RSS feed class in C#

Question

How can I make this more readable?

public class RssFeed
{

    string url = "http://www.pwop.com/feed.aspx?show=dotnetrocks&filetype=master";

    public string responseBody;

    private string DATE_FORMAT = "ddd, dd MMM yyyy HH:mm:ss \\E\\D\\T";

    public Story[] Getstories()
    {
        getContent();
        var stories = Parse(responseBody);
        return GetMostRecent5(stories, new StoryComparer());
    }

    public void getContent()
    {
        HttpWebRequest req = WebRequest.Create(url) as HttpWebRequest;
        WebResponse response = req.GetResponse();
        StreamReader sr = new StreamReader(response.GetResponseStream());
        responseBody = sr.ReadToEnd();
    }

    static Story[] Parse(string content)
    {
        var items = new List<string>();
        int start = 0;
        while (true)
        {

            var nextItemStart = content.IndexOf("<item>", start);
            var nextItemEnd = content.IndexOf("</item>", nextItemStart);
            if (nextItemStart < 0 || nextItemEnd < 0) break;

            String nextItem = content.Substring(nextItemStart, nextItemEnd + 7 - nextItemStart);
            items.Add(nextItem);
            start = nextItemEnd;
        }

        var stories = new List<Story>();
        for (byte i = 0; i < items.Count; i++)
        {
            stories.Add(new Story() {
                title = Regex.Match(items[i], "(?<=<title>).*(?=</title>)").Value,
                link = Regex.Match(items[i], "(?<=<link>).*(?=</link>)").Value,
                date = Regex.Match(items[i], "(?<=<pubDate>).*(?=</pubdate>)").Value
            });                
        }

        return stories.ToArray();
    }

    private static T[] GetMostRecent5<T>(T[] stories, IComparer<T> comparer)
    {
        List<T> recentStories = stories.Take(5).ToList();

        recentStories.Sort(comparer);

        var recentStoriesArray = new T[5];
        for (int i = 0; i <= 5; i++)
        {
            recentStoriesArray[i] = recentStories[i];
        }
        return recentStoriesArray;
    }

    public class Story
    {
        public string title;
        public string link;
        public string date;

        public override bool Equals(object obj)
        {
            return this.Equals(obj as Story);
        }

        public bool Equals(Story story)
        {
            return this.link == story.link;
        }
    }

    private class StoryComparer : IComparer<Story>
    {
        public int Compare(Story x, Story y)
        {
            if (x.Equals(y))
                return 0;
            //redundant else
            else
                return x.date.CompareTo(y.date);
        }
    }
}

Answer 1

Not that ugly. I've seen ugly code, and trust me, this is not ugly.

However, this is kind of a "God Class" that has more than a single responsibility, hence it violates SRP principle.

How to improve

Separate the class to:

ContentFetcher, which is responsible for fetching only

StoryParser, which parses the content and creates instances of your object model (Story[])

Both of the above should implement the Try.. pattern, so that the single method in the ContentFetcher has the following signature:

bool TryFetch(out string content){ /* code */ }

The same goes for StoryParser.

As for the fetcher itself

1. You can choose if the URL is either injected in the constructor, or is part of the method signature. Modern OOP coding is biased towards the constructor technique.

2. The code should implement the using (...) { ... } pattern for classes that implement the IDisposable interface, and be wrapped in a try-catch what so ever.

As for the parser itself

1. since rss is a format on top of xml, I don't think it's a good idea to parse it using regular expressions. Let the framework do the parsing by using either XmlDocument or XDocument. Or use an external library to parse the string for you (hopefully it's implemented by the above techniques, and not by using Regexes).

2. a try-catch might be needed here, too

Putting it all together

So finally, the class you have should use the above two classes (a fetcher and a parser), and then, getting the stories from the feed should look like this:

public Story[] Getstories()
{
    string content;
    if (!this.fetcher.TryGetContent(out content)) return null;
    Story[] stories;
    if (!this.parser.TryParse(out stories)) return null;        
    return GetMostRecent5(stories, new StoryComparer());
}

As you can see, null is a special value for failure. You can change that to TryGetStories which returns a boolean and and out parameter if you want to avoid the special value of null.

The actual instances of fetcher and parser can be created by the class itself (in the constructor) and/or be injected to the class by the constructor. Let's see the injection pattern:

public class RssFeed
{       
    private readonly ContentFetcher fetcher;
    private readonly StoryParser parser;

    public RssFeed(ContentFetcher fetcher, StoryParser parser)
    {
        if (null == fetcher) throw new ArgumentNullException("fetcher");
        if (null == parser) throw new ArgumentNullException("parser");
        this.fetcher = fetcher;
        this.parser = parser;
    }
}

As a final step of refactoring, you can extract the preparing code to its own method, moving the parsed stories to be part of the class' state:

private Story[] stories = null;

private bool Prepare()
{
    if (this.stories != null) return true;
    string content;
    if (!this.fetcher.TryGetContent(out content)) return false;
    Story[] temp;
    if (!this.parser.TryParse(out temp)) return false;
    this.stories = temp;
    return true;
}

public Story[] Getstories()
{
    if (!Prepare()) return null;
    return GetMostRecent5(this.stories, new StoryComparer());
}

Good luck!

