让 .NET 轻松构建中间件模式代码

Intro

在 asp.net core 中中间件的设计令人叹为观止，如此高大上的设计何不集成到自己的代码里呢。

于是就有了封装了一个简单通用的中间件模板的想法，以后有需要的时候就可以拿来即用。

接口定义

这里按执行的委托是同步还是异步分为了同步和异步两种构建方法

//没有返回值的同步中间件构建器
public interface IPipelineBuilder<TContext>
{IPipelineBuilder<TContext> Use(Func<Action<TContext>, Action<TContext>> middleware);Action<TContext> Build();
}
// 异步中间件构建器
public interface IAsyncPipelineBuilder<TContext>
{IAsyncPipelineBuilder<TContext> Use(Func<Func<TContext, Task>, Func<TContext, Task>> middleware);Func<TContext, Task> Build();
}

为了方便使用，定义一下扩展方法，使得可以像 asp.net core 中 app.Use(Fun<HttpContext,Func<Task>,Task>) 一样比较方便的使用，扩展方法定义如下：

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));});
}

为了方便创建对应的 PipelineBuilder ，这里定义了两个方法：

使用 Create 方法就可以创建一个 IPipelineBuilder ，使用 CreateAsync 就可以创建一个 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

来看一个使用示例，这里的示例修改自设计模式里的责任链模式的一个示例，废话不说，来看代码：

这是一个请假的示例，不同的请假时间交由不同的审批主管进行审批，最后模拟了从请假1小时到请假8小时的申请处理情况

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("----------------------------");}
}

运行效果：

实现代码

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