Question

Using C# to copy files using credentials or impersonation

Asked by: brhunt

I am trying to find an easy way to copy files in C# across servers/domains/account.  I assumed that this would be an easy task until I started researching it about 4 hours ago....

The basic scenario is this:
From my workstationA in workgroupA logged in as userA, I would like to copy a directory of files from serverB in domainB to serverC in domainC.  Since userA has no rights in domainA or domainB, credentials need to be used to access both servers (no trust between domains, nor any common user accounts).

I had hoped to use something like File.Copy, but I do not see a way to pass credentials.

Impersonation would seem to be the next choice, but how do I impersonate a user in domainA at the same time that I impersonate a user in domainB so that I can do the copy?

Is it possible to do an impersonation into domainA, map a drive, drop the impersonation (while still keeping drive mapping), impersonate into domainB, map another drive, drop the impersonation, then do the file copy?

How best to accomplish this?

Thanks for all assistance.

Bryan Hunt

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Asked On
2008-09-08 at 19:55:50ID23714219
Topics

Microsoft Visual C#.Net

,

C# Programming Language

,

Windows Network Security

Participating Experts
2
Points
250
Comments
6

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Answers

 

by: svdlPosted on 2008-09-08 at 21:32:20ID: 22424300

If you don't mind staging the files to be copied on your workstation, here's how you can do it:
- set the PrincipalPolicy of the AppDomain to WindowsPrincipal:

AppDomain.CurrentDomain.SetPrincipalPolicy(PrincipalPolicy.WindowsPrincipal);

Then create two WindowsIdentity objects, one with a username/password that's valid in the domain you want to copy the files FROM and one with a username/password that's valid in the domain you want to copy TO:

WindowsIdentity fromIdentity=new WindowsIdentity(usernameB,passwordB);
WindowsIdentity toIdentity=new WindowsIdentity(usernameC,passwordC);

Impersonate the fromIdentity and copy the files:

WindowsImpersonationContext context = fromIdentity.Impersonate();
DoCopyFiles(serverB, localmachine); // method to copy the files to your workstation, not shown here

Stop impersonating, then impersonate the toIdentity and copy the files out to domain C:

context.Undo();
context=toIdentity.Impersonate();
DoCopyFiles(localmachine, serverC);
context.Undo() //resume your original identity


Another, far simpler way would be generating a simple batch file that maps  drives using username/password combinations that are valid for domain B resp domain C:

net use y: \\serverB\shareB passwordB /USER:domainB\userB
net use z: \\serverC\shareC passwordC /USER:domainC\userC

run the batch file from C#, and then copy the files from y:\ to z:\
Don't forget to clean up the shares after use!

 

by: brhuntPosted on 2008-09-09 at 04:56:51ID: 22426398

svdl,

Thanks for the quick reply.  

I had considered both of these options.  

I would rather not use the 'net use' option because I may want to allow people to locate the shares via a GUI interface.  

I had really hoped to find a way to copy the files "point to point" rather that source-to-me, me-to-target.  It seems odd to be able to do something in DOS/CMD that I am unable to do in C#.Net.

If no one can suggest a better way, I will use the first method and award points to you.

Thanks.

Bryan Hunt

 

by: svdlPosted on 2008-09-09 at 11:12:44ID: 22430433

Another option, without intermediate storage on the local workstation: use two threads. One reader thread, impersonationg a user in the source domain, and one writer thread, created in another AppDomain (use CreateDomain to create that second domain) impersonating a user in the target domain.
The source thread would read a file (in chunks) into a queue of chunk objects that can be read (and written out (by the other thread.
I'd recommend 4096 bytes as the chunk size - not too much memory overhead, and it's also the most widely used cluster size on NTFS and FAT32 disks, making for efficient reads and writes.

 

by: brhuntPosted on 2008-09-16 at 09:31:26ID: 22490313

svdl,

Thanks for the information here.  I ended up using a different method of accomplishing my goal.  I borrowed some code from this posting

http://www.codeproject.com/KB/system/mapnetdrive.aspx?fid=39622&df=90&mpp=25&noise=3&sort=Position&view=Quick&select=2645114&fr=51

that uses the WNetAddConnection function to map network drives with credentials.  I mapped source and target drives, then copied in one pass.

Thanks.

Bryan Hunt

 

by: pg_indiaPosted on 2009-05-18 at 11:35:08ID: 24415100

Can you please post your complete solution. I am also working on similar issue and need to look into the code.

 

by: brhuntPosted on 2009-06-02 at 05:38:38ID: 24526017

Sorry for the delay in responding.

Here are some code snippets that might help:

First, map a couple of drives:
=======================
            string baseDriveLetter;

            // Map Source IIS drive
            siNetDrive = new aejw.Network.NetworkDrive();
            baseDriveLetter = "z";
            siNetDrive.GetNextOpenDriveLetter(ref baseDriveLetter);
            siNetDrive.LocalDrive = baseDriveLetter;
            siNetDrive.ShareName = @"\\" + srcIISServer.Text + @"\c$";
            try
            {
                siNetDrive.MapDrive(srcIISUser.Text, srcIISPassword.Text);
            }
            catch (System.Exception e)
            {
                MessageBox.Show("Unable to map source IIS network drive: " + e.Message, "Alert", MessageBoxButtons.OK, MessageBoxIcon.Information);
                return true;
            }

            // Map Target IIS drive
            tiNetDrive = new aejw.Network.NetworkDrive();
            baseDriveLetter = "z";
            tiNetDrive.GetNextOpenDriveLetter(ref baseDriveLetter);
            tiNetDrive.LocalDrive = baseDriveLetter;
            tiNetDrive.ShareName = @"\\" + tarIISServer.Text + @"\c$";
            try
            {
                tiNetDrive.MapDrive(tarIISUser.Text, tarIISPassword.Text);
            }
            catch (System.Exception e)
            {
                MessageBox.Show("Unable to map target IIS network drive: " + e.Message, "Alert", MessageBoxButtons.OK, MessageBoxIcon.Information);
                siNetDrive.UnMapDrive();
                return true;
            }
=========
That maps two drives getting the next available drive letter (starting at Z and moving backwards) using a userind and password.

Next, copy a directory of files using a VB method and the two mapped drives:
======================
            try
            {
                Microsoft.VisualBasic.FileIO.FileSystem.CopyDirectory(siNetDrive.LocalDrive + @"\sdbs\" + instanceName.Text, tiNetDrive.LocalDrive + @"\sdbs\" + instanceName.Text, UIOption.AllDialogs);
            }
            catch (System.Exception e)
            {
                MessageBox.Show("Unable copy SDS Instance Program files: " + e.Message, "Alert", MessageBoxButtons.OK, MessageBoxIcon.Information);
                return true;
            }

=============

Hope that helps!

Bryan Hunt

20120131-EE-VQP-002

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