asp.net core启动源码以及监听，到处理请求响应的过程

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddControllers();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
var app = builder.Build();
app.UseSwagger();
app.UseSwaggerUI();
app.UseAuthorization();

app.MapControllers();
app.Run();

 var configuration = new ConfigurationManager();

        configuration.AddEnvironmentVariables(prefix: "ASPNETCORE_");

        _hostApplicationBuilder = new HostApplicationBuilder(new HostApplicationBuilderSettings
        {
            Args = options.Args,
            ApplicationName = options.ApplicationName,
            EnvironmentName = options.EnvironmentName,
            ContentRootPath = options.ContentRootPath,
            Configuration = configuration,
        });

        // Set WebRootPath if necessary
        if (options.WebRootPath is not null)
        {
            Configuration.AddInMemoryCollection(new[]
            {
                new KeyValuePair<string, string?>(WebHostDefaults.WebRootKey, options.WebRootPath),
            });
        }

        // Run methods to configure web host defaults early to populate services
        var bootstrapHostBuilder = new BootstrapHostBuilder(_hostApplicationBuilder);

        // This is for testing purposes
        configureDefaults?.Invoke(bootstrapHostBuilder);

        bootstrapHostBuilder.ConfigureWebHostDefaults(webHostBuilder =>
        {
            // Runs inline.
            webHostBuilder.Configure(ConfigureApplication);

            webHostBuilder.UseSetting(WebHostDefaults.ApplicationKey, _hostApplicationBuilder.Environment.ApplicationName ?? "");
            webHostBuilder.UseSetting(WebHostDefaults.PreventHostingStartupKey, Configuration[WebHostDefaults.PreventHostingStartupKey]);
            webHostBuilder.UseSetting(WebHostDefaults.HostingStartupAssembliesKey, Configuration[WebHostDefaults.HostingStartupAssembliesKey]);
            webHostBuilder.UseSetting(WebHostDefaults.HostingStartupExcludeAssembliesKey, Configuration[WebHostDefaults.HostingStartupExcludeAssembliesKey]);
        },
        options =>
        {
            // We've already applied "ASPNETCORE_" environment variables to hosting config
            options.SuppressEnvironmentConfiguration = true;
        });

        // This applies the config from ConfigureWebHostDefaults
        // Grab the GenericWebHostService ServiceDescriptor so we can append it after any user-added IHostedServices during Build();
        _genericWebHostServiceDescriptor = bootstrapHostBuilder.RunDefaultCallbacks();

        // Grab the WebHostBuilderContext from the property bag to use in the ConfigureWebHostBuilder. Then
        // grab the IWebHostEnvironment from the webHostContext. This also matches the instance in the IServiceCollection.
        var webHostContext = (WebHostBuilderContext)bootstrapHostBuilder.Properties[typeof(WebHostBuilderContext)];
        Environment = webHostContext.HostingEnvironment;

        Host = new ConfigureHostBuilder(bootstrapHostBuilder.Context, Configuration, Services);
        WebHost = new ConfigureWebHostBuilder(webHostContext, Configuration, Services);

   Debug.Assert(_builtApplication is not null);

        // UseRouting called before WebApplication such as in a StartupFilter
        // lets remove the property and reset it at the end so we don't mess with the routes in the filter
        if (app.Properties.TryGetValue(EndpointRouteBuilderKey, out var priorRouteBuilder))
        {
            app.Properties.Remove(EndpointRouteBuilderKey);
        }

        if (context.HostingEnvironment.IsDevelopment())
        {
            app.UseDeveloperExceptionPage();
        }

        // Wrap the entire destination pipeline in UseRouting() and UseEndpoints(), essentially:
        // destination.UseRouting()
        // destination.Run(source)
        // destination.UseEndpoints()

        // Set the route builder so that UseRouting will use the WebApplication as the IEndpointRouteBuilder for route matching
        app.Properties.Add(WebApplication.GlobalEndpointRouteBuilderKey, _builtApplication);

        // Only call UseRouting() if there are endpoints configured and UseRouting() wasn't called on the global route builder already
        if (_builtApplication.DataSources.Count > 0)
        {
            // If this is set, someone called UseRouting() when a global route builder was already set
            if (!_builtApplication.Properties.TryGetValue(EndpointRouteBuilderKey, out var localRouteBuilder))
            {
                app.UseRouting();
            }
            else
            {
                // UseEndpoints will be looking for the RouteBuilder so make sure it's set
                app.Properties[EndpointRouteBuilderKey] = localRouteBuilder;
            }
        }

