Asp.Net Core EndPoint 終點路由工作原理解讀

一、背景

在本打算寫一篇關于Identityserver4?的文章時候，卻發現自己對EndPoint?-終結點路由還不是很了解，故暫時先放棄了IdentityServer4?的研究和編寫；所以才產生了今天這篇關于EndPoint?(終結點路由) 的文章。

還是跟往常一樣，打開電腦使用強大的Google 和百度搜索引擎查閱相關資料，以及打開Asp.net core 3.1 的源代碼進行拜讀，同時終于在我的實踐及測試中對EndPoint?有了不一樣的認識，說到這里更加敬佩微軟對Asp.net core 3.x 的框架中管道模型的設計。

我先來提出以下幾個問題：

1.當訪問一個Web 應用地址時，Asp.Net Core 是怎么執行到Controller?的Action的呢？2.Endpoint?跟普通路由又存在著什么樣的關系？3.UseRouing()?、UseAuthorization()、UserEndpoints()?這三個中間件的關系是什么呢？4.怎么利用Endpoint?編寫自己的中間件以及Endpoint 的應用場景（時間有限，下回分享整理）

二、拜讀源碼解惑

Startup?代碼

我們先來看一下Startup中簡化版的代碼，代碼如下：

public void ConfigureServices(IServiceCollection services) {services.AddControllers(); }public void Configure(IApplicationBuilder app, IWebHostEnvironment env) {app.UseRouting();app.UseAuthorization();app.UseEndpoints(endpoints =>{endpoints.MapControllers();}); }

程序啟動階段：

?第一步：執行services.AddControllers() 將Controller的核心服務注冊到容器中去?第二步：執行app.UseRouting() 將EndpointRoutingMiddleware中間件注冊到http管道中?第三步：執行app.UseAuthorization() 將AuthorizationMiddleware中間件注冊到http管道中?第四步：執行app.UseEndpoints(encpoints=>endpoints.MapControllers()) 有兩個主要的作用：調用endpoints.MapControllers()將本程序集定義的所有Controller和Action轉換為一個個的EndPoint放到路由中間件的配置對象RouteOptions中 將EndpointMiddleware中間件注冊到http管道中

app.UseRouting()?源代碼如下：

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<EndpointRoutingMiddleware>(endpointRouteBuilder);}

EndpointRoutingMiddleware?中間件代碼如下：

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<Matcher> _initializationTask;public EndpointRoutingMiddleware(MatcherFactory matcherFactory,ILogger<EndpointRoutingMiddleware> 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 completelyvar 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 completestatic async Task AwaitMatcher(EndpointRoutingMiddleware middleware, HttpContext httpContext, Task<Matcher> 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 failurevar endpoint = httpContext.GetEndpoint();if (endpoint == null){Log.MatchFailure(_logger);}else{// Raise an event if the route matchedif (_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<Matcher> InitializeAsync(){var initializationTask = _initializationTask;if (initializationTask != null){return initializationTask;}return InitializeCoreAsync();}private Task<Matcher> InitializeCoreAsync(){var initialization = new TaskCompletionSource<Matcher>(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 Action<ILogger, string, Exception> _matchSuccess = LoggerMessage.Define<string>(LogLevel.Debug,new EventId(1, "MatchSuccess"),"Request matched endpoint '{EndpointName}'");private static readonly Action<ILogger, Exception> _matchFailure = LoggerMessage.Define(LogLevel.Debug,new EventId(2, "MatchFailure"),"Request did not match any endpoints");private static readonly Action<ILogger, string, 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);}}}

我們從它的源碼中可以看到，EndpointRoutingMiddleware中間件先是創建matcher，然后調用matcher.MatchAsync(httpContext)去尋找Endpoint，最后通過httpContext.GetEndpoint()驗證了是否已經匹配到了正確的Endpoint并交個下個中間件繼續執行！

