客户端机器：在 Flurl.Http.FlurlClient.ReadResponseCookies 抛出 NullReference 异常

Question

问题只发生在我的客户端机器上。我运行我的应用在4台机器上都没有重现成功。

我想在使用 Flurl 库时寻求建议和帮助调试以下异常：

什么可能导致此异常运行仅在特定机器上？

System.TypeInitializationException：'Module.Performance.PriceProviders.YahooClientFactory' 的类型初始值设定项抛出异常。 ---> System.AggregateException: 发生一个或多个错误。 ---> System.NullReferenceException: 对象引用未设置为对象的实例。在 Flurl.Http.FlurlClient.ReadResponseCookies（HttpResponseMessage 响应）在 Flurl.Http.FlurlClient.d__28.MoveNext() --- 内部异常堆栈跟踪结束 --- 在 System.Threading.Tasks.Task.ThrowIfExceptional（布尔值 includeTaskCanceledExceptions）在 System.Threading.Tasks.Task1.GetResultCore(Boolean waitCompletionNotification) at System.Threading.Tasks.Task1.get_Result() 在 Module.Performance.PriceProviders.YahooClientFactory..cctor() --- 内部异常堆栈跟踪结束 --- 在 Module.Performance.PriceProviders.YahooClientFactory.get_GetYahooClient() 在 Module.Performance.PriceProviders.YahooFlurlClient.d__9.MoveNext() --- 从抛出异常的先前位置开始的堆栈跟踪结束 --- 在 System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess（任务任务）在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）在 Module.Performance.PriceProviders.YahooStockPriceProvider.d__0.MoveNext() --- 从抛出异常的先前位置开始的堆栈跟踪结束 --- 在 System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess（任务任务）在 System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification（任务任务）在 Module.Performance.PriceProviders.PriceProviderBase.d__3.MoveNext()

异常下方的代码如下所示：

YahooClientFactory 是优化请求时间的单例因素。工厂经常被其他异步任务（更高层）调用

public static class YahooClientFactory
{
    public static IFlurlClient GetYahooClient => YahooClientInstance;
    public static string Crumb { get; }

    private static readonly IFlurlClient YahooClientInstance;
    private const string CookieUrl = "https://finance.yahoo.com";

    private static string userAgent = "User-Agent";
    private static string headerString =
        "Mozilla/5.0 (Windows NT 6.1; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/58.0.3029.110 Safari/537.36";

    private const string CrumbUrl = "https://query1.finance.yahoo.com/v1/test/getcrumb";
    private static int MaxRetryCount = 5;

    static YahooClientFactory()
    {
        YahooClientInstance = new FlurlClient()
                .WithHeader(userAgent, headerString)
                .EnableCookies()
                .WithUrl($"{CookieUrl}?{GetRandomString(8)}");

        for (int i = 0; i < MaxRetryCount; i++)
        {
            YahooClientInstance
                .GetAsync(CancellationToken.None)
                .Result
                .EnsureSuccessStatusCode();

            if (YahooClientInstance.Cookies?.Count > 0)
            {
                break;
            }
            if (i == MaxRetryCount)
            {
                throw new Exception("Reached maximum number of retries when connecting to yahoo client.");
            }
            Thread.Sleep(100);
        }

        Crumb = YahooClientInstance
            .WithUrl(CrumbUrl)
            .GetAsync(CancellationToken.None)
            .ReceiveString()
            .Result;
    }

    public static string GetRandomString(int length)
    {
        const string Chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
        return string.Join("", Enumerable.Range(0, length).Select(i => Chars[new Random().Next(Chars.Length)]));
    }
}

Answer 1

您似乎遇到了 known bug where Flurl attempts to read cookies after a failed request without checking for a null response. This is fixed for Flurl.Http 2.0. Please upgrade to the latest prerelease 并报告是否解决了您的问题。

客户端机器：在 Flurl.Http.FlurlClient.ReadResponseCookies 抛出 NullReference 异常

Client Machine : throw NullReference Exception at Flurl.Http.FlurlClient.ReadResponseCookies

c#

asynchronous

factory

http

flurl