Answer 2

To add to what Ron Klein said (in no particular order):

1. Use WebClient (or possibly HttpClient, if you're on .Net 4.5) instead of WebRequest and StreamReader, it will make your code simpler.
2. Consider using var more in your code (although this is a question of style and not everybody would agree with that).
3. If you know a method returns more specific type than its return type claims (such as WebRequest.Create() with HTTP URL), use cast instead of as. This way, if something goes wrong, you will immediately get a helpful InvalidCastException, instead of a confusing NullReferenceException later.
4. Use consistent naming conventions, ideally the ones recommended by Microsoft. (So, don't call one method getContent and another GetStories).
5. Consider using interfaces like IEnumerable<T> and IList<T> (and IReadOnlyList<T> if you're on .Net 4.5) instead of arrays. Arrays cannot change their length, but the items in them can change. Most of the time, this isn't what you want. You either want to allow mutating both the length and the individual items (in that case, use IList<T>), or don't allow mutating either (in that case use IEnumerable<T> or IReadOnlyList<T>).
6. A method like GetMostRecent5() is awfully specific, consider changing it to something like GetMostRecent() and passing the number as parameter.
7. Don't use fields the way you use responseBody. Instead use return value of the method (or out parameter, as Ron suggested).
8. Don't use regular expressions to parse XML, use an XML library, such as LINQ to XML. (Ron already mentioned this, but I think this is so important it bears repeating.)

Answer 3

A few additional things:

• Story should probably implement IEquatable<Story>, since you already have the method implementation present on the class.
• Since you are overriding Equals on Story, you should also override GetHashCode. The compiler should actually be giving you warnings about this already.
• Consider changing Story to expose its values as properties rather than public fields. This gives you the flexibility to change their underlying behavior later without breaking anyone referencing the class.
• Re: the XML parsing - I would agree with the sentiment that you should avoid Regex for this. You may consider using Data Contracts.
• If the date order is something you always want to use for stories, you may consider moving the comparison code to the Story class and mark it as implementing IComparable<Story>. Once you do that, your list.Sort will no longer require the comparer parameter, as it will identify Story as IComparable and use its CompareTo method.
• Alternatively, you may simply use a LINQ IEnumerable<T>.OrderBy statement instead of List<T>.Sort.

Answer 4

1. I want to emphasize how important it is to override GetHashCode() is when you override Equals. If you don't, all hashtable based collections/algorithms will sometimes fail in unexpected ways. This includes HashSet<T>, Dictionary<K,V> and LINQ functions like Distinct or GroupBy.

2. GetMostRecent5 can be simplified:

   • You can use ToArray to create an array from a list instead of writing a loop

     private static T[] GetMostRecent5<T>(T[] stories, IComparer<T> comparer)
     {
         List<T> recentStories = stories.Take(5).ToList();
         recentStories.Sort(comparer);
         var recentStoriesArray = recentStories.ToArray();
         return recentStoriesArray;
     }
     

   • You can use Array.Sort so you don't need to copy from a list.

     private static T[] GetMostRecent5<T>(T[] stories, IComparer<T> comparer)
     {
         T[] recentStories = stories.Take(5).ToArray();
         Array.Sort(recentStories, comparer);
         return recentStories;
     }
     

   • You can use LINQ for sorting, so you don't need a temporary array.

     private static T[] GetMostRecent5b<T>(T[] stories, IComparer<T> comparer)
     {
         return stories.Take(5).OrderBy(story => story, comparer).ToArray();
     }
     

   • You don't need a custom comparer. LINQ's OrderBy takes a projection as first parameter. You can simply project to story.Date.

     private static T[] GetMostRecent5b<T>(T[] stories)
     {
         return stories.Take(5).OrderBy(story => story.Date).ToArray();
     }
     

   At this point it's so short that it might not even deserve its own method anymore.

3. Since you call Take(5) before sorting you're relying on the items being sorted by the Date in descending order. If that assumption is correct you don't actually need to sort again, you can simply reverse the order to ascending.

   stories.Take(5).Reverse().ToArray();
   

   If that assumption is not always true you need to sort before calling Take(5), else you won't get the most recent items.

   stories.OrderBy(story => story.Date).Take(5).Reverse().ToArray();