c# - Can gzip compression be selectively disabled in ASP.NET/IIS 7?

Question

I am using a long-lived asynchronous HTTP connection to send progress updates to a client via AJAX. When compression is enabled, the updates are not received in discrete chunks (for obvious reasons). Disabling compression (by adding a <urlCompression> element to <system.webServier>) does solve the problem:

<urlCompression doStaticCompression="true" doDynamicCompression="false" />

However, this disables compression site-wide. I would like to preserve compression for every other controller and/or action except for this one. Is this possible? Or am I going to have to create a new site/area with its own web.config? Any suggestions welcome.

P.S. the code that does the writing to the HTTP response is:

var response = HttpContext.Response;
response.Write(s);
response.Flush();

Answer 1

@Aristos' answer will work for WebForms, but with his help, I've adapted a solution more inline with ASP.NET/MVC methodology.

Create a new filter to provide the gzipping functionality:

public class GzipFilter : ActionFilterAttribute
{
    public override void OnActionExecuted(ActionExecutedContext filterContext)
    {
        base.OnActionExecuted(filterContext);

        var context = filterContext.HttpContext;
        if (filterContext.Exception == null && 
            context.Response.Filter != null &&
            !filterContext.ActionDescriptor.IsDefined(typeof(NoGzipAttribute), true))
        {
            string acceptEncoding = context.Request.Headers["Accept-Encoding"].ToLower();;

            if (acceptEncoding.Contains("gzip"))
            {
                context.Response.Filter = new GZipStream(context.Response.Filter, CompressionMode.Compress);
                context.Response.AppendHeader("Content-Encoding", "gzip");
            }                       
            else if (acceptEncoding.Contains("deflate"))
            {
                context.Response.Filter = new DeflateStream(context.Response.Filter, CompressionMode.Compress);
                context.Response.AppendHeader("Content-Encoding", "deflate");
            } 
        }
    }
}

Create the NoGzip attribute:

public class NoGzipAttribute : Attribute {
}

Prevent IIS7 from gzipping using web.config:

<system.webServer>
    ...
    <urlCompression doStaticCompression="true" doDynamicCompression="false" />
</system.webServer>

Register your global filter in Global.asax.cs:

protected void Application_Start()
{
    ...
    GlobalFilters.Filters.Add(new GzipFilter());
}

Finally, consume the NoGzip attribute:

public class MyController : AsyncController
{
    [NoGzip]
    [NoAsyncTimeout]
    public void GetProgress(int id)
    {
        AsyncManager.OutstandingOperations.Increment();
        ...
    }

    public ActionResult GetProgressCompleted() 
    {
        ...
    }
}

P.S. Once again, many thanks to @Aristos, for his helpful idea and solution.