        // Wire the source pipeline to run in the destination pipeline
        app.Use(next =>
        {
            _builtApplication.Run(next);
            return _builtApplication.BuildRequestDelegate();
        });

        if (_builtApplication.DataSources.Count > 0)
        {
            // We don't know if user code called UseEndpoints(), so we will call it just in case, UseEndpoints() will ignore duplicate DataSources
            app.UseEndpoints(_ => { });
        }

        // Copy the properties to the destination app builder
        foreach (var item in _builtApplication.Properties)
        {
            app.Properties[item.Key] = item.Value;
        }

        // Remove the route builder to clean up the properties, we're done adding routes to the pipeline
        app.Properties.Remove(WebApplication.GlobalEndpointRouteBuilderKey);

        // reset route builder if it existed, this is needed for StartupFilters
        if (priorRouteBuilder is not null)
        {
            app.Properties[EndpointRouteBuilderKey] = priorRouteBuilder;
        }

 public static ControllerActionEndpointConventionBuilder MapControllers(this IEndpointRouteBuilder endpoints)
    {
        if (endpoints == null)
        {
            throw new ArgumentNullException(nameof(endpoints));
        }

        EnsureControllerServices(endpoints);

        return GetOrCreateDataSource(endpoints).DefaultBuilder;
    }

  private static ControllerActionEndpointDataSource GetOrCreateDataSource(IEndpointRouteBuilder endpoints)
    {
        var dataSource = endpoints.DataSources.OfType<ControllerActionEndpointDataSource>().FirstOrDefault();
        if (dataSource == null)
        {
            var orderProvider = endpoints.ServiceProvider.GetRequiredService<OrderedEndpointsSequenceProviderCache>();
            var factory = endpoints.ServiceProvider.GetRequiredService<ControllerActionEndpointDataSourceFactory>();
            dataSource = factory.Create(orderProvider.GetOrCreateOrderedEndpointsSequenceProvider(endpoints));
            endpoints.DataSources.Add(dataSource);
        }

        return dataSource;
    }

 public async Task StartAsync<TContext>(IHttpApplication<TContext> application, CancellationToken cancellationToken) where TContext : notnull
    {
        try
        {
            ValidateOptions();

            if (_hasStarted)
            {
                // The server has already started and/or has not been cleaned up yet
                throw new InvalidOperationException(CoreStrings.ServerAlreadyStarted);
            }
            _hasStarted = true;

            ServiceContext.Heartbeat?.Start();

            async Task OnBind(ListenOptions options, CancellationToken onBindCancellationToken)
            {
                var hasHttp1 = options.Protocols.HasFlag(HttpProtocols.Http1);
                var hasHttp2 = options.Protocols.HasFlag(HttpProtocols.Http2);
                var hasHttp3 = options.Protocols.HasFlag(HttpProtocols.Http3);
                var hasTls = options.IsTls;

                // Filter out invalid combinations.

                if (!hasTls)
                {
                    // Http/1 without TLS, no-op HTTP/2 and 3.
                    if (hasHttp1)
                    {
                        hasHttp2 = false;
                        hasHttp3 = false;
                    }
                    // Http/3 requires TLS. Note we only let it fall back to HTTP/1, not HTTP/2
                    else if (hasHttp3)
                    {
                        throw new InvalidOperationException("HTTP/3 requires HTTPS.");
                    }
                }

                // Quic isn't registered if it's not supported, throw if we can't fall back to 1 or 2
                if (hasHttp3 && _multiplexedTransportFactory is null && !(hasHttp1 || hasHttp2))
                {
                    throw new InvalidOperationException("This platform doesn't support QUIC or HTTP/3.");
                }

                // Disable adding alt-svc header if endpoint has configured not to or there is no
                // multiplexed transport factory, which happens if QUIC isn't supported.
                var addAltSvcHeader = !options.DisableAltSvcHeader && _multiplexedTransportFactory != null;

