var builder = WebApplication.CreateBuilder(args);
//這是重點(diǎn)，是ASP.NET Core自身提供的
builder.Services.AddEndpointsApiExplorer();
//添加swagger配置
builder.Services.AddSwaggerGen(c =>
{
    c.SwaggerDoc("v1", new() 
    { 
	Title = builder.Environment.ApplicationName,
	Version = "v1"
    });
});
var app = builder.Build();
if (app.Environment.IsDevelopment())
{
    //swagger終結(jié)點(diǎn)
    app.UseSwagger();
    app.UseSwaggerUI(c => c.SwaggerEndpoint("/swagger/v1/swagger.json", 
                          $"{builder.Environment.ApplicationName} v1"));
}
app.MapGet("/swag", () => "Hello Swagger!");
app.Run();

public class SwaggerGenerator : ISwaggerProvider
{
    private readonly IApiDescriptionGroupCollectionProvider _apiDescriptionsProvider;
    private readonly ISchemaGenerator _schemaGenerator;
    private readonly SwaggerGeneratorOptions _options;
    public SwaggerGenerator(
        SwaggerGeneratorOptions options,
        IApiDescriptionGroupCollectionProvider apiDescriptionsProvider,
        ISchemaGenerator schemaGenerator)
    {
        _options = options ?? new SwaggerGeneratorOptions();
        _apiDescriptionsProvider = apiDescriptionsProvider;
        _schemaGenerator = schemaGenerator;
    }
    /// <summary>
    /// 獲取Swagger文檔的核心方法
    /// </summary>
    public OpenApiDocument GetSwagger(string documentName, string host = null, string basePath = null)
    {
        if (!_options.SwaggerDocs.TryGetValue(documentName, out OpenApiInfo info))
            throw new UnknownSwaggerDocument(documentName, _options.SwaggerDocs.Select(d => d.Key));
        //組裝OpenApiDocument核心數(shù)據(jù)源源來自_apiDescriptionsProvider
        var applicableApiDescriptions = _apiDescriptionsProvider.ApiDescriptionGroups.Items
            .SelectMany(group => group.Items)
            .Where(apiDesc => !(_options.IgnoreObsoleteActions && apiDesc.CustomAttributes().OfType<ObsoleteAttribute().Any()))
            .Where(apiDesc => _options.DocInclusionPredicate(documentName, apiDesc));
        var schemaRepository = new SchemaRepository(documentName);
        var swaggerDoc = new OpenApiDocument
        {
            Info = info,
            Servers = GenerateServers(host, basePath),
            // Paths組裝是來自applicableApiDescriptions
            Paths = GeneratePaths(applicableApiDescriptions, schemaRepository),
            Components = new OpenApiComponents
            {
                Schemas = schemaRepository.Schemas,
                SecuritySchemes = new Dictionary<string, OpenApiSecurityScheme>(_options.SecuritySchemes)
            },
            SecurityRequirements = new List<OpenApiSecurityRequirement>(_options.SecurityRequirements)
        };
        //省略其他代碼
        return swaggerDoc;
    }
}

{
  "openapi": "3.0.1",
  "info": {
    "title": "MyTest.WebApi",
    "description": "測試接口",
    "version": "v1"
  },
  "paths": {
    "/": {
      "get": {
        "tags": [
          "MyTest.WebApi"
        ],
        "responses": {
          "200": {
            "description": "Success",
            "content": {
              "text/plain": {
                "schema": {
                  "type": "string"
                }
              }
            }
          }
        }
      }
    }
  },
  "components": {}
}

public static IServiceCollection AddEndpointsApiExplorer(this IServiceCollection services)
{
    services.TryAddSingleton<IActionDescriptorCollectionProvider, DefaultActionDescriptorCollectionProvider>();
    //swagger用到的核心操作IApiDescriptionGroupCollectionProvider
    services.TryAddSingleton<IApiDescriptionGroupCollectionProvider, ApiDescriptionGroupCollectionProvider>();
    services.TryAddEnumerable(
        ServiceDescriptor.Transient<IApiDescriptionProvider, EndpointMetadataApiDescriptionProvider>());
    return services;
}

