Ocelot自定义管道中间件

Ocelot是啥就不介绍了哈，网关大家都知道，如果大家看过源码会发现其核心就是由一个个的管道中间件组成的，当然这也是Net Core的亮点之一。一个请求到来，会按照中间件的注册顺序进行处理，今天的问题出在Ocelot管道中间件这里，现在有个需求是想要在网关层面对数据进行加密解密，前端会对数据进行加密，通过网关的时候进行解密传递下游，下游返回数据网关进行加密返回给前端。

所以这里就想在走Ocelot管道前后注册两个中间件对请求和结果数据进行处理。然后就按想的去做，但悲催的是，Ocelot处理完后就直接返回数据给调用方了，根本没有走它后面的管道中间件，查资料才知道Ocelot之后不会再调用下一个管道中间件了，这就蛋疼了，怎么办？？

突然想到Ocelot应该会提供扩展来让使用者自定义管道中间件吧，回答当然是可以的，本篇我们就来自定义一个管道中间件放在Ocelot中。

首先需要写一个自己的中间件，需要继承OcelotMiddleware：

public class TestResponseMiddleware: OcelotMiddleware
    {
        private readonly OcelotRequestDelegate _next;
        public TestResponseMiddleware(OcelotRequestDelegate next,IOcelotLoggerFactory loggerFactory)
            : base(loggerFactory.CreateLogger<TestResponseMiddleware>())
        {
            _next = next;
        }


        public async Task Invoke(DownstreamContext context)
        {
            if (!context.IsError && context.HttpContext.Request.Method.ToUpper() != "OPTIONS")
            {
                //对返回结果进行加密
                //Logger.LogInformation("");
                if (context.HttpContext.Response != null && context.DownstreamResponse.Content.Headers.ContentLength > 0)
                {
                    var result= await context.DownstreamResponse.Content.ReadAsStringAsync();
                    using (var md5 = MD5.Create())
                    {
                        var md5Result = md5.ComputeHash(Encoding.ASCII.GetBytes(result));
                        var strResult = BitConverter.ToString(md5Result);
                        strResult = strResult.Replace("-", "");
                        context.HttpContext.Response.Body.Write(Encoding.UTF8.GetBytes(strResult));
                    }
                }
            }
            else
            {
                await _next.Invoke(context);
            }
        }
    }

这个逻辑就是拿到请求结果之后对数据进行MD5加密，然后再返回。

然后我们新建一个注册类，创建专门用来注册管道中间件的方法：

    public static class TestServiceExtension
    {
        public static IOcelotPipelineBuilder UseTestResponseMiddleware(this IOcelotPipelineBuilder builder)
        {
            return builder.UseMiddleware<TestResponseMiddleware>();
        }
    }

然后就是重点了！！我们需要去翻Ocelot的源码，找到其中注册管道中间件的地方，然后把那个类文件复制过来，放到自己的项目中引用，你可以理解为修改了源码来用。我们首先要看的是OcelotMiddlewareExtensions.cs文件，这里是Ocelot管道中间件的调用入口，不信你看UseOcelot扩展方法：

public static class OcelotMiddlewareExtensions
    {
        public static async Task<IApplicationBuilder> UseOcelot(this IApplicationBuilder builder)
        {
            await builder.UseOcelot(new OcelotPipelineConfiguration());
            return builder;
        }

我们要看的是这里面的另外一个方法，Ocelot管道的CreateOcelotPipeline：

        private static IApplicationBuilder CreateOcelotPipeline(IApplicationBuilder builder, OcelotPipelineConfiguration pipelineConfiguration)
        {
            var pipelineBuilder = new OcelotPipelineBuilder(builder.ApplicationServices);

            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;
        }

可以看到里面 pipelineBuilder.BuildOcelotPipeline(pipelineConfiguration)这句代码，这是Ocelot管道中间件的创建方法，我们要修改的就是这两个地方，这个方法在OcelotPipelineExtensions.cs类文件里，点进去看一下：

 public static class OcelotPipelineExtensions
    {
        public static OcelotRequestDelegate BuildCustomeOcelotPipeline(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)
            {
                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();

            //添加自定义测试中间件
         builder.UseTestResponseMiddleware();

            return builder.Build();
        }

        private static void UseIfNotNull(this IOcelotPipelineBuilder builder,
            Func<DownstreamContext, Func<Task>, Task> middleware)
        {
            if (middleware != null)
            {
                builder.Use(middleware);
            }
        }
    }

我们可以看到其实就是一个个的扩展方法的调用，也是我们所说的中间件，我在最后把刚才写的中间件加了上去，就是标红的那里，现在所有进入Ocelot的请求就都会走我们的中间件处理了，使用的时候需要将修改的OcelotPipelineExtensions.cs类文件放在自己项目里哦。

大功告成！