.NET Core开发日志——简述路由
2019-07-26

有过ASP.NET或其它现代Web框架开发经历的开发者对路由这一名字应该不陌生。如果要用一句话解释什么是路由,可以这样形容:通过对URL的解析,指定相应的处理程序。

回忆下在Web Forms应用程序中使用路由的方式:

public static void RegisterRoutes(RouteCollection routes){ routes.MapPageRoute("", "Category/{action}/{categoryName}", "~/categoriespage.aspx");}

然后是MVC应用程序:

public static void RegisterRoutes(RouteCollection routes){ routes.IgnoreRoute("{resource}.axd/{*pathInfo}"); routes.MapRoute( "Default", "{controller}/{action}/{id}", new { controller = "Home", action = "Index", id = "" } );}

再到了ASP.NET Core:

public void Configure(IApplicationBuilder app){ app.UseMvc(routes => { routes.MapRoute( name: "default", template: "{controller=Home}/{action=Index}/{id?}"); });}

还可以用更简单的写法:

public void Configure(IApplicationBuilder app){ app.UseMvcWithDefaultRoute();}

从源码上看这两个方法的实现是一样的。

public static IApplicationBuilder UseMvcWithDefaultRoute(this IApplicationBuilder app){ if (app == null) { throw new ArgumentNullException(nameof(app)); } return app.UseMvc(routes => { routes.MapRoute( name: "default", template: "{controller=Home}/{action=Index}/{id?}"); });}

关键是内部UseMvc方法的内容:

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());}

其中的处理过程,首先实例化了一个RouteBuilder对象,并对它的DefaultHandler属性赋值为MvcRouteHandler。接着以其为参数,执行routes.MapRoute方法。

MapRoute的处理过程就是为RouteBuilder里的Routes集合新增一个Route对象。

public static IRouteBuilder MapRoute( this IRouteBuilder routeBuilder, string name, string template, object defaults, object constraints, object dataTokens){ ... 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;}

有此一个Route对象仍不夠,程序里又插入了一个AttributeRoute。

随后执行routes.Build(),返回RouteCollection集合。该集合实现了IRouter接口。

public IRouter Build(){ var routeCollection = new RouteCollection(); foreach (var route in Routes) { routeCollection.Add(route); } return routeCollection;}

最终使用已完成配置的路由。

public static IApplicationBuilder UseRouter(this IApplicationBuilder builder, IRouter router){ ... return builder.UseMiddleware<RouterMiddleware>(router);}

于是又看到了熟悉的Middleware。它的核心方法里先调用了RouteCollection的RouteAsync处理。

public async Task Invoke(HttpContext httpContext){ var context = new RouteContext(httpContext); context.RouteData.Routers.Add(_router); await _router.RouteAsync(context); if (context.Handler == null) { _logger.RequestDidNotMatchRoutes(); await _next.Invoke(httpContext); } else { httpContext.Features[typeof(IRoutingFeature)] = new RoutingFeature() { RouteData = context.RouteData, }; await context.Handler(context.HttpContext); }}

其内部又依次执行各个Route的RouteAsync方法。

public async virtual Task RouteAsync(RouteContext context){ ... for (var i = 0; i < Count; i++) { var route = this[i]; context.RouteData.Routers.Add(route); try { await route.RouteAsync(context); if (context.Handler != null) { break; } } ... }}

之前的逻辑中分别在RouteCollection里加入了AttributeRoute与Route。*循环中会判断Handler是否被赋值,这是为了避免在路由已被匹配的情况下,继续进行其它的匹配。从执行顺序来看,很容易明白AttributeRoute比一般Route优先级高的道理。

先执行AttributeRoute里的RouteAsync方法:

public Task RouteAsync(RouteContext context){ var router = GetTreeRouter(); return router.RouteAsync(context);}

里面调用了TreeRouter的RouteAsync方法:

public async Task RouteAsync(RouteContext context){ foreach (var tree in _trees) { var tokenizer = new PathTokenizer(context.HttpContext.Request.Path); var root = tree.Root; var treeEnumerator = new TreeEnumerator(root, tokenizer); ... while (treeEnumerator.MoveNext()) { var node = treeEnumerator.Current; foreach (var item in node.Matches) { var entry = item.Entry; var matcher = item.TemplateMatcher; try { if (!matcher.TryMatch(context.HttpContext.Request.Path, context.RouteData.Values)) { continue; } if (!RouteConstraintMatcher.Match( entry.Constraints, context.RouteData.Values, context.HttpContext, this, RouteDirection.IncomingRequest, _constraintLogger)) { continue; } _logger.MatchedRoute(entry.RouteName, entry.RouteTemplate.TemplateText); context.RouteData.Routers.Add(entry.Handler); await entry.Handler.RouteAsync(context); if (context.Handler != null) { return; } } ... } } }}

如果所有AttributeRoute路由都不能匹配,则不会进一步作处理。否则的话,将继续执行Handler中的RouteAsync方法。这里的Handler是MvcAttributeRouteHandler。

public Task RouteAsync(RouteContext context){ ... var actionDescriptor = _actionSelector.SelectBestCandidate(context, Actions); if (actionDescriptor == null) { _logger.NoActionsMatched(context.RouteData.Values); return Task.CompletedTask; } foreach (var kvp in actionDescriptor.RouteValues) { if (!string.IsNullOrEmpty(kvp.Value)) { context.RouteData.Values[kvp.Key] = kvp.Value; } } 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 Task.CompletedTask;}

该方法内部的处理仅是为RouteContext的Handler属性赋值。实际的操作则是要到RouterMiddleware中Invoke方法的context.Handler(context.HttpContext)这一步才被执行的。

至于Route里的RouteAsync方法:

public virtual Task RouteAsync(RouteContext context){ ... EnsureMatcher(); EnsureLoggers(context.HttpContext); var requestPath = context.HttpContext.Request.Path; if (!_matcher.TryMatch(requestPath, context.RouteData.Values)) { // If we got back a null value set, that means the URI did not match return Task.CompletedTask; } // Perf: Avoid accessing dictionaries if you don"t need to write to them, these dictionaries are all // created lazily. if (DataTokens.Count > 0) { MergeValues(context.RouteData.DataTokens, DataTokens); } if (!RouteConstraintMatcher.Match( Constraints, context.RouteData.Values, context.HttpContext, this, RouteDirection.IncomingRequest, _constraintLogger)) { return Task.CompletedTask; } _logger.MatchedRoute(Name, ParsedTemplate.TemplateText); return OnRouteMatched(context);}

只有路由被匹配的时候才在OnRouteMatched里调用target的RouteAsync方法。

protected override Task OnRouteMatched(RouteContext context){ context.RouteData.Routers.Add(_target); return _target.RouteAsync(context);}

此处的target即是最初创建RouteBuilder时传入的MvcRouteHandler。

public Task RouteAsync(RouteContext context){ ... var candidates = _actionSelector.SelectCandidates(context); if (candidates == null || candidates.Count == 0) { _logger.NoActionsMatched(context.RouteData.Values); return Task.CompletedTask; } var actionDescriptor = _actionSelector.SelectBestCandidate(context, candidates); if (actionDescriptor == null) { _logger.NoActionsMatched(context.RouteData.Values); return Task.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 Task.CompletedTask;}

处理过程与MvcAttributeRouteHandler相似,一样是要在RouterMiddleware的Invoke里才执行Handler的方法。

以一张思维导图可以简单概括上述的过程。

或者用三句话也可以描述整个流程。

添加路由匹配地址处理请求