httpWebRequest超時/筆記本休眠和交換網絡後連接失敗

Question

我有一個奇怪的問題，我的應用程序嘗試執行HTTPWebRequest POST來調用API。通常情況下，這並沒有問題，但是如果用戶將筆記本電腦帶回家並通過家庭網絡連接，然後休眠機器並在第二天返回工作，則HTTPWebRequest將失敗，並出現超時錯誤或者僅僅是URL無法被達到。只要他們重新啓動筆記本電腦，連接通常會再次正常。

我花了很多天試圖找出可能導致此問題的原因，例如筆記本電腦中的代理連接問題或網卡問題，但尚未成功進行診斷或修復。

任何人有什麼問題可能會有什麼建議，或者我怎麼能更好地診斷這個？

代碼：

Private Function WRequestMainDynamic(URL As String, method As String, POSTdata As String, timeout As Integer, Optional ByRef proxyType As Integer = 0) 
    Dim responseData As String = "" 
    Dim hwrequest As Net.HttpWebRequest = Nothing 
    Dim postByteArray() As Byte = Nothing 
    Dim connectionSuccess As Boolean = False 
    Dim count As Integer = 0 

    While connectionSuccess = False And count < 6 
     Try 
      hwrequest = Net.WebRequest.Create(URL) 
      hwrequest.Accept = "*/*" 
      hwrequest.AllowAutoRedirect = True 
      hwrequest.UserAgent = "http_requester/0.1" 
      hwrequest.Timeout = timeout 
      hwrequest.Method = method 
      hwrequest.KeepAlive = True 

      Select Case proxyType 
       Case 0 
        hwrequest.Proxy = Nothing 
       Case 1 
       'don't set anything 
       Case 2 
        hwrequest.Proxy.Credentials = System.Net.CredentialCache.DefaultCredentials 
       Case Else 
        hwrequest.Proxy = Nothing 
      End Select 

      ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls Or SecurityProtocolType.Ssl3 
      ServicePointManager.Expect100Continue = False 

      If hwrequest.Method = "POST" Then 
       hwrequest.ContentType = "application/json" 
       Dim encoding As New Text.UTF8Encoding() 'Use UTF8Encoding for XML requests 
       postByteArray = encoding.GetBytes(POSTdata) 
       hwrequest.ContentLength = postByteArray.Length 
       Using postStream As IO.Stream = hwrequest.GetRequestStream() 
        postStream.Write(postByteArray, 0, postByteArray.Length) 
       End Using 
      End If 

      Using hwresponse As Net.HttpWebResponse = hwrequest.GetResponse() 
       If hwresponse.StatusCode = Net.HttpStatusCode.OK Then 
        Using responseStream As IO.StreamReader = New IO.StreamReader(hwresponse.GetResponseStream()) 
         responseData = responseStream.ReadToEnd() 
        End Using 
       End If 
      End Using 

      connectionSuccess = True 

     Catch webex As WebException 
      If webex.Status = WebExceptionStatus.Timeout Then 
       Throw 
      Else 
       proxyType += 1 
       If proxyType = 3 Then proxyType = 0 
       count += 1 
       If count = 6 Then Throw 
      End If 
     Catch e As Exception 
      Throw 
      responseData = "" 
     Finally 
      postByteArray = Nothing 
      hwrequest = Nothing 
      GC.Collect() 
     End Try 
    End While 

Answer 1

好像不同的代理需要與Net.HttpWebRequest對象的代理性質不同的配置，甚至不同的連接類型的WiFi/LAN行爲方式了。

在大多數情況下，沒有做任何事情可以正常工作，但是我們發現有時您需要將Proxy.Credentials專門設置爲默認值，因爲它無法自動獲取它們，而在其他情況下更容易設置代理=完全繞過它。

爲了說明所有情況，我們將所有三個代碼嵌入到上面的代碼中，並傳入一個ByRef proxyType變量，該變量存儲連接正常的最新一個（整數）。在每個HttpRequest上，如果它失敗了，那麼在其他方法中循環其他方法，如果是這樣的話，那麼將它傳遞迴變量以用於下一次調用。如果在X次嘗試之後全部失敗，則引發異常。

我原來的問題中的代碼是這樣做的，只要確保每次都正確地返回proxyType變量！