.NET Core HttpClient 有拦截器的概念吗？

Question

我想围绕我的 ASP.NET Core 应用通过 HttpClient 进行的所有调用封装一些计时逻辑，包括从 3rd 方库进行的调用。

.NET Core 中的HttpClient 是否有一些我可以插入的东西来在每个请求上运行一些代码？

Answer 1

是的，确实如此。 HttpClient 通过 DelegatingHandler 链产生一个 HTTP 请求。要拦截HttpClient 请求，您可以将具有覆盖SendAsync 方法的派生处理程序添加到该链。

用法：

var handler = new ExampleHttpHandler(fooService);

var client = new HttpClient(new ExampleHttpHandler(handler));

var response = await client.GetAsync("http://google.com");

实施：

public class ExampleHttpHandler : DelegatingHandler
{
    //use this constructor if a handler is registered in DI to inject dependencies
    public ExampleHttpHandler(FooService service) : this(service, null)
    {
    }

    //Use this constructor if a handler is created manually.
    //Otherwise, use DelegatingHandler.InnerHandler public property to set the next handler.
    public ExampleHttpHandler(FooService service, HttpMessageHandler innerHandler)
    {
        //the last (inner) handler in the pipeline should be a "real" handler.
        //To make a HTTP request, create a HttpClientHandler instance.
        InnerHandler = innerHandler ?? new HttpClientHandler();
    }

    protected override async Task<HttpResponseMessage> SendAsync(
        HttpRequestMessage request,
        CancellationToken cancellationToken)
    {
        //add any logic here
        return await base.SendAsync(request, cancellationToken);
    }
}

顺便说一句，我建议将尽可能多的业务逻辑从自定义处理程序中移出，以简化对其进行单元测试。