前几天有人在我的《ASP.NET Core框架揭秘》读者群跟我留言说:“我最近在看ASP.NET Core MVC的源代码,发现整个系统太复杂,涉及的东西太多,完全找不到方向,你能不能按照《200行代码,7个对象——让你了解ASP.NET Core框架的本质》这篇文章思路剖析一下MVC框架”。对于ASP.NET Core MVC框架的涉及和实现,说难也难,毕竟一个Model Binding就够很多人啃很久,其实说简单也简单,因为整个流程是很清晰的。ASP.NET Core MVC支持基于Controller和Page的两种编程模式,虽然编程方式开起来不太一样,底层针对请求的处理流程其实是一致的。接下来,我同样使用简单的代码构建一个Mini版的MVC框架,让大家了解一下ASP.NET Core MVC背后的总体设计,以及针对请求的处理流程。
一、描述Action方法
二、注册路由终结点
三、绑定Action方法参数
四、执行Action方法
五、响应执行结果
六、编排整个处理流程
七、跑起来看看
一、描述Action方法
MVC应用提供的功能体现在一个个Action方法上,所以MVC框架定义了专门的类型ActionDescriptor来描述每个有效的Action方法。但是Action方法和ActionDescriptor对象并非一对一的关系,而是一对多的关系。具体来说,采用“约定路由”的Action方法对应一个ActionDescriptor对象,如果采用“特性路由”,MVC框架会针对每个注册的路由创建一个ActionDescriptor。Action方法与ActionDescriptor之间的映射关系可以通过如下这个演示实例来验证。如代码片段所示,我们调用MapControllerRoute扩展方法注册了4个“约定路由”。HomeController类中定义了两个合法的Action方法,其中方法Foo采用“约定路由”,而方法Bar通过标注的两个HttpGetAttribute特性注册了两个“特性路由”。按照上述的规则,将有三个ActionDescriptor被创建出来,方法Foo有一个,而方法Bar有两个。
var builder = WebApplication.CreateBuilder(args); builder.Services.AddControllers(); var app = builder.Build(); app.MapControllers(); app.MapControllerRoute("v1", "v1/{controller}/{action}"); app.MapControllerRoute("v2", "v2/{controller}/{action}"); app.MapControllerRoute("v3", "v2/{controllerx}/{action}"); app.MapControllerRoute("v3", "v4/{controller}/{actionx}"); app.MapGet("/actions", (IActionDescriptorCollectionProvider provider) => { var actions = provider.ActionDescriptors.Items; var builder = new StringBuilder(); foreach (var action in actions.OfType<ControllerActionDescriptor>()) { builder.AppendLine($"{action.ControllerTypeInfo.Name}.{action.MethodInfo.Name}({action.AttributeRouteInfo?.Template ?? "N/A"})"); } return builder.ToString(); }); app.Run("http://localhost:5000"); public class HomeController { public string Foo() => $"{nameof(HomeController)}.{nameof(Foo)}"; [HttpGet("home/bar1")] [HttpGet("home/bar2")] public string Bar() => $"{nameof(HomeController)}.{nameof(Bar)}"; }
我们注册了一个指向路径“/actions”的路由终结点将所有ActionDescriptor列出来。如代码片段所示,路由处理委托(Lambda表达式)注入了IActionDescriptorCollectionProvider 对象,我们利用它的ActionDescriptors属性得到当前应用承载的所有ActionDescriptor对象。我们将其转化成ControllerActionDescriptor(派生于ActionDescriptor,用于描述定义在Controller类型中的Action方法,另一个派生类PageActionDescriptor用于描述定义在Page类型的Action方法),并将对应的Controller类型和方法名称,以及特性路由模板输出来。如下所示的输出结果验证了上述针对Action方法与ActionDescriptor映射关系的论述。
在模拟框架中,我们ActionDescriptor类型作最大的简化。如代码片段所示,创建一个ActionDescriptor对象时只需提供描述目标Action方法的MethodInfo对象(必需),和一个用来定义特性路由的IRouteTemplateProvider对象(可选,仅针对特性路由)。我们利用MethodInfo的声明类型得到Controller的类型,将剔除“Controller”后缀的类型名称作为ControllerName属性(表示Controller的名称),作为Action名称的ActionName属性则直接返回方法名称。Parameters属性返回一个ParameterDescriptor数组,而根据ParameterInfo对象构建的ParameterDescriptor是对参数的描述。
public class ActionDescriptor { public MethodInfo MethodInfo { get; } public IRouteTemplateProvider? RouteTemplateProvider { get; } public string ControllerName { get; } public string ActionName { get; } public ParameterDescriptor[] Parameters { get; } public ActionDescriptor(MethodInfo methodInfo, IRouteTemplateProvider? routeTemplateProvider) { MethodInfo = methodInfo; RouteTemplateProvider = routeTemplateProvider; ControllerName = MethodInfo.DeclaringType!.Name; ControllerName = ControllerName[..^"Controller".Length]; ActionName = MethodInfo.Name; Parameters = methodInfo.GetParameters().Select(it => new ParameterDescriptor(it)).ToArray(); } } public class ParameterDescriptor(ParameterInfo parameterInfo) { public ParameterInfo ParameterInfo => parameterInfo; }
