使用Flurl设置默认的Polly策略 [英] Set a default Polly policy with Flurl

问题描述

我目前正在一起使用Polly和Flurl，但是我有一个通用的重试策略，必须将其添加到每个请求中.我注意到Polly允许您使用AddPolicyHandler(...)设置默认值，但这需要IHttpClientBuilder，而且我看不到任何从Flurl掌握此方法的方法.

I'm currently using Polly and Flurl together, but I have a common retry policy that I have to add to every request. I notice that Polly allows you to set a default using AddPolicyHandler(...) but this requires an IHttpClientBuilder and I can't see any way of getting hold of this from Flurl.

我认为过载DefaultHttpClientFactory可能是解决方法，但这只能让我访问HttpClient，而不能访问IHttpClientBuilder.

I thought overloading DefaultHttpClientFactory might be the way to go, but that only gives me access to the HttpClient, not the IHttpClientBuilder.

我知道我可以制作自己的HttpClient并将其传递给Flurl，但我希望避免这种情况，因为我希望Flurl管理它们的生命周期.

I know I could make my own HttpClients and pass them into Flurl, but I'd rather avoid that if I can as I'd like Flurl to manage their lifecycle.

目前有一种方法可以做我想做的事吗?

Is there currently a way of doing what I want to do?

推荐答案

好问题. Flurl为您提供了所有必要的钩子.首先定义一个采用Polly策略的DelegatingHandler:

Great question. Flurl gives you all the necessary hooks to do this. First define a DelegatingHandler that takes a Polly policy:

public class PollyHandler : DelegatingHandler
{
    private readonly IAsyncPolicy<HttpResponseMessage> _policy;

    public PollyHandler(IAsyncPolicy<HttpResponseMessage> policy) {
        _policy = policy;
    }

    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken) {
        return _policy.ExecuteAsync(ct => base.SendAsync(request, ct), cancellationToken);
    }
}

然后创建一个自定义IHttpClientFactory，该自定义处理程序将默认处理程序作为其InnerHandler返回您的自定义处理程序:

Then create a custom IHttpClientFactory that returns your custom handler with the default handler as its InnerHandler:

public class PollyFactory : DefaultHttpClientFactory
{
    private readonly IAsyncPolicy<HttpResponseMessage> _policy;

    public PollyFactory(IAsyncPolicy<HttpResponseMessage> policy) {
        _policy = policy;
    }

    public override HttpMessageHandler CreateMessageHandler() {
        return new PollyHandler(_policy) {
            InnerHandler = base.CreateMessageHandler()
        };
    }
}

最后，在应用启动时，定义您的策略并向Flurl注册:

Finally, on app startup, define your policy and register it with Flurl:

var policy = Policy
    .Handle<HttpRequestException>()
    .OrResult<HttpResponseMessage>(r => !r.IsSuccessStatusCode)
    .RetryAsync(5);

FlurlHttp.Configure(settings => settings.HttpClientFactory = new PollyFactory(policy));

一个重要的注意事项是，此方法不适用于处理FlurlHttpException的策略.那是因为您在这里拦截HttpMessageHandler级别的呼叫. Flurl将响应和错误转换为堆栈中更高的FlurlHttpException，因此使用这种方法不会陷入或重试这些响应和错误.上面示例中的策略陷阱HttpRequestException和HttpResponseMessage(具有非2XX状态代码)，它们将起作用.

One important note is that this approach will not work with a policy that handles FlurlHttpException. That's because you're intercepting calls at the HttpMessageHandler level here. Flurl converts responses and errors to FlurlHttpExceptions higher up the stack, so those won't get trapped/retried with this approach. The policy in the example above traps HttpRequestException and HttpResponseMessage (with non-2XX status codes), which will work.

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