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