asp.Netcore 3.1 Routing(二)

public static class EndpointRoutingApplicationBuilderExtensions
    {
        private const string EndpointRouteBuilder = "__EndpointRouteBuilder";

        /// 

        /// Adds a  middleware to the specified .
        /// 
        /// The  to add the middleware to.
        /// A reference to this instance after the operation has completed.
        /// 
        /// 
        /// A call to  must be followed by a call to
        ///  for the same 
        /// instance.
        /// 
        /// 
        /// The  defines a point in the middleware pipeline where routing decisions are
        /// made, and an  is associated with the . The 
        /// defines a point in the middleware pipeline where the current  is executed. Middleware between
        /// the  and  may observe or change the
        ///  associated with the .
        /// 
        /// 
        public static IApplicationBuilder UseRouting(this IApplicationBuilder builder)
        {
            if (builder == null)
            {
                throw new ArgumentNullException(nameof(builder));
            }

            VerifyRoutingServicesAreRegistered(builder);

            var endpointRouteBuilder = new DefaultEndpointRouteBuilder(builder);
            builder.Properties[EndpointRouteBuilder] = endpointRouteBuilder;

            return builder.UseMiddleware(endpointRouteBuilder);
        }

        /// 

        /// Adds a  middleware to the specified 
        /// with the  instances built from configured .
        /// The  will execute the  associated with the current
        /// request.
        /// 
        /// The  to add the middleware to.
        /// An  to configure the provided .
        /// A reference to this instance after the operation has completed.
        /// 
        /// 
        /// A call to  must be preceded by a call to
        ///  for the same 
        /// instance.
        /// 
        /// 
        /// The  defines a point in the middleware pipeline where routing decisions are
        /// made, and an  is associated with the . The 
        /// defines a point in the middleware pipeline where the current  is executed. Middleware between
        /// the  and  may observe or change the
        ///  associated with the .
        /// 
        /// 
        public static IApplicationBuilder UseEndpoints(this IApplicationBuilder builder, Action configure)
        {
            if (builder == null)
            {
                throw new ArgumentNullException(nameof(builder));
            }

            if (configure == null)
            {
                throw new ArgumentNullException(nameof(configure));
            }

            VerifyRoutingServicesAreRegistered(builder);

            VerifyEndpointRoutingMiddlewareIsRegistered(builder, out var endpointRouteBuilder);

            configure(endpointRouteBuilder);

            // Yes, this mutates an IOptions. We're registering data sources in a global collection which
            // can be used for discovery of endpoints or URL generation.
            //
            // Each middleware gets its own collection of data sources, and all of those data sources also
            // get added to a global collection.
            var routeOptions = builder.ApplicationServices.GetRequiredService>();
            foreach (var dataSource in endpointRouteBuilder.DataSources)
            {
                routeOptions.Value.EndpointDataSources.Add(dataSource);
            }

            return builder.UseMiddleware();
        }

        private static void VerifyRoutingServicesAreRegistered(IApplicationBuilder app)
        {
            // Verify if AddRouting was done before calling UseEndpointRouting/UseEndpoint
            // We use the RoutingMarkerService to make sure if all the services were added.
            if (app.ApplicationServices.GetService(typeof(RoutingMarkerService)) == null)
            {
                throw new InvalidOperationException(Resources.FormatUnableToFindServices(
                    nameof(IServiceCollection),
                    nameof(RoutingServiceCollectionExtensions.AddRouting),
                    "ConfigureServices(...)"));
            }
        }

        private static void VerifyEndpointRoutingMiddlewareIsRegistered(IApplicationBuilder app, out DefaultEndpointRouteBuilder endpointRouteBuilder)
        {
            if (!app.Properties.TryGetValue(EndpointRouteBuilder, out var obj))
            {
                var message =
                    $"{nameof(EndpointRoutingMiddleware)} matches endpoints setup by {nameof(EndpointMiddleware)} and so must be added to the request " +
                    $"execution pipeline before {nameof(EndpointMiddleware)}. " +
                    $"Please add {nameof(EndpointRoutingMiddleware)} by calling '{nameof(IApplicationBuilder)}.{nameof(UseRouting)}' inside the call " +
                    $"to 'Configure(...)' in the application startup code.";
                throw new InvalidOperationException(message);
            }

