Enable gzip compression for assets in NancyFx

NancyGzipCompression.cs

using System.Collections.Generic;
using System.IO.Compression;
using System.Linq;
using Nancy;
using Nancy.Bootstrapper;

namespace SendExplorerPlus.Portal.Utilities
{
    public class NancyGzipCompression : IApplicationStartup
    {
        public void Initialize(IPipelines pipelines)
        {
            pipelines.AfterRequest += CheckForCompression;
        }

        private static void CheckForCompression(NancyContext context)
        {
            if (!RequestIsGzipCompatible(context.Request)) return;
            if (context.Response.StatusCode != HttpStatusCode.OK) return;
            if (!ResponseIsCompatibleMimeType(context.Response)) return;
            if (ContentLengthIsTooSmall(context.Response)) return;

            CompressResponse(context.Response);
        }

        private static void CompressResponse(Response response)
        {
            response.Headers["Content-Encoding"] = "gzip";

            var contents = response.Contents;
            response.Contents = responseStream =>
            {
                using (var compression = new GZipStream(responseStream, CompressionMode.Compress))
                {
                    contents(compression);
                }
            };
        }

        private static bool ContentLengthIsTooSmall(Response response)
        {
            string contentLength;
            if (response.Headers.TryGetValue("Content-Length", out contentLength))
            {
                var length = long.Parse(contentLength);
                if (length < 4096) return true;
            }
            return false;
        }

        private static readonly List<string> ValidMimes = new List<string>
        {
            "application/json",
            "application/json; charset=utf-8"
        };

        private static bool ResponseIsCompatibleMimeType(Response response)
        {
            return ValidMimes.Any(x => x == response.ContentType);
        }

        private static bool RequestIsGzipCompatible(Request request)
        {
            return request.Headers.AcceptEncoding.Any(x => x.Contains("gzip"));
        }
    }
}