gzip/deflate failure when an exception is thrown

Question

I have an interesting issue with a gzip/deflate ActionFilterAttribute in ASP.NET MVC 3. If an exception is thrown by my application, instead of getting a YSOD, I get a full page of gibberish as seen below.

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If I remove my CompressAttribute, it works as expected (I see the YSOD). So it seems that my exception handling (ElmahHandleErrorAttribute from Elmah.Contrib.Mvc) halts the remaining filters, including CompressAttribute and the response is not deflated.

Relevant code:

public sealed class CompressAttribute : ActionFilterAttribute
{
    private const string _acceptEncodingHeader = "Accept-Encoding";
    private const string _contentEncodingHeader = "Content-Encoding";

    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        HttpRequestBase request = filterContext.HttpContext.Request;

        string acceptEncoding = request.Headers[_acceptEncodingHeader];

        if (String.IsNullOrEmpty(acceptEncoding))
        {
            return;
        }

        acceptEncoding = acceptEncoding.ToUpperInvariant();

        HttpResponseBase response = filterContext.HttpContext.Response;

        if (acceptEncoding.Contains("GZIP"))
        {
            response.AppendHeader(_contentEncodingHeader, "gzip");
            response.Filter = new GZipStream(response.Filter, CompressionMode.Compress);
        }
        else if (acceptEncoding.Contains("DEFLATE"))
        {
            response.AppendHeader(_contentEncodingHeader, "deflate");
            response.Filter = new DeflateStream(response.Filter, CompressionMode.Compress);
        }
    }
}

Filter registration:

GlobalFilterCollection filters = GlobalFilters.Filters;
filters.Add(new ElmahHandleErrorAttribute(), 999); // Elmah.Contrib.Mvc
filters.Add(new CompressAttribute());

How can I make sure that the response is readable even when exceptions are thrown?

Mock

I'm also open to other/better methods for enabling http compression. – Mock

Have you looked into IIS's built in dynamic compression? – Hokeypokey

@Hokeypokey I have not. Do you have a link? – Mock

this and this and many more. Ask Google :) – Hokeypokey

I like the idea of IIS compression since one setting can work for all sites on a server. I'll do some reading. – Mock

Answer 1

This is because when there is an error in your application ASP.Net removes all your custom headers but the filter is still there. You could reset the filter on application error that should make the problem go away.

protected void Application_Error(object sender, EventArgs e)
{
        Response.Filter = null;
}

Germinative

Answer 2

Here is a slightly better answer inspired by the answer from iaimtomisbehave. It lets you keep all of the code within the one class.

Add the following override to your CompressAttribute class:

public override void OnResultExecuted(ResultExecutedContext filterContext)
{
    if (filterContext.Exception != null)
    {
        filterContext.HttpContext.Response.Filter = null;
    }
}

Pedicab

This is actually what I ended up doing. – Mock

This works if I put it in OnActionExecuted, but not in OnResultExecuted. – Bakst

Answer 3

Googled the internet for a solution of the same problem and ended up here. Quite helpful answers inspired me to implement my own version mentioned below:

static public void EnableGzip()
{
    var c = HttpContext.Current;
    string a = c.Request.Headers["Accept-Encoding"];
    if (String.IsNullOrEmpty(a))
        return;
    if (!a.Contains("gzip"))
        return;
    c.Response.Filter = new GZipStream(
        c.Response.Filter, CompressionMode.Compress);
    c.Response.AppendHeader("Content-Encoding", "gzip");
    EventHandler errorHandler = null;
    errorHandler = delegate
    {
        c.Response.Filter = null;
        c.ApplicationInstance.Error -= errorHandler;
    };
    c.ApplicationInstance.Error += errorHandler;
}

Please feel free to criticize this out.

Leonaleonanie