            // If someone messes with this, just let it crash.
            endpointRouteBuilder = (DefaultEndpointRouteBuilder)obj;

            // This check handles the case where Map or something else that forks the pipeline is called between the two
            // routing middleware.
            if (!object.ReferenceEquals(app, endpointRouteBuilder.ApplicationBuilder))
            {
                var message =
                    $"The {nameof(EndpointRoutingMiddleware)} and {nameof(EndpointMiddleware)} must be added to the same {nameof(IApplicationBuilder)} instance. " +
                    $"To use Endpoint Routing with 'Map(...)', make sure to call '{nameof(IApplicationBuilder)}.{nameof(UseRouting)}' before " +
                    $"'{nameof(IApplicationBuilder)}.{nameof(UseEndpoints)}' for each branch of the middleware pipeline.";
                throw new InvalidOperationException(message);
            }
        }
    }

internal sealed class EndpointRoutingMiddleware
    {
        private const string DiagnosticsEndpointMatchedKey = "Microsoft.AspNetCore.Routing.EndpointMatched";

        private readonly MatcherFactory _matcherFactory;
        private readonly ILogger _logger;
        private readonly EndpointDataSource _endpointDataSource;
        private readonly DiagnosticListener _diagnosticListener;
        private readonly RequestDelegate _next;

        private Task _initializationTask;

        public EndpointRoutingMiddleware(
            MatcherFactory matcherFactory,
            ILogger logger,
            IEndpointRouteBuilder endpointRouteBuilder,
            DiagnosticListener diagnosticListener,
            RequestDelegate next)
        {
            if (endpointRouteBuilder == null)
            {
                throw new ArgumentNullException(nameof(endpointRouteBuilder));
            }

            _matcherFactory = matcherFactory ?? throw new ArgumentNullException(nameof(matcherFactory));
            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
            _diagnosticListener = diagnosticListener ?? throw new ArgumentNullException(nameof(diagnosticListener));
            _next = next ?? throw new ArgumentNullException(nameof(next));

            _endpointDataSource = new CompositeEndpointDataSource(endpointRouteBuilder.DataSources);
        }

        public Task Invoke(HttpContext httpContext)
        {
            // There's already an endpoint, skip maching completely
            var endpoint = httpContext.GetEndpoint();
            if (endpoint != null)
            {
                Log.MatchSkipped(_logger, endpoint);
                return _next(httpContext);
            }

            // There's an inherent race condition between waiting for init and accessing the matcher
            // this is OK because once `_matcher` is initialized, it will not be set to null again.
            var matcherTask = InitializeAsync();
            if (!matcherTask.IsCompletedSuccessfully)
            {
                return AwaitMatcher(this, httpContext, matcherTask);
            }

            var matchTask = matcherTask.Result.MatchAsync(httpContext);
            if (!matchTask.IsCompletedSuccessfully)
            {
                return AwaitMatch(this, httpContext, matchTask);
            }

            return SetRoutingAndContinue(httpContext);

            // Awaited fallbacks for when the Tasks do not synchronously complete
            static async Task AwaitMatcher(EndpointRoutingMiddleware middleware, HttpContext httpContext, Task matcherTask)
            {
                var matcher = await matcherTask;
                await matcher.MatchAsync(httpContext);
                await middleware.SetRoutingAndContinue(httpContext);
            }

            static async Task AwaitMatch(EndpointRoutingMiddleware middleware, HttpContext httpContext, Task matchTask)
            {
                await matchTask;
                await middleware.SetRoutingAndContinue(httpContext);
            }

        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private Task SetRoutingAndContinue(HttpContext httpContext)
        {
            // If there was no mutation of the endpoint then log failure
            var endpoint = httpContext.GetEndpoint();
            if (endpoint == null)
            {
                Log.MatchFailure(_logger);
            }
            else
            {
                // Raise an event if the route matched
                if (_diagnosticListener.IsEnabled() && _diagnosticListener.IsEnabled(DiagnosticsEndpointMatchedKey))
                {
                    // We're just going to send the HttpContext since it has all of the relevant information
                    _diagnosticListener.Write(DiagnosticsEndpointMatchedKey, httpContext);
                }

