对于ASP.NET Core MVC框架的设计和实现,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,虽然编程方式看起来不太一样,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
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 IArgumentBinder
{
public ValueTask<object?> BindAsync(
ActionContext actionContext,
ParameterDescriptor parameterDescriptor);
}
public class ArgumentBinder : IArgumentBinder
{
private readonly ConcurrentDictionary<Type, object?> _defaults = new();
private readonly MethodInfo _method =
typeof(ArgumentBinder).GetMethod(nameof(GetDefaultValue))!;
public ValueTask<object?> BindAsync(
ActionContext actionContext,
ParameterDescriptor parameterDescriptor)
{
var requestServices = actionContext.HttpContext.RequestServices;
var parameterInfo = parameterDescriptor.ParameterInfo;
var parameterName = parameterInfo.Name!;
var parameterType = parameterInfo.ParameterType;
// From registered service
var result = requestServices.GetService(parameterType);
if (result is not null)
{
return ValueTask.FromResult(result)!;
}
// From query, route, body
var request = actionContext.HttpContext.Request;
if (request.Query.TryGetValue(parameterName, out var value1))
{
return ValueTask.FromResult(
Convert.ChangeType((string)value1!, parameterType))!;
}
if (request.RouteValues.TryGetValue(parameterName, out var value2))
{
return ValueTask.FromResult(
Convert.ChangeType(value2, parameterType)!)!;
}
if (request.ContentLength > 0)
{
return JsonSerializer.DeserializeAsync(request.Body, parameterType);
}
// From default value
var defaultValue = _defaults
.GetOrAdd(parameterType,
type=> _method.MakeGenericMethod(parameterType)
.Invoke(null,null));
return ValueTask.FromResult(defaultValue);
}
public static T GetDefaultValue<T>() => default!;
}
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);
// 堆代码 duidaima.com
[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}