## 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：
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！！
