Asp.Net Core EndPoint 终结点路由工作原理解读

Asp.Net Core EndPoint 终点路由工作原理解读

一、背景

在本打算写一篇关于Identityserver4 的文章时候，却发现自己对EndPoint -终结点路由还不是很了解，故暂时先放弃了IdentityServer4 的研究和编写；所以才产生了今天这篇关于EndPoint (终结点路由) 的文章。

还是跟往常一样，打开电脑使用强大的Google 和百度搜索引擎查阅相关资料，以及打开Asp.net core 3.1 的源代码进行拜读，同时终于在我的实践及测试中对EndPoint 有了不一样的认识，说到这里更加敬佩微软对Asp.net core 3.x 的框架中管道模型的设计。

我先来提出以下几个问题：

1.当访问一个Web 应用地址时，Asp.Net Core 是怎么执行到Controller 的Action的呢？2.Endpoint 跟普通路由又存在着什么样的关系？3.UseRouing() 、UseAuthorization()、UserEndpoints() 这三个中间件的关系是什么呢？4.怎么利用Endpoint 编写自己的中间件以及Endpoint 的应用场景（时间有限，下回分享整理）

二、拜读源码解惑

`Startup` 代码

我们先来看一下Startup中简化版的代码，代码如下：

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

程序启动阶段：

•第一步：执行services.AddControllers() 将Controller的核心服务注册到容器中去•第二步：执行app.UseRouting() 将EndpointRoutingMiddleware中间件注册到http管道中•第三步：执行app.UseAuthorization() 将AuthorizationMiddleware中间件注册到http管道中•第四步：执行app.UseEndpoints(encpoints=>endpoints.MapControllers()) 有两个主要的作用：调用endpoints.MapControllers()将本程序集定义的所有Controller和Action转换为一个个的EndPoint放到路由中间件的配置对象RouteOptions中将EndpointMiddleware中间件注册到http管道中

`app.UseRouting()` 源代码如下：

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 中间件代码如下：

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);}}}

我们从它的源码中可以看到，EndpointRoutingMiddleware中间件先是创建matcher，然后调用matcher.MatchAsync(httpContext)去寻找Endpoint，最后通过httpContext.GetEndpoint()验证了是否已经匹配到了正确的Endpoint并交个下个中间件继续执行！

`app.UseEndpoints()` 源代码

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;}

代码中构建了DefaultEndpointRouteBuilder 终结点路由构建者对象，该对象中存储了Endpoint的集合数据；同时把终结者路由集合数据存储在了routeOptions 中，并注册了EndpointMiddleware 中间件到http管道中； Endpoint对象代码如下：

/// <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 对象代码中有两个关键类型属性分别是EndpointMetadataCollection 类型和RequestDelegate：

•EndpointMetadataCollection：存储了Controller 和Action相关的元素集合，包含Action 上的Attribute 特性数据等•RequestDelegate ：存储了Action 也即委托，这里是每一个Controller 的Action 方法

再回过头来看看EndpointMiddleware 中间件和核心代码，EndpointMiddleware 的一大核心代码主要是执行Endpoint 的RequestDelegate 委托，也即Controller 中的Action 的执行。

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. 当访问一个Web 应用地址时，Asp.Net Core 是怎么执行到`Controller` 的`Action`的呢？

答：程序启动的时候会把所有的Controller 中的Action 映射存储到routeOptions 的集合中，Action 映射成Endpoint终结者的RequestDelegate 委托属性，最后通过UseEndPoints 添加EndpointMiddleware 中间件进行执行，同时这个中间件中的Endpoint 终结者路由已经是通过Rouing匹配后的路由。

2. `EndPoint` 跟普通路由又存在着什么样的关系？

答：Ednpoint 终结者路由是普通路由map 转换后的委托路由，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()` 这三个中间件的关系是什么呢？

答：UseRouing 中间件主要是路由匹配，找到匹配的终结者路由Endpoint ；UseEndpoints 中间件主要针对UseRouing 中间件匹配到的路由进行委托方法的执行等操作。 UseAuthorization 中间件主要针对 UseRouing 中间件中匹配到的路由进行拦截做授权验证操作等，通过则执行下一个中间件UseEndpoints(),具体的关系可以看下面的流程图：