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

iisiis-7.5pdf

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 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 browser 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?

Note: Modifiyng the code is not a solution. We have third party controls (Telerik RadGrid) on the site that have the same problem with their "Export to PDF" feature.

Best Answer

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>
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