I am happy to announce the launch of my latest Facebook Application: Telstra HeroMessage. You can read all about it at the  Telstra HeroMessage® Facebook Application About Page.

I am pretty excited about it, a massive national media campaign is already underway.

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acts_as_scheduled allows you to manage scheduled events for your models.

A good example of this is scheduling the update of RSS Feeds in a background process using Cron or BackgroundRB.

With acts_as_scheduled your schedule manager can simply call “Model.find_next_scheduled()” to grab the next item from the database.

At the moment it assumes you are working with MySQL.

All you need to get started is to add two extra columns to your table:

t.integer frequency
t.datetime last_scheduled

frequency is the number of seconds for your schedule.
last_scheduled is the date and time the record was last processed.

Ruby on Rails is real smart with times, so you don’t have to worry too much about calculating frequency values:

model.frequency = 1.day
model.frequency = 1.minute
model.frequency = 10.second

In your model class your simply declare “acts_as_scheduled” and you now have two extra methods find_next_scheduled and schedule_complete.

find_next_scheduled
Returns the next scheduled record from the table.
The next scheduled record is calculated as “the record who’s last_scheduled value is less than the current time minus the specified frequency in seconds”.

Which is the complex way of saying “if freqency is 1 minute, return the record if it was last_scheduled more than 1 minute ago”

If there is more than one record, records scheduled to occur more frequently will be handled first (so records with minute schedules are returned before records with daily schedules.

schedule_complete
Sets the record’s last_scheduled value to Time.now

Example

class ScheduledItem < ActiveRecord::Base
acts_as_scheduled
end

schedule_minute = ScheduledItem.new(:frequency => 1.minute, :last_scheduled => 2.seconds.ago)
schedule_minute.save

schedule_day = ScheduledItem.new(:name =>”day”, :frequency => 1.day, :last_scheduled => 25.hours.ago)
schedule_day.save

#returns thing_day because it was last_scheduled 25 hours ago
schedule_day = ScheduledItem.find_next_scheduled
schedule_day.do_some_stuff
schedule_day.schedule_complete
schedule_day.save

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This new feature provides reliable, persistent storage volumes, for use with Amazon EC2 instances. These volumes exist independently from any Amazon EC2 instances, and will behave like raw, unformatted hard drives or block devices, which may then be formatted and configured based on the needs of your application. The volumes will be significantly more durable than the local disks within an Amazon EC2 instance. Additionally, our persistent storage feature will enable you to automatically create snapshots of your volumes and back them up to Amazon S3 for even greater reliability.

Until now the only way to get real MySQL storage has been to jump through some hoops with multiple EC2 instances or back the database onto S3 (with subsequent latency overhead). With 100GB of outbound data transfer the smallest ECV2 image will cost you about $90/month for 1.7GB of memory and a dedicated CPU core. The price just cannot be beat.

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The basic requirement is to be able to accept some Ruby code from the client in order to allow customisation of the HTML output from an RSS feed.

This is obviously a rather dangerous thing. I essentially need to allow arbitrary Ruby to be executed with an eval

However, in Ruby, we can run code in SAFE mode.

At Level 4:

Ruby effectively partitions the running program in two. Nontainted objects may not be modified. Typically, this will be used to create a sandbox: the program sets up an environment using a lower $SAFE level, then resets $SAFE to 4 to prevent subsequent changes to that environment

The core of my approach is to create a new Thread, set the SAVE level to 4 and call a method.

feed = FeedNormalizer::FeedNormalizer.parse(open(self.url))
thread = Thread.start {
$SAFE = 4
html = safe_method(feed, script)}
}
thread.join #wait for the thread to finish

The safe_method itself does a sanity check on the safe level. The method takes a feed object and a script - the script is processed using eval and because the feed object is in the context, the script has access to it. However, the safe level prevents any malicious code from attempting to use Ruby magic and meta-programming to gain access to variables outside the thread or any globals

def safe_method(feed,script)
if ( $SAFE < 4 )
raise “SecurityException: attempting to execute UNSAFE script”
end

html = “”
eval(script)
return html
end

The user can then pass in code that looks like:

html << “<h2>#{feed.title}</h2>”
html << “<ul>”
feed.entries.each do |entry|
  html << “<li><a href=\”#{entry.urls.first}\”>#{entry.title}</a></li>”
end
html << “</ul>”

And the feed is processed without (too much) risk.

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The t-shirt provdes the wearer with the following powers:

1. Effortlessly win any technical discussion instantly!
2. Impress your friends!
3. Immediately dismiss any rival language or framework!

“BUT WILL IT SCALE“?

Available in LARGE, EXTRA-LARGE, GRID, and the apparently defunct N-TIER.

I like to wear mine in a cluster (simply buy two or more t-shirts and wear simultaneously).

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My latest project is live and generating a lot of traffic. I built the promotional site for the latest Gillette product -  The Gillette Fusion Power Phantom. Very tight deadline, but I made it on time and under budget.

I’ve also been involved with some work on Hotel.com.au, which is actually old-school MS Access and Visual Basic. I am quite enjoying it. Sure beats the hell out of PHP.

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I’ve uploaded the slides for my Introduction to Facebook Development talk.  I had to leave early due to some client commitments, but the talks were excellent and I met some very interesting people working in the Facebook space.

There is also a Melbourne Facebook Developer Group - I am keen to get another event organised really soon.

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backup_fu makes managing Amazon S3 backups really simple.

I have been running my own Rake Task for MySQL Backup to Amazon S3, but I’ve switched my projects over to backup_fu instead because it has much better control over your backups and will even backup stored files.

I’ve also created a patch for backup_fu that allows you to specify the mysqldump options. It should get rolled into an upcoming release, but if you would like it sooner, just contact me at toby…@info-architects.net.

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