MVC Bundling and Minification: converts embedded images to to URL paths

If you don't want to extract the embedded images to actual files and you can't wait for a new version of the Microsoft.AspNet.Web.Optimization nuget, you can use the following class.

It's a verbatim copy of CssRewriteUrlTransform except it ignores (crudely ;)) URL's with the data URI syntax.

Gist: https://gist.github.com/janv8000/fa69b2ab6886f635e3df

/// <remarks>Part of Microsoft.AspNet.Web.Optimization.1.1.3, forked to ignore data-uri</remarks>
public class CssRewriteUrlTransformIgnoringDataUri : IItemTransform
{
    internal static string RebaseUrlToAbsolute(string baseUrl, string url)
    {
        if (string.IsNullOrWhiteSpace(url) || string.IsNullOrWhiteSpace(baseUrl) || url.StartsWith("/", StringComparison.OrdinalIgnoreCase))
            return url;
        if (!baseUrl.EndsWith("/", StringComparison.OrdinalIgnoreCase))
            baseUrl = baseUrl + "/";
        return VirtualPathUtility.ToAbsolute(baseUrl + url);
    }

    internal static string ConvertUrlsToAbsolute(string baseUrl, string content)
    {
        if (string.IsNullOrWhiteSpace(content))
        { return content; }

        return new Regex("url\\(['\"]?(?<url>[^)]+?)['\"]?\\)").Replace(content, match =>
        {
            var format = match.Groups["url"].Value;
            if (format.StartsWith("data:image", StringComparison.CurrentCultureIgnoreCase))
            {
                return format;
            }

            return "url(" + RebaseUrlToAbsolute(baseUrl, format) + ")";
        });
    }

    public string Process(string includedVirtualPath, string input)
    {
        if (includedVirtualPath == null)
        {
            throw new ArgumentNullException("includedVirtualPath");
        }
        return ConvertUrlsToAbsolute(VirtualPathUtility.GetDirectory(includedVirtualPath.Substring(1)), input);
    }
}

Scrap that question. This is a known bug. Currently work around is to separate your css into embedded images and images via url.

Vote for these work-items: https://aspnetoptimization.codeplex.com/workitem/88 and https://aspnetoptimization.codeplex.com/workitem/108

Checkout my workaround which I've 'bundled' nicely into a NuGet package. https://github.com/benmccallum/AspNetBundling

Otherwise just upgrade to grunt/gulp ;)