rAtom

rAtom is a library for working with the Atom Syndication Format and the Atom Publishing Protocol (APP).

rAtom was originally built to support the communication between a number of applications built by Peerworks, via the Atom Publishing protocol. However, it supports, or aims to support, all the Atom Syndication Format and Publication Protocol and can be used to access Atom feeds or to script publishing entries to a blog supporting APP.

Prerequisites

libxml-ruby in turn requires the libxml2 library to be installed. libxml2 can be downloaded from xmlsoft.org/downloads.html or installed using whatever tools are provided by your platform. At least version 2.6.31 is required.

Mac OSX

Mac OSX by default comes with an old version of libxml2 that will not work with rAtom. You will need to install a more recent version. If you are using Macports:

port install libxml2

Installation

You can install via gem using:

gem install ratom

Usage

To fetch a parse an Atom Feed you can simply:

feed = Atom::Feed.load_feed(URI.parse("http://example.com/feed.atom"))

And then iterate over the entries in the feed using:

feed.each_entry do |entry|
  # do cool stuff
end

To construct the following example Feed is from the Atom spec:

<?xml version="1.0" encoding="utf-8"?>
<feed xmlns="http://www.w3.org/2005/Atom">

  <title>Example Feed</title> 
  <link href="http://example.org/"/>
  <updated>2003-12-13T18:30:02Z</updated>
  <author> 
    <name>John Doe</name>
  </author> 
  <id>urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6</id>

  <entry>
    <title>Atom-Powered Robots Run Amok</title>
    <link href="http://example.org/2003/12/13/atom03"/>
    <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
    <updated>2003-12-13T18:30:02Z</updated>
    <summary>Some text.</summary>
  </entry>

</feed>

To build this in rAtom we would do:

feed = Atom::Feed.new do |f|
  f.title = "Example Feed"
  f.links << Atom::Link.new(:href => "http://example.org/")
  f.updated = Time.parse('2003-12-13T18:30:02Z')
  f.authors << Atom::Person.new(:name => 'John Doe')
  f.id = "urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6"
  f.entries << Atom::Entry.new do |e|
    e.title = "Atom-Powered Robots Run Amok"
    e.links << Atom::Link.new(:href => "http://example.org/2003/12/13/atom03")
    e.id = "urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a"
    e.updated = Time.parse('2003-12-13T18:30:02Z')
    e.summary = "Some text."
  end
end

To output the Feed as XML use to_xml

> puts feed.to_xml
<?xml version="1.0"?>
<feed xmlns="http://www.w3.org/2005/Atom">
  <id>urn:uuid:60a76c80-d399-11d9-b93C-0003939e0af6</id>
  <title>Example Feed</title>
  <updated>2003-12-13T18:30:02Z</updated>
  <link href="http://example.org/"/>
  <author>
    <name>John Doe</name>
  </author>
  <entry>
    <title>Atom-Powered Robots Run Amok</title>
    <id>urn:uuid:1225c695-cfb8-4ebb-aaaa-80da344efa6a</id>
    <summary>Some text.</summary>
    <updated>2003-12-13T18:30:02Z</updated>
    <link href="http://example.org/2003/12/13/atom03"/>
  </entry>
</feed>

See Feed and Entry for details on the methods and attributes of those classes.

Publishing

To publish to a remote feed using the Atom Publishing Protocol, first you need to create a collection to publish to:

require 'atom/pub'

collection = Atom::Pub::Collection.new(:href => 'http://example.org/myblog')

Then create a new entry

entry = Atom::Entry.new do |entry|
  entry.title = "I have discovered rAtom"
  entry.authors << Atom::Person.new(:name => 'A happy developer')
  entry.updated = Time.now
  entry.id = "http://example.org/myblog/newpost"
  entry.content = Atom::Content::Html.new("<p>rAtom lets me post to my blog using Ruby, how cool!</p>")
end

And publish it to the Collection:

published_entry = collection.publish(entry)

Publish returns an updated entry filled out with any attributes to server may have set, including information required to let us update to the entry. For example, lets change the content and republished:

published_entry.content =  Atom::Content::Html.new("<p>rAtom lets me post to and edit my blog using Ruby, how cool!</p>")
published_entry.updated = Time.now
published_entry.save!

To update an existing Entry:

existing_entry = Entry.load_entry(URI.parse("http://example.org/afeedentry.atom"))

existing_entry.title = "I have discovered rAtom"
existing_entry.updated = Time.now
existing_entry.save!

You can also delete an entry using the destroy! method, but we won't do that will we?.

Extension elements

As of version 0.3.0, rAtom support simple extension elements on feeds and entries. As defined in the Atom Syndication Format, simple extension elements consist of XML elements from a non-Atom namespace that have no attributes or child elements, i.e. they are empty or only contain text content. These elements are treated as a name value pair where the element namespace and local name make up the key and the content of the element is the value, empty elements will be treated as an empty string.

