Simple Asset Bundling for NancyFx

Bundle.cs

using System;
using System.Collections.Concurrent;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using Nancy;
using Nancy.Helpers;
using Nancy.Responses;

namespace SendExplorer.utilities
{
    public static class Bundle
    {
        private const string CssMimeType = "text/css";
        private const string JsMimeType = "application/x-javascript";
        private static readonly ConcurrentDictionary<int, AssetBundle> BundleCache = new ConcurrentDictionary<int, AssetBundle>();

        public static Response Styles(this IResponseFormatter formatter, IEnumerable<string> files, IRootPathProvider rootPathProvider)
        {
            return formatter.GetBundle(files, rootPathProvider, CssMimeType);
        }

        public static Response Scripts(this IResponseFormatter formatter, IEnumerable<string> files, IRootPathProvider rootPathProvider)
        {
            return formatter.GetBundle(files, rootPathProvider, JsMimeType);
        }

        public static Response GetBundle(this IResponseFormatter formatter, IEnumerable<string> files,
            IRootPathProvider rootPathProvider, string contentType)
        {
            var hash = BundleHash(files, rootPathProvider);
            if (BundleCache.ContainsKey(hash) == false)
            {
                var text = ConcatTextFiles(files, rootPathProvider);
                var bytes = Encoding.UTF8.GetBytes(text);
                var lastWriteTimeUtc = DateTime.UtcNow;
                var etag = string.Concat("\"", lastWriteTimeUtc.Ticks.ToString("x"), "\"");
                var assetBundle = new AssetBundle {LastUpdate = lastWriteTimeUtc, ETag = etag, Bytes = bytes};
                BundleCache.TryAdd(hash, assetBundle);
            }
            var bundle = BundleCache[hash];

            return (CacheHelpers.ReturnNotModified(bundle.ETag, bundle.LastUpdate, formatter.Context))
                ? ResponseNotModified()
                : ResponseFromBundle(bundle, contentType);
        }

        public static async Task<Response> StylesAsync(this IResponseFormatter formatter, IEnumerable<string> files, IRootPathProvider rootPathProvider)
        {
            return await formatter.GetBundleAsync(files, rootPathProvider, CssMimeType);
        }

        public static async Task<Response> ScriptsAsync(this IResponseFormatter formatter, IEnumerable<string> files, IRootPathProvider rootPathProvider)
        {
            return await formatter.GetBundleAsync(files, rootPathProvider, JsMimeType);
        }

        public static async Task<Response> GetBundleAsync(this IResponseFormatter formatter, IEnumerable<string> files,
            IRootPathProvider rootPathProvider, string contentType)
        {
            var responseTask = new Task<Response>(() => GetBundle(formatter, files, rootPathProvider, contentType));
            responseTask.Start();
            return await responseTask;
        }

        private static int BundleHash(IEnumerable<string> files, IRootPathProvider rootPathProvider)
        {
            return files
                .Select(file => FullPath(file, rootPathProvider))
                .Select(file => new FileInfo(file).LastWriteTimeUtc.GetHashCode() ^ file.GetHashCode())
                .Aggregate((a, b) => a ^ b);
        }

        private static Response ResponseNotModified()
        {
            return new Response
            {
                StatusCode = HttpStatusCode.NotModified,
                ContentType = null,
                Contents = Response.NoBody
            };
        }

        private static Response ResponseFromBundle(AssetBundle assetBundle, string contentType)
        {
            var stream = new MemoryStream(assetBundle.Bytes);
            var response = new StreamResponse(() => stream, contentType);
            response.Headers["ETag"] = assetBundle.ETag;
            response.Headers["Last-Modified"] = assetBundle.LastUpdate.ToString("R");
            return response;
        }

        private static string ConcatTextFiles(IEnumerable<string> files, IRootPathProvider rootPathProvider)
        {
            return string.Join(Environment.NewLine, files.Select(p => ReadTextFile(p, rootPathProvider)));
        }

        private static string ReadTextFile(string path, IRootPathProvider rootPathProvider)
        {
            return File.ReadAllText(FullPath(path, rootPathProvider));
        }

        private static string FullPath(string path, IRootPathProvider rootPathProvider)
        {
            return (Path.Combine(rootPathProvider.GetRootPath(), path));
        }

        public class AssetBundle
        {
            public DateTime LastUpdate { get; set; }
            public string ETag { get; set; }
            public byte[] Bytes { get; set; }
        }
    }
}

Blog post: http://mike-ward.net/blog/post/00907/asset-bundling-in-nancyfx-ndash-part-2