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Asp.Net Core EndPoint 终点路由工作原理解读

Jlion 人气:1
## 一、背景 在本打算写一篇关于`Identityserver4` 的文章时候,确发现自己对`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` 终结者路由来拦截Action 的执行并且记录相关操作日志?(时间有限,下一篇文章再来分享整理) ## 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(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 _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 Action _matchSuccess = LoggerMessage.Define( 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 Action _matchingSkipped = LoggerMessage.Define( 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 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(); } internal class DefaultEndpointRouteBuilder : IEndpointRouteBuilder { public DefaultEndpointRouteBuilder(IApplicationBuilder applicationBuilder) { ApplicationBuilder = applicationBuilder ?? throw new ArgumentNullException(nameof(applicationBuilder)); DataSources = new List(); } public IApplicationBuilder ApplicationBuilder { get; } public IApplicationBuilder CreateApplicationBuilder() => ApplicationBuilder.New(); public ICollection 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: ``` /// /// Represents a logical endpoint in an application. /// 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(); } ``` `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() != 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); } } } ``` #### 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: ![](https://img2020.cnblogs.com/blog/824291/202003/824291-20200305222447968-1474571766.png) 上面流程图中省略了一些部分,主要是把UseRouing 、UseAuthorization 、UseEndpoint 这三个中间件的关系突显出来。 以上如果有错误得地方,请大家积极纠正,谢谢大家得支持!!

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