Posts tagged with rss

Behind the scenes at xbox.com – RSS enabling web marketplace

A number of people were requesting additional RSS feeds for the xbox.com web marketplace. (We had just one that included all new arrivals)

Looking across our site as the various lists of products we display today the significant views are:

  • Browse games by department
  • Search results
  • Promotions (e.g. Deal of the week)
  • Game detail (shows downloads available beneath it)
  • Avatar item browse

These views also have sorting options and a set of filters available for things like product type, game genre, content rating etc.

So we had a couple of options:

  1. Write controller actions that expose the results of specific queries as RSS
  2. Introduce a mechanism whereby any of our product result pages can render as RSS including any user-defined filtering

Our web marketplace is written in ASP.NET MVC (like most of xbox.com) so while option 1 sounds simpler MVC really helps us make option 2 more attractive by way of a useful feature called ActionFilters that let us jump in and reshape the way existing actions behave.

ActionFilters

ActionFilters can be applied to either to an individual action method on a controller or to the controller class itself which applies it to all the actions on that controller. They provide hooks into the processing pipeline where you can jump in and perform additional processing.

The most interesting events are:

  • OnActionExecuting
  • OnActionExecuted
  • OnResultExecuting
  • OnResultExecuted

We’re going to hook in to the OnActionExecuted step – this is because we always want to run after the code in the controller action has executed but before the ActionResult has done it’s work – i.e. before page or RSS rendering.

Writing our ActionFilter

The first thing we want to do is identify that a request wants the RSS version. One way is to read the accepts header and switch when it requests mime/type but this can be a little trickier to test,  another is to append a query parameter on the url which is very easy to test.

Once we’ve identified the incoming request should be for RSS we need to identify the data we want to turn into RSS and re-purpose it.

All the views we identified at the start of this post share a common rendering mechanism and each view model sub-classes from one of our base models. For simplicity though we’ll imagine an interface that just exposes an IEnumerable property.

public class RssEnabledAttribute : ActionFilterAttribute {
  public override void OnActionExecuted(ActionExecutedContext filterContext) {
    var viewModel = filterContext.Controller.ViewData.Model as IProductResultViewModel;
    if (viewModel == null)
        return;

    var rssFeedTitle = FeedHelper.MakeTitle(viewModel.Results);
    filterContext.Controller.ViewData.Add("RssFeedTitle", rssFeedTitle);

    var format = filterContext.RequestContext.HttpContext.Request.QueryString["format"];
    if (format == "rss" && rssFeedTitle != null) {
      var urlHelper = new UrlHelper(filterContext.RequestContext);
      var url = QueryStringUtility.RemoveQueryStringParameter(filterContext.RequestContext.HttpContext.Request.Url.ToString(), "format");
      var feedItems = FeedHelper.GetSyndicationItems(viewModel.Results, urlHelper);
      filterContext.Result = FeedHelper.CreateProductFeed(rssFeedTitle, viewModel.Description, new Uri(url), feedItems);
    }

    base.OnActionExecuted(filterContext);
  }
}

This class relies on our FeedHelper class to achieve three things it needs:

  1. MakeTitle takes the request details – i.e. which page, type of products, filtering and sorting is selected and makes a title by re-using our breadcrumbs
  2. GetSyndicationItems takes the IEnumerable and turns it into IEnumerable by way of a foreach projecting Product into SyndicationItem with some basic HTML formatting, combining the product image and setting the correct category (with a yield thrown in for good measure)
  3. CreateProductFeed then creates a Syndication feed with the appropriate Copyright and Language set and chooses the formatter – in our case RSS 2.0 but could easily be Atom 1.0, e.g.
public static SyndicationFeedResult CreateProductFeed(string title, string description, Uri link, IEnumerable<SyndicationItem> syndicationItems)
{
    var feed = new SyndicationFeed(title, description, link, syndicationItems) {
        Copyright = new TextSyndicationContent(String.Format(Resources.FeedCopyrightFormat, DateTime.Now.Year)),
        Language = CultureInfo.CurrentUICulture.Name
    };

    return new FeedResult(new Rss20FeedFormatter(feed, false));
}

The FeedResult class is a simple one that takes the built-in .NET SyndicationFeed class and wires it up to MVC by implementing an ActionResult that writes the XML of the SyndicationFeedFormatter into the response as well as setting the application/rss+xml content type and encoding.

