ASP.NET bundling/minification: including dynamically generated Javascript

Question

I have a site that dynamically generates Javascript. The generated code describes type-metadata and some server-side constants so that the clients can easily consume the server's services - so it's very cacheable.

The generated Javascript is served by an ASP.NET MVC controller; so it has a Uri; say ~/MyGeneratedJs.

I'd like to include this Javascript in a Javascript bundle with other static Javascript files (e.g. jQuery etc): so just like static files I want it to be referenced separately in debug mode and in minified form bundled with the other files in non-debug mode.

How can I include dynamically generated Javascript in a bundle?

Answer 1

With VirtualPathProviders this is now possible. Integration of dynamic content into the bundling process requires the following steps:

1. Writing the logic that requests / builds the required content. Generating content from Controller directly requires a bit of work:

   public static class ControllerActionHelper
   {
       public static string RenderControllerActionToString(string virtualPath)
       {
           HttpContext httpContext = CreateHttpContext(virtualPath);
           HttpContextWrapper httpContextWrapper = new HttpContextWrapper(httpContext);
   
           RequestContext httpResponse = new RequestContext()
           {
               HttpContext = httpContextWrapper,
               RouteData = RouteTable.Routes.GetRouteData(httpContextWrapper)
           };
   
           // Set HttpContext.Current if RenderActionToString is called outside of a request
           if (HttpContext.Current == null)
           {
               HttpContext.Current = httpContext;
           }
   
           IControllerFactory controllerFactory = ControllerBuilder.Current.GetControllerFactory();
           IController controller = controllerFactory.CreateController(httpResponse,
               httpResponse.RouteData.GetRequiredString("controller"));
           controller.Execute(httpResponse);
   
           return httpResponse.HttpContext.Response.Output.ToString();
       }
   
       private static HttpContext CreateHttpContext(string virtualPath)
       {
           HttpRequest httpRequest = new HttpRequest(string.Empty, ToDummyAbsoluteUrl(virtualPath), string.Empty);
           HttpResponse httpResponse = new HttpResponse(new StringWriter());
   
           return new HttpContext(httpRequest, httpResponse);
       }
   
       private static string ToDummyAbsoluteUrl(string virtualPath)
       {
           return string.Format("http://dummy.net{0}", VirtualPathUtility.ToAbsolute(virtualPath));
       }
   }
   

2. Implement a virtual path provider that wraps the existing one and intercept all virtual paths that should deliver the dynamic content.

   public class ControllerActionVirtualPathProvider : VirtualPathProvider
   {
       public ControllerActionVirtualPathProvider(VirtualPathProvider virtualPathProvider)
       {
           // Wrap an existing virtual path provider
           VirtualPathProvider = virtualPathProvider;
       }
   
       protected VirtualPathProvider VirtualPathProvider { get; set; }
   
       public override string CombineVirtualPaths(string basePath, string relativePath)
       {
           return VirtualPathProvider.CombineVirtualPaths(basePath, relativePath);
       }
   
       public override bool DirectoryExists(string virtualDir)
       {
           return VirtualPathProvider.DirectoryExists(virtualDir);
       }
   
       public override bool FileExists(string virtualPath)
       {
           if (ControllerActionHelper.IsControllerActionRoute(virtualPath))
           {
               return true;
           }
   
           return VirtualPathProvider.FileExists(virtualPath);
       }
   
       public override CacheDependency GetCacheDependency(string virtualPath, IEnumerable virtualPathDependencies,
           DateTime utcStart)
       {
           AggregateCacheDependency aggregateCacheDependency = new AggregateCacheDependency();
   
           List<string> virtualPathDependenciesCopy = virtualPathDependencies.Cast<string>().ToList();
   
           // Create CacheDependencies for our virtual Controller Action paths
           foreach (string virtualPathDependency in virtualPathDependenciesCopy.ToList())
           {
               if (ControllerActionHelper.IsControllerActionRoute(virtualPathDependency))
               {
                   aggregateCacheDependency.Add(new ControllerActionCacheDependency(virtualPathDependency));
                   virtualPathDependenciesCopy.Remove(virtualPathDependency);
               }
           }
   
           // Aggregate them with the base cache dependency for virtual file paths
           aggregateCacheDependency.Add(VirtualPathProvider.GetCacheDependency(virtualPath, virtualPathDependenciesCopy,
               utcStart));
   
           return aggregateCacheDependency;
       }
   
       public override string GetCacheKey(string virtualPath)
       {
           return VirtualPathProvider.GetCacheKey(virtualPath);
       }
   
       public override VirtualDirectory GetDirectory(string virtualDir)
       {
           return VirtualPathProvider.GetDirectory(virtualDir);
       }
   
       public override VirtualFile GetFile(string virtualPath)
       {
           if (ControllerActionHelper.IsControllerActionRoute(virtualPath))
           {
               return new ControllerActionVirtualFile(virtualPath,
                   new MemoryStream(Encoding.Default.GetBytes(ControllerActionHelper.RenderControllerActionToString(virtualPath))));
           }
   
           return VirtualPathProvider.GetFile(virtualPath);
       }
   
       public override string GetFileHash(string virtualPath, IEnumerable virtualPathDependencies)
       {
           return VirtualPathProvider.GetFileHash(virtualPath, virtualPathDependencies);
       }
   
       public override object InitializeLifetimeService()
       {
           return VirtualPathProvider.InitializeLifetimeService();
       }
   }
   
   public class ControllerActionVirtualFile : VirtualFile
   {
       public CustomVirtualFile (string virtualPath, Stream stream)
           : base(virtualPath)
       {
           Stream = stream;
       }
   
       public Stream Stream { get; private set; }
   
       public override Stream Open()
       {
            return Stream;
       }
   }
   

   You also have to implement CacheDependency if you need it:

   public class ControllerActionCacheDependency : CacheDependency
   {
       public ControllerActionCacheDependency(string virtualPath, int actualizationTime = 10000)
       {
           VirtualPath = virtualPath;
           LastContent = GetContentFromControllerAction();
   