当前应用涉及的所有ActionActionDescriptor由IActionDescriptorCollectionProvider对象的ActionDescriptors属性来提供。实现类型ActionDescriptorCollectionProvider 从当前启动程序集中提取有效的Controller类型,并将定义其中的有效Action方法转换成ActionDescriptor对象。用于定义“特性路由”的IRouteTemplateProvider对象来源于标注到方法上的特性(简单起见,我们忽略了标注到Controller类型上的特性),比如HttpGetAttribute特性等,同一个Action方法针对注册的特性路由来创建ActionDescriptor就体现在这里。
public interface IActionDescriptorCollectionProvider { IReadOnlyList<ActionDescriptor> ActionDescriptors { get; } } public class ActionDescriptorCollectionProvider : IActionDescriptorCollectionProvider { private readonly Assembly _assembly; private List<ActionDescriptor>? _actionDescriptors; public IReadOnlyList<ActionDescriptor> ActionDescriptors => _actionDescriptors ??= Resolve(_assembly.GetExportedTypes()).ToList(); public ActionDescriptorCollectionProvider(IWebHostEnvironment environment) { var assemblyName = new AssemblyName(environment.ApplicationName); _assembly = Assembly.Load(assemblyName); } private IEnumerable<ActionDescriptor> Resolve(IEnumerable<Type> types) { var methods = types .Where(IsValidController) .SelectMany(type => type.GetMethods() .Where(method => method.DeclaringType == type && IsValidAction(method))); foreach (var method in methods) { var providers = method.GetCustomAttributes().OfType<IRouteTemplateProvider>(); if (providers.Any()) { foreach (var provider in providers) { yield return new ActionDescriptor(method, provider); } } else { yield return new ActionDescriptor(method, null); } } } private static bool IsValidController(Type candidate) => candidate.IsPublic && !candidate.IsAbstract && candidate.Name.EndsWith("Controller"); private static bool IsValidAction(MethodInfo methodInfo) => methodInfo.IsPublic | !methodInfo.IsAbstract; }
二、注册路由终结点
MVC利用“路由”对外提供服务,它会将每个ActionDescriptor转换成“零到多个”路由终结点。ActionDescriptor与终结点之间的对应关系为什么是“零到多”,而不是“一对一”或者“一对多”呢?这也与Action方法采用的路由默认有关,采用特性路由的ActionDescriptor(RouteTemplateProvider 属性不等于Null)总是对应着一个确定的路由,但是如何为采用“约定路由”的ActionDescriptor创建对应的终结点,则取决于多少个约定路由与之匹配。针对每一个基于“约定”路由的ActionDescriptor,系统会为每个与之匹配的路由创建对应的终结点。如果没有匹配的约定路由,对应的Action方法自然就不会有对应的终结点。
我还是利用上面演示实例来说明ActionDescriptor与路由终结点之间的映射关系。为此我们注册如下这个指向路径“/endpoints”的路由终结点,我们通过注入的EndpointDataSource 对象得到终结点列表。由于针对某个Action方法创建的路由终结点都会将ActionDescriptor对象作为元数据,所以我们试着将它(具体类型为ControllerActionDescriptor)提取出来,并输出Controller类型和Action方法的名称,以及路由模板。
... app.MapGet("/endpoints", (EndpointDataSource source) => { var builder = new StringBuilder(); foreach (var endpoint in source.Endpoints.OfType<RouteEndpoint>()) { var action = endpoint.Metadata.GetMetadata<ControllerActionDescriptor>(); if (action is not null) { builder.AppendLine($"{action.ControllerTypeInfo.Name}.{action.MethodInfo.Name}({endpoint.RoutePattern.RawText})"); } } return builder.ToString(); }); ...
