I have a FTP class that is being used widely and it has a weird issue when I download a big file. Basically, this has been running for weeks. But, this big backup file I want to automate and have on my PC is not fitting very well within the actual code. Here is the FTP.Download() method I am using. I know it could be a little bit difficult to someone to try to see what could be enhanced to support that but here is is:

        ' Download a file
        Public Function Download() As Boolean
            Dim lcMinute As String = ""
            Dim lcURI As String = ""
            Dim llSuccess As Boolean = False
            Dim lnActual As Long = 0
            Dim lnActualABS As Long = 0
            Dim lnBytesRead As Integer = 0
            Dim lnContentLength As Long = 0
            Dim lnElapse As Integer = 0
            Dim lnEnd As Double = 0
            Dim lnLast As Integer = 0
            Dim lnPercentage As Integer = 0
            Dim lnDownloaded As Long = 0
            Dim lnRemaining As Long = 0
            Dim lnStart As Double = Date.Now.Ticks
            Dim loBuffer(nBuffer) As Byte
            Dim loDownloadedData(0) As Byte
            Dim loFileStream As FileStream = Nothing
            Dim loFtpWebRequest As System.Net.FtpWebRequest = Nothing
            Dim loFtpWebResponse As System.Net.FtpWebResponse = Nothing
            Dim loProgressBar As Framework.ProgressBar = New Framework.ProgressBar(oApp)
            Dim loMemoryStream As MemoryStream = New MemoryStream()
            Dim loStream As Stream = Nothing
            Dim loStreamReader As StreamReader = Nothing

            ' Reset the values
            cError = ""
            lError = False

            Try

                ' If we have an originator
                If Not oOriginator Is Nothing Then
                    loProgressBar.oOriginator = oOriginator
                End If

                ' Initialize the progress bar
                loProgressBar.ShowProgress(0, cDownloading + " " + cLocalFile + "...")

                ' URI
                lcURI = "ftp://" + cHost + "/" + cRemoteDirectory + "/" + cRemoteFile

                ' Because there is a bug in the .NET Framework with the use of
                ' System.Net.WebRequestMethods.Ftp.DownloadFile which will always return -1,
                ' we have to use a two step process to achieve this method

                ' FTP setup
                loFtpWebRequest = System.Net.FtpWebRequest.Create(New Uri(lcURI))
                loFtpWebRequest.Credentials = New System.Net.NetworkCredential(cUsername, cPassword)
                loFtpWebRequest.Method = System.Net.WebRequestMethods.Ftp.GetFileSize
                loFtpWebRequest.UseBinary = True

                loFtpWebResponse = loFtpWebRequest.GetResponse()

                ' Get the length
                lnContentLength = loFtpWebResponse.ContentLength

                loFtpWebResponse.Close()

                ' FTP setup
                loFtpWebRequest = System.Net.FtpWebRequest.Create(New Uri(lcURI))
                loFtpWebRequest.Credentials = New System.Net.NetworkCredential(cUsername, cPassword)
                loFtpWebRequest.Method = System.Net.WebRequestMethods.Ftp.DownloadFile
                loFtpWebRequest.UseBinary = True

                loFtpWebResponse = loFtpWebRequest.GetResponse()

                loStream = loFtpWebResponse.GetResponseStream()

                ' While there is something to download
                While True

                    ' Prevent application from crashing
                    System.Windows.Forms.Application.DoEvents()

                    ' Try to read the data
                    lnBytesRead = loStream.Read(loBuffer, 0, loBuffer.Length)

                    If lnBytesRead = 0 Then

                        ' Nothing was read, finished downloading
                        System.Windows.Forms.Application.DoEvents()

                        Exit While
                    Else

                        ' Write the downloaded data
                        loMemoryStream.Write(loBuffer, 0, lnBytesRead)

                        ' Increment the number of uploaded bytes
                        lnDownloaded = lnDownloaded + lnBytesRead

                        lnActual = lnDownloaded / lnContentLength * 100

                        lnActualABS = Math.Abs(lnActual)

                        ' If the last is not the same as the actual
                        If lnLast <> lnActual Then

                            lnElapse = ((Date.Now.Ticks - lnStart) / 10000000)

                            lcMinute = oApp.SecondToFormat(lnElapse)

                            lnRemaining = lnContentLength - lnDownloaded

                            ' Update the progress bar
                            loProgressBar.ShowProgress(lnActual, _
                             cDownloading + " " + cLocalFile + "..." + oApp.cCR + _
                             oApp.GetFormatValue(lnDownloaded, ",") + " bytes " + cOf + " " + _
                             oApp.GetFormatValue(lnContentLength, ",").ToString + " - " + cRemaining + " " + _
                             oApp.GetFormatValue(lnRemaining, ",").ToString + " bytes - " + lcMinute)

                        Else

                            ' Update the progress bar
                            loProgressBar.ShowProgress(lnActual)

                        End If

                        lnLast = lnActualABS

                    End If

                End While

                ' Elapse time it took for the download
                nSecond = lnElapse

                ' Convert the downloaded stream to a byte array
                loDownloadedData = loMemoryStream.ToArray()

                loMemoryStream.Close()
                loStream.Close()
                loFtpWebResponse.Close()

                ' Create the file
                Try
                    loFileStream = New FileStream(cLocalFile, FileMode.Create)
                    loFileStream.Write(loDownloadedData, 0, loDownloadedData.Length)
                    loFileStream.Close()
                Catch loError As Exception
                    lError = True
                    cError = cUnableToCreateLocalFile
                    Exit Try
                End Try

                llSuccess = True
            Catch loError As Exception
                lError = True
                cError = loError.Message
            End Try

            ' Make sure to remove it
            loProgressBar.Dispose()

            ' Force a refresh
            Windows.Forms.Application.DoEvents()

            Return llSuccess
        End Function

Basically, the file I am downloading is 2.2 GB. That usually takes 2.5 hours with WSFTP. Now, I want to handle that from an application. So, I am using my FTP class for that. After about 20 minutes, I have this memory exception thrown error that stops the process.

I think the loMemoryStream, declared with the MemoryStream(), cannot handle too much in memory. Basically, after about 20 minutes, I would say the download is about between 200 MB to 400 MB transferred. So, I am assuming that I would have to change my approach to negotiate with such a big files. Any idea?