.net core 源码解析-mvc route的注册，激活，调用流程(三)

.net core mvc route的注册，激活，调用流程

mvc的入口是route，当前请求的url匹配到合适的route之后，mvc根据route所指定的controller和action激活controller并调用action完成mvc的处理流程。下面我们看看服务器是如何调用route的。

core mvc startup基本代码。重点在AddMvc和UseMvc

public class Startup
{
    public IConfigurationRoot Configuration { get; }
    // This method gets called by the runtime. Use this method to add services to the container.
    public void ConfigureServices(IServiceCollection services)
    {
        services.AddMvc();
    }
    // This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
    public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
    {
        app.UseStaticFiles();
        app.UseMvc(routes =>
        {
            routes.MapRoute(
                name: "default",
                template: "{controller=Home}/{action=Index}/{id?}");
        });
    }
}

AddMvc：把各种service加入IOC容器。比如格式化提供程序，action定位器，controllerFactory，controller激活器等等，一应服务全部在这里加入。

UseMvc：最重要的一行代码：builder.UseMiddleware(router); 看到这行代码就清楚的知道route 这个handler 在这里加入到请求委托链拉

public static IMvcBuilder AddMvc(this IServiceCollection services)
{
    var builder = services.AddMvcCore();
    builder.AddJsonFormatters();
    builder.AddCors();
    return new MvcBuilder(builder.Services, builder.PartManager);
}
public static IMvcCoreBuilder AddMvcCore(this IServiceCollection services, Action<MvcOptions> setupAction)
{
    var builder = services.AddMvcCore();
    services.Configure(setupAction);
    return builder;
}
internal static void AddMvcCoreServices(IServiceCollection services)
{
    services.TryAddSingleton<IActionSelector, ActionSelector>();
    services.TryAddSingleton<ActionConstraintCache>();
    services.TryAddSingleton<IActionSelectorDecisionTreeProvider, ActionSelectorDecisionTreeProvider>();

    // This has a cache, so it needs to be a singleton
    services.TryAddSingleton<IControllerFactory, DefaultControllerFactory>();

    // Will be cached by the DefaultControllerFactory
    services.TryAddTransient<IControllerActivator, DefaultControllerActivator>();
    services.TryAddEnumerable(ServiceDescriptor.Transient<IControllerPropertyActivator, DefaultControllerPropertyActivator>());

    // Route Handlers
    services.TryAddSingleton<MvcRouteHandler>(); // Only one per app
    services.TryAddTransient<MvcAttributeRouteHandler>(); // Many per app
}
public static IApplicationBuilder UseMvc(this IApplicationBuilder app, Action<IRouteBuilder> configureRoutes)
{
    var routes = new RouteBuilder(app)
    {
        DefaultHandler = app.ApplicationServices.GetRequiredService<MvcRouteHandler>(),
    };
    configureRoutes(routes);
    routes.Routes.Insert(0, AttributeRouting.CreateAttributeMegaRoute(app.ApplicationServices));
    return app.UseRouter(routes.Build());
}
public static IApplicationBuilder UseRouter(this IApplicationBuilder builder, IRouter router)
{
    return builder.UseMiddleware<RouterMiddleware>(router);
}