public class ApiDescriptionGroupCollectionProvider : IApiDescriptionGroupCollectionProvider
{
	private readonly IActionDescriptorCollectionProvider _actionDescriptorCollectionProvider;
	private readonly IApiDescriptionProvider[] _apiDescriptionProviders;
	private ApiDescriptionGroupCollection? _apiDescriptionGroups;
	public ApiDescriptionGroupCollectionProvider(
		IActionDescriptorCollectionProvider actionDescriptorCollectionProvider,
		IEnumerable<IApiDescriptionProvider> apiDescriptionProviders)
	{
		_actionDescriptorCollectionProvider = actionDescriptorCollectionProvider;
		_apiDescriptionProviders = apiDescriptionProviders.OrderBy(item => item.Order).ToArray();
	}
	public ApiDescriptionGroupCollection ApiDescriptionGroups
	{
		get
		{
			var actionDescriptors = _actionDescriptorCollectionProvider.ActionDescriptors;
			if (_apiDescriptionGroups == null || _apiDescriptionGroups.Version != actionDescriptors.Version)
			{
				//如果_apiDescriptionGroups為null則使用GetCollection方法返回的數(shù)據(jù)
				_apiDescriptionGroups = GetCollection(actionDescriptors);
			}
			return _apiDescriptionGroups;
		}
	}
	private ApiDescriptionGroupCollection GetCollection(ActionDescriptorCollection actionDescriptors)
	{
		var context = new ApiDescriptionProviderContext(actionDescriptors.Items);
		//這里使用了_apiDescriptionProviders
		foreach (var provider in _apiDescriptionProviders)
		{
			provider.OnProvidersExecuting(context);
		}
		for (var i = _apiDescriptionProviders.Length - 1; i >= 0; i--)
		{
			_apiDescriptionProviders[i].OnProvidersExecuted(context);
		}
		var groups = context.Results
			.GroupBy(d => d.GroupName)
			.Select(g => new ApiDescriptionGroup(g.Key, g.ToArray()))
			.ToArray();
		return new ApiDescriptionGroupCollection(groups, actionDescriptors.Version);
	}
}

internal class EndpointMetadataApiDescriptionProvider : IApiDescriptionProvider
{
    private readonly EndpointDataSource _endpointDataSource;
    private readonly IHostEnvironment _environment;
    private readonly IServiceProviderIsService? _serviceProviderIsService;
    private readonly ParameterBindingMethodCache ParameterBindingMethodCache = new();
    public EndpointMetadataApiDescriptionProvider(
        EndpointDataSource endpointDataSource,
        IHostEnvironment environment,
        IServiceProviderIsService? serviceProviderIsService)
    {
        _endpointDataSource = endpointDataSource;
        _environment = environment;
        _serviceProviderIsService = serviceProviderIsService;
    }
    public void OnProvidersExecuting(ApiDescriptionProviderContext context)
    {
        //核心數(shù)據(jù)來自EndpointDataSource類
        foreach (var endpoint in _endpointDataSource.Endpoints)
        {
            if (endpoint is RouteEndpoint routeEndpoint &&
                routeEndpoint.Metadata.GetMetadata<MethodInfo>() is { } methodInfo &&
                routeEndpoint.Metadata.GetMetadata<IHttpMethodMetadata>() is { } httpMethodMetadata &&
                routeEndpoint.Metadata.GetMetadata<IExcludeFromDescriptionMetadata>() is null or { ExcludeFromDescription: false })
            {
                foreach (var httpMethod in httpMethodMetadata.HttpMethods)
                {
                    context.Results.Add(CreateApiDescription(routeEndpoint, httpMethod, methodInfo));
                }
            }
        }
    }
    private ApiDescription CreateApiDescription(RouteEndpoint routeEndpoint, string httpMethod, MethodInfo methodInfo)
    {
        //實(shí)現(xiàn)代碼省略	
    }
}

private static RouteHandlerBuilder Map(this IEndpointRouteBuilder endpoints,
			RoutePattern pattern, Delegate handler, bool disableInferBodyFromParameters)
{
	//省略部分代碼
	var requestDelegateResult = RequestDelegateFactory.Create(handler, options);
	var builder = new RouteEndpointBuilder(requestDelegateResult.RequestDelegate,pattern,defaultOrder)
	{
		//路由名稱
		DisplayName = pattern.RawText ?? pattern.DebuggerToString(),
	};
	//獲得httpmethod
	builder.Metadata.Add(handler.Method);
	if (GeneratedNameParser.TryParseLocalFunctionName(handler.Method.Name, out var endpointName)
		|| !TypeHelper.IsCompilerGeneratedMethod(handler.Method))
	{
		endpointName ??= handler.Method.Name;
		builder.DisplayName = $"{builder.DisplayName} => {endpointName}";
	}
	var attributes = handler.Method.GetCustomAttributes();
	foreach (var metadata in requestDelegateResult.EndpointMetadata)
	{
		builder.Metadata.Add(metadata);
	}
	if (attributes is not null)
	{
		foreach (var attribute in attributes)
		{
			builder.Metadata.Add(attribute);
		}
	}
	// 添加ModelEndpointDataSource
	var dataSource = endpoints.DataSources.OfType<ModelEndpointDataSource>().FirstOrDefault();
	if (dataSource is null)
	{
		dataSource = new ModelEndpointDataSource();
		endpoints.DataSources.Add(dataSource);
	}
	//將RouteEndpointBuilder添加到ModelEndpointDataSource
	return new RouteHandlerBuilder(dataSource.AddEndpointBuilder(builder));
}

internal class ModelEndpointDataSource : EndpointDataSource
{
}

public interface IEndpointRouteBuilder
{
    IApplicationBuilder CreateApplicationBuilder();
    IServiceProvider ServiceProvider { get; }
    //這里是一個(gè)EndpointDataSource的集合
    ICollection<EndpointDataSource> DataSources { get; }
}

