Question

My web app generates a CSV file on the fly, but whenever I use GZIP compression, the download fails:

HTTP/1.1 200 OK
Cache-Control: private, s-maxage=0,no-store, no-cache
Transfer-Encoding: chunked
Content-Type: text/csv;charset=utf-8
Content-Encoding: gzip
Vary: Accept-Encoding
Server: Microsoft-IIS/7.5
X-AspNetMvc-Version: 3.0
Content-Disposition: attachment;filename="filename.csv"
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
p3p: CP="CAO PSA OUR"
Date: Fri, 03 Feb 2012 11:27:27 GMT

The download appears as “Interrupted” in Google Chrome, and in Internet Explorer appears an error that says “Content decoding has failed” .

HTTP/1.1 200 OK
Cache-Control: private, s-maxage=0,no-store, no-cache
Transfer-Encoding: chunked
Content-Type: text/csv;charset=utf-8
Server: Microsoft-IIS/7.5
X-AspNetMvc-Version: 3.0
Content-Disposition: attachment;filename="filename.csv"
X-AspNet-Version: 4.0.30319
X-Powered-By: ASP.NET
p3p: CP="CAO PSA OUR"
Date: Fri, 03 Feb 2012 11:23:30 GMT

The solution is disabling compression on that action, but… why does this happen?

Cheers.

UPDATE: The compression filter that I use:

public class EnableCompressionAttribute : ActionFilterAttribute
{
    const CompressionMode compress = CompressionMode.Compress;
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        if (filterContext.IsChildAction)
            return;

        var actionAttributes = filterContext.ActionDescriptor.GetCustomAttributes(true);
        if (actionAttributes != null && actionAttributes.Any(attr => attr is SkipCompressionAttribute))
            return;

        HttpRequestBase request = filterContext.HttpContext.Request;
        HttpResponseBase response = filterContext.HttpContext.Response;
        String acceptEncoding = request.Headers["Accept-Encoding"];

        if (acceptEncoding == null || response.Filter == null)
            return;

        if (acceptEncoding.ToLower().Contains("gzip"))
        {
            response.Filter = new GZipStream(response.Filter, compress);
            response.AppendHeader("Content-Encoding", "gzip");
            response.AppendHeader("Vary", "Accept-Encoding");
        }
        else if (acceptEncoding.ToLower().Contains("deflate"))
        {
            response.Filter = new DeflateStream(response.Filter, compress);
            response.AppendHeader("Content-Encoding", "deflate");
            response.AppendHeader("Vary", "Accept-Encoding");
        }
    }
}

Answer 1

Try:

Response.Headers.Remove("Content-Encoding");
Response.AppendHeader("Content-Encoding", "gzip");

Another problem may be the caching: what if a client accepts compressed content, but the next client doesn’t, and the server cached the compressed data? what the second client will get? A cached compressed page that won’t decode!

To fix that, add another method:

public override string GetVaryByCustomString(HttpContext context, string custom)
{
    if (custom == "GZIP")
    {
        string acceptEncoding = HttpContext.Current.Response.Headers["Content-Encoding"];

        if (string.IsNullOrEmpty(acceptEncoding))
            return "";
        else if (acceptEncoding.Contains("gzip"))
            return "GZIP";
        else if (acceptEncoding.Contains("deflate"))
            return "DEFLATE";

        return "";
    }

    return base.GetVaryByCustomString(context, custom);
}