CODEWITHSUNDEEP
.netvb.netwinapipinvokecreatefile
Instance Hunter
Instance Hunter

Reputation: 7925

How can I check if a directory can be renamed in VB.NET?

My thought is to use CreateFile from kernel32 and check for sharing violations. I believe this will work because I watched the file system activity with Process Monitor while issuing a rename command from CMD that I knew would fail and the last activity was a failed CreateFile call that resulted in a sharing violation.

This is the Process Monitor information on the call.

Desired Access: Read Attributes, Delete, Synchronize
Disposition: Open 
Options: Synchronous IO Non-Alert, Open Reparse Point 
Attributes: n/a 
ShareMode: Read, Write, Delete 
AllocationSize: n/a

Using this VB code, I produced a call which gave the same information in Process Monitor but did not cause the sharing violation.

CreateFile(theDirectoryPath, _
           FILE_READ_ATTRIBUTES Or DELETE Or SYNCHRONIZE, _
           FILE_SHARE_READ Or FILE_SHARE_WRITE Or FILE_SHARE_DELETE, _
           Nothing, _
           OPEN_EXISTING, _
           FILE_ATTRIBUTE_DIRECTORY Or FILE_FLAG_BACKUP_SEMANTICS _
               Or FILE_FLAG_OPEN_REPARSE_POINT, _
           Nothing)

The constants are pulled from various MSDN and pinvoke.net sources.

If I call the above code recursively on all subfolders it will eventually cause the sharing violation, but when CMD refused to rename, it did not recurse.

Yes, I know I could just try and catch the exception. But the point at which I want to know if the directory can be renamed and the point at which I want to rename the directory are not the same.

EDIT:

There may have been a source of confusion in this question. I am not concerned with permissions; I am concerned with file locks.

Upvotes: 0

Views: 809

Answers (2)

richardtallent
richardtallent

Reputation: 35374

Untested, but this should work:

Dim fp As New FileIOPermission(FileIOPermissionAccess.Write, "C:\myfolderpath")
Try
    fp.Demand()
Catch e As SecurityException
    Console.WriteLine("I can't rename this folder.")
End Try

This will "demand" Read and Write permissions on the folder without actually renaming anything.

Edit: The above doesn't do what I thought it would, see Stephen's comment below.

If this doesn't work, perhaps attempting to rename the file with the same filename will trigger the security exception without actually doing anything destructive (though it will probably "touch" the directory).

Upvotes: 1

JP Alioto
JP Alioto

Reputation: 45127

Yes, I know I could just try and catch the exception. But the point at which I want to know if the directory can be renamed and the point at which I want to rename the directory are not the same.

In my opinion, this is a design problem that creates a race condition. If you check first and rename later, you will not know that the time of rename if your previous check was valid.

Upvotes: 3

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