MVC4 StyleBundle not resolving images

Question

According to this thread on MVC4 css bundling and image references, if you define your bundle as:

bundles.Add(new StyleBundle("~/Content/css/jquery-ui/bundle")
                   .Include("~/Content/css/jquery-ui/*.css"));

Where you define the bundle on the same path as the source files that made up the bundle, the relative image paths will still work. The last part of the bundle path is really the file name for that specific bundle (i.e., /bundle can be any name you like).

This will only work if you are bundling together CSS from the same folder (which I think makes sense from a bundling perspective).

Update

As per the comment below by @Hao Kung, alternatively this may now be achieved by applying a CssRewriteUrlTransformation (Change relative URL references to CSS files when bundled).

NOTE: I have not confirmed comments regarding issues with rewriting to absolute paths within a virtual directory, so this may not work for everyone (?).

bundles.Add(new StyleBundle("~/Content/css/jquery-ui/bundle")
                   .Include("~/Content/css/jquery-ui/*.css",
                    new CssRewriteUrlTransform()));

Grinn / ThePirat solution works well.

I did not like that it new'd the Include method on bundle, and that it created temporary files in the content directory. (they ended up getting checked in, deployed, then the service wouldn't start!)

So to follow the design of Bundling, I elected to perform essentially the same code, but in an IBundleTransform implementation::

class StyleRelativePathTransform
    : IBundleTransform
{
    public StyleRelativePathTransform()
    {
    }

    public void Process(BundleContext context, BundleResponse response)
    {
        response.Content = String.Empty;

        Regex pattern = new Regex(@"url\s*\(\s*([""']?)([^:)]+)\1\s*\)", RegexOptions.IgnoreCase);
        // open each of the files
        foreach (FileInfo cssFileInfo in response.Files)
        {
            if (cssFileInfo.Exists)
            {
                // apply the RegEx to the file (to change relative paths)
                string contents = File.ReadAllText(cssFileInfo.FullName);
                MatchCollection matches = pattern.Matches(contents);
                // Ignore the file if no match 
                if (matches.Count > 0)
                {
                    string cssFilePath = cssFileInfo.DirectoryName;
                    string cssVirtualPath = context.HttpContext.RelativeFromAbsolutePath(cssFilePath);
                    foreach (Match match in matches)
                    {
                        // this is a path that is relative to the CSS file
                        string relativeToCSS = match.Groups[2].Value;
                        // combine the relative path to the cssAbsolute
                        string absoluteToUrl = Path.GetFullPath(Path.Combine(cssFilePath, relativeToCSS));

                        // make this server relative
                        string serverRelativeUrl = context.HttpContext.RelativeFromAbsolutePath(absoluteToUrl);

                        string quote = match.Groups[1].Value;
                        string replace = String.Format("url({0}{1}{0})", quote, serverRelativeUrl);
                        contents = contents.Replace(match.Groups[0].Value, replace);
                    }
                }
                // copy the result into the response.
                response.Content = String.Format("{0}\r\n{1}", response.Content, contents);
            }
        }
    }
}

And then wrapped this up in a Bundle Implemetation:

public class StyleImagePathBundle 
    : Bundle
{
    public StyleImagePathBundle(string virtualPath)
        : base(virtualPath)
    {
        base.Transforms.Add(new StyleRelativePathTransform());
        base.Transforms.Add(new CssMinify());
    }

    public StyleImagePathBundle(string virtualPath, string cdnPath)
        : base(virtualPath, cdnPath)
    {
        base.Transforms.Add(new StyleRelativePathTransform());
        base.Transforms.Add(new CssMinify());
    }
}

Sample Usage:

static void RegisterBundles(BundleCollection bundles)
{
...
    bundles.Add(new StyleImagePathBundle("~/bundles/Bootstrap")
            .Include(
                "~/Content/css/bootstrap.css",
                "~/Content/css/bootstrap-responsive.css",
                "~/Content/css/jquery.fancybox.css",
                "~/Content/css/style.css",
                "~/Content/css/error.css",
                "~/Content/validation.css"
            ));

Here is my extension method for RelativeFromAbsolutePath:

   public static string RelativeFromAbsolutePath(this HttpContextBase context, string path)
    {
        var request = context.Request;
        var applicationPath = request.PhysicalApplicationPath;
        var virtualDir = request.ApplicationPath;
        virtualDir = virtualDir == "/" ? virtualDir : (virtualDir + "/");
        return path.Replace(applicationPath, virtualDir).Replace(@"\", "/");
    }

Better yet (IMHO) implement a custom Bundle that fixes the image paths. I wrote one for my app.

using System;
using System.Collections.Generic;
using IO = System.IO;
using System.Linq;
using System.Text.RegularExpressions;
using System.Web;
using System.Web.Optimization;

...

public class StyleImagePathBundle : Bundle
{
    public StyleImagePathBundle(string virtualPath)
        : base(virtualPath, new IBundleTransform[1]
      {
        (IBundleTransform) new CssMinify()
      })
    {
    }

    public StyleImagePathBundle(string virtualPath, string cdnPath)
        : base(virtualPath, cdnPath, new IBundleTransform[1]
      {
        (IBundleTransform) new CssMinify()
      })
    {
    }

    public new Bundle Include(params string[] virtualPaths)
    {
        if (HttpContext.Current.IsDebuggingEnabled)
        {
            // Debugging. Bundling will not occur so act normal and no one gets hurt.
            base.Include(virtualPaths.ToArray());
            return this;
        }

        // In production mode so CSS will be bundled. Correct image paths.
        var bundlePaths = new List<string>();
        var svr = HttpContext.Current.Server;
        foreach (var path in virtualPaths)
        {
            var pattern = new Regex(@"url\s*\(\s*([""']?)([^:)]+)\1\s*\)", RegexOptions.IgnoreCase);
            var contents = IO.File.ReadAllText(svr.MapPath(path));
            if(!pattern.IsMatch(contents))
            {
                bundlePaths.Add(path);
                continue;
            }


            var bundlePath = (IO.Path.GetDirectoryName(path) ?? string.Empty).Replace(@"\", "/") + "/";
            var bundleUrlPath = VirtualPathUtility.ToAbsolute(bundlePath);
            var bundleFilePath = String.Format("{0}{1}.bundle{2}",
                                               bundlePath,
                                               IO.Path.GetFileNameWithoutExtension(path),
                                               IO.Path.GetExtension(path));
            contents = pattern.Replace(contents, "url($1" + bundleUrlPath + "$2$1)");
            IO.File.WriteAllText(svr.MapPath(bundleFilePath), contents);
            bundlePaths.Add(bundleFilePath);
        }
        base.Include(bundlePaths.ToArray());
        return this;
    }

}

To use it, do:

bundles.Add(new StyleImagePathBundle("~/bundles/css").Include(
  "~/This/Is/Some/Folder/Path/layout.css"));

...instead of...

bundles.Add(new StyleBundle("~/bundles/css").Include(
  "~/This/Is/Some/Folder/Path/layout.css"));

What it does is (when not in debug mode) looks for url(<something>) and replaces it with url(<absolute\path\to\something>). I wrote the thing about 10 seconds ago so it might need a little tweaking. I've taken into account fully-qualified URLs and base64 DataURIs by making sure there's no colons (:) in the URL path. In our environment, images normally reside in the same folder as their css files, but I've tested it with both parent folders (url(../someFile.png)) and child folders (url(someFolder/someFile.png).

It is not necessary to specify a transform or have crazy subdirectory paths. After much troubleshooting I isolated it to this "simple" rule (is it a bug?)...

If your bundle path does not start with relative root of the items being included, then the web application root will not be taken into account.

Sounds like more of a bug to me, but anyway that's how you fix it with the current .NET 4.51 version. Perhaps the other answers were necessary on older ASP.NET builds, can't say don't have time to retrospectively test all that.

To clarify, here is an example:

I have these files...

~/Content/Images/Backgrounds/Some_Background_Tile.gif
~/Content/Site.css  - references the background image relatively, i.e. background: url('Images/...')

Then setup the bundle like...

BundleTable.Add(new StyleBundle("~/Bundles/Styles").Include("~/Content/Site.css"));

And render it like...

@Styles.Render("~/Bundles/Styles")

And get the "behaviour" (bug), the CSS files themselves have the application root (e.g. "http://localhost:1234/MySite/Content/Site.css") but the CSS image within all start "/Content/Images/..." or "/Images/..." depending on whether I add the transform or not.

Even tried creating the "Bundles" folder to see if it was to do with the path existing or not, but that didn't change anything. The solution to the problem is really the requirement that the name of the bundle must start with the path root.

Meaning this example is fixed by registering and rendering the bundle path like..

BundleTable.Add(new StyleBundle("~/Content/StylesBundle").Include("~/Content/Site.css"));
...
@Styles.Render("~/Content/StylesBundle")

So of course you could say this is RTFM, but I am quite sure me and others picked-up this "~/Bundles/..." path from the default template or somewhere in documentation at MSDN or ASP.NET web site, or just stumbled upon it because actually it's a quite logical name for a virtual path and makes sense to choose such virtual paths which do not conflict with real directories.

Anyway, that's the way it is. Microsoft see no bug. I don't agree with this, either it should work as expected or some exception should be thrown, or an additional override to adding the bundle path which opts to include the application root or not. I can't imagine why anyone would not want the application root included when there was one (normally unless you installed your web site with a DNS alias/default web site root). So actually that should be the default anyway.