.NET 云原生架构师训练营（模板方法 && 建造者）--学习笔记

private static ControllerActionEndpointDataSource GetOrCreateDataSource(IEndpointRouteBuilder endpoints)
{
    var dataSource = endpoints.DataSources.OfType<ControllerActionEndpointDataSource>().FirstOrDefault();
    if (dataSource == null)
    {
        var orderProvider = endpoints.ServiceProvider.GetRequiredService<OrderedEndpointsSequenceProviderCache>();
        var factory = endpoints.ServiceProvider.GetRequiredService<ControllerActionEndpointDataSourceFactory>();
        dataSource = factory.Create(orderProvider.GetOrCreateOrderedEndpointsSequenceProvider(endpoints));
        endpoints.DataSources.Add(dataSource);
    }

    return dataSource;
}

在 ControllerActionEndpointDataSource 中遍历 actions

for (var i = 0; i < actions.Count; i++)
{
    if (actions[i] is ControllerActionDescriptor action)
    {
        _endpointFactory.AddEndpoints(endpoints, routeNames, action, _routes, conventions, CreateInertEndpoints);

这些 actions 来自于基类 ActionEndpointDataSourceBase

public ActionEndpointDataSourceBase(IActionDescriptorCollectionProvider actions)
{
    _actions = actions;

    Conventions = new List<Action<EndpointBuilder>>();
}

actions 通过 CreateEndpoints 绑定到 RequestDelegate

protected override List<Endpoint> CreateEndpoints(IReadOnlyList<ActionDescriptor> actions, IReadOnlyList<Action<EndpointBuilder>> conventions)

CreateEndpoints 中有一个 AddEndpoints 方法

_endpointFactory.AddEndpoints(endpoints, routeNames, action, _routes, conventions, CreateInertEndpoints);

在 AddEndpoints 方法中将一个 action 转换为一个 endpoint

var builder = new InertEndpointBuilder()
{
    DisplayName = action.DisplayName,
    RequestDelegate = _requestDelegate,
};
AddActionDataToBuilder(
    builder,
    routeNames,
    action,
    routeName: null,
    dataTokens: null,
    suppressLinkGeneration: false,
    suppressPathMatching: false,
    conventions,
    Array.Empty<Action<EndpointBuilder>>());
endpoints.Add(builder.Build());

接着看一下 _requestDelegate

_requestDelegate = CreateRequestDelegate();

这里才是真正执行每个 web api 请求的入口

private static RequestDelegate CreateRequestDelegate()
{
    // We don't want to close over the Invoker Factory in ActionEndpointFactory as
    // that creates cycles in DI. Since we're creating this delegate at startup time
    // we don't want to create all of the things we use at runtime until the action
    // actually matches.
    //
    // The request delegate is already a closure here because we close over
    // the action descriptor.
    IActionInvokerFactory? invokerFactory = null;

    return (context) =>
    {
        var endpoint = context.GetEndpoint()!;
        var dataTokens = endpoint.Metadata.GetMetadata<IDataTokensMetadata>();

        var routeData = new RouteData();
        routeData.PushState(router: null, context.Request.RouteValues, new RouteValueDictionary(dataTokens?.DataTokens));

        // Don't close over the ActionDescriptor, that's not valid for pages.
        var action = endpoint.Metadata.GetMetadata<ActionDescriptor>()!;
        var actionContext = new ActionContext(context, routeData, action);

        if (invokerFactory == null)
        {
            invokerFactory = context.RequestServices.GetRequiredService<IActionInvokerFactory>();
        }

        var invoker = invokerFactory.CreateInvoker(actionContext);
        return invoker!.InvokeAsync();
    };
}

首先从 context 获取 endpoint，接着从 endpoint 得到 ActionDescriptor，再将它封装成一个 ActionContext

通过 invokerFactory 创建一个 invoker，最后调用 InvokeAsync，所以整个执行过程是一个委托，在执行 MapControllers 的时候已经将委托挂到整个执行的 endpoint

每个路由的 endpoint 最后都是指向同一个地方，全部指向同一个 Delegate，只不过这个 Delegate 从 endpoint 的 Metadata 中拿到的 action 的定义，包括 controller, method, parameter

最后通过 invoker 的形式调用，所以才用到了 ResourceInvoker, PageActionInvoker, 和 ControllerActionInvoker 三种方式，发挥了模板方法作用