Tower of Power

Too sweet to be sour.

PHP, Mumbles (Growl), and DBus: Sweeet

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.

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:

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<?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?

Damn right I did!

Though with a caveat: 

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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

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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!

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