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RSS reading and writing

Really Simple Syndication (RSS) is a family of formats that describe ‘feeds,’ specially constructed XML documents that allow an interested person to subscribe and receive updates from a particular web service. This portion of the standard library provides tooling to read and create these feeds.

The standard library supports RSS 0.91, 1.0, 2.0, and Atom, a related format. Here are some links to the standards documents for these formats:

• RSS

  • 0.9.1

  • 1.0

  • 2.0

• Atom

Consuming RSS

If you’d like to read someone’s RSS feed with your Ruby code, you’ve come to the right place. It’s really easy to do this, but we’ll need the help of open-uri:

require 'rss'
require 'open-uri'

url = 'http://www.ruby-lang.org/en/feeds/news.rss'
open(url) do |rss|
  feed = RSS::Parser.parse(rss)
  puts "Title: #{feed.channel.title}"
  feed.items.each do |item|
    puts "Item: #{item.title}"
  end
end

As you can see, the workhorse is RSS::Parser#parse, which takes the source of the feed and a parameter that performs validation on the feed. We get back an object that has all of the data from our feed, accessible through methods. This example shows getting the title out of the channel element, and looping through the list of items.

Producing RSS

Producing our own RSS feeds is easy as well. Let’s make a very basic feed:

require "rss"

rss = RSS::Maker.make("atom") do |maker|
  maker.channel.author = "matz"
  maker.channel.updated = Time.now.to_s
  maker.channel.about = "http://www.ruby-lang.org/en/feeds/news.rss"
  maker.channel.title = "Example Feed"

  maker.items.new_item do |item|
    item.link = "http://www.ruby-lang.org/en/news/2010/12/25/ruby-1-9-2-p136-is-released/"
    item.title = "Ruby 1.9.2-p136 is released"
    item.updated = Time.now.to_s
  end
end

puts rss

As you can see, this is a very Builder-like DSL. This code will spit out an Atom feed with one item. If we needed a second item, we’d make another block with maker.items.new_item and build a second one.

Copyright

Copyright © 2003-2007 Kouhei Sutou <[email protected]>

You can redistribute it and/or modify it under the same terms as Ruby.

There is an additional tutorial by the author of RSS at: http://www.cozmixng.org/~rwiki/?cmd=view;name=RSS+Parser%3A%3ATutorial.en

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