                Log.MatchSuccess(_logger, endpoint);
            }

            return _next(httpContext);
        }

        // Initialization is async to avoid blocking threads while reflection and things
        // of that nature take place.
        //
        // We've seen cases where startup is very slow if we  allow multiple threads to race
        // while initializing the set of endpoints/routes. Doing CPU intensive work is a
        // blocking operation if you have a low core count and enough work to do.
        private Task InitializeAsync()
        {
            var initializationTask = _initializationTask;
            if (initializationTask != null)
            {
                return initializationTask;
            }

            return InitializeCoreAsync();
        }

        private Task InitializeCoreAsync()
        {
            var initialization = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
            var initializationTask = Interlocked.CompareExchange(ref _initializationTask, initialization.Task, null);
            if (initializationTask != null)
            {
                // This thread lost the race, join the existing task.
                return initializationTask;
            }

            // This thread won the race, do the initialization.
            try
            {
                var matcher = _matcherFactory.CreateMatcher(_endpointDataSource);

                // Now replace the initialization task with one created with the default execution context.
                // This is important because capturing the execution context will leak memory in ASP.NET Core.
                using (ExecutionContext.SuppressFlow())
                {
                    _initializationTask = Task.FromResult(matcher);
                }

                // Complete the task, this will unblock any requests that came in while initializing.
                initialization.SetResult(matcher);
                return initialization.Task;
            }
            catch (Exception ex)
            {
                // Allow initialization to occur again. Since DataSources can change, it's possible
                // for the developer to correct the data causing the failure.
                _initializationTask = null;

                // Complete the task, this will throw for any requests that came in while initializing.
                initialization.SetException(ex);
                return initialization.Task;
            }
        }

        private static class Log
        {
            private static readonly Actionstring, Exception> _matchSuccess = LoggerMessage.Define<string>(
                LogLevel.Debug,
                new EventId(1, "MatchSuccess"),
                "Request matched endpoint '{EndpointName}'");

            private static readonly Action _matchFailure = LoggerMessage.Define(
                LogLevel.Debug,
                new EventId(2, "MatchFailure"),
                "Request did not match any endpoints");

            private static readonly Actionstring, Exception> _matchingSkipped = LoggerMessage.Define<string>(
                LogLevel.Debug,
                new EventId(3, "MatchingSkipped"),
                "Endpoint '{EndpointName}' already set, skipping route matching.");

            public static void MatchSuccess(ILogger logger, Endpoint endpoint)
            {
                _matchSuccess(logger, endpoint.DisplayName, null);
            }

            public static void MatchFailure(ILogger logger)
            {
                _matchFailure(logger, null);
            }

            public static void MatchSkipped(ILogger logger, Endpoint endpoint)
            {
                _matchingSkipped(logger, endpoint.DisplayName, null);
            }
        }
    }

EndpointRoutingMiddlewareはまずHttpContextからEndpointを取得し、nullでない場合は次のミドルウェアの呼び出しを続行します.
見つからない場合は、DfaMatcherクラスのMatchAsyncを呼び出して対応するEndpointを見つけ、HttpContextを設定します.
具体的にどのように対応するEndpointを探し当てて、ここで詳しく言いません
Endpointを見て

public class Endpoint
    {
        /// 

        /// Creates a new instance of .
        /// 
        /// The delegate used to process requests for the endpoint.
        /// 
        /// The endpoint . May be null.
        /// 
        /// 
        /// The informational display name of the endpoint. May be null.
        /// 
        public Endpoint(
            RequestDelegate requestDelegate,
            EndpointMetadataCollection metadata,
            string displayName)
        {
            // All are allowed to be null
            RequestDelegate = requestDelegate;
            Metadata = metadata ?? EndpointMetadataCollection.Empty;
            DisplayName = displayName;
        }

        /// 

        /// Gets the informational display name of this endpoint.
        /// 
        public string DisplayName { get; }

        /// 

        /// Gets the collection of metadata associated with this endpoint.
        /// 
        public EndpointMetadataCollection Metadata { get; }

