Parsing Nagios Objects in Ruby Redux

When I was with MediaOcean, one of the projects I was working on was a stack of ruby code for parsing/writing nagios configs. This was in parallel with setting up puppet. I actually got pretty far along but then DDS had a RIF and I was back on the market.

I had to put the code aside and just recently pulled it out again. Some/most of it is pretty ugly. I had quite a bit done though.

So here I am "refactoring" (and I use that term VERY VERY loosely) the code base. So I'm happily parsing away - iterating over the cfg_file/cfg_dir entries and build a nice big hash to hold all the object definitions. I dump it to a YAML file for validation when I notice this nice bit of junk in my timeperiod dump:

	4:
	- name: us-holidays
	- timeperiod_name: us-holidays
	- alias: U.S. Holidays
	- january: 1 00:00-00:00
	- monday: -1 may 00:00-00:00
	- july: 4 00:00-00:00
	- monday: 1 september 00:00-00:00
	- thursday: -1 november 00:00-00:00
	- december: 25 00:00-00:00

view raw gistfile1.yml hosted with ❤ by GitHub

Oh yeah...that looks right =/

For those who don't know, nagios object definitions are pretty straightforward. Here's an example:

	define host {
	use linux-server
	host_name oio
	alias oio
	address oio.mydomain.int
	hostgroups webs
	}

view raw gistfile1.txt hosted with ❤ by GitHub

Easy enough to parse, right? Object type named (host). A clear beginning and end denoted by curly braces. Object attributes in a seemingly key/value type markup. Some people smash the opening brace up against the object type definition but that's easily caught.

Iterating over the definition in Ruby is pretty straightforward (assuming a perfect example):

	objfile.each_line do |line|
	if line =~ /^define/
	def_start, obj_type, open_brace = line.split
	next
	end
	unless line =~ /\}/
	obj_param, obj_val =- line.split(nil,2)
	# Do something
	end
	end

view raw gistfile1.builder hosted with ❤ by GitHub

What becomes a problem is timeperiod defintions. The syntax for those is somewhat complicated. Looking back at the YAML fragment above, you can see why. For timeperiods, while the rightmost value is the actual time frame, the left part (usually a day of the week) can actually be a specific day. So if I wanted to create an entry for Christmas in the U.S., I would define it like so:

december 25 00:00-00:00


Things can be even MORE complicated if I wanted to handle non-date holidays:

monday 1 september 00:00-00:00 ; Labor Day (first Monday in September)
thursday -1 november 00:00-00:00 ; Thanksgiving (last Thursday in November)


Ugly, no? I searched high and low for the ability to split starting from the right and didn't find anything native. I had to resort to implementing my own rsplit method for String:

	class String
	def rsplit(delim,count)
	self.reverse.split(delim, count).map(&:reverse).reverse
	end
	end

view raw rsplit.rb hosted with ❤ by GitHub

It works but I also can't use it across the board. If I do, I break things that were working (alias, service_description) that can have a space in the value.

I'm not even going to get into trying to convert timeperiod definitions into Date objects yet. That gives me cold sweats.