                // Add the HTTP middleware as the terminal connection middleware
                if (hasHttp1 || hasHttp2
                    || options.Protocols == HttpProtocols.None) // TODO a test fails because it doesn't throw an exception in the right place
                                                                // when there is no HttpProtocols in KestrelServer, can we remove/change the test?
                {
                    if (_transportFactory is null)
                    {
                        throw new InvalidOperationException($"Cannot start HTTP/1.x or HTTP/2 server if no {nameof(IConnectionListenerFactory)} is registered.");
                    }

                    options.UseHttpServer(ServiceContext, application, options.Protocols, addAltSvcHeader);
                    var connectionDelegate = options.Build();

                    // Add the connection limit middleware
                    connectionDelegate = EnforceConnectionLimit(connectionDelegate, Options.Limits.MaxConcurrentConnections, Trace);

                    options.EndPoint = await _transportManager.BindAsync(options.EndPoint, connectionDelegate, options.EndpointConfig, onBindCancellationToken).ConfigureAwait(false);
                }

                if (hasHttp3 && _multiplexedTransportFactory is not null)
                {
                    options.UseHttp3Server(ServiceContext, application, options.Protocols, addAltSvcHeader);
                    var multiplexedConnectionDelegate = ((IMultiplexedConnectionBuilder)options).Build();

                    // Add the connection limit middleware
                    multiplexedConnectionDelegate = EnforceConnectionLimit(multiplexedConnectionDelegate, Options.Limits.MaxConcurrentConnections, Trace);

                    options.EndPoint = await _transportManager.BindAsync(options.EndPoint, multiplexedConnectionDelegate, options, onBindCancellationToken).ConfigureAwait(false);
                }
            }

            AddressBindContext = new AddressBindContext(_serverAddresses, Options, Trace, OnBind);

            await BindAsync(cancellationToken).ConfigureAwait(false);
        }
        catch
        {
            // Don't log the error https://github.com/dotnet/aspnetcore/issues/29801
            Dispose();
            throw;
        }

        // Register the options with the event source so it can be logged (if necessary)
        KestrelEventSource.Log.AddServerOptions(Options);
    }

 private async Task BindAsync(CancellationToken cancellationToken)
    {
        await _bindSemaphore.WaitAsync(cancellationToken).ConfigureAwait(false);

        try
        {
            if (_stopping == 1)
            {
                throw new InvalidOperationException("Kestrel has already been stopped.");
            }

            IChangeToken? reloadToken = null;

            _serverAddresses.InternalCollection.PreventPublicMutation();

            if (Options.ConfigurationLoader?.ReloadOnChange == true && (!_serverAddresses.PreferHostingUrls || _serverAddresses.InternalCollection.Count == 0))
            {
                reloadToken = Options.ConfigurationLoader.Configuration.GetReloadToken();
            }

            Options.ConfigurationLoader?.Load();

            await AddressBinder.BindAsync(Options.ListenOptions, AddressBindContext!, cancellationToken).ConfigureAwait(false);
            _configChangedRegistration = reloadToken?.RegisterChangeCallback(TriggerRebind, this);
        }
        finally
        {
            _bindSemaphore.Release();
        }
    }

 var strategy = CreateStrategy(
            listenOptions.ToArray(),
            context.Addresses.ToArray(),
            context.ServerAddressesFeature.PreferHostingUrls);

        // reset options. The actual used options and addresses will be populated
        // by the address binding feature
        context.ServerOptions.OptionsInUse.Clear();
        context.Addresses.Clear();

        await strategy.BindAsync(context, cancellationToken).ConfigureAwait(false);

 public static IConnectionBuilder UseHttpServer<TContext>(this IConnectionBuilder builder, ServiceContext serviceContext, IHttpApplication<TContext> application, HttpProtocols protocols, bool addAltSvcHeader) where TContext : notnull
    {
        var middleware = new HttpConnectionMiddleware<TContext>(serviceContext, application, protocols, addAltSvcHeader);
        return builder.Use(next =>
        {
            return middleware.OnConnectionAsync;
        });
    }

    public static IMultiplexedConnectionBuilder UseHttp3Server<TContext>(this IMultiplexedConnectionBuilder builder, ServiceContext serviceContext, IHttpApplication<TContext> application, HttpProtocols protocols, bool addAltSvcHeader) where TContext : notnull
    {
        var middleware = new HttpMultiplexedConnectionMiddleware<TContext>(serviceContext, application, protocols, addAltSvcHeader);
        return builder.Use(next =>
        {
            return middleware.OnConnectionAsync;
        });
    }

