ASP.NET Core 中间件(Middleware)的使用及其源码解析（三）- 对中间件管道 ...

灌篮少年 · 2022-9-16 17:16:46

如果业务逻辑比较简单的话，一条主管道就够了，确实用不到分支管道。不过当业务逻辑比较复杂的时候，有时候我们可能希望根据情况的不同使用特殊的一组中间件来处理 HttpContext。这种情况下如果只用一条管道，处理起来会非常麻烦和混乱。此时就可以使用 Map/MapWhen/UseWhen 建立一个分支管道，当条件符合我们的设定时，由这个分支管道来处理 HttpContext。使用 Map/MapWhen/UseWhen 添加分支管道是很容易的，只要提供合适跳转到分支管道的判断逻辑，以及分支管道的构建方法就可以了。

一、对中间件管道进行分支

废话不多说，我们直接通过一个Demo来看一下如何对中间件管道进行分支，如下：

using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.Extensions.Configuration;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using NETCoreMiddleware.Middlewares;
namespace NETCoreMiddleware
{
public class Startup
{
public Startup(IConfiguration configuration)
{
Configuration = configuration;
}
public IConfiguration Configuration { get; }
//服务注册（往容器中添加服务）
// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
services.AddControllersWithViews();
}
/// <summary>
/// 配置Http请求处理管道
/// Http请求管道模型---就是Http请求被处理的步骤
/// 所谓管道，就是拿着HttpContext，经过多个步骤的加工，生成Response，这就是管道
/// </summary>
/// <param name="app"></param>
/// <param name="env"></param>
// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
#region 环境参数
if (env.IsDevelopment())
{
app.UseDeveloperExceptionPage();
}
else
{
app.UseExceptionHandler("/Home/Error");
}
#endregion 环境参数
//静态文件中间件
app.UseStaticFiles();
#region 创建管道分支
//Map管道分支
app.Map("/map1", HandleMapTest1);
app.Map("/map2", HandleMapTest2);
//MapWhen管道分支
app.MapWhen(context => context.Request.Query.ContainsKey("mapwhen"), HandleBranch);
//UseWhen管道分支
//UseWhen 与 MapWhen 不同的是，如果这个分支不发生短路或包含终端中间件，则会重新加入主管道
app.UseWhen(context => context.Request.Query.ContainsKey("usewhen"), HandleBranchAndRejoin);
#endregion 创建管道分支
#region Use中间件
//中间件1
app.Use(next =>
{
Console.WriteLine("middleware 1");
return async context =>
{
await Task.Run(() =>
{
Console.WriteLine("");
Console.WriteLine("===================================Middleware===================================");
Console.WriteLine($"This is middleware 1 Start");
});
await next.Invoke(context);
await Task.Run(() =>
{
Console.WriteLine($"This is middleware 1 End");
Console.WriteLine("===================================Middleware===================================");
});
};
});
//中间件2
app.Use(next =>
{
Console.WriteLine("middleware 2");
return async context =>
{
await Task.Run(() => Console.WriteLine($"This is middleware 2 Start"));
await next.Invoke(context); //可通过不调用 next 参数使请求管道短路
await Task.Run(() => Console.WriteLine($"This is middleware 2 End"));
};
});
//中间件3
app.Use(next =>
{
Console.WriteLine("middleware 3");
return async context =>
{
await Task.Run(() => Console.WriteLine($"This is middleware 3 Start"));
await next.Invoke(context);
await Task.Run(() => Console.WriteLine($"This is middleware 3 End"));
