Download File With Start / Pause / Stop - vb.net

Question

Is there any way i can pause a file download in my vb program?? I have tried both the http method and the my.computer.net method with no luck. I have also tried pausing the background worker by this method: [URL] But even if the bgworker is paused the download goes on.....
Dim locationfiledownload As String
Dim whereToSave As String 'Where the program save the file
Delegate Sub ChangeTextsSafe(ByVal length As Long, ByVal position As Integer, ByVal percent As Integer, ByVal speed As Double)
Delegate Sub DownloadCompleteSafe(ByVal cancelled As Boolean)
Public Sub DownloadComplete(ByVal cancelled As Boolean)
ToolStripButton2.Enabled = True
ToolStripButton3.Enabled = False
If cancelled Then
Me.Label4.Text = "Cancelled"
MessageBox.Show("Download aborted", "Aborted", MessageBoxButtons.OK, MessageBoxIcon.Information)
Else
Me.Label4.Text = "Successfully downloaded"
MessageBox.Show("Successfully downloaded!", "All OK", MessageBoxButtons.OK, MessageBoxIcon.Information)
End If
Me.RadProgressBar1.Value1 = 0
Me.Label4.Text = ""
End Sub
Public Sub ChangeTexts(ByVal length As Long, ByVal position As Integer, ByVal percent As Integer, ByVal speed As Double)
Me.Label4.Text = "Downloaded " & Math.Round((position / 1024), 2) & " KB of " & Math.Round((length / 1024), 2) & "KB"
Me.RadProgressBar1.Value1 = percent
End Sub
Public Sub btnDownload_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ToolStripButton2.Click
locationfiledownload = GetPage("http://asankonkur.ir/update/locationfiledownload.txt")
If locationfiledownload <> "" AndAlso locationfiledownload.StartsWith("http://") Then
Me.SaveFileDialog1.FileName = locationfiledownload.Split("/"c)(locationfiledownload.Split("/"c).Length - 1)
If Me.SaveFileDialog1.ShowDialog = Windows.Forms.DialogResult.OK Then
Me.whereToSave = Me.SaveFileDialog1.FileName
Me.SaveFileDialog1.FileName = ""
ToolStripButton2.Enabled = False
ToolStripButton3.Enabled = True
Me.BackgroundWorker2.RunWorkerAsync() 'Start download
End If
Else
MessageBox.Show("Please insert valid URL for download", "Warning", MessageBoxButtons.OK, MessageBoxIcon.Warning)
End If
End Sub
Private Sub BackgroundWorker2_DoWork(ByVal sender As System.Object, ByVal e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker2.DoWork
'Creating the request and getting the response
Dim theResponse As HttpWebResponse
Dim theRequest As HttpWebRequest
Try 'Checks if the file exist
theRequest = WebRequest.Create(locationfiledownload)
theResponse = theRequest.GetResponse
Catch ex As Exception
MessageBox.Show("An error occurred while downloading file. Possibe causes:" & ControlChars.CrLf & _
"1) File doesn't exist" & ControlChars.CrLf & _
"2) Remote server error", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
Dim cancelDelegate As New DownloadCompleteSafe(AddressOf DownloadComplete)
Me.Invoke(cancelDelegate, True)
Exit Sub
End Try
Dim length As Long = theResponse.ContentLength 'Size of the response (in bytes)
Dim safedelegate As New ChangeTextsSafe(AddressOf ChangeTexts)
Me.Invoke(safedelegate, length, 0, 0, 0) 'Invoke the TreadsafeDelegate
Dim writeStream As New IO.FileStream(Me.whereToSave, IO.FileMode.Create)
'Replacement for Stream.Position (webResponse stream doesn't support seek)
Dim nRead As Integer
'To calculate the download speed
Dim speedtimer As New Stopwatch
Dim currentspeed As Double = -1
Dim readings As Integer = 0
Do
If BackgroundWorker2.CancellationPending Then 'If user abort download
Exit Do
End If
speedtimer.Start()
Dim readBytes(4095) As Byte
Dim bytesread As Integer = theResponse.GetResponseStream.Read(readBytes, 0, 4096)
nRead += bytesread
Dim percent As Short = (nRead * 100) / length
Me.Invoke(safedelegate, length, nRead, percent, currentspeed)
If bytesread = 0 Then Exit Do
writeStream.Write(readBytes, 0, bytesread)
speedtimer.Stop()
readings += 1
If readings >= 5 Then 'For increase precision, the speed it's calculated only every five cicles
currentspeed = 20480 / (speedtimer.ElapsedMilliseconds / 1000)
speedtimer.Reset()
readings = 0
End If
Loop
'Close the streams
theResponse.GetResponseStream.Close()
writeStream.Close()
If Me.BackgroundWorker2.CancellationPending Then
IO.File.Delete(Me.whereToSave)
Dim cancelDelegate As New DownloadCompleteSafe(AddressOf DownloadComplete)
Me.Invoke(cancelDelegate, True)
Exit Sub
End If
Dim completeDelegate As New DownloadCompleteSafe(AddressOf DownloadComplete)
Me.Invoke(completeDelegate, False)
End Sub
Private Sub mainForm_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Me.Label4.Text = ""
End Sub
Private Sub btnCancel_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ToolStripButton3.Click
Me.BackgroundWorker2.CancelAsync() 'Send cancel request
End Sub

Answer 1

In your code, you are using WebRequest.Create(locationfiledownload). By default, this creates a request header that asks for the entire file. You need to edit the request and add a Range header that asks for the specific byte range of the file you're looking for. E.g., adding to the WebRequest.Headers.Range.Ranges collection. Unfortunately, this is going to make your code quite a bit more complex as you will need to store details of what's already been download somewhere (assuming you want to resume after application close/restart). You'll need to know;
How much of the file (if any) is already downloaded
How much you intend downloading at any one time
Once you know this, you will have to form a request with a Range header for X bytes of the file. Once you receive it, you'll need to save it and ask for the next section. An example written in C# is available on The Code Project here: http://www.codeproject.com/Tips/307548/Resume-Suppoert-Downloading