 public Task OnConnectionAsync(ConnectionContext connectionContext)
    {
        var memoryPoolFeature = connectionContext.Features.Get<IMemoryPoolFeature>();
        var protocols = connectionContext.Features.Get<HttpProtocolsFeature>()?.HttpProtocols ?? _endpointDefaultProtocols;
        var localEndPoint = connectionContext.LocalEndPoint as IPEndPoint;
        var altSvcHeader = _addAltSvcHeader && localEndPoint != null ? HttpUtilities.GetEndpointAltSvc(localEndPoint, protocols) : null;

        var httpConnectionContext = new HttpConnectionContext(
            connectionContext.ConnectionId,
            protocols,
            altSvcHeader,
            connectionContext,
            _serviceContext,
            connectionContext.Features,
            memoryPoolFeature?.MemoryPool ?? System.Buffers.MemoryPool<byte>.Shared,
            localEndPoint,
            connectionContext.RemoteEndPoint as IPEndPoint);
        httpConnectionContext.Transport = connectionContext.Transport;

        var connection = new HttpConnection(httpConnectionContext);

        return connection.ProcessRequestsAsync(_application);
    }

 public async Task<EndPoint> BindAsync(EndPoint endPoint, ConnectionDelegate connectionDelegate, EndpointConfig? endpointConfig, CancellationToken cancellationToken)
    {
        if (_transportFactory is null)
        {
            throw new InvalidOperationException($"Cannot bind with {nameof(ConnectionDelegate)} no {nameof(IConnectionListenerFactory)} is registered.");
        }

        var transport = await _transportFactory.BindAsync(endPoint, cancellationToken).ConfigureAwait(false);
        StartAcceptLoop(new GenericConnectionListener(transport), c => connectionDelegate(c), endpointConfig);
        return transport.EndPoint;
    }

    public async Task<EndPoint> BindAsync(EndPoint endPoint, MultiplexedConnectionDelegate multiplexedConnectionDelegate, ListenOptions listenOptions, CancellationToken cancellationToken)
    {
        if (_multiplexedTransportFactory is null)
        {
            throw new InvalidOperationException($"Cannot bind with {nameof(MultiplexedConnectionDelegate)} no {nameof(IMultiplexedConnectionListenerFactory)} is registered.");
        }

        var features = new FeatureCollection();

        // This should always be set in production, but it's not set for InMemory tests.
        // The transport will check if the feature is missing.
        if (listenOptions.HttpsOptions != null)
        {
            features.Set(HttpsConnectionMiddleware.CreateHttp3Options(listenOptions.HttpsOptions));
        }

        var transport = await _multiplexedTransportFactory.BindAsync(endPoint, features, cancellationToken).ConfigureAwait(false);
        StartAcceptLoop(new GenericMultiplexedConnectionListener(transport), c => multiplexedConnectionDelegate(c), listenOptions.EndpointConfig);
        return transport.EndPoint;
    }

    private void StartAcceptLoop<T>(IConnectionListener<T> connectionListener, Func<T, Task> connectionDelegate, EndpointConfig? endpointConfig) where T : BaseConnectionContext
    {
        var transportConnectionManager = new TransportConnectionManager(_serviceContext.ConnectionManager);
        var connectionDispatcher = new ConnectionDispatcher<T>(_serviceContext, connectionDelegate, transportConnectionManager);
        var acceptLoopTask = connectionDispatcher.StartAcceptingConnections(connectionListener);

        _transports.Add(new ActiveTransport(connectionListener, acceptLoopTask, transportConnectionManager, endpointConfig));
    }

 public ValueTask<IConnectionListener> BindAsync(EndPoint endpoint, CancellationToken cancellationToken = default)
    {
        var transport = new SocketConnectionListener(endpoint, _options, _logger);
        transport.Bind();
        return new ValueTask<IConnectionListener>(transport);
    }

internal void Bind()
    {
        if (_listenSocket != null)
        {
            throw new InvalidOperationException(SocketsStrings.TransportAlreadyBound);
        }

        Socket listenSocket;
        try
        {
            listenSocket = _options.CreateBoundListenSocket(EndPoint);
        }
        catch (SocketException e) when (e.SocketErrorCode == SocketError.AddressAlreadyInUse)
        {
            throw new AddressInUseException(e.Message, e);
        }

        Debug.Assert(listenSocket.LocalEndPoint != null);
        EndPoint = listenSocket.LocalEndPoint;

        listenSocket.Listen(_options.Backlog);

