I'm trying to add a Vary: Accept-Encoding header to the response to files that I compress, as advised earlier.

However, for some reason this is not possible - either from the Visual Studio test server, or an IIS server.

I have the following code:

if (url.Contains(".js") || url.Contains(".aspx") || url.Contains(".css"))
{
    app.Response.AppendHeader("Vary", "Accept-Encoding");
    app.Response.AppendHeader("Varye", "Accept-Encoding"); // for testing
    app.Response.AppendHeader("Varye", "Accept-Things");   // for testing
    app.Response.AppendHeader("Vary", "Accept-Stuff");     // for testing
    app.Response.AppendHeader("Var", "Accept-Items");      // for testing

    encodings = encodings.ToLower();

    if (encodings.Contains("gzip") || encodings == "*")
    {
        app.Response.Filter = new GZipStream(baseStream, CompressionMode.Compress);
        app.Response.AppendHeader("Content-Encoding", "gzip");

    }
}

this results in the following response header:

Status=OK - 200
Server=ASP.NET Development Server/10.0.0.0
Date=Fri, 21 Oct 2011 12:24:11 GMT
X-AspNet-Version=4.0.30319
Varye=Accept-Encoding, Accept-Things
Var=Accept-Items
Content-Encoding=gzip
Cache-Control=public
Etag="1CC8F2E9D772300"
Content-Type=text/css
Content-Length=16200
Connection=Close

As you can see, the Vary header is not present. Meaningless headers with similar syntax are present, so there must be something, somewhere, taking out the Vary header before it is sent.

I don't know if it is relevant, but here is where I define my compression module in web.config:

<httpModules>
    <add name="CompressionModule" type="Utility.HttpCompressionModule"/>
</httpModules>

(Where Utility.HttpCompressionModule is the class which the code exc

c# asp.net http-headers
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