The author explains that real-time web development puts the user at the center of all web interactions, and that developers have struggled with solving the push versus pull problem. The pull method requires multiple, periodic queries for updates from server information feeds, something that wastes server CPU and bandwidth when no changes have occurred, and is compounded by the number of different users making these queries. The push method allows the servers to contact the clients when information feeds have been updated, saving CPU and bandwidth.
RSS was designed for easy syndication of information feeds, but it suffers from the limitations of the pull methodology. While several push technologies have been proposed to solve this problem, only Simple Update Protocol (SUP) and PubSubHubbub are covered in detail here. Both of these are demonstrated with PHP code, so they should be easy to implement on hosted web account with PHP and MySQL. The author explains that while SUP isn't a real push methodology, it does address some the CPU and bandwidth issues. PubSubHubbub, a true push methodology when compared to SUP, is described with an equal amount of detail.
Have you ever wished your blog could send live updates to your readers the moment you post them? You'll learn how, using Bayeux protocol, Java, Cometd, and the Jetty web server. The sample code allows you to grasp how long-polling works with modern browsers. Once a client browser opens an HTTP connection to a web server using a POST method, the server leaves this connection open until it has data to deliver to the client. This chapter suggests using Firebug, a Firefox plugin for debugging web applications from the client side, to discover and track long-polling seasons.
Do you need to handle a large amount of incoming data, and then redisplay it on client browsers with almost no delay? Tornado, the Python web server, provides a solution. Tornado was created by FriendFeed, and made open source after being acquired by Facebook. Kudos to Facebook for making Tornado available. Please read Chapter 5 and 6 together, since they both explain how the Tornado server works. The sample code starts with Python threads that cache a Twitter feed, process and filter it, then send it out to web browsers already connected to Tornado using long-polling and asynchronous callbacks. Tornado is then used to implement a peer to peer chat system using long-polling. Again, each client stays connected to the Tornado server until messages are ready to deliver to each chat participant. Taken together, Chapter 5 and 6 lay the groundwork for more advanced Tornado web applications covered later in the book.
This is followed by two chapters using the Google App Engine to support real-time user experiences even though the Google App Engine does not support long-polling. If you have never used Google App Engine before this, don't worry. The author spends 10 pages explaining how to sign up. Then you build an application in the cloud and connect with your IM client, instead of the web browser. You can make your IM server accept commands and respond with information from other web services. The section, "Setting Up an API", gives you a tantalizing glimpse of possibilities explored later in the book. After adding Python code from the next chapter, you have SMS capabilities. Why would you want to do this? Because it allows users to keep informed while they're away from the web, making SMS another part of the real-time user experience.
This book would be good for anyone that needs to quickly learn how to use Tornado and integrate it with other web services. It's also helpful for people who want to integrate the Google App Engine with other web services. Whether you're going to build a real-time web experience from the ground up, or just add a few more dynamic features to an existing site, the lessons you can learn from this book will help you.