        _listenSocket = listenSocket;
    }

   public Task StartAcceptingConnections(IConnectionListener<T> listener)
    {
        ThreadPool.UnsafeQueueUserWorkItem(StartAcceptingConnectionsCore, listener, preferLocal: false);
        return _acceptLoopTcs.Task;
    }

    private void StartAcceptingConnectionsCore(IConnectionListener<T> listener)
    {
        // REVIEW: Multiple accept loops in parallel?
        _ = AcceptConnectionsAsync();

        async Task AcceptConnectionsAsync()
        {
            try
            {
                while (true)
                {
                    var connection = await listener.AcceptAsync();

                    if (connection == null)
                    {
                        // We're done listening
                        break;
                    }

                    // Add the connection to the connection manager before we queue it for execution
                    var id = _transportConnectionManager.GetNewConnectionId();
                    var kestrelConnection = new KestrelConnection<T>(
                        id, _serviceContext, _transportConnectionManager, _connectionDelegate, connection, Log);

                    _transportConnectionManager.AddConnection(id, kestrelConnection);

                    Log.ConnectionAccepted(connection.ConnectionId);
                    KestrelEventSource.Log.ConnectionQueuedStart(connection);

                    ThreadPool.UnsafeQueueUserWorkItem(kestrelConnection, preferLocal: false);
                }
            }
            catch (Exception ex)
            {
                // REVIEW: If the accept loop ends should this trigger a server shutdown? It will manifest as a hang
                Log.LogCritical(0, ex, "The connection listener failed to accept any new connections.");
            }
            finally
            {
                _acceptLoopTcs.TrySetResult();
            }
        }
    }

 void IThreadPoolWorkItem.Execute()
    {
        _ = ExecuteAsync();
    }

    internal async Task ExecuteAsync()
    {
        var connectionContext = _transportConnection;

        try
        {
            KestrelEventSource.Log.ConnectionQueuedStop(connectionContext);

            Logger.ConnectionStart(connectionContext.ConnectionId);
            KestrelEventSource.Log.ConnectionStart(connectionContext);

            using (BeginConnectionScope(connectionContext))
            {
                try
                {
                    await _connectionDelegate(connectionContext);
                }
                catch (Exception ex)
                {
                    Logger.LogError(0, ex, "Unhandled exception while processing {ConnectionId}.", connectionContext.ConnectionId);
                }
            }
        }
        finally
        {
            await FireOnCompletedAsync();

            Logger.ConnectionStop(connectionContext.ConnectionId);
            KestrelEventSource.Log.ConnectionStop(connectionContext);

            // Dispose the transport connection, this needs to happen before removing it from the
            // connection manager so that we only signal completion of this connection after the transport
            // is properly torn down.
            await connectionContext.DisposeAsync();

            _transportConnectionManager.RemoveConnection(_id);
        }
    }

public async Task ProcessRequestsAsync<TContext>(IHttpApplication<TContext> httpApplication) where TContext : notnull
    {
        try
        {
            // Ensure TimeoutControl._lastTimestamp is initialized before anything that could set timeouts runs.
            _timeoutControl.Initialize(_systemClock.UtcNowTicks);

            IRequestProcessor? requestProcessor = null;

            switch (SelectProtocol())
            {
                case HttpProtocols.Http1:
                    // _http1Connection must be initialized before adding the connection to the connection manager
                    requestProcessor = _http1Connection = new Http1Connection<TContext>((HttpConnectionContext)_context);
                    _protocolSelectionState = ProtocolSelectionState.Selected;
                    break;
                case HttpProtocols.Http2:
                    // _http2Connection must be initialized before yielding control to the transport thread,
                    // to prevent a race condition where _http2Connection.Abort() is called just as
                    // _http2Connection is about to be initialized.
                    requestProcessor = new Http2Connection((HttpConnectionContext)_context);
                    _protocolSelectionState = ProtocolSelectionState.Selected;
                    break;
                case HttpProtocols.Http3:
                    requestProcessor = new Http3Connection((HttpMultiplexedConnectionContext)_context);
                    _protocolSelectionState = ProtocolSelectionState.Selected;
                    break;
                case HttpProtocols.None:
                    // An error was already logged in SelectProtocol(), but we should close the connection.
                    break;

                default:
                    // SelectProtocol() only returns Http1, Http2, Http3 or None.
                    throw new NotSupportedException($"{nameof(SelectProtocol)} returned something other than Http1, Http2 or None.");
            }

