Getting Started
Before we begin, create a new folder called 'uploaddemo' in your
C:\inetpub\wwwroot directory (or where-ever else your files are
stored for IIS). Create a new file in there called upload.asp, and another called
uploadcomplete.asp. Leave these files empty for now.
Now, create another directory within 'uploaddemo' called 'files'.
This is where our uploaded files are going to be stored. In order for this to
work, you need to allow IIS to be given write access to this directory. To do
this, go to the Internet Information Services console, select the appropriate
web, and then display the properties for the 'files' directory. In the Directory
tab, ensure the 'Write' checkbox is selected, and click OK.
We're now ready to write some code for upload.asp, where the user will be presented
with a form to select a file, and give the file a description. Add the following
code to the upload.asp file, and then we'll take a closer look at it.
<html>
<head>
<title>VB Web ASP File Upload</title>
</head>
<body>
<form action="uploadcomplete.asp" method="POST" enctype="multipart/form-data">
<p>Please select a file to upload, and enter a description for it.</p>
<p><b>File: </b><input type="file" style="width:
300;" name="thefile"><br>
<b>Description:</b><br><textarea name="description"
rows=4 cols=30></textarea></p>
<input type="submit" value="Upload">
</form>
</body>
</html>
As you can see, the form is currently just plain HTML. However, there are
a few differences that you may not have come across before. The first is this:
<form action="uploadcomplete.asp" method="POST"
enctype="multipart/form-data">
Although at first glance this is a standard form, the enctype
property makes a significant difference! When set to multipart/form-data,
the form is not posted in the standard format - you will not be able to access
the posted data through the standard Request.Form(FieldName)
syntax. However, this format does allow files to be transmitted to the server,
as well as form fields. When we create our ActiveX DLL, it will parse this posted
data, and save the appropriate part into a new file.
The second difference is the
<input type="file" style="width: 300;" name="thefile">
line, which uses the "file" input type. This input field allows the
user to select a file using an Open dialog.
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The 'File' input type
When a form is submitted using this input box, the file, rather than
the filename is transmitted. However, this does have some security consequences...
A website could in theory hide this field, with it's value pre-set, and
then when the user transmits the form, he/she unknowingly sends the server
a file too. Therefore, both IE and Netscape have disabled the value
property for this type of input field. The consequence of this, is if
you use server-side validation (for, say, checking the length of the description),
when you display the form again with the error, you won't be able to use
the input tag's value attribute to remember the file the
user already selected. Something to bear in mind....
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