FTP download files larger than 2GB (VB.net) - vb.net

Question

Missing last few bytes and file gets corrupted - bounty
I now added a bounty to solve this problem. I changed the integer types to int64 which seem to have solved part of the problem, but now when ever it finishes the download it sometimes misses the last 1-5 bytes, which in return corrupts the file, so it can't be unzipped. Is there another way of closing the stream so it ensures the files are fully downloaded, and avoid getting corrupted? I've since tried this simple code, but same problem happens.
Imports System.ComponentModel
Imports System.Net
Public Class Form1
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
Control.CheckForIllegalCrossThreadCalls = False
End Sub
Dim WithEvents WC As New WebClient
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
WC.DownloadFileAsync(New Uri("ftp://dmr-ftp-user:dmrpassword#5.44.137.84/ESStatistikListeModtag/ESStatistikListeModtag-20160327-094743.zip"), "C:\XML\ESStatistikListeModtag-20160327-094743.zip.zip")
End Sub
Private Sub WC_DownloadProgressChanged(ByVal sender As Object, ByVal e As DownloadProgressChangedEventArgs) Handles WC.DownloadProgressChanged
ProgressBar1.Value = e.ProgressPercentage
If e.ProgressPercentage = 100 Then
MsgBox("File download - 100%") 'This message box does trigger once the download is complete, but file is still corrupted.
End If
End Sub
Private Sub WC_DownloadFileCompleted(sender As Object, e As AsyncCompletedEventArgs) Handles WC.DownloadFileCompleted
MsgBox("Complete") ' This message box doesn't trigger!
End Sub
End Class
OLD QUESTION:
I'm trying to download a zip file from an FTP server with my vb.net application. My current source code is posted below. This works fine for smaller files, but when I exceed a limit of 2GB I get the following exception:
"Arithmetic operation resulted in an overflow"
It's a file with the size of about 2.5 GB and increasing slightly each weak (about 20 MB), so I need a solution which can handle large files, hopefully with no limit. Eventually I would like to unzip the file with the program too, so if you have any ideas for doing this, you can post this as well. Thanks!
Private Sub Download(ByVal filePath As String, ByVal fileName As String)
FTPSettings.IP = "0.0.0.0"
FTPSettings.UserID = "ftp-user"
FTPSettings.Password = "ftp-pass"
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 Int64
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

Answer 1

I've had similar problems with WebClient before, specially if using it with the WithEvents statement.
See if re-writing your code like this solves the problem:
Imports System.ComponentModel
Imports System.Net
Public Class Form1
Private wc As New WebClient()
Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
wc = New WebClient()
AddHandler wc.DownloadProgressChanged, Sub(s As Object, ByVal e As DownloadProgressChangedEventArgs)
Me.Invoke(New MethodInvoker(Sub() ProgressBar1.Value = e.ProgressPercentage))
End Sub
AddHandler wc.DownloadFileCompleted, Sub(s As Object, e As ComponentModel.AsyncCompletedEventArgs)
MsgBox("Complete")
End Sub
End Sub
Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
wc.DownloadFileAsync(New Uri("ftp://dmr-ftp-user:dmrpassword#5.44.137.84/ESStatistikListeModtag/ESStatistikListeModtag-20160327-094743.zip"), "C:\XML\ESStatistikListeModtag-20160327-094743.zip.zip")
End Sub
End Class