.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 singletonservices.TryAddSingleton<IControllerFactory, DefaultControllerFactory>();    // Will be cached by the DefaultControllerFactoryservices.TryAddTransient<IControllerActivator, DefaultControllerActivator>();services.TryAddEnumerable(ServiceDescriptor.Transient<IControllerPropertyActivator, DefaultControllerPropertyActivator>());    // Route Handlersservices.TryAddSingleton<MvcRouteHandler>(); // Only one per appservices.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servicevar 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servicepublic 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;
}