dotnet new console -n HttpClientPollyDemo
cd HttpClientPollyDemo

dotnet add package Microsoft.Extensions.Http
dotnet add package Polly
dotnet add package Polly.Extensions.Http

services.AddHttpClient("DemoClient")
    .AddPolicyHandler(GetRetryPolicy())
    .AddPolicyHandler(GetTimeoutPolicy());

using Polly;
using Polly.Extensions.Http;
using System;
using System.Net.Http;

public static class PolicyHandlers
{
    // 自動(dòng)重試策略（最多重試 3 次）
    public static IAsyncPolicy<HttpResponseMessage> GetRetryPolicy()
    {
        return HttpPolicyExtensions
            .HandleTransientHttpError() // 處理 5xx、408、網(wǎng)絡(luò)錯(cuò)誤
            .WaitAndRetryAsync(
                retryCount: 3,
                sleepDurationProvider: retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)), // 2,4,8 秒退避
                onRetry: (outcome, timespan, retryAttempt, context) =>
                {
                    Console.WriteLine($"重試第 {retryAttempt} 次，等待 {timespan.TotalSeconds} 秒。");
                });
    }

    // 超時(shí)策略（每次請求最長 5 秒）
    public static IAsyncPolicy<HttpResponseMessage> GetTimeoutPolicy()
    {
        return Policy.TimeoutAsync<HttpResponseMessage>(5);
    }
}

using Microsoft.Extensions.DependencyInjection;
using System;
using System.Net.Http;
using System.Threading.Tasks;

class Program
{
    static async Task Main()
    {
        var services = new ServiceCollection();

        // 注冊 HttpClient + Polly 策略
        services.AddHttpClient("ResilientClient", client =>
        {
            client.BaseAddress = new Uri("https://httpstat.us/");
            client.DefaultRequestHeaders.Add("User-Agent", "HttpClientPollyDemo");
        })
        .AddPolicyHandler(PolicyHandlers.GetRetryPolicy())
        .AddPolicyHandler(PolicyHandlers.GetTimeoutPolicy());

        var provider = services.BuildServiceProvider();
        var factory = provider.GetRequiredService<IHttpClientFactory>();

        var client = factory.CreateClient("ResilientClient");

        // 調(diào)用測試接口
        await TestHttpRequestAsync(client);
    }

    static async Task TestHttpRequestAsync(HttpClient client)
    {
        try
        {
            // 模擬 500 錯(cuò)誤接口（會(huì)觸發(fā)重試）
            var response = await client.GetAsync("500");
            Console.WriteLine($"最終狀態(tài)碼：{response.StatusCode}");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"請求失?。簕ex.Message}");
        }
    }
}

重試第 1 次，等待 2 秒。
重試第 2 次，等待 4 秒。
重試第 3 次，等待 8 秒。
請求失敗：響應(yīng)狀態(tài)碼不成功，狀態(tài)碼: 500

public static IAsyncPolicy<HttpResponseMessage> GetCircuitBreakerPolicy()
{
    return HttpPolicyExtensions
        .HandleTransientHttpError()
        .CircuitBreakerAsync(
            handledEventsAllowedBeforeBreaking: 2, // 連續(xù) 2 次錯(cuò)誤觸發(fā)熔斷
            durationOfBreak: TimeSpan.FromSeconds(10), // 熔斷 10 秒
            onBreak: (outcome, timespan) => Console.WriteLine($"熔斷開啟 {timespan.TotalSeconds} 秒"),
            onReset: () => Console.WriteLine("熔斷恢復(fù)"),
            onHalfOpen: () => Console.WriteLine("熔斷半開，嘗試恢復(fù)..."));
}

services.AddHttpClient("ResilientClient", client =>
{
    client.BaseAddress = new Uri("https://httpstat.us/");
})
.AddPolicyHandler(PolicyHandlers.GetRetryPolicy())
.AddPolicyHandler(PolicyHandlers.GetTimeoutPolicy())
.AddPolicyHandler(PolicyHandlers.GetCircuitBreakerPolicy());