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A Rails plugin for sending and receiving pingbacks.
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Pingback Engine

Enables your Rails app to receive and send pingbacks as known from wordpress-like blogs.

This engine includes an XML-RPC server controller for receiving pingbacks from other blogs. You can hook into the receiving and process the incoming ping by creating a new comment record that represents that blog ping or whatever your app needs.

Note: the current version only supports receiving pingbacks (that's way harder than sending pingbacks. Sending will be implemented in the next weeks).

What are Pingbacks?

If you're writing in your blog A and refer to some other blog B, your blog system will usually inform the blog B about your article. This is known as a Pingback and is simply a small XML-RPC call saying “Hey there, blog B! We're referencing your article xy. You can find our linking article on blog A at yz.”

That's all the pure pingback does. It's up to blog B to handle the links, check if blog A is really refering, excerpt some content from the blog and display that on blog B. Usually a comment on blog B is created pointing back to blog A.

Read more in the official specification at hixie.ch/specs/pingback/pingback .

Installation

To install, simply cd to your rails app directory and run

script/plugin install git://github.com/apotonick/pingback_engine.git

Receiving pingbacks

Propagating your pingback server url

A blog refering to your site will scan your site for information on where to find your pingback XML-RPC server. You're on the safe side by sending the X-Pingback header as well as including the <link rel="pingback" ...> in your layout.

In the controller class, include

class MyBlogController
  include PingbackHelper
  helper :pingback

  def show_blog
    set_xpingback_header

    # ...

In the application layout, put

<html>
  <head>
    ...
    <%= pingback_link_tag %>
 </head>

Processing incoming pings

After the installation of the engine the XML-RPC server is automatically accessable at /pingback/xml. The server will create a Pingback instance. This object checks the origin link, retrieves the linking page and extracts the matching section from the page. If valid, the hook method you provided is executed and the Pingback object passed as argument.

Currently the hook method goes at the end of config/environment.rb, where Pingback#save_callback attaches the hook:

Pingback.save_callback do |ping|
  AnonymousComment.process_pingback(ping)
end

You can also process the ping directly in the block:

Pingback.save_callback do |ping|
  comment = ArticleComment.new
  comment.author      = ping.title
  comment.author_url  = ping.source_uri
  comment.text        = ping.content

  referenced_article = Article.find_by_url(ping.target_uri)

  if referenced_article
    comment.article_id = referenced_article.id
    comment.save

    ping.reply_ok # report success.
  else
    # report error:
    ping.reply_target_uri_does_not_accept_posts
  end
end

Testing

You can use the plugins' script/send-pingback.rb tool to send an XML-RPC call to your localhost.

pingback_engine$> script/send_pingback.rb http://some.blog.com/the-linking/article http://my-own-blog.de/the-referenced-article

License

Copyright © 2008 Nick Sutterer <apotonick@gmail.com>

The MIT License

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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