Re: System.IO.File.Copy + NTFS Streams + special ACLs

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Hello Mike,

the applikation runs as a service under a least privilege account that only has the "create file" permission in the archive directory, not more, not less. Elevation isn't possible and shouldn't be neccessary. Files that don't have NTFS alternate data streams can be copied without problems. The LastWriteTime is also kept.

Regards,

Peter

Mike wrote:
Ok, the user doesn't have "Modify" access? or Write Attributes?

So how are you going to handle that? Impersonate a higher level account?

If this is a system application, not just a end-user application, it can make sense to raise the process credentials so you can do your system work.

Troubleshooting Exceptions: System.UnauthorizedAccessException
http://msdn.microsoft.com/en-us/library/18b8kx07.aspx

Code Access Security Basics
http://msdn.microsoft.com/en-us/library/33tceax8.aspx

See the Secure Class Libraries and Requesting permission links. > --



Peter Gibbons wrote:
Hello Mike,

thanks for the example code. I changed it a little to my needs.
I'd like to preserve the LastWriteTime like the normal copy functions but I get a "System.UnauthorizedAccessException" due to the NTFS Permissions because the user only has "Create file" permission in the destination directory.


Sub CopyFileWithoutStreams(ByVal sourceFileName As String, ByVal destFileName As String, Optional ByVal buffersize As Integer = &HFFFFUI)
Dim sr As New System.IO.FileStream(sourceFileName, IO.FileMode.Open, IO.FileAccess.Read, IO.FileShare.Read, buffersize, IO.FileOptions.SequentialScan)
Dim sw As New System.IO.FileStream(destFileName, IO.FileMode.CreateNew, IO.FileAccess.Write, IO.FileShare.None, buffersize, IO.FileOptions.SequentialScan Or IO.FileOptions.WriteThrough)
Dim b(buffersize) As Byte
Dim n As Integer
Do
n = sr.Read(b, 0, buffersize)
If n <= 0 Then Exit Do
sw.Write(b, 0, n)
Loop
sw.Close()
sr.Close()
System.IO.File.SetLastWriteTimeUtc(destFileName, System.IO.File.GetLastWriteTimeUtc(sourceFileName))
End Sub

Regards,

Peter


Mike wrote:
Peter Gibbons wrote:

I use System.IO.File.Copy. It doesn't support overlapped IO. The thrown exception is documented as "An I/O error has occurred." It's weird and misleading that it is presented as "The operation completed successfully".

+1. Does seem odd.

Since streams are supports at the RTL level, I wonder if using a "." at the end of the file name will do this?

Adding a . doesn't make a difference in this case.

Right.

Rolling your own "CopyFile" function will work:

Sub CopyFile(byval src as string, tar as string)
Dim sr As New FileStream(src,FileMode.Open,FileAccess.Read)
Dim sw As New FileStream(tar,FileMode.Create,FileAccess.Write)
Dim b(4*1024) As Byte
Do
dim n as integer = sr.Read(b, 0, b.Length)
if n <= 0 then exit do
sw.write(b,0,n)
Loop
sw.Close()
sr.Close()
end sub

usage:

try
CopyFile("afs1.txt","afs2.txt")
catch ex as exception
WriteLine(ex.message)
WriteLine(ex.stacktrace)
end try

To create the test, I used notepad to create the AFS1.TXT file and the meta stream

NotePad afs1.txt

I typed junk lines and saved.

NotePad afs1.txt:meta. <--- NOTE THE ENDING DOT!

I typed junk lines and saved.

You can confirm that a straight DOS copy will copy the streams:

copy afs1.txt junk.txt
notepad junk.txt:meta. <--- NOTE THE ENDING DOT!

You will see the meta data.

Then I ran the above applet to copy the file to afs2.txt, and tested to see if the the meta stream was copied as well:

NotePad afs2.txt:meta. <--- NOTE THE ENDING DOT!

Notepad asked if you want to create it. :-)

Hope this provides you the solution you seek.

--
.

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