app.UseEndpoints()?源代碼

public static IApplicationBuilder UseEndpoints(this IApplicationBuilder builder, Action<IEndpointRouteBuilder> 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<IOptions<RouteOptions>>();foreach (var dataSource in endpointRouteBuilder.DataSources){routeOptions.Value.EndpointDataSources.Add(dataSource);}return builder.UseMiddleware<EndpointMiddleware>(); }internal class DefaultEndpointRouteBuilder : IEndpointRouteBuilder {public DefaultEndpointRouteBuilder(IApplicationBuilder applicationBuilder){ApplicationBuilder = applicationBuilder ?? throw new ArgumentNullException(nameof(applicationBuilder));DataSources = new List<EndpointDataSource>();}public IApplicationBuilder ApplicationBuilder { get; }public IApplicationBuilder CreateApplicationBuilder() => ApplicationBuilder.New();public ICollection<EndpointDataSource> DataSources { get; }public IServiceProvider ServiceProvider => ApplicationBuilder.ApplicationServices;}

代碼中構建了DefaultEndpointRouteBuilder?終結點路由構建者對象，該對象中存儲了Endpoint的集合數據；同時把終結者路由集合數據存儲在了routeOptions?中，并注冊了EndpointMiddleware?中間件到http管道中；?Endpoint對象代碼如下：

/// <summary> /// Represents a logical endpoint in an application. /// </summary> public class Endpoint {/// <summary>/// Creates a new instance of <see cref="Endpoint"/>./// </summary>/// <param name="requestDelegate">The delegate used to process requests for the endpoint.</param>/// <param name="metadata">/// The endpoint <see cref="EndpointMetadataCollection"/>. May be null./// </param>/// <param name="displayName">/// The informational display name of the endpoint. May be null./// </param>public Endpoint(RequestDelegate requestDelegate,EndpointMetadataCollection metadata,string displayName){// All are allowed to be nullRequestDelegate = requestDelegate;Metadata = metadata ?? EndpointMetadataCollection.Empty;DisplayName = displayName;}/// <summary>/// Gets the informational display name of this endpoint./// </summary>public string DisplayName { get; }/// <summary>/// Gets the collection of metadata associated with this endpoint./// </summary>public EndpointMetadataCollection Metadata { get; }/// <summary>/// Gets the delegate used to process requests for the endpoint./// </summary>public RequestDelegate RequestDelegate { get; }public override string ToString() => DisplayName ?? base.ToString();}

Endpoint?對象代碼中有兩個關鍵類型屬性分別是EndpointMetadataCollection?類型和RequestDelegate：

?EndpointMetadataCollection：存儲了Controller?和Action相關的元素集合，包含Action?上的Attribute?特性數據等?RequestDelegate?：存儲了Action 也即委托，這里是每一個Controller 的Action 方法

再回過頭來看看EndpointMiddleware?中間件和核心代碼，EndpointMiddleware?的一大核心代碼主要是執行Endpoint 的RequestDelegate?委托，也即Controller?中的Action?的執行。

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

疑惑解答：

1. 當訪問一個Web 應用地址時，Asp.Net Core 是怎么執行到Controller?的Action的呢？

答：程序啟動的時候會把所有的Controller 中的Action 映射存儲到routeOptions?的集合中，Action 映射成Endpoint終結者 的RequestDelegate?委托屬性，最后通過UseEndPoints?添加EndpointMiddleware?中間件進行執行，同時這個中間件中的Endpoint?終結者路由已經是通過Rouing匹配后的路由。

2.?EndPoint?跟普通路由又存在著什么樣的關系？

答：Ednpoint?終結者路由是普通路由map 轉換后的委托路由，里面包含了路由方法的所有元素信息EndpointMetadataCollection?和RequestDelegate?委托。

3.?UseRouing()?、UseAuthorization()、UseEndpoints()?這三個中間件的關系是什么呢？

答：UseRouing?中間件主要是路由匹配，找到匹配的終結者路由Endpoint?；UseEndpoints?中間件主要針對UseRouing?中間件匹配到的路由進行 委托方法的執行等操作。?UseAuthorization?中間件主要針對?UseRouing?中間件中匹配到的路由進行攔截 做授權驗證操作等，通過則執行下一個中間件UseEndpoints(),具體的關系可以看下面的流程圖：

上面流程圖中省略了一些部分，主要是把UseRouing 、UseAuthorization 、UseEndpoint 這三個中間件的關系突顯出來。

以上如果有錯誤的地方，請大家積極糾正，謝謝大家的支持！！

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