File downloading with COM and ASP

Introduction

This article is about direct file downloading through a COM component. It uses the IResponse interface to send a file directly to the client browser.

With this approach you can protect your files from being downloaded by an unauthorized person.

To send the file to the client you need to register this kind of file within the IIS MIME types. To do it go to the ISS administration and under the HTTP Header add this kind of file. In the sample a zip file is used, so the MIME type is:

Extension=.zip
ContentType=application/x-zip-compressed

To send a file to the browser you must set the Response.Buffer to TRUE and the ContentType to the file type. After this you send the data using the Response object through the BinaryWrite method.

To accomplish this task a component was developed: FileTransfer. The interface used is called IBinaryRead. These are its methods:

If you want to download a custom file type, you must register it in the client machine too.

An example of using the FileTransfer object follows:

<% 
	Option Explicit

	Dim objBinaryRead 
	Dim saBinFile		'if you don't want error safe
	Dim bDownloadStatus
	
	Set objBinaryRead = CreateObject("FileTransfer.BinaryRead")
		 
	Response.Buffer      = true
	Response.ContentType = "application/x-zip-compressed"

	'transfer the file to the client		
	bDownloadStatus = objBinaryRead.ResponseBinaryWrite("c:\temp\test.zip", Response)
	
	'this is not an error safe code
	'if the file doesn't exist the ASP will have an error
	'saBinFile = objBinaryRead.ReadBinFile("c:\temp\test.zip")     
	'Response.BinaryWrite saBinFile
	'Set saBinFile     = nothing
	
	Set objBinaryRead = nothing
%>

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