Polly重试时更改查询字符串 [英] Polly to change query string on retry
问题描述
我正在使用.NET 5,并且想使用Polly更改重试请求的查询字符串.背景-我的IP地址允许每分钟有固定的请求配额.如果超过限制,我将得到一个特定的4xx状态代码.在这种情况下,我想添加查询字符串参数?key = xxx
来处理峰.计入API密钥的请求比较昂贵,并且仅在达到临时配额后才适用.
I'm using .NET 5 and want to use Polly to change the query string of a request on a retry.
Background - I have a fixed quota of requests per minute which is allowed from my IP address. If I exceed the limit, I get a specific 4xx status code. In this case I want to add a query string argument ?key=xxx
to handle peaks. The requests counting towards the API key are more expensive and should only apply if reached the quota temporary.
我在不同的地方多次使用命名的客户端.
I use the named client many times in different places.
这是Polly合适的方案吗?还是从设计的角度来看,以干净的方式在业务逻辑中进行处理?然后,我需要包装此逻辑以避免重复自己.
Is this a scenario for which Polly is suitable? Or from a design perspective, is handling this in business logic the clean way? Then I need to wrap this logic to avoid repeating myself.
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
推荐答案
GetStringAsync
返回 Task< string>
,因此您无法检查响应的StatusCode
.
因此,您需要使用 GetAsync
来返回 Task< HttpResponseMessage>
.
The GetStringAsync
returns a Task<string>
so you can't examine the reponse's StatusCode
.
So, you need to use GetAsync
which returns a Task<HttpResponseMessage>
.
因为请求uri是两次调用之间唯一发生变化的原因,所以您需要将其作为参数接收:
Because the request uri is the only thing which is changing between the calls that's why you need to receive that as a parameter:
private static HttpClient client = new HttpClient(); //or use IHttpClientFactory
static async Task<HttpResponseMessage> PerformRequest(string uri)
{
Console.WriteLine(uri);
return await client.GetAsync(uri);
}
为了执行重试策略可以执行的无参数操作,我们需要一个地址迭代器和一个围绕 PerformRequest
的包装器:
In order to have a parameter-less action which can be performed by the retry policy we need an address iterator and a wrapper around the PerformRequest
:
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;
}
每次调用 GetNewAddressAndPerformRequest
时,它都会检索下一个后备URL,然后针对该URL执行请求.
Each time when you call the GetNewAddressAndPerformRequest
it retrieves the next fallback url and then executes the request against that.
剩下的是重试策略本身:
What's left is the retry policy itself:
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
(因为我们用尽了备用网址),则我们退出重试 - 如果statusCode在200到299之间,则我们退出重试
- 如果statusCode在300到400之间或大于500,则我们退出重试
- 在其他所有情况下,我们都会重试
- If the
GetNewAddressAndPerformRequest
returnsnull
because we have run out of fallback urls then we exit from the retry - If the statusCode is between 200 and 299 then we exit from the retry
- If the statusCode is between 300 and 400 or greater than 500 then we exit from the retry
- In every other case we perform a retry
用法可能是这样的:
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());
为完整起见,以下是完整的源代码:
For the sake of completeness here is the full source code:
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);
}
}
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