};
});
//中间件4
//Use方法的另外一个重载
app.Use(async (context, next) =>
{
await Task.Run(() => Console.WriteLine($"This is middleware 4 Start"));
await next();
await Task.Run(() => Console.WriteLine($"This is middleware 4 End"));
});
#endregion Use中间件
#region UseMiddleware中间件
app.UseMiddleware<CustomMiddleware>();
#endregion UseMiddleware中间件
#region 终端中间件
//app.Use(_ => handler);
app.Run(async context =>
{
await Task.Run(() => Console.WriteLine($"This is Run"));
});
#endregion 终端中间件
#region 最终把请求交给MVC
app.UseRouting();
app.UseAuthorization();
app.UseEndpoints(endpoints =>
{
endpoints.MapControllerRoute(
name: "areas",
pattern: "{area:exists}/{controller=Home}/{action=Index}/{id?}");
endpoints.MapControllerRoute(
name: "default",
pattern: "{controller=Home}/{action=Index}/{id?}");
});
#endregion 最终把请求交给MVC
}
#region 创建管道分支
/// <summary>
/// Map管道分支1
/// </summary>
/// <param name="app"></param>
static void HandleMapTest1(IApplicationBuilder app)
{
//中间件
app.Use(next =>
{
Console.WriteLine("HandleMapTest1");
return async context =>
{
await Task.Run(() =>
{
Console.WriteLine("");
Console.WriteLine($"This is HandleMapTest1 Start");
});
await next.Invoke(context); //可通过不调用 next 参数使请求管道短路
await Task.Run(() => Console.WriteLine($"This is HandleMapTest1 End"));
};
});
}
/// <summary>
/// Map管道分支2
/// </summary>
/// <param name="app"></param>
static void HandleMapTest2(IApplicationBuilder app)
{
//中间件
app.Use(next =>
{
Console.WriteLine("HandleMapTest2");
return async context =>
{
await Task.Run(() =>
{
Console.WriteLine("");
Console.WriteLine($"This is HandleMapTest2 Start");
});
await next.Invoke(context); //可通过不调用 next 参数使请求管道短路
await Task.Run(() => Console.WriteLine($"This is HandleMapTest2 End"));
};
});
}
/// <summary>
/// MapWhen管道分支
/// </summary>
/// <param name="app"></param>
static void HandleBranch(IApplicationBuilder app)
{
//中间件
app.Use(next =>
{
Console.WriteLine("HandleBranch");
return async context =>
{
await Task.Run(() =>
{
Console.WriteLine("");
Console.WriteLine($"This is HandleBranch Start");
});
await next.Invoke(context); //可通过不调用 next 参数使请求管道短路
await Task.Run(() => Console.WriteLine($"This is HandleBranch End"));
};
});
}
/// <summary>
/// UseWhen管道分支
/// </summary>
/// <param name="app"></param>
static void HandleBranchAndRejoin(IApplicationBuilder app)
{
//中间件
app.Use(next =>
{
Console.WriteLine("HandleBranchAndRejoin");
return async context =>
{
await Task.Run(() =>
{
Console.WriteLine("");
Console.WriteLine($"This is HandleBranchAndRejoin Start");
});
await next.Invoke(context); //可通过不调用 next 参数使请求管道短路
await Task.Run(() => Console.WriteLine($"This is HandleBranchAndRejoin End"));
};
});
}
#endregion 创建管道分支
}
}

