Range validator for Grape.

range.rb

class RangeValidator < Grape::Validations::Validator
  def initialize(attrs, options, required, scope)
    @range = options
    @required = required
    raise ArgumentError, "Range provided (#{@range.inspect}) does not implement #cover?" unless @range.respond_to? :cover?
    super
  end
  def validate_param!(attr_name, params)
    if (params[attr_name] || @required) && !@range.cover?(params[attr_name])
      raise Grape::Exceptions::Validation,
        :param => attr_name.to_s,
        :message => "#{attr_name} should be within #{@range}"
    end
  end
end

Example

# code
params do
  optional :limit, :type => Integer, :default => 10, :range => 1 .. 100, :desc => "retrieve at most +limit+ machines. Defaults to 10, max of 100"
end