从如下所示的输出结果可以看出,由于Action方法Bar采用“特性路由”,所以对应的ActionDescriptor分别对应着一个终结点。采用约定路由的Foo方法虽然只有一个ActionDescriptor,但是注册的4个约定路由有两个与它匹配(两个必要的路由参数“controller”和“action”需要定义在路由模板中),所以它也具有两个终结点。
接下来我们在模拟框架中以最简单的方式完成“路由注册”。我们知道每个路由终结点由“路由模式”和“路由处理器”这两个核心元素构成,前者对应一个RoutePattern对象,由注册的路由信息构建而成,后者体现为一个用来处理请求的RequestDelegate委托。一个MVC应用绝大部分的请求处理工作都落在IActionInvoker对象上,所以作为路由处理器的RequestDelegate委托只需要将请求处理任务“移交”给这个对象就可以了。如代码片段所示,IActionInvoker接口定义了一个无参、返回类型为Task的InvokeAsync方法。IActionInvoker不是一个单例对象,而是针对每个请求单独创建的,创建它的工厂由IActionInvokerFactory接口表示。如代码片段所示,定义在该接口的工厂方法CreateInvoker利用指定的ActionContext上下文来创建返回的IActionInvoker对象。ActionContext可以视为MVC应用的请求上下文,我们的模拟框架同样对它做了最大的简化,将它定义对HttpContext上下文和ActionDescriptor对象的封装。
public interface IActionInvoker { Task InvokeAsync(); } public interface IActionInvokerFactory { IActionInvoker CreateInvoker(ActionContext actionContext); } public class ActionContext(HttpContext httpContext, ActionDescriptor actionDescriptor) { public HttpContext HttpContext => httpContext; public ActionDescriptor ActionDescriptor => actionDescriptor; }
我们将路由(终结点)注册实现在一个派生自EndpointDataSource的ActionEndpointDataSource类型中 。对于注册的每个终结点,作为处理器的RequestDelegate委托指向HandleAsync方法,可以看出这个方法的定义非常简单:它从当前终结点中以元数据的形式将ActionDescriptor对象,然后利用它与当前HttpContext将ActionContext上下文创建出来。我们将此ActionContext上下文传递给IActionInvokerFactory工厂将IActionInvoker对象创建出来,并利用它完成后续的请求处理。
public class ActionEndpointDataSource : EndpointDataSource {
... private static Task HandleRequestAsync(HttpContext httpContext) { var endpoint = httpContext.GetEndpoint() ?? throw new InvalidOperationException("No endpoint is matched to the current request."); var actionDescriptor = endpoint.Metadata.GetMetadata<ActionDescriptor>() ?? throw new InvalidOperationException("No ActionDescriptor is attached to the endpoint as metadata."); var actionContext = new ActionContext(httpContext, actionDescriptor); return httpContext.RequestServices.GetRequiredService<IActionInvokerFactory>().CreateInvoker(actionContext).InvokeAsync(); } }
ActionEndpointDataSource 定义了一个AddRoute方法来定义约定路由,注册的约定路由被存储在字段_conventionalRoutes所示的列表中。该方法返回一个EndpointConventionBuilder 对象,后者实现了IEndpointConventionBuilder 接口,我们可以利用它对添加的约定约定路由作进一步设置(比如添加元数据)。
public class ActionEndpointDataSource : EndpointDataSource { private readonly List<(string RouteName, string Template, RouteValueDictionary? Defaults, IDictionary<string, object?>? Constraints, RouteValueDictionary? DataTokens, List<Action<EndpointBuilder>> Conventions, List<Action<EndpointBuilder>> FinallyConventions)> _conventionalRoutes = new(); public IEndpointConventionBuilder AddRoute(string routeName, string pattern, RouteValueDictionary? defaults, IDictionary<string, object?>? constraints, RouteValueDictionary? dataTokens) { var conventions = new List<Action<EndpointBuilder>>(); var finallyConventions = new List<Action<EndpointBuilder>>(); _conventionalRoutes.Add((routeName, pattern, defaults, constraints, dataTokens, conventions, finallyConventions)); return new EndpointConventionBuilder(conventions, finallyConventions); }
private sealed class EndpointConventionBuilder : IEndpointConventionBuilder { private readonly List<Action<EndpointBuilder>> _conventions; private readonly List<Action<EndpointBuilder>> _finallyConventions; public EndpointConventionBuilder(List<Action<EndpointBuilder>> conventions, List<Action<EndpointBuilder>> finallyConventions) { _conventions = conventions; _finallyConventions = finallyConventions; } public void Add(Action<EndpointBuilder> convention) => _conventions.Add(convention); public void Finally(Action<EndpointBuilder> finallyConvention) => _finallyConventions.Add(finallyConvention); } }
