Polly：尊重与自定义异常通信的 Retry-After？

Question

所以我必须使用一个库，该库本质上对可能选择限制流量的远程系统执行 POST。如果是这样，它 returns 429 和特定的秒数在 Retry-After header...

throw new ThrottledException(retryAfterSeconds);

如何设置 Polly 策略来捕获此自定义异常，然后在 exception.RetryAfter 秒后重试？

Answer 1

好的，这比需要的要棘手一些，但这只是因为

在这种情况下，重试通过类型为 SigsThrottledException 的自定义异常进行通信，它有一个包含以秒为单位的请求退避时间的字段。

var policy = Policy
    .Handle<SigsThrottledException>(e => e.RetryAfterInSeconds > 0)
    .WaitAndRetryAsync(
        retryCount: retries,
        sleepDurationProvider: (i, e, ctx) =>
        {
            var ste = (SigsThrottledException)e;
            return TimeSpan.FromSeconds((double)ste.RetryAfterInSeconds);
        },
        onRetryAsync: async (e, ts, i, ctx) =>
        {
            // Do something here
        };);

这是一个如何使用政策的例子。你不能只是。你必须明确地使用它。

[TestMethod]
public async Task SigsPollyRetriesOnThrottle()
{
    var retryResponse = new HttpResponseMessage
    {
        StatusCode = (HttpStatusCode)429,
        Content = new StringContent("{}"),
    };

    retryResponse.Headers.Add("Retry-After", "1");

    var mockMessageHandler = new Mock<HttpMessageHandler>();
    mockMessageHandler.Protected()
        .SetupSequence<Task<HttpResponseMessage>>("SendAsync", ItExpr.IsAny<HttpRequestMessage>(), ItExpr.IsAny<CancellationToken>())
        .ReturnsAsync(retryResponse)
        .ReturnsAsync(new HttpResponseMessage
        {
            StatusCode = HttpStatusCode.OK
        });

    var client = new HttpClient(mockMessageHandler.Object);

    // Retry once after waiting 1 second
    var retryPolicy = Policy
    .Handle<SigsThrottledException>(e => e.RetryAfterInSeconds > 0)
    .WaitAndRetryAsync(
        retryCount: 1,
        sleepDurationProvider: (i, e, ctx) =>
        {
            var ste = (SigsThrottledException)e;
            return TimeSpan.FromSeconds((double)ste.RetryAfterInSeconds);
        },
        onRetryAsync: async (e, ts, i, ctx) =>
        {
            // Do something here
        };);

    Stopwatch stopWatch = new Stopwatch();
    stopWatch.Start();
    var response = await retryPolicy.ExecuteAsync(async () =>
    {
        Uri substrateurl = new Uri("https://substrate.office.com/");
        return await SIGSClient.Instance.PostAsync(client, substrateurl, new UserInfo(), "faketoken", new Signal(), Guid.NewGuid()).ConfigureAwait(false);
    }
    );

    Assert.AreEqual(response.StatusCode, HttpStatusCode.OK);
    stopWatch.Stop();
    Assert.IsTrue(stopWatch.ElapsedMilliseconds > 1000); // Make sure we actually waited at least a second
}

Polly：尊重与自定义异常通信的 Retry-After？

Polly: Honoring Retry-After that is communicated with a custom exception?

c#

polly