disable flushdb and flushall from ruby's redis client

redis.rb

# inspired by this article:   https://www.honeybadger.io/leveling-up/safeguarding-redis/
# and adapted from this gist: https://gist.github.com/joshuap/c1ff2657c150df6fb1257398b1d2716b
#
# * needed a way to disable flushall and flushdb in Production only
# * wanted to add a way to add some basic tests for sanity and explicit documentation
#
############### config/initializers/redis.rb #########################
require 'redis'
require 'redis_dangerous_commands'

class Redis
  prepend DangerousCommands
end

############### lib/redis_dangerous_commands.rb #########################
module DangerousCommands
  class ProhibitedCommandError < StandardError; end

  def self.prepended(base)
    return unless Rails.env.production?

    base.send(:define_method, :flushdb) do
      raise ProhibitedCommandError, error_message('EMPTY THE ENTIRE DATABASE')
    end

    base.send(:define_method, :flushall) do
      raise ProhibitedCommandError, error_message('FLUSH ALL DATABASES')
    end
  end

  def error_message(inner_message)
    "DANGEROUS destructive operation. If you really want to #{inner_message} do it from `redis-cli`."
  end
end

############### spec/lib/redis_dangerous_commands_spec.rb #########################
describe 'DangerousCommands' do
  context 'Production' do
    let(:dumb) { Dummy.new }

    before do
      allow(Rails).to receive(:env).and_return(ActiveSupport::StringInquirer.new('production'))
      class Dummy
        prepend DangerousCommands
      end
    end

    it 'raises ProhibitedCommandError' do
      expect{ dumb.flushdb }.to raise_error DangerousCommands::ProhibitedCommandError
    end

    it 'raises ProhibitedCommandError' do
      expect{ dumb.flushall }.to raise_error DangerousCommands::ProhibitedCommandError
    end
  end

  context 'Non-production' do
    let(:dumb) { DifferentDummy.new }

    before do
      class DifferentDummy
        prepend DangerousCommands
      end
    end

    it 'does not respond to flushdb' do
      expect(dumb).not_to respond_to(:flushdb)
    end

    it 'does not respond to flushall' do
      expect(dumb).not_to respond_to(:flushall)
    end
  end
end