讓 .NET 輕松構建中間件模式代碼

Intro

在 asp.net core 中中間件的設計令人嘆為觀止，如此高大上的設計何不集成到自己的代碼里呢。

于是就有了封裝了一個簡單通用的中間件模板的想法，以后有需要的時候就可以拿來即用。

接口定義

這里按執行的委托是同步還是異步分為了同步和異步兩種構建方法

//沒有返回值的同步中間件構建器 public interface IPipelineBuilder<TContext> {IPipelineBuilder<TContext> Use(Func<Action<TContext>, Action<TContext>> middleware);Action<TContext> Build(); } // 異步中間件構建器 public interface IAsyncPipelineBuilder<TContext> {IAsyncPipelineBuilder<TContext> Use(Func<Func<TContext, Task>, Func<TContext, Task>> middleware);Func<TContext, Task> Build(); }

為了方便使用，定義一下擴展方法，使得可以像 asp.net core 中 app.Use(Fun<HttpContext,Func<Task>,Task>) 一樣比較方便的使用，擴展方法定義如下：

public static IPipelineBuilder<TContext> Use<TContext>(this IPipelineBuilder<TContext> builder, Action<TContext, Action> action) {return builder.Use(next =>context =>{action(context, () => next(context));}); } public static IAsyncPipelineBuilder<TContext> Use<TContext>(this IAsyncPipelineBuilder<TContext> builder, Func<TContext, Func<Task>, Task> func) {return builder.Use(next =>context =>{return func(context, () => next(context));}); }

為了方便創建對應的 PipelineBuilder ，這里定義了兩個方法：

使用 Create 方法就可以創建一個 IPipelineBuilder ，使用 CreateAsync 就可以創建一個 IAsyncPipelineBuilder

public class PipelineBuilder {public static IPipelineBuilder<TContext> Create<TContext>(Action<TContext> completeAction){return new PipelineBuilder<TContext>(completeAction);}public static IAsyncPipelineBuilder<TContext> CreateAsync<TContext>(Func<TContext, Task> completeFunc){return new AsyncPipelineBuilder<TContext>(completeFunc);} }

使用示例

來看一個使用示例，這里的示例修改自設計模式里的責任鏈模式的一個示例，廢話不說，來看代碼：

這是一個請假的示例，不同的請假時間交由不同的審批主管進行審批，最后模擬了從請假1小時到請假8小時的申請處理情況

private class RequestContext {public string RequesterName { get; set; }public int Hour { get; set; } } public static void Test() {var requestContext = new RequestContext(){RequesterName = "Kangkang",Hour = 12,};var builder = PipelineBuilder.Create<RequestContext>(context =>{Console.WriteLine($"{context.RequesterName} {context.Hour}h apply failed");}).Use((context, next) =>{if (context.Hour <= 2){Console.WriteLine("pass 1");}else{next();}}).Use((context, next) =>{if (context.Hour <= 4){Console.WriteLine("pass 2");}else{next();}}).Use((context, next) =>{if (context.Hour <= 6){Console.WriteLine("pass 3");}else{next();}});var requestPipeline = builder.Build();foreach (var i in Enumerable.Range(1, 8)){Console.WriteLine();Console.WriteLine($"--------- h:{i} apply Pipeline------------------");requestContext.Hour = i;requestPipeline.Invoke(requestContext);Console.WriteLine("----------------------------");Console.WriteLine();} } public static async Task AsyncPipelineBuilderTest() {var requestContext = new RequestContext(){RequesterName = "Michael",Hour = 12,};var builder = PipelineBuilder.CreateAsync<RequestContext>(context =>{Console.WriteLine($"{context.RequesterName} {context.Hour}h apply failed");return Task.CompletedTask;}).Use(async (context, next) =>{if (context.Hour <= 2){Console.WriteLine("pass 1");}else{await next();}}).Use(async (context, next) =>{if (context.Hour <= 4){Console.WriteLine("pass 2");}else{await next();}}).Use(async (context, next) =>{if (context.Hour <= 6){Console.WriteLine("pass 3");}else{await next();}});var requestPipeline = builder.Build();foreach (var i in Enumerable.Range(1, 8)){Console.WriteLine($"--------- h:{i} apply AsyncPipeline------------------");requestContext.Hour = i;await requestPipeline.Invoke(requestContext);Console.WriteLine("----------------------------");} }

運行效果：

實現代碼

internal class PipelineBuilder<TContext> : IPipelineBuilder<TContext> {private readonly Action<TContext> _completeFunc;private readonly IList<Func<Action<TContext>, Action<TContext>>> _pipelines = new List<Func<Action<TContext>, Action<TContext>>>();public PipelineBuilder(Action<TContext> completeFunc){_completeFunc = completeFunc;}public IPipelineBuilder<TContext> Use(Func<Action<TContext>, Action<TContext>> middleware){_pipelines.Add(middleware);return this;}public Action<TContext> Build(){var request = _completeFunc;foreach (var pipeline in _pipelines.Reverse()){request = pipeline(request);}return request;} } internal class AsyncPipelineBuilder<TContext> : IAsyncPipelineBuilder<TContext> {private readonly Func<TContext, Task> _completeFunc;private readonly IList<Func<Func<TContext, Task>, Func<TContext, Task>>> _pipelines = new List<Func<Func<TContext, Task>, Func<TContext, Task>>>();public AsyncPipelineBuilder(Func<TContext, Task> completeFunc){_completeFunc = completeFunc;}public IAsyncPipelineBuilder<TContext> Use(Func<Func<TContext, Task>, Func<TContext, Task>> middleware){_pipelines.Add(middleware);return this;}public Func<TContext, Task> Build(){var request = _completeFunc;foreach (var pipeline in _pipelines.Reverse()){request = pipeline(request);}return request;} }

Reference

• https://github.com/WeihanLi/WeihanLi.Common/blob/dev/samples/DotNetCoreSample/PipelineTest.cs

• https://github.com/WeihanLi/WeihanLi.Common/blob/dev/src/WeihanLi.Common/Helpers/Pipelines/PipelineBuilder.cs

• https://github.com/dotnet/aspnetcore/blob/master/src/Http/Http/src/Builder/ApplicationBuilder.cs

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