IIS 7 removes Content-Disposition filename for Content-Type application/pdf

Question

I have the following code that returns a PDF file in my web application:

string path = "help.pdf";
byte[] data = File.ReadAllBytes(path);
Response.Clear();
Response.ClearHeaders();
Response.AddHeader("Content-Length", data.Length.ToString());
Response.AddHeader("Content-Type", "application/pdf");
Response.AddHeader("Content-Disposition", "attachment; filename=help.pdf");
Response.OutputStream.Write(data, 0, data.Length);
Response.End();

When I call the handler of this code in any browser (Chrome, IE or Firefox), I get a "Save as..." dialog with the name of the page (index.aspx) rather than the name provided in the code (help.pdf).

I also checked the following:

• Tested on my local machine. It works there as expected.
• Deactivated compression in IIS: no change
• Deactivated SSL in IIS: no change
• Checked MIME types in IIS: application/pdf is configured
• Replaced Content-Type application/pdf with application/octet-stream: problem is gone (but we are using third party export tools that I can't modify in this way, so this is not a solution)

I checked the HTTP response header with all browsers. It looks like this:

Cache-Control:private
Content-Disposition:attachment
Content-Length:89407
Content-Type:application/pdf
Date:Thu, 07 May 2015 08:43:12 GMT
Server:Microsoft-IIS/7.5
X-Powered-By:ASP.NET
X-UA-Compatible:IE=edge,chrome=1

As you can see the filename parameter is removed from the Content-Disposition field. So the behaviour of the browsers is correct. The web server (IIS) seems to tinker around with the header.

I found somebody with the same problem here. But the problem was never solved. Any ideas?

Answer 1

The problem was that because of an IIS 7.5 issue someone added the following lines to the web.config file of the application:

<outboundRules>
    <rule name="Force pdfs to download" preCondition="only match pdfs">
        <match serverVariable="RESPONSE_Content_Disposition" pattern="(.*)" />
        <action type="Rewrite" value="attachment" />
    </rule>
    <preConditions>
        <preCondition name="only match pdfs">
            <add input="{RESPONSE_CONTENT_TYPE}" pattern="^application/pdf" />
        </preCondition>
    </preConditions>
</outboundRules>