private Task DecodeTrailersAsync(bool endHeaders, Span <byte> payload)
        {
            _hpackDecoder.Decode(payload, endHeaders, handler: this);

            if (endHeaders)
            {
                var endStreamTask = _currentHeadersStream.OnDataAsync(Constants.EmptyData, endStream: true);
                ResetRequestHeaderParsingState();
                return(endStreamTask);
            }

            return(Task.CompletedTask);
        }
        private async Task ProcessHeadersFrameAsync <TContext>(IHttpApplication <TContext> application)
        {
            if (_currentHeadersStream != null)
            {
                throw new Http2ConnectionErrorException(CoreStrings.FormatHttp2ErrorHeadersInterleaved(_incomingFrame.Type, _incomingFrame.StreamId, _currentHeadersStream.StreamId), Http2ErrorCode.PROTOCOL_ERROR);
            }

            if (_incomingFrame.StreamId == 0)
            {
                throw new Http2ConnectionErrorException(CoreStrings.FormatHttp2ErrorStreamIdZero(_incomingFrame.Type), Http2ErrorCode.PROTOCOL_ERROR);
            }

            if (_incomingFrame.HeadersHasPadding && _incomingFrame.HeadersPadLength >= _incomingFrame.Length)
            {
                throw new Http2ConnectionErrorException(CoreStrings.FormatHttp2ErrorPaddingTooLong(_incomingFrame.Type), Http2ErrorCode.PROTOCOL_ERROR);
            }

            if (_incomingFrame.HeadersHasPriority && _incomingFrame.HeadersStreamDependency == _incomingFrame.StreamId)
            {
                throw new Http2ConnectionErrorException(CoreStrings.FormatHttp2ErrorStreamSelfDependency(_incomingFrame.Type, _incomingFrame.StreamId), Http2ErrorCode.PROTOCOL_ERROR);
            }

            if (_streams.TryGetValue(_incomingFrame.StreamId, out var stream))
            {
                // http://httpwg.org/specs/rfc7540.html#rfc.section.5.1
                //
                // ...an endpoint that receives any frames after receiving a frame with the
                // END_STREAM flag set MUST treat that as a connection error (Section 5.4.1)
                // of type STREAM_CLOSED, unless the frame is permitted as described below.
                //
                // (The allowed frame types after END_STREAM are WINDOW_UPDATE, RST_STREAM and PRIORITY)
                if (stream.EndStreamReceived)
                {
                    throw new Http2ConnectionErrorException(CoreStrings.FormatHttp2ErrorStreamHalfClosedRemote(_incomingFrame.Type, stream.StreamId), Http2ErrorCode.STREAM_CLOSED);
                }

                // This is the last chance for the client to send END_STREAM
                if ((_incomingFrame.HeadersFlags & Http2HeadersFrameFlags.END_STREAM) == 0)
                {
                    throw new Http2ConnectionErrorException(CoreStrings.Http2ErrorHeadersWithTrailersNoEndStream, Http2ErrorCode.PROTOCOL_ERROR);
                }

                // Since we found an active stream, this HEADERS frame contains trailers
                _currentHeadersStream      = stream;
                _requestHeaderParsingState = RequestHeaderParsingState.Trailers;

                var endHeaders = (_incomingFrame.HeadersFlags & Http2HeadersFrameFlags.END_HEADERS) == Http2HeadersFrameFlags.END_HEADERS;
                await DecodeTrailersAsync(endHeaders, _incomingFrame.HeadersPayload);
            }
            else if (_incomingFrame.StreamId <= _highestOpenedStreamId)
            {
                // http://httpwg.org/specs/rfc7540.html#rfc.section.5.1.1
                //
                // The first use of a new stream identifier implicitly closes all streams in the "idle"
                // state that might have been initiated by that peer with a lower-valued stream identifier.
                //
                // If we couldn't find the stream, it was previously closed (either implicitly or with
                // END_STREAM or RST_STREAM).
                throw new Http2ConnectionErrorException(CoreStrings.FormatHttp2ErrorStreamClosed(_incomingFrame.Type, _incomingFrame.StreamId), Http2ErrorCode.STREAM_CLOSED);
            }
            else
            {
                // Start a new stream
                _currentHeadersStream = new Http2Stream(new Http2StreamContext
                {
                    ConnectionId                = ConnectionId,
                    StreamId                    = _incomingFrame.StreamId,
                    ServiceContext              = _context.ServiceContext,
                    ConnectionFeatures          = _context.ConnectionFeatures,
                    MemoryPool                  = _context.MemoryPool,
                    LocalEndPoint               = _context.LocalEndPoint,
                    RemoteEndPoint              = _context.RemoteEndPoint,
                    StreamLifetimeHandler       = this,
                    ClientPeerSettings          = _clientSettings,
                    FrameWriter                 = _frameWriter,
                    ConnectionOutputFlowControl = _outputFlowControl,
                    TimeoutControl              = this,
                });