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下面我们使用命令行（CLI）方式启动我们的网站，如下所示：

启动成功后，我们来访问一下 “http://localhost:5000/map1/” ，控制台输出结果如下所示：

访问 “http://localhost:5000/map2/” ，控制台输出结果如下所示：

访问 “http://localhost:5000/home/?mapwhen=1” ，控制台输出结果如下所示：

访问 “http://localhost:5000/home/?usewhen=1” ，控制台输出结果如下所示：

Map 扩展用作约定来创建管道分支。 Map 基于给定请求路径的匹配项来创建请求管道分支。如果请求路径以给定路径开头，则执行分支。
MapWhen 基于给定谓词的结果创建请求管道分支。 Func 类型的任何谓词均可用于将请求映射到管道的新分支。
UseWhen 也基于给定谓词的结果创建请求管道分支。与 MapWhen 不同的是，如果这个分支不发生短路或包含终端中间件，则会重新加入主管道。
二、中间件管道分支源码解析

下面我们结合ASP.NET Core源码来分析下其实现原理：
1、Map扩展原理

我们将光标移动到 Map 处按 F12 转到定义，如下所示：

可以发现它是位于 MapExtensions 扩展类中的，我们找到 MapExtensions 类的源码，如下所示：

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
using System;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Builder.Extensions;
namespace Microsoft.AspNetCore.Builder
{
/// <summary>
/// Extension methods for the <see cref="MapMiddleware"/>.
/// </summary>
public static class MapExtensions
{
/// <summary>
/// Branches the request pipeline based on matches of the given request path. If the request path starts with
/// the given path, the branch is executed.
/// </summary>
/// <param name="app">The <see cref="IApplicationBuilder"/> instance.</param>
/// <param name="pathMatch">The request path to match.</param>
/// <param name="configuration">The branch to take for positive path matches.</param>
/// <returns>The <see cref="IApplicationBuilder"/> instance.</returns>
public static IApplicationBuilder Map(this IApplicationBuilder app, PathString pathMatch, Action<IApplicationBuilder> configuration)
{
if (app == null)
{
throw new ArgumentNullException(nameof(app));
}
if (configuration == null)
{
throw new ArgumentNullException(nameof(configuration));
}
if (pathMatch.HasValue && pathMatch.Value.EndsWith("/", StringComparison.Ordinal))
{
throw new ArgumentException("The path must not end with a '/'", nameof(pathMatch));
}
// create branch
var branchBuilder = app.New();
configuration(branchBuilder);
var branch = branchBuilder.Build();
var options = new MapOptions
{
Branch = branch,
PathMatch = pathMatch,
};
return app.Use(next => new MapMiddleware(next, options).Invoke);
}
}
}

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其中 ApplicationBuilder 类的源码，如下所示：

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Http.Features;
using Microsoft.Extensions.Internal;
namespace Microsoft.AspNetCore.Builder
{
public class ApplicationBuilder : IApplicationBuilder
{
private const string ServerFeaturesKey = "server.Features";
private const string ApplicationServicesKey = "application.Services";
private readonly IList<Func<RequestDelegate, RequestDelegate>> _components = new List<Func<RequestDelegate, RequestDelegate>>();
public ApplicationBuilder(IServiceProvider serviceProvider)
{
Properties = new Dictionary<string, object>(StringComparer.Ordinal);
ApplicationServices = serviceProvider;
}
public ApplicationBuilder(IServiceProvider serviceProvider, object server)
: this(serviceProvider)
{
SetProperty(ServerFeaturesKey, server);
}
private ApplicationBuilder(ApplicationBuilder builder)
{
Properties = new CopyOnWriteDictionary<string, object>(builder.Properties, StringComparer.Ordinal);
}
public IServiceProvider ApplicationServices
{
get
{
return GetProperty<IServiceProvider>(ApplicationServicesKey);
}
set
{
SetProperty<IServiceProvider>(ApplicationServicesKey, value);
}
}
public IFeatureCollection ServerFeatures
{
get
{
return GetProperty<IFeatureCollection>(ServerFeaturesKey);
}
}
public IDictionary<string, object> Properties { get; }
private T GetProperty<T>(string key)
{
object value;
return Properties.TryGetValue(key, out value) ? (T)value : default(T);
}
private void SetProperty<T>(string key, T value)
{
Properties[key] = value;
}
public IApplicationBuilder Use(Func<RequestDelegate, RequestDelegate> middleware)
{
_components.Add(middleware);
return this;
}
public IApplicationBuilder New()
{
return new ApplicationBuilder(this);
}
public RequestDelegate Build()
{
RequestDelegate app = context =>
{
// If we reach the end of the pipeline, but we have an endpoint, then something unexpected has happened.
// This could happen if user code sets an endpoint, but they forgot to add the UseEndpoint middleware.
var endpoint = context.GetEndpoint();
var endpointRequestDelegate = endpoint?.RequestDelegate;
if (endpointRequestDelegate != null)
{
var message =
$"The request reached the end of the pipeline without executing the endpoint: '{endpoint.DisplayName}'. " +
$"Please register the EndpointMiddleware using '{nameof(IApplicationBuilder)}.UseEndpoints(...)' if using " +
$"routing.";
throw new InvalidOperationException(message);
}
context.Response.StatusCode = 404;
return Task.CompletedTask;
};
foreach (var component in _components.Reverse())
{
app = component(app);
}
return app;
}
}
}

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Microsoft.AspNetCore.Builder.ApplicationBuilder类源码其中 MapMiddleware 类的源码，如下所示：

