YARP简介 —— IHttpProxy

在YARP框架中，核心处理类是IHttpProxy，其接口定义如下：

Task ProxyAsync(HttpContext context, string destinationPrefix, HttpMessageInvoker httpClient, RequestProxyOptions requestOptions, HttpTransformer transformer)

从它的接口定义基本可以看出它的功能：从 HttpContext 创建 Http 查询信息、发送到目标地址，并将响应结果写会HttpContext。

IhttpProxy特点如下：

1. 灵活，能根据请求动态选择代理目标
2. 强大，能修改http请求和响应的头
3. 支持gRPC或WebSockets这种流式协议
4. 支持异常处理

它简单灵活，本身是一个反向代理的功能类的。 用它本身是可以非常简单的实现一个反向代理功能的。代码如下： 

 1 public void ConfigureServices(IServiceCollection services)
 2 {
 3     services.AddHttpProxy();
 4 }
 5 
 6 public void Configure(IApplicationBuilder app, IHttpProxy httpProxy)
 7 {
 8     var httpClient = new HttpMessageInvoker(new SocketsHttpHandler()
 9     {
10         UseProxy = false,
11         AllowAutoRedirect = false,
12         AutomaticDecompression = DecompressionMethods.None,
13         UseCookies = false
14     });
15     var transformer = new CustomTransformer(); // or HttpTransformer.Default;
16     var requestOptions = new RequestProxyOptions { Timeout = TimeSpan.FromSeconds(100) };
17 
18     app.UseRouting();
19     app.UseAuthorization();
20     app.UseEndpoints(endpoints =>
21     {
22         endpoints.Map("/{**catch-all}", async httpContext =>
23         {
24             await httpProxy.ProxyAsync(httpContext, "https://localhost:10000/", httpClient,
25                 requestOptions, transformer);
26 
27             var errorFeature = httpContext.GetProxyErrorFeature();
28             if (errorFeature != null)
29             {
30                 var error = errorFeature.Error;
31                 var exception = errorFeature.Exception;
32             }
33         });
34     });
35 }

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