重新整理 .net core 实践篇——— UseEndpoints中间件[四十八]

前言

前文已经提及到了endponint 是怎么匹配到的，也就是说在UseRouting 之后的中间件都能获取到endpoint了，如果能够匹配到的话，那么UseEndpoints又做了什么呢？它是如何执行我们的action的呢。

正文

直接按顺序看代码好了:

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>();
}

这里面首先做了两个验证，一个是VerifyRoutingServicesAreRegistered 验证路由服务是否注册了，第二个VerifyEndpointRoutingMiddlewareIsRegistered是验证烟油中间件是否注入了。

验证手法也挺简单的。

VerifyRoutingServicesAreRegistered 直接验证是否serviceCollection 是否可以获取该服务。

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(...)"));
	}
}

VerifyEndpointRoutingMiddlewareIsRegistered 这个验证Properties 是否有EndpointRouteBuilder

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);
	}
}

然后判断是否endpointRouteBuilder.ApplicationBuilder 和 app 是否相等，这里使用的是object.ReferenceEquals，其实是判断其中的引用是否相等，指针概念。

上面的验证只是做了一个简单的验证了，但是从中可以看到，肯定是该中间件要使用endpointRouteBuilder的了。

中间件就是大一点的方法，也逃不出验证参数、执行核心代码、返回结果的三步走。

var routeOptions = builder.ApplicationServices.GetRequiredService<IOptions<RouteOptions>>();
foreach (var dataSource in endpointRouteBuilder.DataSources)
{
	routeOptions.Value.EndpointDataSources.Add(dataSource);
}

这里就是填充RouteOptions的EndpointDataSources了。

那么具体看EndpointMiddleware吧。

public EndpointMiddleware(
	ILogger<EndpointMiddleware> logger,
	RequestDelegate next,
	IOptions<RouteOptions> 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<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);
		}
	}
}

EndpointMiddleware 初始化的时候注入了routeOptions。

然后直接看invoke了。

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);
	}
}

这里面判断了如果有IAuthorizeData 元数据，如果没有权限中间件的统一抛出异常。

然后如果有ICorsMetadata元数据的，这个是某个action指定了跨域规则的，统一抛出异常。

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;

这一段就是执行我们的action了，RequestDelegate 这一个就是在执行我们的action，同样注入了httpContext。

里面的逻辑非常简单哈。

那么这里就有人问了，前面你不是说要用到IEndpointRouteBuilder，怎么没有用到呢？

看这个，前面我们一直谈及到IEndpointRouteBuilder 管理着datasource，我们从来就没有看到datasource 是怎么生成的。

在UseRouting中，我们看到:

这里new 了一个DefaultEndpointRouteBuilder，DefaultEndpointRouteBuilder 继承IEndpointRouteBuilder，但是我们看到这里没有datasource注入。

那么我们的action 是如何转换为endponit的呢？可以参考endpoints.MapControllers();。

这个地方值得注意的是:

这些地方不是在执行中间件哈，而是在组合中间件，中间件是在这里组合完毕的。

那么简单看一下MapControllers 是如何生成datasource的吧,当然有很多生成datasource的，这里只介绍一下这个哈。

ControllerActionEndpointConventionBuilder MapControllers(
  this IEndpointRouteBuilder endpoints)
{
  if (endpoints == null)
	throw new ArgumentNullException(nameof (endpoints));
  ControllerEndpointRouteBuilderExtensions.EnsureControllerServices(endpoints);
  return ControllerEndpointRouteBuilderExtensions.GetOrCreateDataSource(endpoints).DefaultBuilder;
}

看下EnsureControllerServices:

private static void EnsureControllerServices(IEndpointRouteBuilder endpoints)
{
  if (endpoints.ServiceProvider.GetService<MvcMarkerService>() == null)
	throw new InvalidOperationException(Microsoft.AspNetCore.Mvc.Core.Resources.FormatUnableToFindServices((object) "IServiceCollection", (object) "AddControllers", (object) "ConfigureServices(...)"));
}

这里检查我们是否注入mvc服务。这里我们是值得借鉴的地方了，每次在服务注入的时候专门有一个服务注入的标志，这样就可以检测出服务是否注入了，这样我们就可以更加准确的抛出异常，而不是通过依赖注入服务来抛出。

private static ControllerActionEndpointDataSource GetOrCreateDataSource(
  IEndpointRouteBuilder endpoints)
{
  ControllerActionEndpointDataSource endpointDataSource = endpoints.DataSources.OfType<ControllerActionEndpointDataSource>().FirstOrDefault<ControllerActionEndpointDataSource>();
  if (endpointDataSource == null)
  {
	OrderedEndpointsSequenceProviderCache requiredService = endpoints.ServiceProvider.GetRequiredService<OrderedEndpointsSequenceProviderCache>();
	endpointDataSource = endpoints.ServiceProvider.GetRequiredService<ControllerActionEndpointDataSourceFactory>().Create(requiredService.GetOrCreateOrderedEndpointsSequenceProvider(endpoints));
	endpoints.DataSources.Add((EndpointDataSource) endpointDataSource);
  }
  return endpointDataSource;
}

这里的匹配方式暂时就不看了，总之就是生成endpointDataSource ，里面有一丢丢小复杂，有兴趣可以自己去看下，就是扫描那一套了。

结

下一节，介绍一下文件上传。