Tower Of Power

I had an issue recently where I needed to calculate the Unix timestamp for the daylight savings time boundaries. According to the United States Naval Observatory, daylight savings time begins the Second Sunday of March and ends on the First Sunday of November.

Awkward date calculations if you don’t have the magical strtotime() function in PHP. strtotime() is able to do relativistic time conversions from the common “+1 hours” to the more complex (and more relevant) “Second Sunday March 0″.

Why do we do the ‘March 0′ in the above string to calculate the start boundary? Doing some tests with strtotime() reveals some behavior you should be aware of.

strtotime("March"); doesn’t actually give you the first of March, it gives you the current day in the month specified (date('D, F j, Y, g:i a', strtotime("March")); returns Tue, March 10, 2009, 12:00 am at the time of this post). Doing a similar test but substituting April for March results in the 10th of April (at 12 am).

Now in most cases doing a strtotime("March 1") will suffice (date('D, F j, Y, g:i a', strtotime("March 1")); results in Sun, March 1, 2009, 12:00 am). However, as you can tell, this month is going to be awkward because the first day of the month is a Sunday. strtotime(), when calculating the fuzzy “Second Sunday,” doesn’t include the current day. So calculating date('D, F j, Y, g:i a', strtotime("Second Sunday March 1")); will actually return the 3rd Sunday (Sun, March 15, 2009, 12:00 am).

So our solution is actually to take a step back and return the PREVIOUS day to the first day of March and then calculate the Second Sunday from there (since we know that starting from the next day will account for the first). Normally, dealing with the last day in February is a headache, BUT again thanks to PHP magic we don’t have to figure out if it’s February 28th or 29th, we merely do a “March 0″ which steps us back a month (date('D, F j, Y, g:i a', strtotime("March 0")); returns Sat, February 28, 2009, 12:00 am). From there we can calculate the Second Sunday with ease and eventually determine that the second sunday is March 8th, which is confirmed by the above USNO website.

Applying these lessons to calculating the first Sunday in November we come up with the following snippit:

<?php
$remove_hour = strtotime("Second Sunday March 0");
$add_hour = strtotime("First Sunday November 0");

$time  = time();

if( $time >= $remove_hour && $time < $add_hour )
{
    var_dump("Lost an hour");
}
else
{
    var_dump("Gained an hour");
}

Cheers!

So, after reading Mark Shuttlework’s blog on ideas for notifications in Ubuntu (basically mimicking Growl notifications for the Mac), I decided I wanted that kind of functionality, but… you know, NOW!

There are a multitude of options available but currently I’m liking Mumbles. Unlike, say, Specto, which does the monitoring itself, Mumbles provides a DBus interface, a command-line app named mumbles-send, and (I’m not sure if it’s implemented in the current stable download) libnotify support. Woutc, from the Specto project, commented below explaining that Specto is not intended to be a Mumbles competitor, but a package to easily monitor system internals (I quote “…the purposes from mumbles and specto are different…specto is monitoring what happens outside your desktop, mumbles monitors what happens on your desktop (or in your network)…”) Apparently he has plans to build a Mumbles plugin so that one can optionally have Specto send its messages to Mumbles for display.

I decided the best easiest route is to access the internal DBus API, however the forums and other resources on the Mumbles site… well… just plain suck. And by suck I mean tell you that something exists and… thaaats about it.

D-Feet browsing Mumble's Growl interface

Well in my Google quest I discovered the existence of D-Feet, a DBus debugging tool (on Ars of all places). Thanks to a quick sudo apt-get install d-feet I found the existence of a public interface in info.growl.Growl that allows for a Notify(title, message) signal to be passed.

Well, with a place to access all I needed was DBus integration with PHP (because I want to start sending debug notification via Growl/Mumbles like this idea on the Zend Framework incubator).

Luckily, GREE Labs provides a DBus C extension for PHP that was easily downloaded and installed. Once installed I read the documentation to get an idea on how to use the API (which is a 1:1 mapping to the DBus API).

After a bit of hacking I finally came up with an alpha product:

<?php
function null_callback()
{
        var_dump(func_get_args());
}

$dbus = dbus_bus_get(DBUS_BUS_SESSION);

$m = new DBusMessage(DBUS_MESSAGE_TYPE_SIGNAL);

$m->setPath('/info/growl/Growl');
$m->setInterface('info.growl.Growl');
$m->setMember('Notify');
$m->appendArgs('Hello World!');
$m->appendArgs('Lorem Ipsum Dolor Sit Amet. (' . time() . ')');

$r= $dbus->send($m);

After running the script in the console, did I see success?

Mumbles and PHP Test: Success!

Damn right I did!

Though with a caveat:

Warning: dbusconnection::sendwithreplyandblock(): dbus_connection_send_with_reply_and_block() failed (Traceback (most recent call last):
File "/var/lib/python-support/python2.5/dbus/service.py", line 643, in _message_cb
(candidate_method, parent_method) = _method_lookup(self, method_name, interface_name)
File "/var/lib/python-support/python2.5/dbus/service.py", line 244, in _method_lookup
raise UnknownMethodException('%s is not a valid method of interface %s' % (method_name, dbus_interface))
UnknownMethodException: org.freedesktop.DBus.Error.UnknownMethod: Unknown method: Notify is not a valid method of interface info.growl.Growl
) in /home/daniel/test.php on line 21

Call Stack:
0.0002 64496 1. {main}() /home/daniel/test.php:0
0.0024 66372 2. dbusconnection->sendwithreplyandblock() /home/daniel/test.php:21


Apparently Mumbles seems to be throwing an Exception that it’s failing to to find the Notify signal (though everything works correctly). I guess I could ignore this, use the error suppressor (@), or even yell at GREE Labs to have the objects throw exceptions so I can catch them… I guess I’ll hack on it some more and report back. I should probably spend more time learning the DBus specs since this is my first project playing with DBus…

Update: Though it’s not listed on the API page for PHP DBus’s API, there is a method send() that takes only a single argument (the message object).

Edit:

I saw a question on Reddit asking what is the use of this technique if it’s limited to the desktop it was called on and PHP is primarily a server side language. Why not do this in Python or Perl?

Well, Mumbles was written in Python so there’s no point in me doing this in Python: it’s already been done.

However, the primary use case of a technique like this is having a web app post notifications and errors for the developer. When I work on a site I have a local copy running on my desktop and/or laptop, so when it posts Growl/Mumbles notifications, I get them on my desktop. It’s great for situations where, say, I have a page in my PHP app that never displays its contents because it processes data then redirects to another page. If a warning or other non-fatal error that I should really fix occurs, then I would normally have to dig through the system wide PHP error log (if you even have error logging enabled). However, if I wrote a custom error handler that posts errors to Growl/Mumbles as they happen, when I visit a transitory page like I described I get little Growl/Mumbles notifications showing that I screwed up!