            _requestProcessor = requestProcessor;

            if (requestProcessor != null)
            {
                var connectionHeartbeatFeature = _context.ConnectionFeatures.Get<IConnectionHeartbeatFeature>();
                var connectionLifetimeNotificationFeature = _context.ConnectionFeatures.Get<IConnectionLifetimeNotificationFeature>();

                // These features should never be null in Kestrel itself, if this middleware is ever refactored to run outside of kestrel,
                // we'll need to handle these missing.
                Debug.Assert(connectionHeartbeatFeature != null, nameof(IConnectionHeartbeatFeature) + " is missing!");
                Debug.Assert(connectionLifetimeNotificationFeature != null, nameof(IConnectionLifetimeNotificationFeature) + " is missing!");

                // Register the various callbacks once we're going to start processing requests

                // The heart beat for various timeouts
                connectionHeartbeatFeature?.OnHeartbeat(state => ((HttpConnection)state).Tick(), this);

                // Register for graceful shutdown of the server
                using var shutdownRegistration = connectionLifetimeNotificationFeature?.ConnectionClosedRequested.Register(state => ((HttpConnection)state!).StopProcessingNextRequest(), this);

                // Register for connection close
                using var closedRegistration = _context.ConnectionContext.ConnectionClosed.Register(state => ((HttpConnection)state!).OnConnectionClosed(), this);

                await requestProcessor.ProcessRequestsAsync(httpApplication);
            }
        }
        catch (Exception ex)
        {
            Log.LogCritical(0, ex, $"Unexpected exception in {nameof(HttpConnection)}.{nameof(ProcessRequestsAsync)}.");
        }
    }

internal interface IRequestProcessor
{
    Task ProcessRequestsAsync<TContext>(IHttpApplication<TContext> application) where TContext : notnull;
    void StopProcessingNextRequest();
    void HandleRequestHeadersTimeout();
    void HandleReadDataRateTimeout();
    void OnInputOrOutputCompleted();
    void Tick(DateTimeOffset now);
    void Abort(ConnectionAbortedException ex);
}

  private async Task ProcessRequests<TContext>(IHttpApplication<TContext> application) where TContext : notnull
    {
        while (_keepAlive)
        {
            if (_context.InitialExecutionContext is null)
            {
                // If this is a first request on a non-Http2Connection, capture a clean ExecutionContext.
                _context.InitialExecutionContext = ExecutionContext.Capture();
            }
            else
            {
                // Clear any AsyncLocals set during the request; back to a clean state ready for next request
                // And/or reset to Http2Connection's ExecutionContext giving access to the connection logging scope
                // and any other AsyncLocals set by connection middleware.
                ExecutionContext.Restore(_context.InitialExecutionContext);
            }

            BeginRequestProcessing();

            var result = default(ReadResult);
            bool endConnection;
            do
            {
                if (BeginRead(out var awaitable))
                {
                    result = await awaitable;
                }
            } while (!TryParseRequest(result, out endConnection));

            if (endConnection)
            {
                // Connection finished, stop processing requests
                return;
            }

            var messageBody = CreateMessageBody();
            if (!messageBody.RequestKeepAlive)
            {
                _keepAlive = false;
            }

            IsUpgradableRequest = messageBody.RequestUpgrade;

            InitializeBodyControl(messageBody);

            var context = application.CreateContext(this);

            try
            {
                KestrelEventSource.Log.RequestStart(this);

                // Run the application code for this request
                await application.ProcessRequestAsync(context);

                // Trigger OnStarting if it hasn't been called yet and the app hasn't
                // already failed. If an OnStarting callback throws we can go through
                // our normal error handling in ProduceEnd.
                // https://github.com/aspnet/KestrelHttpServer/issues/43
                if (!HasResponseStarted && _applicationException == null && _onStarting?.Count > 0)
                {
                    await FireOnStarting();
                }

                if (!_connectionAborted && !VerifyResponseContentLength(out var lengthException))
                {
                    ReportApplicationError(lengthException);
                }
            }
            catch (BadHttpRequestException ex)
            {
                // Capture BadHttpRequestException for further processing
                // This has to be caught here so StatusCode is set properly before disposing the HttpContext
                // (DisposeContext logs StatusCode).
                SetBadRequestState(ex);
                ReportApplicationError(ex);
            }
            catch (Exception ex)
            {
                ReportApplicationError(ex);
            }

