HttpClientFactory 结合 Polly 轻松实现重试机制
Intro
我们的服务里有一个 API 会去调用第三方的接口,设置了超时时间,最近偶尔会发生超时的情况,微软在提供 HttpClientFactory
的同时,也提供了一个基于 Polly
的一个扩展,我们可以借助它轻松地实现重试,熔断等行为。
Sample
使用 Polly 扩展需要引用 nuget 包 :Microsoft.Extensions.Http.Polly
使用示例:
services.AddHttpClient(ServiceConst.IterableHttpClientName, x =>
{x.Timeout = new TimeSpan(0, 0, 3);
}).AddTransientHttpErrorPolicy(builder =>{return builder.Or<TaskCanceledException>().Or<OperationCanceledException>().Or<TimeoutException>().OrResult(res => res.StatusCode == HttpStatusCode.TooManyRequests || (int)res.StatusCode >= 500).RetryAsync(5);})
通过 AddTransientHttpErrorPolicy
扩展方法来注册一个 Polly 的 policy,具体可以通过 policyBuilder
委托来定制自己要处理的情况和 policy 行为,支持方式有很多可以简单的指定重试,也可以指定 WaitANdRetryAsync
等待一段时间后重试,可以重试一次也可以一直重试下去,非常的灵活,可以根据自己的业务场景进行定制化配置,这里的示例直接是用了简单的重试机制
单元测试
下面提供了一个测试重试的单元测试,也可以作为使用示例的一个参考:
[Fact]
public async Task TaskCanceledException()
{var ticks = new ConcurrentBag<long>();var retryLimit = 5;var services = new ServiceCollection();services.AddHttpClient("test", x =>{x.Timeout = TimeSpan.FromSeconds(1);}).AddTransientHttpErrorPolicy(builder =>{return builder.Or<TaskCanceledException>().Or<OperationCanceledException>().Or<TimeoutException>().OrResult(res =>res.StatusCode == HttpStatusCode.TooManyRequests || (int)res.StatusCode >= 500).RetryAsync(retryLimit);}).AddHttpMessageHandler(() => new MockHttpHandler(request =>{ticks.Add(DateTime.UtcNow.Ticks);throw new TaskCanceledException();}));await using var provider = services.BuildServiceProvider();try{using var response = await provider.GetRequiredService<IHttpClientFactory>().CreateClient("test").GetAsync("api/test");}catch (Exception e){Assert.True(e is OperationCanceledException);}Assert.Equal(retryLimit + 1, ticks.Count);
}private class MockHttpHandler : DelegatingHandler
{private readonly Func<HttpRequestMessage, HttpResponseMessage> _getResponseFunc;public MockHttpHandler(Func<HttpRequestMessage, HttpResponseMessage> getResponseFunc){_getResponseFunc = getResponseFunc;}protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken){return Task.FromResult(_getResponseFunc(request));}
}
More
除了 AddTransientHttpErrorPolicy
之外,Polly 扩展还支持 AddPolicyHandler
/AddPolicyHandlerFromRegistry
扩展方法,有兴趣的可以自己探索一下哈~~
Reference
https://www.nuget.org/packages/Microsoft.Extensions.Http.Polly
https://github.com/dotnet/aspnetcore/tree/master/src/HttpClientFactory/Polly/src