            // After receiving a RST_STREAM on a stream, the receiver MUST NOT send additional frames for that stream, with the exception of PRIORITY.
            this.outgoing.Clear();

            // https://github.com/Benedicht/BestHTTP-Issues/issues/77
            // Unsubscribe from OnSettingChangedEvent to remove reference to this instance.
            this.settings.RemoteSettings.OnSettingChangedEvent -= OnRemoteSettingChanged;

            HTTPManager.Logger.Information("HTTP2Stream", "Stream removed: " + this.Id.ToString(), this.Context, this.AssignedRequest.Context, this.parent.Context);
        }
    }
}

#endif