        /// 

        /// Gets the delegate used to process requests for the endpoint.
        /// 
        public RequestDelegate RequestDelegate { get; }

        public override string ToString() => DisplayName ?? base.ToString();
    }

internal sealed class EndpointMiddleware
    {
        internal const string AuthorizationMiddlewareInvokedKey = "__AuthorizationMiddlewareWithEndpointInvoked";
        internal const string CorsMiddlewareInvokedKey = "__CorsMiddlewareWithEndpointInvoked";

        private readonly ILogger _logger;
        private readonly RequestDelegate _next;
        private readonly RouteOptions _routeOptions;

        public EndpointMiddleware(
            ILogger logger,
            RequestDelegate next,
            IOptions routeOptions)
        {
            _logger = logger ?? throw new ArgumentNullException(nameof(logger));
            _next = next ?? throw new ArgumentNullException(nameof(next));
            _routeOptions = routeOptions?.Value ?? throw new ArgumentNullException(nameof(routeOptions));
        }

        public Task Invoke(HttpContext httpContext)
        {
            var endpoint = httpContext.GetEndpoint();
            if (endpoint?.RequestDelegate != null)
            {
                if (!_routeOptions.SuppressCheckForUnhandledSecurityMetadata)
                {
                    if (endpoint.Metadata.GetMetadata() != null &&
                        !httpContext.Items.ContainsKey(AuthorizationMiddlewareInvokedKey))
                    {
                        ThrowMissingAuthMiddlewareException(endpoint);
                    }

                    if (endpoint.Metadata.GetMetadata() != null &&
                        !httpContext.Items.ContainsKey(CorsMiddlewareInvokedKey))
                    {
                        ThrowMissingCorsMiddlewareException(endpoint);
                    }
                }

                Log.ExecutingEndpoint(_logger, endpoint);

                try
                {
                    var requestTask = endpoint.RequestDelegate(httpContext);
                    if (!requestTask.IsCompletedSuccessfully)
                    {
                        return AwaitRequestTask(endpoint, requestTask, _logger);
                    }
                }
                catch (Exception exception)
                {
                    Log.ExecutedEndpoint(_logger, endpoint);
                    return Task.FromException(exception);
                }

                Log.ExecutedEndpoint(_logger, endpoint);
                return Task.CompletedTask;
            }

            return _next(httpContext);

            static async Task AwaitRequestTask(Endpoint endpoint, Task requestTask, ILogger logger)
            {
                try
                {
                    await requestTask;
                }
                finally
                {
                    Log.ExecutedEndpoint(logger, endpoint);
                }
            }
        }

        private static void ThrowMissingAuthMiddlewareException(Endpoint endpoint)
        {
            throw new InvalidOperationException($"Endpoint {endpoint.DisplayName} contains authorization metadata, " +
                "but a middleware was not found that supports authorization." +
                Environment.NewLine +
                "Configure your application startup by adding app.UseAuthorization() inside the call to Configure(..) in the application startup code. The call to app.UseAuthorization() must appear between app.UseRouting() and app.UseEndpoints(...).");
        }

        private static void ThrowMissingCorsMiddlewareException(Endpoint endpoint)
        {
            throw new InvalidOperationException($"Endpoint {endpoint.DisplayName} contains CORS metadata, " +
                "but a middleware was not found that supports CORS." +
                Environment.NewLine +
                "Configure your application startup by adding app.UseCors() inside the call to Configure(..) in the application startup code. The call to app.UseAuthorization() must appear between app.UseRouting() and app.UseEndpoints(...).");
        }

        private static class Log
        {
            private static readonly Actionstring, Exception> _executingEndpoint = LoggerMessage.Define<string>(
                LogLevel.Information,
                new EventId(0, "ExecutingEndpoint"),
                "Executing endpoint '{EndpointName}'");

            private static readonly Actionstring, Exception> _executedEndpoint = LoggerMessage.Define<string>(
                LogLevel.Information,
                new EventId(1, "ExecutedEndpoint"),
                "Executed endpoint '{EndpointName}'");

            public static void ExecutingEndpoint(ILogger logger, Endpoint endpoint)
            {
                _executingEndpoint(logger, endpoint.DisplayName, null);
            }

            public static void ExecutedEndpoint(ILogger logger, Endpoint endpoint)
            {
                _executedEndpoint(logger, endpoint.DisplayName, null);
            }
        }
    }

EndpointMiddlewareミドルウェアは、HttpContextのEndPointを取得し、EndpointのRequestDelegate処理要求を呼び出す