Polly在重试时更改查询字符串

Question

这是波莉适合的场景吗？或者从设计的角度来看，在业务逻辑中处理这个是干净的方式吗？然后我需要包装这个逻辑以避免重复我自己。

var response = await client.GetStringAsync("https://test.com");
if (!response.IsSuccessStatusCode && response.StatusCode == 4xx)
  response = await client.GetStringAsync("https://test.com?key=XXX")

// continue with regular workflow - handling errors or process response

Answer 1

getStringAsync返回一个任务 ，所以您不能检查reponse的statuscode。
因此，您需要使用getAsync返回一个任务 。

因为请求uri是调用之间唯一变化的东西，所以需要将其作为参数接收：

private static HttpClient client = new HttpClient(); //or use IHttpClientFactory
static async Task<HttpResponseMessage> PerformRequest(string uri)
{
    Console.WriteLine(uri);
    return await client.GetAsync(uri);
}

为了使重试策略能够执行无参数操作，我们需要一个地址迭代器和围绕performrequest的包装器：

static IEnumerable<string> GetAddresses()
{
    yield return "https://test.com";
    yield return "https://test.com?key=XXX";
    ...
}

private static readonly IEnumerator<string> UrlIterator = GetAddresses().GetEnumerator();
static async Task<HttpResponseMessage> GetNewAddressAndPerformRequest()
{
    if (UrlIterator.MoveNext())
        return await PerformRequest(UrlIterator.Current);
    return null;
}

剩下的是重试策略本身：

var retryPolicyForNotSuccessAnd4xx = Policy
    .HandleResult<HttpResponseMessage>(response => response != null && !response.IsSuccessStatusCode)
    .OrResult(response => response != null && (int)response.StatusCode > 400 && (int)response.StatusCode < 500)
    .WaitAndRetryForeverAsync(_ => TimeSpan.FromSeconds(1));

• 如果GetNewAddresSandPerformRequest返回null，因为我们已经用完了回退URL，那么我们将退出重试
• 如果statusCode在200到299之间，则退出重试
• 如果statusCode在300到400之间或大于500，则退出重试
• 在其他情况下，我们执行重试

用法可能如下所示：

var response = await retryPolicyForNotSuccessAnd4xx.ExecuteAsync(async () => await GetNewAddressAndPerformRequest());
if (response == null)
{
    Console.WriteLine("All requests failed");
    Environment.Exit(1);
}
    
Console.WriteLine(await response.Content.ReadAsStringAsync());

class Program
{
    private static HttpClient client = new HttpClient();
    static async Task Main(string[] args)
    {
        var retryPolicyForNotSuccessAnd4xx = Policy
            .HandleResult<HttpResponseMessage>(response => response != null && !response.IsSuccessStatusCode)
            .OrResult(response => response != null && (int)response.StatusCode > 400 && (int)response.StatusCode < 500)
            .WaitAndRetryForeverAsync(_ => TimeSpan.FromSeconds(1));

        var response = await retryPolicyForNotSuccessAnd4xx.ExecuteAsync(async () => await GetNewAddressAndPerformRequest());
        if (response == null)
        {
            Console.WriteLine("All requests failed");
            Environment.Exit(1);
        }

        Console.WriteLine(await response.Content.ReadAsStringAsync());
    }

    static IEnumerable<string> GetAddresses()
    {
        yield return "https://test.com";
        yield return "https://test.com?key=XXX";
    }

    private static readonly IEnumerator<string> UrlIterator = GetAddresses().GetEnumerator();
    
    static async Task<HttpResponseMessage> GetNewAddressAndPerformRequest()
        => UrlIterator.MoveNext() ? await PerformRequest(UrlIterator.Current) : null;
    
    static async Task<HttpResponseMessage> PerformRequest(string uri)
    {
        Console.WriteLine(uri);
        return await client.GetAsync(uri);
    }
}