To access extension elements use the [] method on the Feed or Entry. For example, if we are parsing the follow Atom document with extensions:

<?xml version="1.0"?>
<feed xmlns="http://www.w3.org/2005/Atom" xmlns:ex="http://example.org">
  <title>Feed with extensions</title>
  <ex:myelement>Something important</ex:myelement>
</feed>

We could then access the extension element on the feed using:

> feed["http://example.org", "myelement"]
=> ["Something important"]

Note that the return value is an array. This is because XML allows multiple instances of the element.

To set an extension element you append to the array:

> feed['http://example.org', 'myelement'] << 'Something less important'
=> ["Something important", "Something less important"]

You can then call to_xml and rAtom will serialize the extension elements into xml.

> puts feed.to_xml
<?xml version="1.0"?>
<feed xmlns="http://www.w3.org/2005/Atom">
  <myelement xmlns="http://example.org">Something important</myelement>
  <myelement xmlns="http://example.org">Something less important</myelement>
</feed>

Notice that the output repeats the xmlns attribute for each of the extensions, this is semantically the same the input XML, just a bit ugly. It seems to be a limitation of the libxml-Ruby API. But if anyone knows a work around I'd gladly accept a patch (or even advice).

Custom Extension Classes

As of version 0.5.0 you can also define your own classes for a extension elements. This is done by first creating an alias for the namespace for the class and then using the element method on the Atom::Feed or Atom::Entry class to tell rAtom to use your custom class when it encounters the extension element.

For example, say we have the following piece Atom XML with a structured extension element:

<?xml version='1.0' encoding='UTF-8'?>
<entry xmlns='http://www.w3.org/2005/Atom' xmlns:custom='http://custom.namespace'>
  <id>https://custom.namespace/id/1</id>
  <link rel='self' type='application/atom+xml' href='https://custom.namespace/id/1'/>
  <custom:property name='foo' value='bar'/>
  <custom:property name='baz' value='bat'/>
</entry>

And we want the custom:property elements to be parsed as our own custom class called Custom::Property that is defined like this:

class Custom::Property
  attr_accessor :name, :value
  def initialize(xml)
    # Custom XML handling
  end
end

We can tell rAtom about our custom namespace and custom class using the following method calls:

Atom::Feed..add_extension_namespace :custom, "http://custom.namespace"
Atom::Entry.elements "custom:property", :class => Custom::Property

The first method call registers an alias for the “custom.namespace” namespace and the second method call tell rAtom that when it encounters a custom:property element within a Feed it should create an instance of Custom::Property and pass the XML Reader to the constructor of the instance. It is then up to the constructor to populate the objects attributes from the XML. Note that the alias you create using add_extension_namespace can be anything you want, it doesn't need to match the alias in the actual XML itself.

The custom property will then be available as a method on the rAtom class. In the above example:

@feed.custom_property.size == 2
@feed.custom_property.first.name == 'foo'
@feed.custom_property.first.value == 'bar'

There is one caveat to this. By using this type of extension support you are permanently modifying the rAtom classes. So if your application process one type of atom extension and you are happy with permanently modified rAtom classes, the extra extensibility might work for you. If on the other hand you process lots of different types of extension you might want to stick with simpler extension mechanism using the [namespace, element] method described above.

(Thanks to nachokb for this feature!!)

Basic Authentication

All methods that involve HTTP requests now support HTTP Basic Authentication. Authentication credentials are passed as :user and :pass parameters to the methods that invoke the request. For example you can load a feed with HTTP Basic Authentication using:

Atom::Feed.load_entry(URI.parse("http://example.org/feed.atom"), :user => 'username', :pass => 'password')

Likewise all the Atom Pub methods support similar parameters, for example you can publish an Entry to a Feed with authentication using:

feed.publish(entry, :user => 'username', :pass => 'password')

Or destroy an entry with:

entry.destroy!(:user => 'username', :pass => 'password')

rAtom doesn't store these credentials anywhere within the object model so you will need to pass them as arguments to every method call that requires them. This might be a bit of a pain but it does make things simpler and it means that I'm not responsible for protecting your credentials, although if you are using HTTP Basic Authentication there is a good chance your credentials aren't very well protected anyway.

AuthHMAC authentication

As of version 0.5.1 rAtom also support authentication via HMAC request signing using the AuthHMAC gem. This is made available using the :hmac_access_id and :hmac_secret_key parameters which can be passed to the same methods as the HTTP Basic credentials support.

TODO

Source Code

The source repository is accessible via GitHub:

git clone git://github.com/seangeo/ratom.git

Contact Information

The project page is at github.com/seangeo/ratom. Please file any bugs or feedback using the trackers and forums there.

Authors and Contributors

rAtom was developed by Peerworks and written by Sean Geoghegan.