Puppet users - May 2010 - Writing a properly-formed custom type (configxml)

Please hold my hand.

After studying the wiki, several unofficial pages, various mailing list entries,
and the operation of the "iptables" type as found on the net, I have
created a custom type, lovingly named ``configxml''''.
It updates attributes on the first element matching a supplied XPath in a given
XML file. The first use case is configuring Atlassian JIRA to use Postgres ..

The custom type:
- Detects the need to update attribute values
- Updates attribute values
- Pretty prints to the log, ex. when run with ``puppetd -dtv''''
- Solves today''s immediate need, but I don''t trust its ability
to properly integrate into the dependency tree, nor even its return value

Initially this was split into a type and a provider, which didn''t work.
I don''t clearly understand how provider functionality is invoked, nor
its relationship with a type.

How should this custom type be better structured and written?

I greatly appreciate feedback and pointers.


I''ve attached relevant code, sorry if its a little long ..
As you might sense from reading the code, today marks my 3rd day as a Ruby
newbie ..

---- 8< ---- manifest snippet ---- 8< ---- 

node ''jira'' inherits ''basenode'' {
        ...
        configxml {
''/opt/jira/atlassian-jira/WEB-INF/classes/entityengine.xml'':
                xpath =>
"/entity-config/datasource[@name=''defaultDS'']",
                attributes =>
''field-type-name=postgres72,schema-name=public'',
        }
        ...
}

---- 8< ---- configxml.rb ---- 8< ---- 

module Puppet
	newtype(:configxml) do
		@doc = "Modify attributes of the first element matching the XPath
expression in an XML file."

		require ''rexml/document''
		require ''set''

		def test_it
			doc = REXML::Document.new(File.open(value(:name)))

			# Take the first element matching the provided XPath expression
			attrs = doc.elements[value(:xpath) + "[1]"].attributes

			# Split up the comma-separated key-value pairs into an array and then isolate
the keys
			keys = value(:attributes).split(/,/).map { |s| s.split(/=/)[0] }

			# Build up an array of attributes for the specified keys
			keys.map { |k| "#{k}=#{attrs[k]}" }
		end

		def set_it
			doc = REXML::Document.new(File.open(value(:name)))

			# Take the first element matching the provided XPath expression
			attrs = doc.elements[value(:xpath) + "[1]"].attributes

			# Split up the list comma-separated key-value pairs and convert the array to
hash
			updates = Hash[*value(:attributes).split(/,/).map { |s| s.split(/=/)
}.flatten]

			# Update this element''s attributes
			updates.each { |k, v| attrs[k] = v }

			# Write the changes back
			doc.write(File.open(value(:name), ''w''))
		end

		newparam(:name) do
			desc "Full path of the XML document."
		end

		newparam(:xpath) do
			desc "XPath expression selecting target elements; the first of which
whose attributes will be set."
		end

		newparam(:attributes) do
			desc "An array of strings, each containing ''key=value''
expressions setting element attributes."
		end

		def evaluate
			cur_attrs = test_it
			if Set.new(value(:attributes).split(/,/)) == Set.new(cur_attrs)
				debug("Attributes for element at #{value(:xpath)} already
#{value(:attributes)}. No changes necessary.")
				return [] # TODO what goes here?
			else
				notice("Updating attributes for element at #{value(:xpath)} to
#{value(:attributes)}.")
				set_it
				return [] # TODO what goes here?
			end
		end
	end
end

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This post enlightened me.
http://groups.google.com/group/puppet-users/browse_thread/thread/449e106437c3f673/ca9ff7055797f18c?lnk=gst

I''ve split configxml into a provider and a type and it appears to work
properly now.
In more detail, I rewrote "attributes" as a property.
All logic is moved into an eponymous provider in 2 methods:
"attributes" and "attributes=(value)".

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Hello,
> I''ve split configxml into a provider and a type and it appears to
work
> properly now.
> In more detail, I rewrote "attributes" as a property.
> All logic is moved into an eponymous provider in 2 methods:
> "attributes" and "attributes=(value)".
Just wondering if you are planning to publish your work once it''s
finished ? I''ve been doing this sort of thing using Exec''s of
"xmlstarlet", but a pure puppet type is much smarter !

Marc


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On May 19, 12:04 am, Marc Fournier <marc.fourn...@camptocamp.com>
wrote:
> Just wondering if you are planning to publish your work once it''s
> finished ? I''ve been doing this sort of thing using
Exec''s of
> "xmlstarlet", but a pure puppet type is much smarter !
Allow me to publish it here. The code:
* Assumes error-free operation; there is no validation, error
checking, etc.
* Unforgivingly expects the value of the attributes property to
conform to the syntax "key=value,key=value,key=value" ..
Obviously, the code will benefit from some T.L.C., but it functions in
my use case as-is.

BTW, I, too, was using xmlstarlet in shell scripts, whose essence are
being migrated into Puppet wholesale.

---- 8< ---- Manifest snippet, for your delectation ---- 8< ----

        configxml { ''/opt/jira/atlassian-jira/WEB-INF/classes/
entityengine.xml'':
                xpath => "/entity-config/
datasource[@name=''defaultDS'']",
                attributes => ''field-type-name=postgres72,schema-
name=public'',
        }

        configxml { ''/opt/jira/conf/server.xml'':
                xpath => "/Server/Service/Engine/Host/Context/
Resource[@name=''jdbc/JiraDS'']",
                attributes =>
"username=$username,password$password,driverClassName=org.postgresql.Driver,url=jdbc:postgresql://
$host/$database",
        }

---- 8< ---- /etc/puppet/modules/common/lib/puppet/type/configxml.rb
---- 8< ----

Puppet::Type.newtype(:configxml) do
	@doc = "Modify attributes of the first element matching the XPath
expression in an XML file."

	newparam(:name) do
		desc "Full path of the XML document."
	end

	newparam(:xpath) do
		desc "XPath expression selecting target elements; the first of which
whose attributes will be set."
	end

	newproperty(:attributes) do
		desc "An array of strings, each containing ''key=value''
expressions
setting element attributes."
	end
end

---- 8< ---- /etc/puppet/modules/common/lib/puppet/provider/configxml/
configxml.rb ---- 8< ----

Puppet::Type.type(:configxml).provide(:configxml) do
	desc "TODO"

	require ''rexml/document''
	require ''set''

	def attributes
		doc = REXML::Document.new(File.open(resource[:name]))

		# Take the first element matching the provided XPath expression
		attrs = doc.elements[resource[:xpath] + "[1]"].attributes

		# Split up the comma-separated key-value pairs into an array and
then isolate the keys
		keys = resource[:attributes].split(/,/).map { |s| s.split(/=/, 2)
[0] }

		# Build up an array of attributes for the specified keys. Arrange
keys in order of appearance
		# in resource[:attributes] so that Puppet can compare the desired
and current values.
		keys.map { |k| "#{k}=#{attrs[k]}" }.join('','')
	end

	def attributes=(value)
		doc = REXML::Document.new(File.open(resource[:name]))

		# Take the first element matching the provided XPath expression
		attrs = doc.elements[resource[:xpath] + "[1]"].attributes

		# Split up the comma-separated key-value pairs and convert the
resulting array to a hash
		updates = Hash[*resource[:attributes].split(/,/).map { |s| s.split(/
=/, 2) }.flatten]

		# Update this element''s attributes
		updates.each { |k, v| attrs[k] = v }

		# Write the changes back
		doc.write(File.open(resource[:name], ''w''))
	end

end

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