Advertising the feed in the head

Now that we have the ability to serve up RSS we need to let browsers know it exists.

The ActionFilter we wrote above needs to know the title of the RSS feed regardless of whether it is rendering the RSS (which needs a title) or rendering the page (which will need to advertise the RSS title) so it always calculates it and then puts it into the ViewData dictionary with the key RssFeedTitle.

Now finally our site’s master page can check for the existence of that key/value pair and advertise it out with a simple link tag:

var rssFeedTitle = ViewData["RssFeedTitle"] as string;
if (!String.IsNullOrEmpty(rssFeedTitle)) { %>
<link rel="alternate" type="application/rss+xml" title="<%:rssFeedTitle%>" href="<%:Url.ForThisAsRssFeed%>" />
<% }

This code requires just one more thing – a very small UrlHelper which will append “format=rss” to the query string (taking into account whether there existing query parameters or not).

The result of this is we can now just add [RssEnabled] in front of any controller or action to turn on RSS feeds for that portion of our marketplace! :)

[)amien

Creating RSS feeds in ASP.NET MVC

ASP.NET MVC is the technology that brought me to Microsoft and the west-coast and it’s been fun getting to grips with it these last few weeks.

Last week I needed to expose RSS feeds and checked out some examples online but was very disappointed.

If you find yourself contemplating writing code to solve technical problems rather than the specific business domain you work in you owe it to your employer and fellow developers to see what exists before churning out code to solve it.

The primary excuse (and I admit to using it myself) is “X is too bloated, I only need a subset. I can write that quicker than learn their solution.” but a quick reality check:

  • Time – code always takes longer than you think
  • Bloat – indicates the problem is more complex than you realize
  • Growth – todays requirements will grow tomorrow
  • Maintenance – fixing code outside your business domain
  • Isolation – nobody coming in will know your home-grown solution

The RSS examples I found had their own ‘feed’ and ‘items’ classes and implemented flaky XML rendering by themselves or as MVC view pages.

If these people had spent a little time doing some research they would have discovered .NET’s built in SyndicatedFeed and SyndicatedItem class for content and two classes (Rss20FeedFormatter and Atom10FeedFormatter )  to handle XML generation with correct encoding, formatting and optional fields.

All that is actually required is a small class to wire up these built-in classes to MVC.

using System;
using System.ServiceModel.Syndication;
using System.Text;
using System.Web;
using System.Web.Mvc;
using System.Xml;

namespace MyApplication.Something
{
  public class FeedResult : ActionResult {
    public Encoding ContentEncoding { get; set; }
    public string ContentType { get; set; }

    private readonly SyndicationFeedFormatter feed;
    public SyndicationFeedFormatter Feed{
      get { return feed; }
    }

    public FeedResult(SyndicationFeedFormatter feed) {
      this.feed = feed;
    }

    public override void ExecuteResult(ControllerContext context) {
      if (context == null)
        throw new ArgumentNullException("context");

      var response = context.HttpContext.Response;
      response.ContentType = !string.IsNullOrEmpty(ContentType) ? ContentType : "application/rss+xml";

      if (ContentEncoding != null)
        response.ContentEncoding = ContentEncoding;

      if (feed != null) {
        using (var xmlWriter = new XmlTextWriter(response.Output)) {
          xmlWriter.Formatting = Formatting.Indented;
          feed.WriteTo(xmlWriter);
        }
      }
    }
  }
}

In a controller that supplies RSS feed simply project your data onto SyndicationItems and create a SyndicationFeed then return a FeedResult with the FeedFormatter of your choice.