var dataSources = new ObservableCollection<EndpointDataSource>();
services.TryAddEnumerable(ServiceDescriptor.Transient<IConfigureOptions<RouteOptions>, ConfigureRouteOptions>(
    serviceProvider => new ConfigureRouteOptions(dataSources)));
services.TryAddSingleton<EndpointDataSource>(s =>
{
    return new CompositeEndpointDataSource(dataSources);
});

public sealed class CompositeEndpointDataSource : EndpointDataSource
{
    private readonly ICollection<EndpointDataSource> _dataSources = default!;
    internal CompositeEndpointDataSource(ObservableCollection<EndpointDataSource> dataSources) : this()
    {
        _dataSources = dataSources;
    }
    public IEnumerable<EndpointDataSource> DataSources => _dataSources;
}

public static IApplicationBuilder UseEndpoints(this IApplicationBuilder builder, Action<IEndpointRouteBuilder> configure)
{
    // 省略一堆代碼
    //得到IEndpointRouteBuilder實(shí)例
    VerifyEndpointRoutingMiddlewareIsRegistered(builder, out var endpointRouteBuilder);
    //獲取RouteOptions
    var routeOptions = builder.ApplicationServices.GetRequiredService<IOptions<RouteOptions>>();
    //遍歷IEndpointRouteBuilder的DataSources
    foreach (var dataSource in endpointRouteBuilder.DataSources)
    {
        if (!routeOptions.Value.EndpointDataSources.Contains(dataSource))
        {
            //dataSource放入RouteOptions的EndpointDataSources集合
            routeOptions.Value.EndpointDataSources.Add(dataSource);
        }
    }
    return builder.UseMiddleware<EndpointMiddleware>();
}
private static void VerifyEndpointRoutingMiddlewareIsRegistered(IApplicationBuilder app, out IEndpointRouteBuilder endpointRouteBuilder)
{
    if (!app.Properties.TryGetValue(EndpointRouteBuilder, out var obj))
    {
        throw new InvalidOperationException();
    }
    endpointRouteBuilder = (IEndpointRouteBuilder)obj!;
    if (endpointRouteBuilder is DefaultEndpointRouteBuilder defaultRouteBuilder && !object.ReferenceEquals(app, defaultRouteBuilder.ApplicationBuilder))
    {
        throw new InvalidOperationException();
    }
}

var dataSources = new ObservableCollection<EndpointDataSource>();
services.TryAddEnumerable(ServiceDescriptor.Transient<IConfigureOptions<RouteOptions>, ConfigureRouteOptions>(
	serviceProvider => new ConfigureRouteOptions(dataSources)));

internal class ConfigureRouteOptions : IConfigureOptions<RouteOptions>
{
    private readonly ICollection<EndpointDataSource> _dataSources;
    public ConfigureRouteOptions(ICollection<EndpointDataSource> dataSources)
    {
        if (dataSources == null)
        {
            throw new ArgumentNullException(nameof(dataSources));
        }
        _dataSources = dataSources;
    }
    public void Configure(RouteOptions options)
    {
        if (options == null)
        {
            throw new ArgumentNullException(nameof(options));
        }
        options.EndpointDataSources = _dataSources;
    }
}

private void ConfigureApplication(WebHostBuilderContext context, IApplicationBuilder app)
{
    // 省略部分代碼
    // 注冊UseDeveloperExceptionPage全局異常中間件
    if (context.HostingEnvironment.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    app.Properties.Add(WebApplication.GlobalEndpointRouteBuilderKey, _builtApplication);
    if (_builtApplication.DataSources.Count > 0)
    {
        // 注冊UseRouting中間件
        if (!_builtApplication.Properties.TryGetValue(EndpointRouteBuilderKey, out var localRouteBuilder))
        {
            app.UseRouting();
        }
        else
        {
            app.Properties[EndpointRouteBuilderKey] = localRouteBuilder;
        }
    }
    app.Use(next =>
    {
        //調(diào)用WebApplication的Run方法
        _builtApplication.Run(next);
        return _builtApplication.BuildRequestDelegate();
    });
    // 如果DataSources集合有數(shù)據(jù)則注冊UseEndpoints
    if (_builtApplication.DataSources.Count > 0)
    {
        app.UseEndpoints(_ => { });
    }
    // 省略部分代碼
}

public class ApiDoc
{
    /// <summary>
    /// 接口分組
    /// </summary>
    public string Group { get; set; }
    /// <summary>
    /// 接口路由
    /// </summary>
    public string Route { get; set; }
    /// <summary>
    /// http方法
    /// </summary>
    public string HttpMethod { get; set; }
}

app.MapGet("/apiinfo", (IApiDescriptionGroupCollectionProvider provider) => {
    List<ApiDoc> docs = new List<ApiDoc>();
    foreach (var group in provider.ApiDescriptionGroups.Items)
    {
        foreach (var apiDescription in group.Items)
        {
            docs.Add(new ApiDoc 
            { 
                Group = group.GroupName, 
                Route = apiDescription.RelativePath,
                HttpMethod = apiDescription.HttpMethod
            });
        }
    }
    return docs;
});