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我正在尝试每周自动下载一次大型 zip 文件。到目前为止，我已经设法检查是否上传了新文件并且我已准备好开始下载，但我遇到了一些问题。我正在下载的文件超过 2.2 GB (Zip)，所以这是一个相当大的文件，每次我测试新的代码时，我都需要等待 5-10 分钟才能再次下载文件。我在底部有一个更复杂的代码，这里先有一个简单的代码。一旦传输最后几个字节，两者都会导致相同的错误。

Try
    My.Computer.Network.DownloadFile(
"ftp://dmr-ftp-user:dmrpassword@5.44.137.84/ESStatistikListeModtag/ESStatistikListeModtag-20160110-093818.zip",
"C:\ZipDownload\Test.zip")
Catch ex As Exception
   MsgBox(ex.Message)
End Try

是的，这是 ftp 主机的实际登录信息，所以如果您想在发布可能的解决方案之前测试您的代码 - 请随意。一旦文件即将完成下载，我就会收到此异常：

Exception: The underlying connection was closed: An unexpected error occurred on a receive.

我也试过这个我在网上找到的稍微复杂的版本：

Private Sub Download(ByVal filePath As String, ByVal fileName As String)
        FTPSettings.IP = "5.44.137.84"
        FTPSettings.UserID = "dmr-ftp-user"
        FTPSettings.Password = "dmrpassword"
        Dim reqFTP As FtpWebRequest = Nothing
        Dim ftpStream As Stream = Nothing
        Try
            Dim outputStream As New FileStream(filePath + "\" + fileName, FileMode.Create)
            reqFTP = DirectCast(FtpWebRequest.Create(New Uri("ftp://" + FTPSettings.IP + "/" + fileName)), FtpWebRequest)
            reqFTP.Method = WebRequestMethods.Ftp.DownloadFile
            reqFTP.UseBinary = True
            reqFTP.Credentials = New NetworkCredential(FTPSettings.UserID, FTPSettings.Password)
            Dim response As FtpWebResponse = DirectCast(reqFTP.GetResponse(), FtpWebResponse)
            ftpStream = response.GetResponseStream()
            Dim cl As Long = response.ContentLength
            Dim bufferSize As Integer = 2048
            Dim readCount As Integer
            Dim buffer As Byte() = New Byte(bufferSize - 1) {}
            Dim size As Int64

            readCount = ftpStream.Read(buffer, 0, bufferSize)
            While readCount > 0
                outputStream.Write(buffer, 0, readCount)
                readCount = ftpStream.Read(buffer, 0, bufferSize)

                If readCount = bufferSize Then
                    size += readCount
                    Label1.Text = size
                    Label1.Refresh()
                End If

              End While

            ftpStream.Close()
            outputStream.Close()
            response.Close()
        Catch ex As Exception
            MsgBox(ex.Message)
            If ftpStream IsNot Nothing Then
                ftpStream.Close()
                ftpStream.Dispose()
            End If
            Throw New Exception(ex.Message.ToString())
        End Try
    End Sub
    Public NotInheritable Class FTPSettings
        Private Sub New()
        End Sub
        Public Shared Property IP() As String
            Get
                Return m_IP
            End Get
            Set(ByVal value As String)
                m_IP = value
            End Set
        End Property
        Private Shared m_IP As String
        Public Shared Property UserID() As String
            Get
                Return m_UserID
            End Get
            Set(ByVal value As String)
                m_UserID = value
            End Set
        End Property
        Private Shared m_UserID As String
        Public Shared Property Password() As String
            Get
                Return m_Password
            End Get
            Set(ByVal value As String)
                m_Password = value
            End Set
        End Property
        Private Shared m_Password As String
    End Class
End Class

这两种解决方案似乎都工作得很好，我可以在我的测试文件夹上跟踪文件大小的增加，直到它冻结几秒钟然后返回相同的异常：

Exception: The underlying connection was closed: An unexpected error occurred on a receive.

希望你对这个问题有一个解释！

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