ActionEndpointDataSource 针对终结点的创建并不复杂:在利用IActionDescriptorCollectionProvider 对象得到所有的ActionDescriptor对象后,它将每个ActionDescriptor对象交付给CreateEndpoints来创建相应的终结点。针对约定路由的终结点列表由CreateConventionalEndpoints方法进行创建,一个ActionDescriptor对象对应”零到多个“终结点的映射规则就体现在这里。针对特性路由的ActionDescriptor对象则在CreateAttributeEndpoint方法中转换成一个单一的终结点。EndpointDataSource还通过GetChangeToken方法返回的IChangeToken 对象感知终结点的实时变化,真正的MVC框架正好利用了这一点实现了”动态模块加载“的功能。我们的模拟框架直接返回一个单例的NullChangeToken对象。
public class ActionEndpointDataSource : EndpointDataSource { private readonly IServiceProvider _serviceProvider; private readonly IActionDescriptorCollectionProvider _actions; private readonly RoutePatternTransformer _transformer; private readonly List<Action<EndpointBuilder>> _conventions = new(); private readonly List<Action<EndpointBuilder>> _finallyConventions = new(); private int _routeOrder; private List<Endpoint>? _endpoints; private readonly List<(string RouteName, string Template, RouteValueDictionary? Defaults, IDictionary<string, object?>? Constraints, RouteValueDictionary? DataTokens, List<Action<EndpointBuilder>> Conventions, List<Action<EndpointBuilder>> FinallyConventions)> _conventionalRoutes = new(); public ActionEndpointDataSource(IServiceProvider serviceProvider) { _serviceProvider = serviceProvider; _actions = serviceProvider.GetRequiredService<IActionDescriptorCollectionProvider>(); _transformer = serviceProvider.GetRequiredService<RoutePatternTransformer>(); DefaultBuilder = new EndpointConventionBuilder(_conventions, _finallyConventions); } public override IReadOnlyList<Endpoint> Endpoints => _endpoints ??= _actions.ActionDescriptors.SelectMany(CreateEndpoints).ToList(); public override IChangeToken GetChangeToken() => NullChangeToken.Singleton; public IEndpointConventionBuilder AddRoute(string routeName, string pattern, RouteValueDictionary? defaults, IDictionary<string, object?>? constraints, RouteValueDictionary? dataTokens) { var conventions = new List<Action<EndpointBuilder>>(); var finallyConventions = new List<Action<EndpointBuilder>>(); _conventionalRoutes.Add((routeName, pattern, defaults, constraints, dataTokens, conventions, finallyConventions));
}
private IEnumerable<Endpoint> CreateEndpoints(ActionDescriptor actionDescriptor) { var routeValues = new RouteValueDictionary { {"controller", actionDescriptor.ControllerName }, { "action", actionDescriptor.ActionName } }; var attributes = actionDescriptor.MethodInfo.GetCustomAttributes(true).Union(actionDescriptor.MethodInfo.DeclaringType!.GetCustomAttributes(true)); var routeTemplateProvider = actionDescriptor.RouteTemplateProvider; if (routeTemplateProvider is null) { foreach (var endpoint in CreateConventionalEndpoints(actionDescriptor, routeValues, attributes)) { yield return endpoint; } } else { yield return CreateAttributeEndpoint(actionDescriptor, routeValues, attributes)); } }
private IEnumerable<Endpoint> CreateConventionalEndpoints(ActionDescriptor actionDescriptor, RouteValueDictionary routeValues, IEnumerable<object> attributes ) { foreach (var (routeName, template, defaults, constraints, dataTokens, conventionals, finallyConventionals) in _conventionalRoutes) { var pattern = RoutePatternFactory.Parse(template, defaults, constraints); pattern = _transformer.SubstituteRequiredValues(pattern, routeValues); if (pattern is not null) { var builder = new RouteEndpointBuilder(requestDelegate: HandleRequestAsync, routePattern: pattern, _routeOrder++) { ApplicationServices = _serviceProvider }; builder.Metadata.Add(actionDescriptor); foreach (var attribute in attributes) { builder.Metadata.Add(attribute); } yield return builder.Build(); } } }
private Endpoint CreateAttributeEndpoint(ActionDescriptor actionDescriptor, RouteValueDictionary routeValues, IEnumerable<object> attributes) { var routeTemplateProvider = actionDescriptor.RouteTemplateProvider!; var pattern = RoutePatternFactory.Parse(routeTemplateProvider.Template!); var builder = new RouteEndpointBuilder(requestDelegate: HandleRequestAsync, routePattern: pattern, _routeOrder++) { ApplicationServices = _serviceProvider }; builder.Metadata.Add(actionDescriptor); foreach (var attribute in attributes) { builder.Metadata.Add(attribute); } if (routeTemplateProvider is IActionHttpMethodProvider httpMethodProvider) { builder.Metadata.Add(new HttpMethodActionConstraint(httpMethodProvider.HttpMethods)); } return builder.Build(); } }
三、绑定Action方法参数
现在我们完成了路由(终结点)注册,此时匹配的请求总是会被路由到对应的终结点,后者将利用IActionInvokerFactory工厂创建的IActionInvoker对象来处理请求。IActionInvoker最终需要调用对应的Action方法,但是要完成针对目标方法的调用,得先绑定其所有参数,MVC框架为此构建了一套名为“模型绑定(Model Binding)”的系统来完成参数绑定的任务,毫无疑问这是MVC框架最为复杂的部分。在我么简化的模拟框架中,我们将针对单个参数的绑定交给IArgumentBinder对象来完成。
如代码片段所示,定义在IArgumentBinder中的BindAsync方法具有两个参数,一个是当前ActionContext上下文,另一个是描述目标参数的ParameterDescriptor 对象。该方法返回类型为ValueTask<object?>,泛型参数代表的object就是执行Action方法得到的返回值(对于返回类型为void的方法,这个值总是Null)。默认实现的ArgumentBinder类型完成了最基本的参数绑定功能,它可以帮助我们完成源自依赖服务、请求查询字符串、路由参数、主体内容(默认采用JSON反序列化)和默认值的参数绑定。
public interface IActionMethodExecutor { object? Execute(object controller, ActionDescriptor actionDescriptor, object?[] arguments); } public class ActionMethodExecutor : IActionMethodExecutor { private readonly ConcurrentDictionary<MethodInfo, Func<object, object?[], object?>> _executors = new(); public object? Execute(object controller, ActionDescriptor actionDescriptor, object?[] arguments) => _executors.GetOrAdd(actionDescriptor.MethodInfo, CreateExecutor).Invoke(controller, arguments); private Func<object, object?[], object?> CreateExecutor(MethodInfo methodInfo) { var controller = Expression.Parameter(typeof(object)); var arguments = Expression.Parameter(typeof(object?[])); var parameters = methodInfo.GetParameters(); var convertedArguments = new Expression[parameters.Length]; for (int index = 0; index < parameters.Length; index++) { convertedArguments[index] = Expression.Convert(Expression.ArrayIndex(arguments, Expression.Constant(index)), parameters[index].ParameterType); } var convertedController = Expression.Convert(controller, methodInfo.DeclaringType!); var call = Expression.Call(convertedController, methodInfo, convertedArguments); var convertResult = Expression.Convert(call, typeof(object)); return Expression.Lambda<Func<object, object?[], object?>>(convertResult, controller, arguments).Compile(); } }
四、执行Action方法
在模拟框架中,针对目标Action方法的执行体现在如下所示的IActionMethodExecutor接口的Execute方法上,该方法的三个参数分别代表Controller对象、描述目标Action方法的ActionDescriptor和通过“参数绑定”得到的参数列表。Execute方法的返回值就是执行目标Action方法的返回值。如下所示的实现类型ActionMethodExecutor 利用“表达式树”的方式将Action方法对应的MethodInfo转换成对应的Func<object, object?[], object?>委托,并利用后者执行Action方法。