如此，mvc的入口route handler就加入了我们的请求委托链中。后续服务器接收到的请求就能交由route匹配，查找action，激活action处理。

router middleware的激活调用

middleware 请求调用委托链的激活调用请看这篇文章

//middleware加入_components请求处理委托链
public IApplicationBuilder Use(Func<RequestDelegate, RequestDelegate> middleware)
{
    _components.Add(middleware);
    return this;
}
public static class UseMiddlewareExtensions
{
    private const string InvokeMethodName = "Invoke";
    private static readonly MethodInfo GetServiceInfo = typeof(UseMiddlewareExtensions).GetMethod(nameof(GetService), BindingFlags.NonPublic | BindingFlags.Static);
    //注册middleware
    public static IApplicationBuilder UseMiddleware(this IApplicationBuilder app, Type middleware, params object[] args)
    {
        var applicationServices = app.ApplicationServices;
        //将middleware 加入请求处理委托链
        return app.Use(next =>
        {
        //解析方法和参数。查找类的Invoke方法作为入口方法。所以middleware只要是个class就行。只要有一个功公共的Invoke方法即可。
            var methods = middleware.GetMethods(BindingFlags.Instance | BindingFlags.Public);
            var invokeMethods = methods.Where(m => string.Equals(m.Name, InvokeMethodName, StringComparison.Ordinal)).ToArray();
            var methodinfo = invokeMethods[0];
            var parameters = methodinfo.GetParameters();
            var ctorArgs = new object[args.Length + 1];
            ctorArgs[0] = next;
            Array.Copy(args, 0, ctorArgs, 1, args.Length);
            //创建middleware的实例。并且通过构造函数注入相关的service
            var instance = ActivatorUtilities.CreateInstance(app.ApplicationServices, middleware, ctorArgs);
            //如果方法只有一个参数，默认它就是httpcontext。
            if (parameters.Length == 1)
                {
                    return (RequestDelegate)methodinfo.CreateDelegate(typeof(RequestDelegate), instance);
                }
            //多余一个参数的则构建一个func。并从ioc容器解析参数注入
            var factory = Compile<object>(methodinfo, parameters);
            return context =>
            {
                var serviceProvider = context.RequestServices ?? applicationServices;
                return factory(instance, context, serviceProvider);
            };
        });
    }
//代码中的创建实例注入service，创建有多个参数的invoke方法注入service具体代码就不贴上来了，占地方。
//构造函数就是匹配最适合的构造函数，然后从IServiceProvider get实例，注入。
//多个参数的invoke就更简单了。直接从IServiceProvider get实例注入。

上述源代码git地址，aspnet/HttpAbstractions项目

route handler middleware代码

public class RouterMiddleware
{
    private readonly ILogger _logger;
    private readonly RequestDelegate _next;
    private readonly IRouter _router;
    //创建middleware的实例。并且通过构造函数注入相关的service
    public RouterMiddleware(RequestDelegate next, ILoggerFactory loggerFactory, IRouter router)
    {
        _next = next;
        _router = router;
        _logger = loggerFactory.CreateLogger<RouterMiddleware>();
    }
    //被调用的方法。从这里开始进入mvc route。
    public async Task Invoke(HttpContext httpContext)
    {
        //此处的 IRouter router对象。是我们在Startup中routes.MapRoute...配置的route集合对象：RouteCollection。当然也还有比如attributeroute等等好几种route。

        var context = new RouteContext(httpContext);
        context.RouteData.Routers.Add(_router);

        await _router.RouteAsync(context);
        if (context.Handler == null)
        {
        //没有匹配到route的情况
            _logger.RequestDidNotMatchRoutes();
            await _next.Invoke(httpContext);
        }
        else
        {
            httpContext.Features[typeof(IRoutingFeature)] = new RoutingFeature()
            {
                RouteData = context.RouteData,
            };
            //匹配到路由处理
            await context.Handler(context.HttpContext);
        }
    }
}
//Microsoft.AspNetCore.Routing.RouteCollection
public async virtual Task RouteAsync(RouteContext context)
{
    // Perf: We want to avoid allocating a new RouteData for each route we need to process.
    // We can do this by snapshotting the state at the beginning and then restoring it
    // for each router we execute.
    var snapshot = context.RouteData.PushState(null, values: null, dataTokens: null);
    for (var i = 0; i < Count; i++)
    {
        var route = this[i];
        context.RouteData.Routers.Add(route);
        try
        {
          //循环所有routes规则，逐一匹配，匹配到一个自然就break。
            await route.RouteAsync(context);
            if (context.Handler != null)
                break;
        }
        finally
        {
            if (context.Handler == null)
                snapshot.Restore();
        }
    }
}

