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+---
+layout: default
+title: Validator Plugins
+---
+[DDL]: /mcollective/reference/plugins/ddl.html
+
+## Overview
+MCollective provides extensive input data validation to prevent attacks and
+injections into your agents preventing attack vectors like Shell Injection
+Attacks.
+
+Traditionally we shipped a number of pre-made validator plugins that could be
+used in agents and DDL files but you were not capable fo adding your own easily.
+
+As of version 2.2.0 you can write new Validator plugins that allow you to extend
+the DDL and Agent validation methods.
+
+## Writing A New Validator
+We'll write a new validator plugin that can validate a string matches valid Exim
+message IDs like *1Svk5S-0001AW-I5*.
+
+Validator plugins and their DDL files goes in the libdir in the *validator*
+directory on both the servers and the clients.
+
+### The Ruby Plugin
+The basic validator plugin that will validate any data against this regular
+expression can be seen here:
+
+{% highlight ruby %}
+module MCollective
+  module Validator
+    class Exim_msgidValidator
+      def self.validate(msgid)
+        Validator.typecheck(msgid, :string)
+
+        raise "Not a valid Exim Message ID" unless msgid.match(/(?:[+-]\d{4} )?(?:\[\d+\] )?(\w{6}\-\w{6}\-\w{2})/)
+      end
+    end
+  end
+end
+{% endhighlight %}
+
+All you need to do is provide a *self.validate* method that takes 1 argument and
+do whatever validation you want to do against the input data.
+
+Here we first confirm it is a string and then we do the regular expression match
+against that.  Any Exception that gets raised will result in validation failing.
+
+### The DDL
+As with other plugins these plugins need a DDL file, all they support is the
+metadata section.
+
+{% highlight ruby %}
+metadata    :name        => "Exim Message ID",
+            :description => "Validates that a string is a Exim Message ID",
+            :author      => "R.I.Pienaar <rip@devco.net>",
+            :license     => "ASL 2.0",
+            :version     => "1.0",
+            :url         => "http://devco.net/",
+            :timeout     => 1
+{% endhighlight %}
+
+## Using the Validator in a DDL
+You can use the validator in any DDL file, here is a snippet matching an input
+using the new *exim_msgid* validator:
+
+{% highlight ruby %}
+action "retrymsg", :description => "Retries a specific message" do
+    display :ok
+
+    input :msgid,
+          :prompt      => "Message ID",
+          :description => "Valid message id currently in the mail queue",
+          :type        => :string,
+          :validation  => :exim_msgid,
+          :optional    => false,
+          :maxlength   => 16
+
+    output :status,
+           :description => "Status Message",
+           :display_as  => "Status"
+end
+{% endhighlight %}
+
+Note here we are using our new validator to validate the *msgid* input.
+
+## Using the Validator in an Agent
+Agents can also have validation, traditionally this included the normal things
+like regular expressions but now here you can also use the validator plugins:
+
+{% highlight ruby %}
+action "retrymsg" do
+  validate :msgid, :exim_msgid
+
+  # call out to exim to retry the message
+end
+{% endhighlight %}
+
+Here we've extended the basic *validate* helper of the RPC Agent with our own
+plugin and used it to validate a specific input.
+
+## Listing available Validators
+You can obtain a list of validators using the *plugin* application:
+
+{% highlight ruby %}
+% mco plugin doc
+
+Please specify a plugin. Available plugins are:
+
+.
+.
+.
+
+Validator Plugins:
+  array                     Validates that a value is included in a list
+  exim_msgid                Validates that a string is a Exim Message ID
+  ipv4address               Validates that a value is an ipv4 address
+  ipv6address               Validates that a value is an ipv6 address
+  length                    Validates that the length of a string is less or equal to a specified value
+  regex                     Validates that a string matches a supplied regular expression
+  shellsafe                 Validates that a string is shellsafe
+  typecheck                 Validates that a value is of a certain type
+
+{% endhighlight %}
+
+Note our new *exim_msgid* plugin appears in this list.
+