Question

I am experiencing an issue where, when a server error occurs in my web application, I see a gzip’ed server error rendered to the screen, not the actual error message. I am attempting to resolve this by calling GZIP Decompress on Application_Error.

I am unable to decompress the HttpContext.Current.Response stream because it is not able to be read. That is, CanRead is false, but CanWrite is true. This leads me to believe I am doing something wholly incorrect, so I am also open for suggestions.

protected void Application_Error(object sender, EventArgs e)
{
    if (HttpContext.Current.Error != null)
    {
        this.GetType().GetLogger().Error(HttpContext.Current.Error);
    }

    CompressionManager.Decompress();
}

public static void Decompress()
{
    //Determine types of compression possible.
    string acceptEncoding = HttpContext.Current.Request.Headers["Accept-Encoding"];
    if (string.IsNullOrEmpty(acceptEncoding)) return;

    //Make sure the stream is actually compressed.
    HttpResponse response = HttpContext.Current.Response;
    bool compressed = response.Headers.AllKeys.Contains("Content-encoding");
    if (!compressed) return;

    acceptEncoding = acceptEncoding.ToUpperInvariant();

    using ( MemoryStream memStream = new MemoryStream() )
    {
        byte[] buffer = new byte[1024];
        int byteCount;
        do
        {
            byteCount = response.Read(buffer, 0, buffer.Length);
            memStream.Write(buffer, 0, byteCount);
        } while (byteCount > 0);

        // If you're going to be reading from the stream afterwords you're going to want to seek back to the beginning.
        memStream.Seek(0, SeekOrigin.Begin);

        if (acceptEncoding.Contains("GZIP"))
        {
            using (GZipStream decompress = new GZipStream(memStream, CompressionMode.Decompress))
            {
                decompress.CopyTo(response.Filter);
            }
        }
        else if (acceptEncoding.Contains("DEFLATE"))
        {
            response.Filter = new DeflateStream(response.Filter, CompressionMode.Decompress);
        }

        response.Headers.Remove("Content-encoding");
    }
}

I’ve been googling for a while now, but have not made much progress. As far as I can tell I should be working with “Request.GetResponseStream()” and not the response object, but I think GetResponseStream requires a non-static Request.

Open to anything. Thanks.

Derp. Just do this:

CompressionManager.Decompress(HttpContext.Current.Error.Message);

public static void Decompress(string errorMsg)
{
    HttpContext.Current.Response.Filter = new DeflateStream(new MemoryStream(ASCIIEncoding.Default.GetBytes(errorMsg)), CompressionMode.Compress);
}

Answer 1

I would suggest you do a Response.Clear and then set the appropriate headers, then send the data. It is correct that you cannot read the response stream this way.

It might be that your response stream is compressed by settings in IIS and that you cannot change this through code. Update the IIS compression settings and try again.