帶有無限超時的HttpClient拋出超時異常

Question

我的HttpClient使用摘要身份驗證連接到服務器，並期望搜索查詢作爲響應。這些搜索查詢可以隨時進行，因此客戶希望始終保持連接的開放。

的連接是用下面的代碼製成：

public static async void ListenForSearchQueries(int resourceId) 
{ 
    var url = $"xxx/yyy/{resourceId}/waitForSearchRequest?token=abc"; 

    var httpHandler = new HttpClientHandler { PreAuthenticate = true }; 

    using (var digestAuthMessageHandler = new DigestAuthMessageHandler(httpHandler, "user", "password")) 
    using (var client = new HttpClient(digestAuthMessageHandler)) 
    { 
     client.Timeout = TimeSpan.FromMilliseconds(Timeout.Infinite); 

     var request = new HttpRequestMessage(HttpMethod.Get, url); 

     var tokenSource = new CancellationTokenSource(); 
      tokenSource.CancelAfter(TimeSpan.FromMilliseconds(Timeout.Infinite)); 

     using (var response = await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, tokenSource.Token)) 
     { 
      Console.WriteLine("\nResponse code: " + response.StatusCode); 

      using (var body = await response.Content.ReadAsStreamAsync()) 
      using (var reader = new StreamReader(body)) 
       while (!reader.EndOfStream) 
        Console.WriteLine(reader.ReadLine()); 
     } 
    } 
} 

這是如何被在控制檯應用程序的主方法中使用的方法。

private static void Main(string[] args) 
{ 
    const int serviceId = 128; 
    . 
    . 
    . 
    ListenForSearchQueries(resourceId); 
    Console.ReadKey(); 
} 

這是在控制檯窗口中輸出的樣子：

Response code: OK 
--searchRequestBoundary 

即使客戶端的超時時間設置爲無窮大，連接超時後大約5分鐘（這是不在第一個輸出後，HttpClient的默認超時）拋出以下異常。

System.IO.IOException occurred 
    HResult=0x80131620 
    Message=The read operation failed, see inner exception. 
    Source=System.Net.Http 
    StackTrace: 
    at System.Net.Http.HttpClientHandler.WebExceptionWrapperStream.Read(Byte[] buffer, Int32 offset, Int32 count) 
    at System.Net.Http.DelegatingStream.Read(Byte[] buffer, Int32 offset, Int32 count) 
    at System.IO.StreamReader.ReadBuffer() 
    at System.IO.StreamReader.get_EndOfStream() 
    at ConsoleTester.Program.<ListenSearchQueriesDigestAuthMessageHandler>d__10.MoveNext() in C:\Users\xyz\ProjName\ConsoleTester\Program.cs:line 270 

Inner Exception 1: 
WebException: The operation has timed out. 

的DelegateHandler用於認證是的this代碼粗略適配（參見源部分）。

爲什麼客戶端超時，我該如何防止這種情況發生？

我的最終目標是撥打電話並無限期地等待迴應。當答案確實出現時，我不希望關聯，因爲未來可能會有更多答覆。不幸的是，我不能在服務器端改變任何東西。

Answer 1

雖然Stream.CanTimeoutis false，返回通過response.Content.ReadAsStreamAsync()流的默認值給出其中CanTimeout屬性返回true流。

此流的默認讀取和寫入超時is 5 minutes。這是5分鐘不活動後，該流將拋出異常。與問題中顯示的異常非常相似。

要更改此行爲，可以調整流的ReadTimeout和/或WriteTimeout屬性。

下面是將ReadTimeout更改爲無限的ListenForSearchQueries方法的修改版本。

public static async void ListenForSearchQueries(int resourceId) 
{ 
    var url = $"xxx/yyy/{resourceId}/waitForSearchRequest?token=abc"; 

    var httpHandler = new HttpClientHandler { PreAuthenticate = true }; 

    using (var digestAuthMessageHandler = new DigestAuthMessageHandler(httpHandler, "user", "password")) 
    using (var client = new HttpClient(digestAuthMessageHandler)) 
    { 
     client.Timeout = TimeSpan.FromMilliseconds(Timeout.Infinite); 

     var request = new HttpRequestMessage(HttpMethod.Get, url); 

     var tokenSource = new CancellationTokenSource(); 
      tokenSource.CancelAfter(TimeSpan.FromMilliseconds(Timeout.Infinite)); 

     using (var response = await client.SendAsync(request, HttpCompletionOption.ResponseHeadersRead, tokenSource.Token)) 
     { 
      Console.WriteLine("\nResponse code: " + response.StatusCode); 

      using (var body = await response.Content.ReadAsStreamAsync()) 
      { 
       body.ReadTimeout = Timeout.Infinite; 

       using (var reader = new StreamReader(body)) 
        while (!reader.EndOfStream) 
         Console.WriteLine(reader.ReadLine()); 
      } 
     } 
    } 
} 

這修正了實際上由流拋出的異常，但似乎是被HttpClient拋出的異常。

Answer 2

使該方法返回一個Task

public static async Task ListenForSearchQueries(int resourceId) { 
    //...code removed for brevity 
} 

更新控制檯的主要方法Wait在Task來完成。

public static void Main(string[] args) { 
    const int serviceId = 128; 
    . 
    . 
    . 
    ListenForSearchQueries(resourceId).Wait(); 
    Console.ReadKey(); 
}