Subscribe to an RSS Feed

Question

I am writing a very simple RSS reader - all it needs to do is get the xml doc, and print to the console the title and publish date of every item. I got started using these two questions:

How can I get started making a C# RSS Reader?

Reading the Stack Overflow RSS feed

I'm trying to figure out how to subscribe, and as far as I can figure you do it one of two ways. Send an HTTP request to the feed site so it pushes you updates as they come, or poll the site every X seconds and simply print the new ones.

I find it difficult the believe that there is no way to subscribe due to the millions of RSS readers running at any given moment, popular RSS sites like facebook, twitter, or myspace would be hit hundreds of millions of times per second due to all the RSS readers "subscribed" to it and look like a DOS attack.

So what is the "standard" way to subscribe to an RSS feed, if such a standard truely exists?

Answer 1

The standard way is to poll. Not every x seconds but every x minutes or x hours.

The reasoning behind RSS is to keep the feed extremely simple. Small download and the same file can be served to all subscribers (easy to cache in memory and no processing overhead to find out exactly what and when to send to each client).

Answer 2

Not sure you quite understand the concept of RSS feeds.

It is simple:

1. You application (RSS reader) sends an HTTP GET request to given RSS feed url.
2. You get XML in return.
3. You parse that XML and show that data on your UI.

And generally, the websites you mentioned are smart enough to identify DOS attacks (for example, frequent requests from same IP in very short time). So, you don't have to worry about that.

Also, while creating an RSS reader, every time you get new XML from feed url, you have to identify new posts from old ones (that you already have on your UI). Timestamps are generally used to identify posts, but, there no standard way of doing that.

Answer 3

RSS on a site / server does not manage any suscriptions. The suscription is only a concept in the RSS reader. That keeps stuff simple on the RSS server side, as there's no need for suscription management which made the protocol easy to adopt.

You have to periodically poll the RSS feed by an HTTP GET to the feed URL. You get a XML document in the RSS format in return. Then you parse it and display the infos you like. Voila.