                if ((_incomingFrame.HeadersFlags & Http2HeadersFrameFlags.END_STREAM) == Http2HeadersFrameFlags.END_STREAM)
                {
                    await _currentHeadersStream.OnDataAsync(Constants.EmptyData, endStream : true);
                }

                _currentHeadersStream.Reset();

                var endHeaders = (_incomingFrame.HeadersFlags & Http2HeadersFrameFlags.END_HEADERS) == Http2HeadersFrameFlags.END_HEADERS;
                await DecodeHeadersAsync(application, endHeaders, _incomingFrame.HeadersPayload);
            }
        }
        private async Task ProcessHeadersFrameAsync <TContext>(IHttpApplication <TContext> application)
        {
            if (_currentHeadersStream != null)
            {
                throw new Http2ConnectionErrorException(Http2ErrorCode.PROTOCOL_ERROR);
            }

            if (_incomingFrame.StreamId == 0)
            {
                throw new Http2ConnectionErrorException(Http2ErrorCode.PROTOCOL_ERROR);
            }

            if (_incomingFrame.HeadersHasPadding && _incomingFrame.HeadersPadLength >= _incomingFrame.Length)
            {
                throw new Http2ConnectionErrorException(Http2ErrorCode.PROTOCOL_ERROR);
            }

            if (_incomingFrame.HeadersHasPriority && _incomingFrame.HeadersStreamDependency == _incomingFrame.StreamId)
            {
                throw new Http2ConnectionErrorException(Http2ErrorCode.PROTOCOL_ERROR);
            }

            if (_streams.TryGetValue(_incomingFrame.StreamId, out var stream))
            {
                // http://httpwg.org/specs/rfc7540.html#rfc.section.5.1
                //
                // ...an endpoint that receives any frames after receiving a frame with the
                // END_STREAM flag set MUST treat that as a connection error (Section 5.4.1)
                // of type STREAM_CLOSED, unless the frame is permitted as described below.
                //
                // (The allowed frame types for this situation are WINDOW_UPDATE, RST_STREAM and PRIORITY)
                if (stream.EndStreamReceived)
                {
                    throw new Http2ConnectionErrorException(Http2ErrorCode.STREAM_CLOSED);
                }

                // TODO: trailers
            }
            else if (_incomingFrame.StreamId <= _highestOpenedStreamId)
            {
                // http://httpwg.org/specs/rfc7540.html#rfc.section.5.1.1
                //
                // The first use of a new stream identifier implicitly closes all streams in the "idle"
                // state that might have been initiated by that peer with a lower-valued stream identifier.
                //
                // If we couldn't find the stream, it was previously closed (either implicitly or with
                // END_STREAM or RST_STREAM).
                throw new Http2ConnectionErrorException(Http2ErrorCode.STREAM_CLOSED);
            }
            else
            {
                // Start a new stream
                _currentHeadersStream = new Http2Stream <TContext>(application, new Http2StreamContext
                {
                    ConnectionId          = ConnectionId,
                    StreamId              = _incomingFrame.StreamId,
                    ServiceContext        = _context.ServiceContext,
                    ConnectionFeatures    = _context.ConnectionFeatures,
                    PipeFactory           = _context.PipeFactory,
                    LocalEndPoint         = _context.LocalEndPoint,
                    RemoteEndPoint        = _context.RemoteEndPoint,
                    StreamLifetimeHandler = this,
                    FrameWriter           = _frameWriter
                });

                if ((_incomingFrame.HeadersFlags & Http2HeadersFrameFlags.END_STREAM) == Http2HeadersFrameFlags.END_STREAM)
                {
                    await _currentHeadersStream.OnDataAsync(Constants.EmptyData, endStream : true);
                }

                _currentHeadersStream.Reset();

                var endHeaders = (_incomingFrame.HeadersFlags & Http2HeadersFrameFlags.END_HEADERS) == Http2HeadersFrameFlags.END_HEADERS;
                await DecodeHeadersAsync(endHeaders, _incomingFrame.HeadersPayload);
            }
        }