【.NET Core项目实战-统一认证平台】第二章网关篇-重构Ocelot来满足需求

【.NET Core项目实战-统一认证平台】开篇及目录索引

这篇文章，我们将从Ocelot的中间件源码分析，目前Ocelot已经实现那些功能，还有那些功能在我们实际项目中暂时还未实现，如果我们要使用这些功能，应该如何改造等方面来说明。

一、Ocelot源码解读

在使用一个组件前，最好我们要了解其中的一些原理，否则在使用过程中遇到问题，也无从下手，今天我带着大家一起来解读下Ocelot源码，并梳理出具体实现的原理和流程，便于我们根据需求扩展应用。
Ocelot源码地址[https://github.com/ThreeMammals/Ocelot],
Ocelot文档地址[https://ocelot.readthedocs.io/en/latest/]

查看.NETCORE相关中间件源码，我们优先找到入口方法，比如Ocelot中间件使用的是app.UseOcelot(),我们直接搜索UserOcelot,我们会找到OcelotMiddlewareExtensions方法，里面是Ocelot中间件实际运行的方式和流程。

然后继续顺藤摸瓜，查看详细的实现，我们会发现如下代码

public static async Task<IApplicationBuilder> UseOcelot(this IApplicationBuilder builder, OcelotPipelineConfiguration pipelineConfiguration) { //创建配置信息 var configuration = await CreateConfiguration(builder); //监听配置信息 ConfigureDiagnosticListener(builder); //创建执行管道 return CreateOcelotPipeline(builder, pipelineConfiguration); }

然后我们继续跟踪到创建管道方法，可以发现Ocelot的执行流程已经被找到，现在问题变的简单了，直接查看

private static IApplicationBuilder CreateOcelotPipeline(IApplicationBuilder builder, OcelotPipelineConfiguration pipelineConfiguration) { var pipelineBuilder = new OcelotPipelineBuilder(builder.ApplicationServices); //详细创建的管道顺序在此方法 pipelineBuilder.BuildOcelotPipeline(pipelineConfiguration); var firstDelegate = pipelineBuilder.Build(); /* inject first delegate into first piece of asp.net middleware..maybe not like this then because we are updating the http context in ocelot it comes out correct for rest of asp.net.. */ builder.Properties["analysis.NextMiddlewareName"] = "TransitionToOcelotMiddleware"; builder.Use(async (context, task) => { var downstreamContext = new DownstreamContext(context); await firstDelegate.Invoke(downstreamContext); }); return builder; }

管道创建流程及实现，会不会感觉到摸到大动脉了，核心的功能及原理基本找到了，那以后动手术也就可以避开一些坑了，我们可以对着这个执行顺序，再查看详细的源码，按照这个执行顺序查看源码，您就会发现整个思路非常清晰，每一步的实现一目了然。为了更直观的介绍源码的解读方式，这里我们就拿我们后续要操刀的中间件来讲解下中间件的具体实现。

public static class OcelotPipelineExtensions { public static OcelotRequestDelegate BuildOcelotPipeline(this IOcelotPipelineBuilder builder, OcelotPipelineConfiguration pipelineConfiguration) { // This is registered to catch any global exceptions that are not handled // It also sets the Request Id if anything is set globally builder.UseExceptionHandlerMiddleware(); // If the request is for websockets upgrade we fork into a different pipeline builder.MapWhen(context => context.HttpContext.WebSockets.IsWebSocketRequest, app => { app.UseDownstreamRouteFinderMiddleware(); app.UseDownstreamRequestInitialiser(); app.UseLoadBalancingMiddleware(); app.UseDownstreamUrlCreatorMiddleware(); app.UseWebSocketsProxyMiddleware(); }); // Allow the user to respond with absolutely anything they want. builder.UseIfNotNull(pipelineConfiguration.PreErrorResponderMiddleware); // This is registered first so it can catch any errors and issue an appropriate response builder.UseResponderMiddleware(); // Then we get the downstream route information builder.UseDownstreamRouteFinderMiddleware(); // This security module, IP whitelist blacklist, extended security mechanism builder.UseSecurityMiddleware(); //Expand other branch pipes if (pipelineConfiguration.MapWhenOcelotPipeline != null) { foreach (var pipeline in pipelineConfiguration.MapWhenOcelotPipeline) { builder.MapWhen(pipeline); } } // Now we have the ds route we can transform headers and stuff? builder.UseHttpHeadersTransformationMiddleware(); // Initialises downstream request builder.UseDownstreamRequestInitialiser(); // We check whether the request is ratelimit, and if there is no continue processing builder.UseRateLimiting(); // This adds or updates the request id (initally we try and set this based on global config in the error handling middleware) // If anything was set at global level and we have a different setting at re route level the global stuff will be overwritten // This means you can get a scenario where you have a different request id from the first piece of middleware to the request id middleware. builder.UseRequestIdMiddleware(); // Allow pre authentication logic. The idea being people might want to run something custom before what is built in. builder.UseIfNotNull(pipelineConfiguration.PreAuthenticationMiddleware); // Now we know where the client is going to go we can authenticate them. // We allow the ocelot middleware to be overriden by whatever the // user wants if (pipelineConfiguration.AuthenticationMiddleware == null) { builder.UseAuthenticationMiddleware(); } else { builder.Use(pipelineConfiguration.AuthenticationMiddleware); } // The next thing we do is look at any claims transforms in case this is important for authorisation builder.UseClaimsToClaimsMiddleware(); // Allow pre authorisation logic. The idea being people might want to run something custom before what is built in. builder.UseIfNotNull(pipelineConfiguration.PreAuthorisationMiddleware); // Now we have authenticated and done any claims transformation we // can authorise the request // We allow the ocelot middleware to be overriden by whatever the // user wants if (pipelineConfiguration.AuthorisationMiddleware == null) {//使用自定义认证，移除默认的认证方式 //builder.UseAuthorisationMiddleware(); } else { builder.Use(pipelineConfiguration.AuthorisationMiddleware); } // Now we can run the claims to headers transformation middleware builder.UseClaimsToHeadersMiddleware(); // Allow the user to implement their own query string manipulation logic builder.UseIfNotNull(pipelineConfiguration.PreQueryStringBuilderMiddleware); // Now we can run any claims to query string transformation middleware builder.UseClaimsToQueryStringMiddleware(); // Get the load balancer for this request builder.UseLoadBalancingMiddleware(); // This takes the downstream route we retrieved earlier and replaces any placeholders with the variables that should be used builder.UseDownstreamUrlCreatorMiddleware(); // Not sure if this is the best place for this but we use the downstream url // as the basis for our cache key. builder.UseOutputCacheMiddleware(); //We fire off the request and set the response on the scoped data repo builder.UseHttpRequesterMiddleware(); return builder.Build(); } private static void UseIfNotNull(this IOcelotPipelineBuilder builder, Func<DownstreamContext, Func<Task>, Task> middleware) { if (middleware != null) { builder.Use(middleware); } } }

限流中间件实现解析