// Copyright (c) .NET Foundation. All rights reserved.
// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
namespace Microsoft.AspNetCore.Builder.Extensions
{
/// <summary>
/// Represents a middleware that maps a request path to a sub-request pipeline.
/// </summary>
public class MapMiddleware
{
private readonly RequestDelegate _next;
private readonly MapOptions _options;
/// <summary>
/// Creates a new instance of <see cref="MapMiddleware"/>.
/// </summary>
/// <param name="next">The delegate representing the next middleware in the request pipeline.</param>
/// <param name="options">The middleware options.</param>
public MapMiddleware(RequestDelegate next, MapOptions options)
{
if (next == null)
{
throw new ArgumentNullException(nameof(next));
}
if (options == null)
{
throw new ArgumentNullException(nameof(options));
}
_next = next;
_options = options;
}
/// <summary>
/// Executes the middleware.
/// </summary>
/// <param name="context">The <see cref="HttpContext"/> for the current request.</param>
/// <returns>A task that represents the execution of this middleware.</returns>
public async Task Invoke(HttpContext context)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
PathString matchedPath;
PathString remainingPath;
if (context.Request.Path.StartsWithSegments(_options.PathMatch, out matchedPath, out remainingPath))
{
// Update the path
var path = context.Request.Path;
var pathBase = context.Request.PathBase;
context.Request.PathBase = pathBase.Add(matchedPath);
context.Request.Path = remainingPath;
try
{
await _options.Branch(context);
}
finally
{
context.Request.PathBase = pathBase;
context.Request.Path = path;
}
}
else
{
await _next(context);
}
}
}
}

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在前两篇文章中我们已经介绍过，中间件的注册和管道的构建都是通过 ApplicationBuilder 进行的。因此要构建一个分支管道，需要一个新的 ApplicationBuilder ，并用它来注册中间件，构建管道。为了在分支管道中也能够共享我们在当前 ApplicationBuilder 中注册的服务（或者说共享依赖注入容器，当然共享的并不止这些），在创建新的 ApplicationBuilder 时并不是直接 new 一个全新的，而是调用当前 ApplicationBuilder 的 New 方法在当前的基础上创建新的，共享了当前 ApplicationBuilder 的 Properties（其中包含了依赖注入容器）。
在使用 Map 注册中间件时我们会传入一个 Action 参数，它的作用就是当我们创建了新的 ApplicationBuilder 后，使用这个方法对其进行各种设置，最重要的就是在新的 ApplicationBuilder 上注册分支管道的中间件。配置完成后调用分支 ApplicationBuilder 的 Build 方法构建管道，并把第一个中间件保存下来作为分支管道的入口。
在使用 Map 注册中间件时传入了一个 PathString 参数，PathString 对象我们可以简单地认为是 string 。它用于记录 HttpContext.HttpRequest.Path 中要匹配的区段（Segment）。这个字符串参数结尾不能是“/”。如果匹配成功则进入分支管道，匹配失则败继续当前管道。
新构建的管道和用于匹配的字符串保存为 MapOptions 对象，保存了 Map 规则和分支管道的入口。之后构建 MapMiddleware 对象，并把它的 Invoke 方法包装为 RequestDelegate ，使用当前 ApplicationBuilder 的 Use 方法注册中间件。
2、MapWhen扩展原理

我们将光标移动到 MapWhen 处按 F12 转到定义，如下所示：

可以发现它是位于 MapWhenExtensions 扩展类中的，我们找到 MapWhenExtensions 类的源码，如下所示：

// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
using System;
using Microsoft.AspNetCore.Http;
using Microsoft.AspNetCore.Builder.Extensions;
namespace Microsoft.AspNetCore.Builder
{
using Predicate = Func<HttpContext, bool>;
/// <summary>
/// Extension methods for the <see cref="MapWhenMiddleware"/>.
/// </summary>
public static class MapWhenExtensions
{
/// <summary>
/// Branches the request pipeline based on the result of the given predicate.
/// </summary>
/// <param name="app"></param>
/// <param name="predicate">Invoked with the request environment to determine if the branch should be taken</param>
/// <param name="configuration">Configures a branch to take</param>
/// <returns></returns>
public static IApplicationBuilder MapWhen(this IApplicationBuilder app, Predicate predicate, Action<IApplicationBuilder> configuration)
{
if (app == null)
{
throw new ArgumentNullException(nameof(app));
}
if (predicate == null)
{
throw new ArgumentNullException(nameof(predicate));
}
if (configuration == null)
{
throw new ArgumentNullException(nameof(configuration));
}
// create branch
var branchBuilder = app.New();
configuration(branchBuilder);
var branch = branchBuilder.Build();
// put middleware in pipeline
var options = new MapWhenOptions
{
Predicate = predicate,
Branch = branch,
};
return app.Use(next => new MapWhenMiddleware(next, options).Invoke);
}
}
}

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其中 MapWhenMiddleware 类的源码，如下所示：

// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
using System;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Http;
namespace Microsoft.AspNetCore.Builder.Extensions
{
/// <summary>
/// Represents a middleware that runs a sub-request pipeline when a given predicate is matched.
/// </summary>
public class MapWhenMiddleware
{
private readonly RequestDelegate _next;
private readonly MapWhenOptions _options;
/// <summary>
/// Creates a new instance of <see cref="MapWhenMiddleware"/>.
/// </summary>
/// <param name="next">The delegate representing the next middleware in the request pipeline.</param>
/// <param name="options">The middleware options.</param>
public MapWhenMiddleware(RequestDelegate next, MapWhenOptions options)
{
if (next == null)
{
throw new ArgumentNullException(nameof(next));
}
if (options == null)
{
throw new ArgumentNullException(nameof(options));
}
_next = next;
_options = options;
}
/// <summary>
/// Executes the middleware.
/// </summary>
/// <param name="context">The <see cref="HttpContext"/> for the current request.</param>
/// <returns>A task that represents the execution of this middleware.</returns>
public async Task Invoke(HttpContext context)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
if (_options.Predicate(context))
{
await _options.Branch(context);
}
else
{
await _next(context);
}
}
}
}

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Map 主要通过 URL 中的 Path 来判断是否需要进入分支管道，但有时候我们很可能会有别的需求，例如我想对所有 Method 为 DELETE 的请求用特殊管道处理，这时候就需要用 MapWhen 了。MapWhen 是一种通用的 Map，可以由使用者来决定什么时候进入分支管道什么时候不进入。可以说 Map 是 MapWhen 的一种情况，因为这种情况太常见了，所以官方实现了一个。这样看来 MapWhen 就很简单了，在 Map 中我们传入参数 PathString 来进行 HttpRequest.Path 的匹配，而在 MapWhen 中我们传入 Func 参数，由我们自行指定，当返回 true 时进入分支管道，返回 false 则继续当前管道。
3、UseWhen扩展原理

我们将光标移动到 UseWhen 处按 F12 转到定义，如下所示：

可以发现它是位于 UseWhenExtensions 扩展类中的，我们找到 UseWhenExtensions 类的源码，如下所示：

// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
using System;
using Microsoft.AspNetCore.Http;
namespace Microsoft.AspNetCore.Builder
{
using Predicate = Func<HttpContext, bool>;
/// <summary>
/// Extension methods for <see cref="IApplicationBuilder"/>.
/// </summary>
public static class UseWhenExtensions
{
/// <summary>
/// Conditionally creates a branch in the request pipeline that is rejoined to the main pipeline.
/// </summary>
/// <param name="app"></param>
/// <param name="predicate">Invoked with the request environment to determine if the branch should be taken</param>
/// <param name="configuration">Configures a branch to take</param>
/// <returns></returns>
public static IApplicationBuilder UseWhen(this IApplicationBuilder app, Predicate predicate, Action<IApplicationBuilder> configuration)
{
if (app == null)
{
throw new ArgumentNullException(nameof(app));
}
if (predicate == null)
{
throw new ArgumentNullException(nameof(predicate));
}
if (configuration == null)
{
throw new ArgumentNullException(nameof(configuration));
}
// Create and configure the branch builder right away; otherwise,
// we would end up running our branch after all the components
// that were subsequently added to the main builder.
var branchBuilder = app.New();
configuration(branchBuilder);
return app.Use(main =>
{
// This is called only when the main application builder
// is built, not per request.
branchBuilder.Run(main);
var branch = branchBuilder.Build();
return context =>
{
if (predicate(context))
{
return branch(context);
}
else
{
return main(context);
}
};
});
}
}
}

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UseWhen 也基于给定谓词的结果创建请求管道分支。与 MapWhen 不同的是，如果这个分支不发生短路或包含终端中间件，则会重新加入主管道。

本文部分内容参考博文：https://www.cnblogs.com/durow/p/5752055.html
更多关于ASP.NET Core 中间件的相关知识可参考微软官方文档： https://docs.microsoft.com/zh-cn/aspnet/core/fundamentals/middleware/?view=aspnetcore-6.0
至此本文就全部介绍完了，如果觉得对您有所启发请记得点个赞哦！！！

Demo源码：

链接：https://pan.baidu.com/s/18I66dBmKZUpfPCNn85HI2g
提取码：2xcj

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此文由博主精心撰写转载请保留此原文链接：https://www.cnblogs.com/xyh9039/p/16492284.html
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