让 .NET 轻松构建中间件模式代码

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
{
    IPipelineBuilder Use(Func, Action> middleware);

    Action Build();
}
// 异步中间件构建器
public interface IAsyncPipelineBuilder
{
    IAsyncPipelineBuilder Use(Func, Func> middleware);

    Func 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, Task>) 一样比较方便的使用，扩展方法定义如下：

public static IPipelineBuilder Use(this IPipelineBuilder builder, Action action)

{
    return builder.Use(next =>
                       context =>
                       {
                           action(context, () => next(context));
                       });
}

public static IAsyncPipelineBuilder Use(this IAsyncPipelineBuilder builder,  Func, 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 Create(Action completeAction)
    {
        return new PipelineBuilder(completeAction);
    }

    public static IAsyncPipelineBuilder CreateAsync(Func completeFunc)
    {
        return new AsyncPipelineBuilder(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(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(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 : IPipelineBuilder
{
    private readonly Action _completeFunc;
    private readonly IList, Action>> _pipelines = new List, Action>>();

    public PipelineBuilder(Action completeFunc)
    {
        _completeFunc = completeFunc;
    }

    public IPipelineBuilder Use(Func, Action> middleware)
    {
        _pipelines.Add(middleware);
        return this;
    }

    public Action Build()
    {
        var request = _completeFunc;
        foreach (var pipeline in _pipelines.Reverse())
        {
            request = pipeline(request);
        }
        return request;
    }
}

internal class AsyncPipelineBuilder : IAsyncPipelineBuilder
{
    private readonly Func _completeFunc;
    private readonly IList, Func>> _pipelines = new List, Func>>();

    public AsyncPipelineBuilder(Func completeFunc)
    {
        _completeFunc = completeFunc;
    }

    public IAsyncPipelineBuilder Use(Func, Func> middleware)
    {
        _pipelines.Add(middleware);
        return this;
    }

    public Func 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