UseMvc中有一行非常重要的代码。给RouteBuilder的DefaultHandler赋值一个handler。记住这行代码，我们继续往下看。

public static IApplicationBuilder UseMvc(this IApplicationBuilder app, Action<IRouteBuilder> configureRoutes)
{
    var routes = new RouteBuilder(app)
    {
        DefaultHandler = app.ApplicationServices.GetRequiredService<MvcRouteHandler>(),
    };
}
//我们在Startup中routes.MapRoute的所有调用最终调用方法都是这个。new Route( routeBuilder.DefaultHandler，....)
//全部都指定了_target为routeBuilder.DefaultHandler
public static IRouteBuilder MapRoute(this IRouteBuilder routeBuilder, string name, string template, object defaults, object constraints, object dataTokens)
{
    if (routeBuilder.DefaultHandler == null)
        throw new RouteCreationException(Resources.FormatDefaultHandler_MustBeSet(nameof(IRouteBuilder)));
    var inlineConstraintResolver = routeBuilder.ServiceProvider.GetRequiredService<IInlineConstraintResolver>();
    routeBuilder.Routes.Add(new Route(
        routeBuilder.DefaultHandler,
        name, template, new RouteValueDictionary(defaults), new RouteValueDictionary(constraints), new RouteValueDictionary(dataTokens), inlineConstraintResolver));
    return routeBuilder;
}

到这里，我们的逻辑有点绕了，让我们理理清楚：

1.请求进到RouterMiddleware.Invoke()方法

2.调用RouteCollection.RouteAsync()方法，RouteCollection.RouteAsync方法中循环注册的每一个route对象。

并调用route对象的RouteAsync()方法(route对象的RouteAsync方法在它的父类中Microsoft.AspNetCore.Routing.RouteBase)。

这里说的route对象即时Startup中routes.MapRoute生成的route对象（Microsoft.AspNetCore.Routing.Route）。Route继承RouteBase，RouteBase实现IRouter接口

3.RouteBase.RouteAsync()判断当前请求是否符合当前route规则，如果匹配的话，则调用抽象方法OnRouteMatched

4.RouteBase的抽象方法OnRouteMatched，又回到Route对象的OnRouteMatched方法中。调用_target.RouteAsync();_target对象即上面代码中的routeBuilder.DefaultHandler。

5.来到Microsoft.AspNetCore.Mvc.Internal.MvcRouteHandler.RouteAsync()方法中。最重要的一行代码： context.Handler =....

6.调用堆栈最终返回到1中(RouterMiddleware.Invoke())。判断context.Handler == null。为null没找到route匹配的action。不为null则await context.Handler(context.HttpContext)

7.context.Handler即为5中赋值的func。即下面的代码，定位action，调用action。

//Microsoft.AspNetCore.Mvc.Internal.MvcRouteHandler.RouteAsync
public Task RouteAsync(RouteContext context)
{
    var candidates = _actionSelector.SelectCandidates(context);
    if (candidates == null || candidates.Count == 0)
    {
        _logger.NoActionsMatched();
        return TaskCache.CompletedTask;
    }
    var actionDescriptor = _actionSelector.SelectBestCandidate(context, candidates);
    if (actionDescriptor == null)
    {
        _logger.NoActionsMatched();
        return TaskCache.CompletedTask;
    }
    context.Handler = (c) =>
    {
        var routeData = c.GetRouteData();
        var actionContext = new ActionContext(context.HttpContext, routeData, actionDescriptor);
        if (_actionContextAccessor != null)
            _actionContextAccessor.ActionContext = actionContext;
        var invoker = _actionInvokerFactory.CreateInvoker(actionContext);
        if (invoker == null)
            throw new InvalidOperationException( Resources.FormatActionInvokerFactory_CouldNotCreateInvoker(actionDescriptor.DisplayName));
        return invoker.InvokeAsync();
    };
    return TaskCache.CompletedTask;
}

至此，route的处理流程大约交代清楚了。包括route的注册，route的激活，route的选择等。