Parse an AWS ARN with Ruby

readme.md

You can use this code to reliably parse an AWS ARN and get its various sections.

Paste this class into your library, or put arn_parse.rb into your project's lib folder and require it. Then you can feed it an ARN and get back an object:

require_relative 'lib/arn_parse.rb'

my_arn = Arn.parse 'arn:aws:sns:*:123456789012:my_corporate_topic'  => #<Arn:0x00007f91550a6e80 @partition="aws", @service="sns", @region="*", @account="123456789012", @resource="my_corporate_topic">
my_arn.service                                                      => "sns"

arn_parse.rb

class Arn
  attr_accessor :partition
  attr_accessor :service
  attr_accessor :region
  attr_accessor :account
  attr_accessor :resource

  def initialize(partition, service, region, account, resource)
    @partition = partition
    @service = service
    @region = region
    @account = account
    @resource = resource
  end

  def self.parse(arn)
    raise TypeError, 'ARN must be supplied as a string' unless arn.is_a?(String)

    arn_components = arn.split(':', 6)
    raise ArgumentError, 'Could not parse ARN' if arn_components.length < 6

    Arn.new arn_components[1],
            arn_components[2],
            arn_components[3],
            arn_components[4],
            arn_components[5]
  end
end

I hope you find it useful! Beware that I did find some arns later that didn't... reliably fit into this parsing scheme. You can end up with arn.resource strings that contain colons.

I don't know whether or not it's always valid, but I was pretty convinced when I wrote the class :)

Please note that you can parse ARNs with https://docs.aws.amazon.com/sdk-for-ruby/v3/api/Aws/ARNParser.html