Using Microsoft's Posting Acceptor in ASP Pages

A Data Access Worldwide White Paper
by Dennis Piccioni

August 25, 2000
Last Edited: August 2, 2005

Overview

The ability for browser users to upload files to a Web application is a feature that many developers may want to implement at some point. An example use for this might be an Intranet application where employees can share files.

Note: The Microsoft Posting Acceptor is no longer supported on newer operating systems, starting with Windows Server 2003. There are many controls available on the internet, JavaScript controls, for example, that you can use instead.

The first real life application I used the posting acceptor in is the in-house version of the Data Access Worldwide Technical Knowledge Base. This application, written using WebApp Server 2.1, allows Data Access Worldwide technical staff to author Knowledge Base articles from where ever they are in the world. Using the posting acceptor, article authors can add files to articles and the application moves the files to the correct location and adds links to the articles for each file.

This paper will show you how to install the Microsoft Posting Acceptor, how to prepare your IIS Server to use it and how to implement this component in ASP pages.

The Posting Acceptor is a free component of Microsoft Site Server that allows Internet Information Server (IIS) applications to accept file uploads from browser clients.

Microsoft's own documentation for using this component leaves much to be desired. I was only able to get the Posting Acceptor working after extensive research in the Microsoft Newsgroups, the Microsoft Knowledge Base and many third party Web sites, piecing together bits of information from all of them. I prepared this document so that you do not have to go through as much trouble as I did to get this powerful little component into your Web applications.

I successfully tested the Microsoft Posting Acceptor 1 on the following systems:

• Windows NT 4 Workstation SP 5 using IIS 4
• Windows NT 4 Server SP 5 using IIS 4
• Windows NT 4 Server SP 6.0a using IIS 4
• Windows 2000 Professional using IIS 5

Contents

Preliminaries

• Overview
• Contents
• Document Conventions
• Terms

Installation

• Installing the Microsoft Posting Acceptor
• Preparing IIS to Use the Posting Acceptor
• Allow anonymous access to the scripts virtual directory
• Create a virtual directory for uploaded files
• Installing Posting Acceptor on Windows NT 4 Workstation

Implementation

• Selecting a local (client side) file in HTML
  • Creating a file input element in an HTML form
    • Example 1
    • Example 2
  • Setting the ENCTYPE form attribute
    • Example 3
• Uploading the file
• Implementing the Posting Acceptor in an ASP page
  • Example 4
• Tips
  • Using multiple forms in an ASP page
  • Using a different virtual directory for the cpshost.dll file
  • Overwriting upload files

Conclusion

• Additional Reading
• Resources
• Contacting Data Access Worldwide

Document Conventions

• The base font of this document is Arial

• NOTE: - This precedes important information you should definitely not skip over

• Source code or commands to be typed are in monospaced (Courier New) font

<form>
</form>

Specific code that is being discussed in the particular section of the document may be bolded to emphasize it.

• ^ top - a hyperlink to make it easy to get back to the top of this document

Terms

Here are some brief explanations of terms that are used throughout this document. You are expected to be familiar with the terms that are not explained here (i.e. HTML, URL, localhost). I encourage you to find out more about any terms that you are not already familiar with. Information on just about anything discussed in this document is easily found using Web search engines and there are hundreds of books available on HTML, ASP, JavaScript and VBScript, the main technologies used here.

• Scripts virtual directory

  The scripts virtual directory is one of the default virtual directories installed with IIS. The physical location of this directory is usually right below the IIS installed default Web Site directory, such as:

  X:\InetPub\Scripts
  where X is the server drive on which IIS is installed

• Virtual Path

The default Web site is the Web site that comes up in a browser on the local Web server by default, as installed when installing IIS from the Windows NT Option Pack is http://locahost/. The corresponding physical directory is

X:\Inetpub\wwwroot
where X is the server drive on which IIS is installed

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Installation

Installing the Microsoft Posting Acceptor

The Microsoft Knowledge Base, and all other pages I found on the Microsoft site that talk about Posting Acceptor, point to an incorrect file (a Web Publishing Wizard update) as a Posting Acceptor install and give incorrect information regarding the operating systems under which the component can be installed. The Posting Acceptor cannot be directly installed on Windows NT 4 Workstation (not directly anyway). I'll show you how to do this manually in the Installing Posting Acceptor on Windows NT 4 Workstation section).

You can install the Microsoft Posting Acceptor on Windows NT 4 Server from the NT 4 Option Pack CD. Here are the steps to add Posting Acceptor to an existing IIS installation:

1. Run the NT 4 Option Pack setup program
2. Select Add/Remove
3. Select Show Subcomponents under component Site Server Express
4. Select Posting Acceptor 1.01
5. Install

This will be the directory into which the files are uploaded from the browser.