public interface IActionMethodExecutor { object? Execute(object controller, ActionDescriptor actionDescriptor, object?[] arguments); } public class ActionMethodExecutor : IActionMethodExecutor { private readonly ConcurrentDictionary<MethodInfo, Func<object, object?[], object?>> _executors = new(); public object? Execute(object controller, ActionDescriptor actionDescriptor, object?[] arguments) => _executors.GetOrAdd(actionDescriptor.MethodInfo, CreateExecutor).Invoke(controller, arguments); private Func<object, object?[], object?> CreateExecutor(MethodInfo methodInfo) { var controller = Expression.Parameter(typeof(object)); var arguments = Expression.Parameter(typeof(object?[])); var parameters = methodInfo.GetParameters(); var convertedArguments = new Expression[parameters.Length]; for (int index = 0; index < parameters.Length; index++) { convertedArguments[index] = Expression.Convert(Expression.ArrayIndex(arguments, Expression.Constant(index)), parameters[index].ParameterType); } var convertedController = Expression.Convert(controller, methodInfo.DeclaringType!); var call = Expression.Call(convertedController, methodInfo, convertedArguments); return Expression.Lambda<Func<object, object?[], object?>>(call, controller, arguments).Compile(); } }
五、响应执行结果
当我们利用IActionMethodExecutor对象成功执行Action方法后,需要进一步处理其返回值。为了统一处理执行Action方法的结果,于是有了如下这个IActionResult接口,具体的处理逻辑实现在ExecuteResultAsync方法中,方法的唯一参数依然是当前ActionContext上下文。我们定义了如下这个JsonResult实现基于JSON的响应。
public interface IActionResult { Task ExecuteResultAsync(ActionContext actionContext); } public class JsonResult(object data) : IActionResult { public Task ExecuteResultAsync(ActionContext actionContext) { var response = actionContext.HttpContext.Response; response.ContentType = "application/json"; return JsonSerializer.SerializeAsync(response.Body, data); } }
当IActionMethodExecutor成功执行目标方法后,我们会得到作为返回值的Object对象(可能是Null),如果我们能够进一步将它转换成一个IActionResult对象,一切就迎刃而解了,为此我专门定义了如下这个IActionResultConverter接口。如代码片段所示,IActionResultConverter接口的唯一方法ConvertAsync方法会将作为Action方法返回值的Object对象转化成ValueTask<IActionResult>对象。
public interface IActionResultConverter { ValueTask<IActionResult> ConvertAsync(object? result); } public class ActionResultConverter : IActionResultConverter { private readonly MethodInfo _valueTaskConvertMethod = typeof(ActionResultConverter).GetMethod(nameof(ConvertFromValueTask))!; private readonly MethodInfo _taskConvertMethod = typeof(ActionResultConverter).GetMethod(nameof(ConvertFromTask))!; private readonly ConcurrentDictionary<Type, Func<object, ValueTask<IActionResult>>> _converters = new(); public ValueTask<IActionResult> ConvertAsync(object? result) { // Null if (result is null) { return ValueTask.FromResult<IActionResult>(VoidActionResult.Instance); } // Task<IActionResult> if (result is Task<IActionResult> taskOfActionResult) { return new ValueTask<IActionResult>(taskOfActionResult); } // ValueTask<IActionResult> if (result is ValueTask<IActionResult> valueTaskOfActionResult) { return valueTaskOfActionResult; } // IActionResult if (result is IActionResult actionResult) { return ValueTask.FromResult(actionResult); } // ValueTask if (result is ValueTask valueTask) { return Convert(valueTask); } // Task var type = result.GetType(); if (type == typeof(Task)) { return Convert((Task)result); } // ValueTask<T> if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(ValueTask<>)) { return _converters.GetOrAdd(type, t => CreateValueTaskConverter(t, _valueTaskConvertMethod)).Invoke(result); } // Task<T> if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Task<>)) { return _converters.GetOrAdd(type, t => CreateValueTaskConverter(t, _taskConvertMethod)).Invoke(result); } // Object return ValueTask.FromResult<IActionResult>(new ObjectActionResult(result)); } public static async ValueTask<IActionResult> ConvertFromValueTask<T>(ValueTask<T> valueTask) { var result = valueTask.IsCompleted ? valueTask.Result : await valueTask; return result is IActionResult actionResult ? actionResult : new