讓 .NET 輕鬆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。

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

介面定義

這裡按執行的委托是同步還是非同步分為了同步和非同步兩種構建方法

//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();
}
// 非同步中間件構建器
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 ，這裡定義了兩個方法：

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，這裡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，最後模擬了從請假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