在 HttpClient 超时处理 TaskCanceledException

问：

我正在尝试使用策略处理程序进行重试或 http 暂时性错误，但它无法正常工作。Microsoft.Extensions.Http.PollyTaskCanceledException

我在下面编写了最小的 API，只是为了测试：

Program.cs

using Polly;
using Polly.Extensions.Http;
using Polly.Retry;

WebApplicationBuilder builder = WebApplication.CreateBuilder(args);

AsyncRetryPolicy<HttpResponseMessage>? policy = HttpPolicyExtensions.HandleTransientHttpError()
    .Or<TaskCanceledException>()
    .WaitAndRetryAsync(5, _ => TimeSpan.FromSeconds(5));

builder.Services.AddHttpClient("test", client =>
    {
        client.BaseAddress = new Uri("http://localhost:5000");
        client.Timeout = TimeSpan.FromSeconds(2);
    })
    .AddPolicyHandler(policy);

WebApplication app = builder.Build();

app.MapPost("/status/{code}",
    async (string code, IHttpClientFactory httpClientFactory, CancellationToken cancellationToken) =>
    {
        HttpClient client = httpClientFactory.CreateClient("test");
        HttpResponseMessage response = await client.GetAsync($"/status/{code}", cancellationToken);

        response.EnsureSuccessStatusCode();

        return response.Content.ReadAsStringAsync(cancellationToken);
    });

app.MapPost("/timeout/{timeout:int}",
    async (int timeout, IHttpClientFactory httpClientFactory, CancellationToken cancellationToken) =>
    {
        HttpClient client = httpClientFactory.CreateClient("test");
        HttpResponseMessage response = await client.GetAsync($"/timeout/{timeout}", cancellationToken);

        response.EnsureSuccessStatusCode();

        return response.Content.ReadAsStringAsync(cancellationToken);
    });

#region Simulated API

app.MapGet("/status/{code:int}", (int code) => Results.StatusCode(code));

app.MapGet("/timeout/{timeout:int}", async (int timeout) =>
{
    await Task.Delay(TimeSpan.FromSeconds(timeout));
    return Results.Ok();
});

#endregion

app.Run();

调用后，它会引发此异常，而无需任何进一步的尝试：POST http://localhost:5000/timeout/10

Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware[1]
An unhandled exception has occurred while executing the request.
System.Threading.Tasks.TaskCanceledException: The request was canceled due to the configured HttpClient.Timeout of 2 seconds elapsing.
---> System.TimeoutException: A task was canceled.
---> System.Threading.Tasks.TaskCanceledException: A task was canceled.
 at Polly.Retry.AsyncRetryEngine.ImplementationAsync[TResult](Func`3 action, Context context, CancellationToken cancellationToken, ExceptionPredicates shouldRetryExceptionPredicates, ResultPredicates`1 shouldRetryResultPredicates, Func`5 onRetryAsync, Int32 permittedRetryCount, IEnumerable`1 sleepDurationsEnumerable, Func`4 sleepDurationProvider, Boolean continueOnCapturedContext)
 at Polly.AsyncPolicy`1.ExecuteAsync(Func`3 action, Context context, CancellationToken cancellationToken, Boolean continueOnCapturedContext)       
 at Microsoft.Extensions.Http.PolicyHttpMessageHandler.SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
 at Microsoft.Extensions.Http.Logging.LoggingScopeHttpMessageHandler.<>c__DisplayClass5_0.<<SendCoreAsync>g__Core|0>d.MoveNext()
--- End of stack trace from previous location ---
 at System.Net.Http.HttpClient.<SendAsync>g__Core|83_0(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationTokenSource cts, Boolean disposeCts, CancellationTokenSource pendingRequestsCts, CancellationToken originalCancellationToken)
 --- End of inner exception stack trace ---
 --- End of inner exception stack trace ---
 at System.Net.Http.HttpClient.HandleFailure(Exception e, Boolean telemetryStarted, HttpResponseMessage response, CancellationTokenSource cts, CancellationToken cancellationToken, CancellationTokenSource pendingRequestsCts)
 at System.Net.Http.HttpClient.<SendAsync>g__Core|83_0(HttpRequestMessage request, HttpCompletionOption completionOption, CancellationTokenSource cts, Boolean disposeCts, CancellationTokenSource pendingRequestsCts, CancellationToken originalCancellationToken)
 at Program.<>c.<<<Main>$>b__0_3>d.MoveNext() in Z:\Repositories\POCs\PollyRetryTest\PollyRetryTest\Program.cs:line 35
--- End of stack trace from previous location ---
 at Microsoft.AspNetCore.Http.RequestDelegateFactory.<ExecuteTaskOfT>g__ExecuteAwaited|129_0[T](Task`1 task, HttpContext httpContext, JsonTypeInfo`1 jsonTypeInfo)
 at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)     

我做错了什么？是否必须重写主处理程序？