Downloading any file using ASP, FSO and the ADODB Stream object

In this article, we will see how to allow a user to download any file from our web server. They will see a prompt, giving them the option of opening or saving it, rather than simply opening it which is the default. We can achieve this using the FSO and ADODB objects.

Published: May 8, 2002 | Last Edited: Aug 21, 2005
Tested with: ASP 3.0
Category: ASP
100,834 views

Introduction

In this article, we will see how to allow a user to download any file from our web server. They will see a prompt, giving them the option of opening or saving it, rather than simply opening it which is the default. We can achieve this using the FSO and ADODB objects.

The desired effect

There are times when you want users to download a file instead of opening it up in a browser; like images, text files, ASP code files, MS Office files like Powerpoint or Word files, etc. That's easy to do for a ZIP file for example, but hard with a GIF or TXT. The reason is that anything that the browser recognizes as a valid format, it will open right away without giving you the option to save it. We want the user to receive a prompt though, asking them if they want to save or open the file, like below:

We can achieve the above for any file, by simply editing the Response that the browser receives from our web server. By editing the header and the content type, we can prepare the browser to accept binary streams, which would then save as attachments. So, it will always prompt the users to save the content.

ASP Code

1	<%@Language="VBScript"%>
2	<%Option Explicit%>
3	<%Response.Buffer = True%>
4	<%
5	On Error Resume Next
6	Dim strPath
7	strPath = CStr(Request.QueryString("file"))
8	'-- do some basic error checking for the QueryString
9	If strPath = "" Then
10	Response.Clear
11	Response.Write("No file specified.")
12	Response.End
13	ElseIf InStr(strPath, "..") > 0 Then
14	Response.Clear
15	Response.Write("Illegal folder location.")
16	Response.End
17	ElseIf Len(strPath) > 1024 Then
18	Response.Clear
19	Response.Write("Folder path too long.")
20	Response.End
21	Else
22	Call DownloadFile(strPath)
23	End If
24
25	Private Sub DownloadFile(file)
26	'--declare variables
27	Dim strAbsFile
28	Dim strFileExtension
29	Dim objFSO
30	Dim objFile
31	Dim objStream
32	'-- set absolute file location
33	strAbsFile = Server.MapPath(file)
34	'-- create FSO object to check if file exists and get properties
35	Set objFSO = Server.CreateObject("Scripting.FileSystemObject")
36	'-- check to see if the file exists
37	If objFSO.FileExists(strAbsFile) Then
38	Set objFile = objFSO.GetFile(strAbsFile)
39	'-- first clear the response, and then set the appropriate headers
40	Response.Clear
41	'-- the filename you give it will be the one that is shown
42	' to the users by default when they save
43	Response.AddHeader "Content-Disposition", "attachment; filename=" & objFile.Name
44	Response.AddHeader "Content-Length", objFile.Size
45	Response.ContentType = "application/octet-stream"
46	Set objStream = Server.CreateObject("ADODB.Stream")
47	objStream.Open
48	'-- set as binary
49	objStream.Type = 1
50	Response.CharSet = "UTF-8"
51	'-- load into the stream the file
52	objStream.LoadFromFile(strAbsFile)
53	'-- send the stream in the response
54	Response.BinaryWrite(objStream.Read)
55	objStream.Close
56	Set objStream = Nothing
57	Set objFile = Nothing
58	Else 'objFSO.FileExists(strAbsFile)
59	Response.Clear
60	Response.Write("No such file exists.")
61	End If
62	Set objFSO = Nothing
63	End Sub
64	%>

Copy the code above and save it as download.asp on your web server.

To use this code, you link to the page, passing the location of the file you want to send to the user. For example:
<a href="download.asp?file=/images/xefteri.gif">

The first part of the code does some basic error checking. The sub DownloadFile checks to see if the file is there, and if it is then it sends it as a binary stream using the ADODB Stream object. The header Content-Length is set so that the browser can properly display the progress bar.

Possible issues

If you are trying to stream a file bigger than 4MB, then IIS 6 might send back an error saying something to the sort of "Response Buffer Limit Exceeded". This is a maximum file setting in the web server's metabase, which you can easily fix.

Conclusion

Make sure that you have MDAC 2.5+ installed in order for this to work. It would be very easy to add some security to this code. For example, you could combine your database of content access to it. You would then first check if the users have access to content and if they do, only then proceed to send the file to them.