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A File-Uploading Windows Script Component

By Andy Smith


Introduction
Probably one of the most asked question on the ASP Messageboard is how to upload files from a Web form. Usually, the answer is simple: "Buy or Download a component." Unfortunately, not everybody can use 3rd party components on their server, especially those in hosted environments. I was once one of those people. Additionally, those components are oftentimes not very affordable for someone who works with ASP as a hobby. (For a listing of third-party upload components, be sure to check out the Uploading Article Index!)

After having promised a client that I could give them a Web-based file upload, and then finding out I couldn't register a component on the server, I started sweating, imagining many future late nights at work trying to solve this horrible issue.

Then I found a wonderful article on ASPToday.com - Uploading with ASP and VBScript - that solved the problem with a couple functions. Voila! After using it for that client, I came to realize that, while the solution provided there was functional, it wasn't very user friendly. About the same time, I started getting interested in the usefulness of Windows Script Components as a replacement for the inability to register compiled components. (If you are unfamiliar with Windows Script Components be sure to read: Building Windows Script Components!) Naturally, I decided to whip myself up a nicely object oriented, encapsulated and compatible version of the File Upload function I had been using.

The Gist Of It
The whole thing breaks down into three objects, all packaged together into one file.

    The FileUp object
    This serves as a compatibility layer between my object and the normal ASP Request object. It has properties and methods that span my Form Request object as well as the other intrinsic Request objects. It also has routines for setting defaults for the object. It's default property is Item, which gives compatibility with the ASP Request object.

    The Form object
    This one does all the real magic of parsing the Post and giving access to the items. This object essentially takes the place of the Form object in the normal Request. The default property for it is Item, which gives compatibility with the ASP Request.Form object

    The UploadControl object
    Each item is stored in one of these, and is accessed by the Form object's default Item property. The default Value property returns the value of normal form fields, and the filename of file fields.

    Using the object is almost exactly the same as using the normal ASP request object. Here's some sample code that you would use in your page to test if the page had been submitted by testing the value of the submit control, and then writing out a couple of the values as well as saving the file to the current folder.

    Dim MBRequest
    Set MBRequest = GetObject( "script:" & _
                        Server.MapPath( "MetaBuilders.FileUp.wsc" ) )
    
    If MBRequest("submit") = "upload" then
      Response.Write MBRequest("MyTextField") & vbNewLine
      Response.Write MBRequest("File1").Path & _
                     MBRequest("File1").FileName & vbNewLine
      MBRequest("File1").Save
    End If
    

The FileUp Object
When you create the FileUp object, a few things happen. First, it checks to see if it should do anything at all with the line:

If InStr( 1, Request.ServerVariables("HTTP_CONTENT_TYPE"), _
                            "multipart", vbTextCompare ) > 0 Then

This checks to make sure that the form that posted to the page used the encoding type that is need to send files at all. If it wasn't used, then all requests made to the FileUp object will be directly forwarded to the ASP Request object.

Assuming that the proper enctype is found, then a new Form object is created and is told to parse and populate itself with these lines:

set objForm = CreateComponent("Form")
objForm.Build
objForm.SetOverWriteFiles( blnpOverWrite )
objForm.SetSavePath( strpSavePath )

The CreateComponent function is a VBScript function used for WSC's to reference other Components in the WSC Package. Build, tells the object to parse the Post, and the last 2 set default behavior for File Saving operations.

Next a dummy, empty Form object is also created to allow for people trying to access nonexistent items in the request in the same way they can use the ASP Request object. This object has only one UploadControl in it, named "empty" and that is what is always returned when no item can be found that matches what the page asks for. It's created exactly the same as the real object, except that the line:

objEmpty.BuildEmpty = True

is set before it's Build method is called.

The default Item property gives the compatibility with ASP Request. It allows the client to reference items with the Request("itemName") syntax, and it still searches the Request in the same order as ASP would. It does this with code like:

Set strValue = ThisASP.Request.QueryString( strKey )
If strValue <> "" Then
  Set get_Item = strValue
  Exit Function
End If

You can also use the Request.Form("itemName") syntax thanks to the Form property. It searches either itself, or the intrinsic Form object, depending on the enctype of the Post, which was found earlier.

Two new properties are OverWrite and SavePath. These two do what you probably think they do. They tell each UploadControl what to do when .Save or .SaveAs is called on a file object. Setting OverWrite to true allows files to be overwritten without an error. SavePath, which defaults to the folder which the script is running in, tells the UploadControls where to save files to. They do this by calling the Form object's SetOverWriteFiles and SetSavePath methods.

This concludes our examination of the FileUp object. In Part 2 we'll take a close look at the Form and UploadControl objects!

  • Read Part 2!


  • Article Information
    Article Title: A File-Uploading Windows Script Component
    Article Author: Andy Smith
    Published Date: Wednesday, January 24, 2001
    Article URL: http://www.4GuysFromRolla.com/webtech/012401-1.shtml


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