HasChecksum

Automatically calculate checksums and signatures from the values of your class' attributes/methods

Works with POROs and ActiveRecord.

Installation

Add this line to your application's Gemfile:

gem "has_checksum"

And then execute:

bundle

Or install it yourself as:

gem install has_checksum

Usage

Use the has_checksum and/or has_signature class methods to calculate checksums or signatures of your class' columns and/or methods' return values.

has_checksum

class User
  include HasChecksum

  attr_accessor :username

  has_checksum :username
end

user = User.new
user.username = "sshaw"
user.username_checksum # 5b891e901f3c8859115dcdfe323944ec7b4abbde9f7b680430fca7d2c7af89e5

By default SHA256 is used.

Multiple attributes can be specified:

class User
  include HasChecksum

  attr_accessor :username
  attr_accessor :updated_at

  has_checksum :username, :updated_at
end

user = User.new
user.username = "sshaw"
user.updated_at = Time.now
user.username_updated_at_checksum # bf6bfb33a4927184eae61195afcff0b033b13da15d79629d513639717c06e15f

Use the:method and :algorithm arguments to change the method name and algorithm. Here we use an ActiveRecord subclass:

class User < ActiveRecord::Base
  include HasChecksum

  has_checksum :settings, :updated_at, :method => "settings_signature", :algorithm => "md5"
end

user.settings[:timezone] = "America/Los_Angeles"
user.save!
user.settings_signature # 4a390b8df412ab4168b9856291437bba

With ActiveRecord, if the generated method is a database column, the checksum will be persisted:

rails g migration add_settings_signature_to_users settings_signature:string  # should use char(N), really

:algorithm can also be a block:

class User < ActiveRecord::Base
  include HasChecksum

  has_checksum :settings, :updated_at, :algorithm => ->(value) { whirlpool(value) }
end

By default the checksum will be hex encoded but you can change this via :encode:

class User < ActiveRecord::Base
  include HasChecksum

  has_checksum :settings, :updated_at, :encode => "base64"  # or "binary" or "bubblebabble"
end

has_signature

Calculates a hash-based message authentication code (HMAC). This (mostly) works the same as has_checksum but requires a :key argument that will be used as the HMAC's key:

class User < ActiveRecord::Base
  include HasChecksum

  has_signature :id, :created_at, :last_login_at, :key => :some_salt_column, :method => "session_id"
end

If :key is a Symbol it will treated as a method name. If it's a String is will be used literally, as the key. It can also be a Proc that returns the key.

See Also

rspec-checksum-matchers

Author

Skye Shaw (skye.shaw -AT- gmail)

License

The gem is available as open source under the terms of the MIT License.