The document discusses using XMPP and Rails for real-time web applications. It describes how XMPP allows for server push through BOSH and components, and can be used to build features like multi-party negotiations. Examples are given of using an XMPP component to handle events from a Rails application and push updates to clients in real-time. Pros of the approach include powerful XMPP toolkits, built-in server push, and scalability, while some administrative work is required.

1. Real-time Web with Rails
and XMPP
Münchner Ruby on Rails User Group, 2010/12/2
Li Cai (ca168168@gmail.com)
founder: reliwa.de
partner & ex-CTO: 16ds.com

2. Motivation: 16ds.com
• B2B portal and business network for the
chemical industry
• Market indexes for 30+ bulk chemicals
based on prices submitted by diverse
market players
• Real-time multi-party price negotiation
Münchner Ruby on Rails User Group, 2010/12/2

3. Multi-party price negotiation
• User self-organized
• Access control based on organizational structure of the
company
• Customizable quotation templates for each product
• Configurable admission control and protection of sensitive
data (customer identities, price details, etc.)
• Different negotiation modes: fixed price, bargaining, bidding,
moderated bidding
• Real-world near auctions by utilizing “Counting-Down-
Hammer”
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4. Server push in Rails
• Polling: simple (but...)
• Comet: setup external server for server push (Jetty,
glassfish, cometd, ErlyComet, node.js, etc.)
• FlashXML Socket: full-duplex TCP stream socket
connection (extra work for firewall traversal)
• XMPP/BOSH: bidirectional streams over HTTP
connection
• WebSockets: full-duplex over single TCP socket is
being standardized by the W3C (HTML5)
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5. XMPP
• eXtensible Messaging and Presence Protocol
• Data exchanged over a pair of XML streams
• extensibility: very easy to add new features to the protocol
• XMPP Toolkits
• presence
• instant messaging
• Multi User Chat (XEP-0045)
• Publish/Subscribe (XEP-0060)
• and many more...
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6. XMPP
• BOSH (XEP-0124, XEP-0206)
• long-lived bidirectional streams over HTTP connection
• hide user credentials by session attachment
• many XMPP servers have BOSH connection manager
build-in
• XMPP Component (XEP-0114)
• stand-alone server process written with whatever
language you like
• easily extend the server with your own application logic
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7. Extend XMPP with our new
features
• Build multi-party price negotiation on top of MUC
• Create XMPP account for every user, while hiding the
credentials by using session attachment
• Create MUC-rooms on demand, and manage the member
list by our application
• Implement an XMPP component to interact with our
application as well as the clients
• Extend name space and let our application handle stuffs
• Configure default settings of the XMPP server for security
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8. Rails and XMPP
Application Background
Web Client HTTP Server
Instances (Rails) Jobs (Rails)
BOSH Conn.
Message Queue
Manager
XMPP Server
XMPP Server
Component
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9. XMPP servers
• ejabberd
• written in Erlang, well-known for its scalability
• http://www.process-one.net/en/ejabberd/
• Openfire
• written in Java, very easy to install and configure
• http://www.igniterealtime.org/projects/openfire/
• Tigase
• written in Java
• http://www.tigase.org/
• and much more...
Münchner Ruby on Rails User Group, 2010/12/2

10. XMPP libraries - server side
• xmpp4r
• feature-rich, threaded ruby
• http://home.gna.org/xmpp4r/
• blather
• lightweight, DSL-style, evented ruby
• http://sprsquish.github.com/blather/
• skates
• lightweight, MVC-style, evented ruby
• http://skates.rubyforge.org/
• strophe-ruby
• ruby binding for libstrophe, can be run within a Rails-app
• https://github.com/yong/stropheruby
Münchner Ruby on Rails User Group, 2010/12/2

11. XMPP libraries - client side
• strophe.js
• JavaScript
• http://code.stanziq.com/strophe/
• xmpp4js
• JavaScript
• http://xmpp4js.sourceforge.net/
• XIFF
• Flash/ActionScript
• http://www.igniterealtime.org/projects/xiff/
• and many more...
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12. Example: user submits a bid
XMPP Comp. User M User A User B
XMPP MUC Web App
(Spider) (Moderator) (Participant) (Participant)
submit bid
room_jid, user_jid, [bid]
groupchat:x.spider_bid.submitted [bid w. public info]
update bid_list update bid_list update bid_list
private? && msg:x.spider_bid.submitted [bid w. all info]
update bid_list update bid_list
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13. Example: user submits a bid
Rails:
# class RoomBid < ActiveRecord:Base
def submit
# ... authorization check and application level processing ...
Spider.notify "bid.submitted", {
:room_jid => room.jid,
:bid => public_info.to_json
}).merge(public? ? {} : {
:private_recipient_jids => [room.moderator.jid, submitter.jid],
:bid_full => all_info.to_json
})
end
# class Spider
def notify key, options = {}
mq.exchange('spider', :type => :topic).publish(Marshal.dump(options), :key => key)
end
Münchner Ruby on Rails User Group, 2010/12/2

14. Example: user submits a bid
XMPP Component:
# handling of the queue event: “bid.submitted”
send_msg do |xml|
# send broadcast message
xml.message(:to => options[:room_jid], :from => SPIDER_JID, :type => :groupchat) do
xml.x :xmlns => NS_SPIDER_BID do
xml.submitted options[:bid]
end
end
# send private messages
options[:private_recipient_jids] && options[:private_recipient_jids].each do |jid|
xml.message(:to => jid, :from => SPIDER_JID, :type => :normal) do
xml.x :xmlns => NS_SPIDER_BID do
xml.submitted options[:bid_full], :in => options[:room_jid]
end
end
end
end
Münchner Ruby on Rails User Group, 2010/12/2

15. Example: user submits a bid
Client (with strophe.js):
// broadcast messages
on_broadcast_message: function (message) {
var from = $(message).attr('from');
var room = Strophe.getNodeFromJid(from);
msg = $(message).find("x[xmlns='" + NS.SPIDER_BID + "'] > submitted");
if (msg.length > 0) {
Client.on_bid_submitted(room, JSON.parse(msg.text(), true);
}
// other events ...
},
// update local db, render the gui
on_bid_submitted: function (room, bid, broadcasted) {
Room.set_bid(room, bid, broadcasted);
Renderer.render_bid(room, bid);
},
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16. Conclusions
• Pros:
• powerful toolkits for application
• server push for free
• scalability
• transparent for users
• Cons:
• a bit admin work
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17. Demo
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