Redirecting System.Diagnostics.Process.StandardInput

  • Thread starter Thread starter Guest
  • Start date Start date
G

Guest

The code below uses System.Diagnostics.Process to call Net.exe to delete a
mapped network drive. It works well except when the mapped drive is in use in
which case Net.exe prompts the "user" to confirm the drive should be deleted.
I'm sure I should be able to reply to this question by redirected the
Process's StandardInput but despite hours of trying I can't see how. Is it
possible?

Private Sub UnMapNetworkDrive(ByVal DriveLetter As String)
Dim _Process As New System.Diagnostics.Process()
With _Process
Try
With .StartInfo
.FileName = String.Format("{0}\Net.exe",
System.Environment.GetFolderPath(Environment.SpecialFolder.System))
.Arguments = String.Format("use {0}: /delete",
DriveLetter)
.CreateNoWindow = True
.UseShellExecute = False
.RedirectStandardError = True
.RedirectStandardOutput = True
End With
.Start()
.WaitForExit()
Dim _StandardError As String = .StandardError.ReadToEnd
If Not _StandardError = String.Empty Then Throw New
ApplicationException(_StandardError)
Dim _StandardOutput As String = .StandardOutput.ReadToEnd
If Not _StandardOutput.StartsWith(String.Format("{0}: was
deleted successfully.", DriveLetter)) Then Throw New
ApplicationException("The network drive was not unmapped.")
Finally
.Close()
End Try
End With
End Sub
 
....and perhaps you might also say whether this is the best way to add a
mapped network drive using .net. Or should I call wsh. Or is there a better
way?
 
Hi Dick,

Yes, my thought is the same as you to leverage net.exe. However, further
research shows that there is some strange behavior in net.exe which makes
this solution nonapplicable.

To force close the connection, we should input "y" to the net.exe standard
input. So I set RedirectStandardInput proeprty to true and try to send "y"
to the standard input. See the code snippet below:

Private Sub UnMapNetworkDrive(ByVal DriveLetter As String)
Dim _Process As New System.Diagnostics.Process()
Dim path As String =
System.Environment.GetFolderPath(Environment.SpecialFolder.System)
With _Process
With .StartInfo
.FileName = String.Format("{0}\Net.exe", path)
.Arguments = String.Format("use {0} /delete", DriveLetter)
.CreateNoWindow = True
.UseShellExecute = False
.RedirectStandardOutput = True
.RedirectStandardInput = True
End With
.Start()
.WaitForExit()

Dim _StandardOutput As String = .StandardOutput.ReadToEnd
If _StandardOutput.Contains("There are open files and/or
incomplete directory searches pending on the connection") Then
.StandardInput.WriteLine("y")
.StandardInput.Flush()
Else
If Not _StandardOutput.StartsWith(String.Format("{0}: was
deleted successfully.", DriveLetter)) Then Throw New Exception("The network
drive was not unmapped.")
End If
End With
End Sub

However, I find this does not work. Further research reveals that if
net.exe shows "There are open files and/or incomplete directory searches
pending on the connection" for user to input "y", the net.exe process will
not terminate at all, it will wait for the user input through standard
input. However, I find that if we set RedirectStandardOutput or
RedirectStandardInput to true and start the net.exe process, the net.exe
will generate the output and terminate itself immediately without waiting
for the standard input. So net.exe does not give us the chance to input
"y".

I suspect net.exe behaves this way for security reason, because it does not
allow some hacker process to lauch it in background with
RedirectStandardOutput/RedirectStandardInput for driver mapping. Anyway,
this approach can not be done because of this limitation.

So I recommand you go with "Ben Voigt"'s suggestion of p/invoking win32 API
to close the connection. More specificly, you may use WNetCancelConnection2
to close the connection and the second parameter tells the system to close
the connection even there are open files or jobs on the connection. The
sample code snippet below works well on my side, for your information:

Dim CONNECT_UPDATE_PROFILE As Integer = 1
Dim NO_ERROR As Integer = 0
<DllImport("mpr.dll", CharSet:=CharSet.Auto)> _
Public Shared Function WNetCancelConnection2(ByVal name As String,
ByVal flags As Integer, ByVal force As Boolean) As Integer
End Function

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles Button2.Click
Dim ret As Integer = WNetCancelConnection2("z:",
CONNECT_UPDATE_PROFILE, True)
If Not ret = NO_ERROR Then
MessageBox.Show(Marshal.GetLastWin32Error())
End If
End Sub

Hope this helps.

Best regards,
Jeffrey Tan
Microsoft Online Community Support
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