ObjectActionResult(result!); } public static async ValueTask<IActionResult> ConvertFromTask<T>(Task<T> task) { var result = await task; return result is IActionResult actionResult ? actionResult : new ObjectActionResult(result!); } private static async ValueTask<IActionResult> Convert(ValueTask valueTask) { if (!valueTask.IsCompleted) await valueTask; return VoidActionResult.Instance; } private static async ValueTask<IActionResult> Convert(Task task) { await task; return VoidActionResult.Instance; } private static Func<object, ValueTask<IActionResult>> CreateValueTaskConverter(Type valueTaskType, MethodInfo convertMethod) { var parameter = Expression.Parameter(typeof(object)); var convert = Expression.Convert(parameter, valueTaskType); var method = convertMethod.MakeGenericMethod(valueTaskType.GetGenericArguments()[0]); var call = Expression.Call(method, convert); return Expression.Lambda<Func<object, ValueTask<IActionResult>>>(call, parameter).Compile(); } private sealed class VoidActionResult : IActionResult { public static readonly VoidActionResult Instance = new(); public Task ExecuteResultAsync(ActionContext actionContext) => Task.CompletedTask; } private sealed class ObjectActionResult(object result) : IActionResult { public Task ExecuteResultAsync(ActionContext actionContext) { var response = actionContext.HttpContext.Response; response.ContentType = "text/plain"; return response.WriteAsync(result.ToString()!); } } }
作为默认实现的ActionResultConverter 在进行转换的时候,会根据返回值的类型做针对性转换,具体的转换规则如下:
- Null:根据单例的VoidActionResult对象创建一个ValueTask<IActionResult>,VoidActionResult实现的ExecuteResultAsync方法什么都不要做;
- Task<IActionResult>:直接将其转换成ValueTask<IActionResult>;
- ValueTask<IActionResult>:直接返回;
- 实现了IActionResult接口:根据该对象创建ValueTask<IActionResult>;
- ValueTask:调用Convert方法进行转换;
- Task:调用另一个Convert方法进行转换;
- ValueTask<T>:调用ConvertFromValueTask<T>方法进行转换;
- Task<T>:调用ConvertFromTask<T>方法进行转换;
- 其他:根据返回创建一个ObjectActionResult对象(它会将ToString方法返回的字符串作为响应内容),并创建一个ValueTask<IActionResult>对象。
六、编排整个处理流程
到目前为止,我们不经能够执行Action方法,还能将方法的返回值转换成ValueTask<IActionResult>对象,定义一个完成整个请求处理的IActionInvoker实现类型就很容易了。如代码片段所示,如下这个实现了IActionInvoker接口的ActionInvoker对象是根据当前ActionContext创建的,在实现的InvokeAsync方法中,它利用ActionContext上下文提供的ActionDescriptor解析出Controller类型,并利用针对当前请求的依赖注入容器(IServiceProvider)将Controller对象创建出来。
public class ActionInvoker(ActionContext actionContext) : IActionInvoker { public ActionContext ActionContext { get; } = actionContext; public async Task InvokeAsync() { var requestServices = ActionContext.HttpContext.RequestServices; // Create controller instance var controller = ActivatorUtilities.CreateInstance(requestServices, ActionContext.ActionDescriptor.MethodInfo.DeclaringType!); try { // Bind arguments var parameters = ActionContext.ActionDescriptor.Parameters; var arguments = new object?[parameters.Length]; var binder = requestServices.GetRequiredService<IArgumentBinder>(); for (int index = 0; index < parameters.Length; index++) { var valueTask = binder.BindAsync(ActionContext, parameters[index]); if (valueTask.IsCompleted) { arguments[index] = valueTask.Result; } else { arguments[index] = await valueTask; } } // Execute action method var executor = requestServices.GetRequiredService<IActionMethodExecutor>(); var result = executor.Execute(controller, ActionContext.ActionDescriptor, arguments); // Convert result to IActionResult var converter = requestServices.GetRequiredService<IActionResultConverter>(); var convert = converter.ConvertAsync(result); var actionResult = convert.IsCompleted ? convert.Result : await convert; // Execute result await actionResult.ExecuteResultAsync(ActionContext); } finally { (controller as IDisposable)?.Dispose(); } } } public class ActionInvokerFactory : IActionInvokerFactory { public IActionInvoker CreateInvoker(ActionContext actionContext) => new ActionInvoker(actionContext); }