public ActionResult NewPosts() {
  var blog = data.Blogs.SingleOrDefault();
  var postItems = data.Posts.Where(p => p.Blog = blog)
    .OrderBy(p => p.PublishedDate)
    .Take(25)
    .Select(p => new SyndicationItem(p.Title, p.Content, new Uri(p.Url)));

  var feed = new SyndicationFeed(blog.Title, blog.Description, new Uri(blog.Url) , postItems) {
    Copyright = blog.Copyright,
    Language = "en-US"
  };

  return new FeedResult(new Rss20FeedFormatter(feed));
}

This also has a few additional advantages:

  1. Unit tests can ensure the ActionResult is a FeedResult
  2. Unit tests can examine the Feed property to examine results without parsing XML
  3. Switching to Atom format involved just changing the new Rss20FeedFormatter to Atom10FeedFormatter

[)amien

Google Reader – contender for the online aggregator throne?

Screenshot of Google ReaderI wrote a while back about how Rojo’s upgrade was a disaster and that it had led me to look for alternatives.

Bloglines didn’t have the same feeling of a polished interface that Rojo has tempted me with but unlike Rojo but it has been happily consuming the feeds of all my sites and presenting them without fuss or issue since I started using it a few weeks ago.

I got back from London this weekend and found that Google has finally upgraded the user interface for their online reader offering to something on-par with some of the others (at last!)

Apart from looking like Google Mail it also has a great feature whereby as you scroll down items it highlights the current one and if you scroll past it then it assumes it has been read.

This is great compared to the “I’ve read everything in this group” button of Rojo and Bloglines “Well you clicked group X that had 100 posts so I’m assuming it’s read”.

Another cool feature seems to be the response time at which Google Reader picks up articles. It even picked up this article within 3 minutes on my little blog.

Of course the best part of all this is thanks to the guys behind OPML moving from one reader to another is just a case of exporting from one and importing to another – even groups are preserved.

[)amien

Rojo – how not to publish updates to your site

Rojo has been my favorite on-line reader for a while despite the annoyances and quirks but this weekends ‘upgrade’ got me wondering how incompetent the team behind it is and what exactly Six Apart have purchased.

There were a couple of problems before the upgrade – the one most users would have seen is the crazy unread counts which are almost always wrong – but you can learn to live with that.

The second problem was Rojo failing to pull feeds in – if you drill down and there’s nothing to read you are given the “This feed is failing” message which tells you zip about what they think is wrong.

In the case of DamienG.com’s RSS feed I was told by their support staff this was because they couldn’t connect to my server. GrinGod created a feed to my site’s Atom feed that was still updating so that excuse was shot down quite quickly.

It’s not just me either – major big blogs such as blogs.msdn.com would sit for hours with the same message before springing back into life.

Then came this weekends upgrade.

I have some experience with publishing code to commercial sites. This is the sort of plan we use:

  1. Install and configure secondary set of servers
  2. Load software to be tested onto those servers
  3. Let internal testers loose on them
  4. Let trusted end users loose on them
  5. Run load testing software to ensure performance
  6. Repeat until it passes
  7. Schedule the switch with the appropriate teams
  8. Make an announcement
  9. Switch over to the new servers

But the team at Rojo went with a different approach. As far as I can tell here was theirs:

  1. Take current servers off-line with a notice
  2. Load software for 20 hours
  3. Bring servers back on-line

I certainly don’t see testing on that plan.

Even basic developer-level testing should have spotted that the lower “Mark Page Read” link is missing a javascript: prefix rendering it a useless link to a 404, the fact that the “Mark Feed Read” isn’t refreshing the page along with “Add Mojo” too.

“Show unread only” may as well read “Show nothing” as that’s what it’s doing.

These aren’t boundary conditions but primary use-case scenario’s that are failing.

To cap it all now every single feed has disappeared in the last half-hour.

It has been reported that Rojo have raised at least $3.5 million in venture capital so why their software development process looks like an inexperienced developer publishing from his laptop is anyone’s guess.

[)amien