            KestrelEventSource.Log.RequestStop(this);

            // At this point all user code that needs use to the request or response streams has completed.
            // Using these streams in the OnCompleted callback is not allowed.
            try
            {
                Debug.Assert(_bodyControl != null);
                await _bodyControl.StopAsync();
            }
            catch (Exception ex)
            {
                // BodyControl.StopAsync() can throw if the PipeWriter was completed prior to the application writing
                // enough bytes to satisfy the specified Content-Length. This risks double-logging the exception,
                // but this scenario generally indicates an app bug, so I don't want to risk not logging it.
                ReportApplicationError(ex);
            }

            // 4XX responses are written by TryProduceInvalidRequestResponse during connection tear down.
            if (_requestRejectedException == null)
            {
                if (!_connectionAborted)
                {
                    // Call ProduceEnd() before consuming the rest of the request body to prevent
                    // delaying clients waiting for the chunk terminator:
                    //
                    // https://github.com/dotnet/corefx/issues/17330#issuecomment-288248663
                    //
                    // This also prevents the 100 Continue response from being sent if the app
                    // never tried to read the body.
                    // https://github.com/aspnet/KestrelHttpServer/issues/2102
                    //
                    // ProduceEnd() must be called before _application.DisposeContext(), to ensure
                    // HttpContext.Response.StatusCode is correctly set when
                    // IHttpContextFactory.Dispose(HttpContext) is called.
                    await ProduceEnd();
                }
                else if (!HasResponseStarted)
                {
                    // If the request was aborted and no response was sent, there's no
                    // meaningful status code to log.
                    StatusCode = 0;
                }
            }

            if (_onCompleted?.Count > 0)
            {
                await FireOnCompleted();
            }

            application.DisposeContext(context, _applicationException);

            // Even for non-keep-alive requests, try to consume the entire body to avoid RSTs.
            if (!_connectionAborted && _requestRejectedException == null && !messageBody.IsEmpty)
            {
                await messageBody.ConsumeAsync();
            }

            if (HasStartedConsumingRequestBody)
            {
                await messageBody.StopAsync();
            }
        }
    }

 public Context CreateContext(IFeatureCollection contextFeatures)
    {
        Context? hostContext;
        if (contextFeatures is IHostContextContainer<Context> container)
        {
            hostContext = container.HostContext;
            if (hostContext is null)
            {
                hostContext = new Context();
                container.HostContext = hostContext;
            }
        }
        else
        {
            // Server doesn't support pooling, so create a new Context
            hostContext = new Context();
        }

        HttpContext httpContext;
        if (_defaultHttpContextFactory != null)
        {
            var defaultHttpContext = (DefaultHttpContext?)hostContext.HttpContext;
            if (defaultHttpContext is null)
            {
                httpContext = _defaultHttpContextFactory.Create(contextFeatures);
                hostContext.HttpContext = httpContext;
            }
            else
            {
                _defaultHttpContextFactory.Initialize(defaultHttpContext, contextFeatures);
                httpContext = defaultHttpContext;
            }
        }
        else
        {
            httpContext = _httpContextFactory!.Create(contextFeatures);
            hostContext.HttpContext = httpContext;
        }

        _diagnostics.BeginRequest(httpContext, hostContext);
        return hostContext;
    }

    // Execute the request
    public Task ProcessRequestAsync(Context context)
    {
        return _application(context.HttpContext!);
    }

    // Clean up the request
    public void DisposeContext(Context context, Exception? exception)
    {
        var httpContext = context.HttpContext!;
        _diagnostics.RequestEnd(httpContext, exception, context);

        if (_defaultHttpContextFactory != null)
        {
            _defaultHttpContextFactory.Dispose((DefaultHttpContext)httpContext);

            if (_defaultHttpContextFactory.HttpContextAccessor != null)
            {
                // Clear the HttpContext if the accessor was used. It's likely that the lifetime extends
                // past the end of the http request and we want to avoid changing the reference from under
                // consumers.
                context.HttpContext = null;
            }
        }
        else
        {
            _httpContextFactory!.Dispose(httpContext);
        }

        HostingApplicationDiagnostics.ContextDisposed(context);

        // Reset the context as it may be pooled
        context.Reset();
    }