接下来,它同样利用ActionDescriptor得到描述每个参数的ParameterDescriptor对象,并利用IParameterBinder完成参数绑定,最终得到一个传入Action方法的参数列表。接下来ActionInvoker利用IActionMethodExecutor对象成功执行Action方法,并利用IActionResultConverter对象将返回结果转换成IActionResult对象,最终通过执行这个对象完成针对请求的响应工作。如果Controller类型实现了IDisposable接口,在完成了整个处理流程后,我们还会调用其Dispose方法确保资源得到释放。
七、跑起来看看
当目前为止,模拟的MVC框架的核心组件均已构建完成,现在我们补充两个扩展方法。如代码片段所示,针对IServiceCollection接口的扩展方法AddControllers2(为了区别于现有的AddControllers,后面的MapControllerRoute2方法命名也是如此)将上述的接口和实现类型注册为依赖服务;针对IEndpointRouteBuilder 接口的扩展方法MapControllerRoute2完成了针对ActionEndpointDataSource的中,并在此基础上注册一个默认的约定路由。()
public static class Extensions { public static IServiceCollection AddControllers2(this IServiceCollection services) { services.TryAddSingleton<IActionInvokerFactory, ActionInvokerFactory>(); services.TryAddSingleton<IActionMethodExecutor, ActionMethodExecutor>(); services.TryAddSingleton<IActionResultConverter, ActionResultConverter>(); services.TryAddSingleton<IArgumentBinder, ArgumentBinder>(); services.TryAddSingleton<IActionDescriptorCollectionProvider, ActionDescriptorCollectionProvider>(); return services; } public static IEndpointConventionBuilder MapControllerRoute2( this IEndpointRouteBuilder endpoints, string name, [StringSyntax("Route")] string pattern, object? defaults = null, object? constraints = null, object? dataTokens = null) { var source = new ActionEndpointDataSource(endpoints.ServiceProvider); endpoints.DataSources.Add(source); return source.AddRoute( name, pattern, new RouteValueDictionary(defaults), new RouteValueDictionary(constraints), new RouteValueDictionary(dataTokens)); } }
现在我们在此基础上构建如下这个简单的MVC应用。如代码片段所示,我们调用了AddControllers扩展方法完成了核心服务的注册;调用了MapControllerRoute2扩展方法并注册了一个路径模板为“{controller}/{action}/{id?}”的约定路由。定义的HomeController类型中定义了三个Action方法。采用约定路由的Action方法Foo具有三个输入参数x、y和z,返回根据它们构建的Result对象;Action方法Bar具有相同的参数,但返回一个ValueTask<Result>对象,我们通过标注的HttpGetAttribute特性注册了一个路径模板为“bar/{x}/{y}/{z}”的特性路由;Action方法Baz的输入参数类型为Result,返回一个ValueTask<IActionResult>对象(具体返回的是一个JsonResult对象)。标注的HttpPostAttribute特性将路由模板设置为“/baz”。
var builder = WebApplication.CreateBuilder(args); builder.Services.AddControllers2(); var app = builder.Build(); app.MapControllerRoute2(name: "default", pattern: "{controller}/{action}/{id?}"); app.Run(); public class HomeController { public Result Foo(string x, int y, double z) => new Result(x, y, z); [Microsoft.AspNetCore.Mvc.HttpGet("bar/{x}/{y}/{z}")] public ValueTask<Result> Bar(string x, int y, double z) => ValueTask.FromResult(new Result(x, y, z)); [Microsoft.AspNetCore.Mvc.HttpPost("/baz")] public ValueTask<IActionResult> Baz(Result input) => ValueTask.FromResult<IActionResult>(new JsonResult(input)); } public record Result(string X, int Y, double Z);
应用启动后,我们通过路径“/home/foo?x=123&y=456&z=789”访问Action方法Foo,并利用查询字符串指定三个参数值。或者通过路径“/bar/123/456/789”方法ActionBar,并利用路由变量指定三个参数。我们都会得到相同的响应。
我们使用Fiddler向路径“/baz”发送一个POST请求来访问Action方法Baz,我们将请求的主体内容设置为基于Result类型的JSON字符串,我们提供的IArgumentBinder对象利用发序列化请求主体的形式绑定其参数。由于Action方法最终会返回一个JsonResult,所以响应的内容与请求内容保持一致。
POST http://localhost:5000/baz HTTP/1.1 Host: localhost:5000 Content-Length: 29 {"X":"123", "Y":456, "Z":789} HTTP/1.1 200 OK Content-Type: application/json Date: Fri, 03 Nov 2023 06:12:15 GMT Server: Kestrel Content-Length: 27 {"X":"123","Y":456,"Z":789}