           Timer = new Timer(CheckDependencyCallback, this, actualizationTime, actualizationTime);
       }
   
       private string LastContent { get; set; }
   
       private Timer Timer { get; set; }
   
       private string VirtualPath { get; set; }
   
       protected override void DependencyDispose()
       {
           if (Timer != null)
           {
               Timer.Dispose();
           }
   
           base.DependencyDispose();
       }
   
       private void CheckDependencyCallback(object sender)
       {
           if (Monitor.TryEnter(Timer))
           {
               try
               {
                   string contentFromAction = GetContentFromControllerAction();
   
                   if (contentFromAction != LastContent)
                   {
                       LastContent = contentFromAction;
                       NotifyDependencyChanged(sender, EventArgs.Empty);
                   }
               }
               finally
               {
                   Monitor.Exit(Timer);
               }
           }
       }
   
       private string GetContentFromControllerAction()
       {
           return ControllerActionHelper.RenderControllerActionToString(VirtualPath);
       }
   }
   

3. Register your virtual path provider:

   public static void RegisterBundles(BundleCollection bundles)
   {
       // Set the virtual path provider
       BundleTable.VirtualPathProvider = new ControllerActionVirtualPathProvider(BundleTable.VirtualPathProvider);
   
       bundles.Add(new Bundle("~/bundle")
           .Include("~/Content/static.js")
           .Include("~/JavaScript/Route1")
           .Include("~/JavaScript/Route2"));
   }
   

4. Optional: Add Intellisense support to your views. Use <script> tags within your View and let them be removed by a custom ViewResult:

   public class DynamicContentViewResult : ViewResult
   {
       public DynamicContentViewResult()
       {
           StripTags = false;
       }
   
       public string ContentType { get; set; }
   
       public bool StripTags { get; set; }
   
       public string TagName { get; set; }
   
       public override void ExecuteResult(ControllerContext context)
       {
           if (context == null)
           {
               throw new ArgumentNullException("context");
           }
   
           if (string.IsNullOrEmpty(ViewName))
           {
               ViewName = context.RouteData.GetRequiredString("action");
           }
   
           ViewEngineResult result = null;
   
           if (View == null)
           {
               result = FindView(context);
               View = result.View;
           }
   
           string viewResult;
   
           using (StringWriter viewContentWriter = new StringWriter())
           {
               ViewContext viewContext = new ViewContext(context, View, ViewData, TempData, viewContentWriter);
   
               View.Render(viewContext, viewContentWriter);
   
               if (result != null)
               {
                   result.ViewEngine.ReleaseView(context, View);
               }
   
               viewResult = viewContentWriter.ToString();
   
               // Strip Tags
               if (StripTags)
               {
                   string regex = string.Format("<{0}[^>]*>(.*?)</{0}>", TagName);
                   Match res = Regex.Match(viewResult, regex,
                       RegexOptions.IgnoreCase | RegexOptions.IgnorePatternWhitespace | RegexOptions.Multiline | RegexOptions.Singleline);
   
                   if (res.Success && res.Groups.Count > 1)
                   {
                       viewResult = res.Groups[1].Value;
                   }
                   else
                   {
                       throw new InvalidProgramException(
                           string.Format("Dynamic content produced by View '{0}' expected to be wrapped in '{1}' tag.", ViewName, TagName));
                   }
               }
           }
   
           context.HttpContext.Response.ContentType = ContentType;
           context.HttpContext.Response.Output.Write(viewResult);
       }
   }
   

   Use an extension method or add an helper function to your controller:

   public static DynamicContentViewResult JavaScriptView(this Controller controller, string viewName, string masterName, object model)
   {
       if (model != null)
       {
           controller.ViewData.Model = model;
       }
   
       return new DynamicContentViewResult
       {
           ViewName = viewName,
           MasterName = masterName,
           ViewData = controller.ViewData,
           TempData = controller.TempData,
           ViewEngineCollection = controller.ViewEngineCollection,
           ContentType = "text/javascript",
           TagName = "script",
           StripTags = true
       };
   }
   

The steps are similiar for other type of dynamic contents. See Bundling and Minification and Embedded Resources for example.

I added a proof of concept repository to GitHub if you want to try it out.

Answer 2

Darin is right, currently bundling only works on static files. But if you can add a placeholder file with up to date content, bundling does setup file change notifications which will detect automatically when the placeholder file changes.

Also we are going to be moving to using VirtualPathProviders soon which might be a way to serve dynamically generated content.

Update: The 1.1-alpha1 release is out now which has support for VPP

Answer 3

This is not possible. Bundles work only with static files.