Question

我有一个奇怪的问题，我的应用程序正在尝试执行HTTPWebRequest POST来调用API。通常这没有问题，但是如果用户将他们的笔记本电脑带回家并通过他们的家庭网络连接，然后休眠机器并在第二天返回工作，HTTPWebRequest失败并出现超时错误或仅仅是URL无法到达。一旦他们重新启动笔记本电脑，连接通常会再次正常。

我花了很多天试图弄清楚可能导致这种情况的原因，例如笔记本电脑中的代理连接问题或网卡问题，但尚未成功诊断或修复。

任何人都对问题可能是什么或如何更好地诊断这个问题有任何建议？

代码：

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

似乎不同的代理需要使用Net.HttpWebRequest对象的Proxy属性进行不同的配置，甚至不同的连接类型WiFi / LAN的行为也不同。

在大多数情况下，不使用它可以正常工作，但是我们发现有时你需要专门将Proxy.Credentials设置为默认值，因为它无法自动获取它们，而在其他情况下，它更容易设置代理=没有什么可以完全绕过它。

为了考虑所有场景，我们将所有三个嵌入到代码中，并传入一个ByRef proxyType变量，该变量存储连接正常的最新一个（作为整数）。在每个HttpRequest上，如果它失败，那么在其中一个工作的情况下循环其他方法，如果是，则将其传递回变量以在下一个调用中使用。如果在X次尝试后都失败，则引发异常。

我原始问题中的代码执行此操作，只需确保每次都正确传回proxyType变量！

笔记本电脑休眠和交换网络后httpWebRequest超时/连接失败

1 个答案: