How to prevent User-Agent: Eureka/1 to return source code

Question

ASP.NET Mono MVC 4 application uses MVC4 built in bundling and minification for css and js files.

If user agent string in request is changed to Eureka/1 using fiddler

User-Agent: Eureka/1

and request is re-issued, whole source code with all comments are sent to client.

How to prevent this so that comments in source code code cannot inspected by client ?

Source: http://www.codeproject.com/Articles/728146/ASP-NET-MVC-bundles-internals

I tried to add debug='false' to web.config but problem persists.

Answer 1

I was able to remove comments by creating a classes that inherit from IBundleBuilder. This is written for Microsoft ASP.NET Web Optimization Framework 1.1.3 which was updated on 2/20/2014:

public class ScriptBundleBuilder : IBundleBuilder
{
    public virtual string BuildBundleContent(Bundle bundle, BundleContext context, IEnumerable<BundleFile> files)
    {
        var content = new StringBuilder();
        foreach (var file in files)
        {
            FileInfo f = new FileInfo(HttpContext.Current.Server.MapPath(file.VirtualFile.VirtualPath));
            Microsoft.Ajax.Utilities.CodeSettings settings = new Microsoft.Ajax.Utilities.CodeSettings();
            settings.RemoveUnneededCode = true;
            settings.StripDebugStatements = true;
            settings.PreserveImportantComments = false;
            settings.TermSemicolons = true;
            var minifier = new Microsoft.Ajax.Utilities.Minifier();
            content.Append(minifier.MinifyJavaScript(Read(f), settings));
        }

        return content.ToString();
    }

    private string Read(FileInfo file)
    {
        using (var r = file.OpenText())
        {
            return r.ReadToEnd();
        }
    }
} 

public class StyleBundleBuilder : IBundleBuilder
{
    public virtual string BuildBundleContent(Bundle bundle, BundleContext context, IEnumerable<BundleFile> files)
    {
        var content = new StringBuilder();
        foreach (var file in files)
        {   
            FileInfo f = new FileInfo(HttpContext.Current.Server.MapPath(file.VirtualFile.VirtualPath));
            Microsoft.Ajax.Utilities.CssSettings settings = new Microsoft.Ajax.Utilities.CssSettings();
            settings.CommentMode = Microsoft.Ajax.Utilities.CssComment.None;
            var minifier = new Microsoft.Ajax.Utilities.Minifier();
            content.Append(minifier.MinifyStyleSheet(Read(f), settings));
        }

        return content.ToString();
    }

    private string Read(FileInfo file)
    {
        using (var r = file.OpenText())
        {
            return r.ReadToEnd();
        }
    }
} 

And then telling the bundle to use this builder. This example is for a StyleBundle:

public static void RegisterBundles(BundleCollection bundles)
{
    var bundle = new StyleBundle("~/Content/themes/base/css");
    bundle.Builder = new StyleBundleBuilder();
    bundle.Include("~/Content/themes/base/jquery.ui.core.css",
        "~/Content/themes/base/jquery.ui.resizable.css",
        //etc
        );
    bundles.Add(bundle);

    var scriptBundle = new ScriptBundle("~/bundles/modernizr");
    scriptBundle.Builder = new ScriptBundleBuilder();
    scriptBundle.Include("~/Scripts/modernizr-*");
    bundles.Add(scriptBundle);

    BundleTable.EnableOptimizations = true; //for testing
}

This was tested/confirmed in Chrome by changing the user-agent to Eureka/1.0.

For at least some previous versions of the Web Optimization framework (1.0 and prior I think), the only difference was the final parameter. So it would look like public virtual string BuildBundleContent(Bundle bundle, BundleContext context, IEnumerable<FileInfo> files) and requires only minor changes to make work... though you're likely better off just updating.

Concerning this problem and one brought up in another recent SO post about how licensing information gets stripped out during minification... I made a NuGet Package to address these issues.

Answer 2

I know the question is regarding changing the behaviour of the bundle process in MVC, but as an alternative, you could create build/deploy scripts that minify your CSS/JS before being published. You could use some of the applications in this answer