C#通过HttpClient+Polly实现自动重试与超时策略的操作指南

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
{
    // 自动重试策略（最多重试 3 次）
    public static IAsyncPolicy<HttpResponseMessage> GetRetryPolicy()
    {
        return HttpPolicyExtensions
            .HandleTransientHttpError() // 处理 5xx、408、网络错误
            .WaitAndRetryAsync(
                retryCount: 3,
                sleepDurationProvider: retryAttempt => TimeSpan.FromSeconds(Math.Pow(2, retryAttempt)), // 2,4,8 秒退避
                onRetry: (outcome, timespan, retryAttempt, context) =>
                {
                    Console.WriteLine($"重试第 {retryAttempt} 次，等待 {timespan.TotalSeconds} 秒。");
                });
    }

    // 超时策略（每次请求最长 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();

        // 注册 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");

        // 调用测试接口
        await TestHttpRequestAsync(client);
    }

    static async Task TestHttpRequestAsync(HttpClient client)
    {
        try
        {
            // 模拟 500 错误接口（会触发重试）
            var response = await client.GetAsync("500");
            Console.WriteLine($"最终状态码：{response.StatusCode}");
        }
        catch (Exception ex)
        {
            Console.WriteLine($"请求失败：{ex.Message}");
        }
    }
}

重试第 1 次，等待 2 秒。
重试第 2 次，等待 4 秒。
重试第 3 次，等待 8 秒。
请求失败：响应状态码不成功，状态码: 500

public static IAsyncPolicy<HttpResponseMessage> GetCircuitBreakerPolicy()
{
    return HttpPolicyExtensions
        .HandleTransientHttpError()
        .CircuitBreakerAsync(
            handledEventsAllowedBeforeBreaking: 2, // 连续 2 次错误触发熔断
            durationOfBreak: TimeSpan.FromSeconds(10), // 熔断 10 秒
            onBreak: (outcome, timespan) => Console.WriteLine($"熔断开启 {timespan.TotalSeconds} 秒"),
            onReset: () => Console.WriteLine("熔断恢复"),
            onHalfOpen: () => Console.WriteLine("熔断半开，尝试恢复..."));
}

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