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Here are two VBScript functions that check to see if a specified file or folder exist on the server. As such they can be used to improve error handling on ASP pages that read or write files from disk.

The first function ( CheckFileExists ) checks to see if a file exists. It returns 'True' if the file exists, or 'False' if it does not.

%
Function CheckFileExists(sFileName)

Dim FileSystemObject

Set FileSystemObject = Server.CreateObject( Scripting.FileSystemObject )

If (FileSystemObject.FileExists(sFileName)) Then
CheckFileExists = True
Else
CheckFileExists = False
End If

Set FileSystemObject = Nothing

End Function
%

The following code is an example of how to use the function:

%
If CheckFileExists( D:\ProductionReports\July2005\July-12-2005.xls ) Then
Response.Write( The production report for July 2005 is available )
Else
Response.Write( The production report for July 2005 cannot be found )
End If
%

The second function ( CheckFolderExists ) checks to see if a folder exists. It returns 'True' if the folder exists, or 'False' if it does not.

%
Function CheckFolderExists(sFolderName)

Dim FileSystemObject

Set FileSystemObject = Server.CreateObject( Scripting.FileSystemObject )

If (FileSystemObject.FolderExists(sFolderName)) Then
CheckFolderExists = True
Else
CheckFolderExists = False
End If

Set FileSystemObject = Nothing

End Function
%

The following code is an example of how to use the CheckFolderExists function:

%
If CheckFolderExists( D:\ProductionReports\July2005 ) Then
Response.Write( The production reports for July 2005 are available )
Else
Response.Write( The production reports for July 2005 are not available )
End If
%

A problem with these two functions is the fact that they will check for the existence of files and folders, but do not indicate whether the user has the appropriate permissions to view them.

A way around this problem is to use the Permission Checker Component. This Component is supplied with the Internet Information Server 4.0 Resource Kit, and also with the Internet Information Services 5.0 of Windows 2000. This object has one method - HasAccess, which makes it possible to determine if the user has permission to read a specified file.

An example of using the component is below:

%
Set PermissionChecker = Server.CreateObject( MSWC.PermissionChecker )

If PermissionChecker.HasAccess( D:\ProductionReports\July2001\July-19-2001.xls ) Then
Response.Write( You have permission to view the July 2001 production report )
Else
Response.Write( You do not have permission to view the July 2001 production report )
End If

Set PermissionChecker = nothing
%

The Permission Checker Component can also be incorporated into the original CheckFileExists function:

%
Function CheckFileExists(sFileName)

Dim FileSystemObject

Set FileSystemObject = Server.CreateObject( Scripting.FileSystemObject )

If (FileSystemObject.FileExists(sFileName)) Then
Set PermissionChecker = Server.CreateObject( MSWC.PermissionChecker )

If PermissionChecker.HasAccess(sFileName) Then
CheckFileExists = True
End If

Set PermissionChecker = nothing
Else
CheckFileExists = False
End If

Set FileSystemObject = Nothing

End Function
%

The function can then be used in a similar way to before:

%
If CheckFileExists( D:\ProductionReports\July2001\July-12-2001.xls ) Then
Response.Write( The production report for July 2001 is available )
Else
Response.Write( The production report for July 2001 cannot be found or you do not have permission to view it )
End If
%

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