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,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",};
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>>> _pipelines = new List<Func<Func<TContext,Task>>>();
public AsyncPipelineBuilder(Func<TContext,Task> completeFunc)
{
_completeFunc = completeFunc;
}
public IAsyncPipelineBuilder<TContext> Use(Func<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
（编辑：李大同）
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