I recommend that you place this directory in one of the following locations:

• Somewhere below the default Web Site directory
  For example:
  X:\Inetpub\wwwroot\uploads
  where X is the server drive on which IIS is installed
• Somewhere below the virtual directory for your Web application
  For example:
  X:\MyWebApp\AppHtml\uploads
  where X:\MyWebApp\AppHtml is the virtual directory for your Web application

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Implementation

Selecting a local (client side) file in HTML

Now, let's get started on some coding.

Creating a file input element in an HTML form

This is the easy part; it's just plain HTML.

Example 1

Inside of an HTML form, we can add a file input element using the <input> tag with the TYPE attribute set to "file":

<form>
    <input type="file">
</form>

Just using this simple HTML code, you will see a window in your browser, followed by a Browse button that, when clicked, brings up a dialog that allows you to select a file on your local machine, and the path to the selected file is placed in the window.

Try it:

Example 2

We can make this code a bit fancier by specifying a size for the window to be large enough to hold a longer path and adding some text telling the user what to do:

<form>
    Choose a file on your computer: <input type="file" size="40">
</form>

Here is the result:

Choose a file on your computer:

NOTE: A minor annoyance of the file input element is that the browse button cannot be formatted, so depending on the looks of the rest of your page, it may look somewhat out of place.

We'll start with the simple ASP page with a form that we created in example 2. Then, we'll add some other necessary features.

• Add "POST" as the form method

  Setting the form's method attribute to "POST" will allow the upload to start on any submit executed for this form.

  <form enctype="multipart/form-data" method="POST">
      Choose a file on your computer: <input type="file" size="40">
  </form>

• Add cphost.dll as the form action

  The action of the form must be the virtual path to cphost.dll, followed by ?PUBLISH

  <form enctype="multipart/form-data" method="POST" action="http://localhost/scripts/cphost.dll?PUBLISH">
      Choose a file on your computer: <input type="file" size="40">
  </form>

• Add an optional page for relocation to the action attribute

  Following the ?PUBLISH, you can add another ? and the virtual path to another page that will load after the file upload is complete.

  For this example, we'll use the repost.asp file, which comes with the Microsoft Posting director and is installed in the scripts virtual directory. This file is provided as an example of how to retrieve information about the uploaded file once the upload is complete.

  <form enctype="multipart/form-data" action="http://localhost/scripts/cpshost.dll?PUBLISH?http://localhost/scripts/repost.asp">
  </form>

• Add a form input element named TargetURL

  The value of this input element has to be the upload directory (the directory created in section Create a virtual directory for uploaded files). There is no need for the user to see this form element, so we'll make it a hidden form.

  For this example, we'll assume the upload location is a directory called uploads, located immediately below the default Web Site directory.

  <input type="hidden" name="TargetURL" value="http://localhost/uploads/">

• A submit type form button

  Since the form method is "POST", clicking any "submit" button in this form will start the upload.

  <input type="submit" value="Upload">

Example 4

Now we'll put together all of the needed items outlined above into a working example of an ASP page that allows uploading of a file from the client browser using the Microsoft Posting Acceptor.

<form enctype="multipart/form-data" method="POST" action="http://localhost/scripts/cphost.dll?PUBLISH?http://localhost/scripts/repost.asp">
    Choose a file on your computer: <input type="file" size="40">
    <input type="hidden" name="TargetURL" value="http://localhost/uploads/">
    <input type="submit" value="Upload">
</form>

An ASP page with this sample is provided with this paper as MSPAExample4.asp.

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Tips

Using multiple forms in an ASP page

If you have a need for a form that processes a "GET" rather than a "POST", or need additional form processing (e.g. WebApp data entry) on the same page from which you are doing the file upload, you can place several forms on a single ASP page.

Using a different virtual directory for the cpshost.dll file

The Microsoft documentation tells you to place the Posting Acceptor dll (cpshost.dll) into the Scripts virtual directory. Depending on the security settings and requirements on your Web Server, you may want to place this file into another virtual directory. You can do so by simply creating a new virtual directory, with read and execute (including scripts) rights and anonymous access rights granted. If you do so, remember to change all references to the scripts directory in your ASP pages.

Overwriting upload files

One problem with the Microsoft Posting Acceptor version 1 is that on upload there is no overwrite protection. If a file with the same name already exists in the upload target directory, it is simply replaced with the new one.

One way to get around this is to make the upload target directory only a temporary directory. You can upload a file to it, and then have another process move that file to the permanent directory. This is quite simple to do if you use WebApp Server.

Download Troubles

The first place I ran into problems when trying to use the Microsoft Posting Acceptor was trying to find out how and from where to actually install it. I read about this component in numerous places I visited in my research, but all the links on the Microsoft sites to the download for the Posting Acceptor pointed to a file that installs an update for the Web Publishing Wizard, which does install on Windows NT 4 Workstation, but does not install the files needed for the Posting Acceptor.

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Additional Reading

• A Simple ASP Example Using Posting Acceptor, Microsoft Knowledge Base article Q217425, http://support.microsoft.com/support/kb/articles/Q127/4/25.asp.