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Pandurang Waghulde

When your application has a form that’s available to everyone for eg. Contact us, you will be spammed! So what can we do about it?

Well, one option is to have all forms secured by authentication… OR we can use a captcha. So, Here is how you can implement your own simple captcha in Ruby on Rails,

First of all we will create Captcha class in lib folder,

captcha.rb
class Captcha
  attr_accessor :operand1, :operand2, :operator


  def initialize
    @operand1 = (1..10).to_a.sample
    @operand2 = (1..10).to_a.sample
    @operator = [:+, :*, :-].sample
  end


  def initialize_from(secret)
    yml = YAML.load(Base64.decode64(secret))
    @operand1, @operand2, @operator = yml[:operand1], yml[:operand2], yml[:operator]
  end


  def correct?(value)
    result == value.to_i
  end


  def encrypt
    Base64.encode64 to_yaml
  end


  def self.decrypt(secret)
    result = new
    result.initialize_from secret
    result
  end


  def to_yaml
    YAML::dump({
      :operand1 => @operand1,
      :operand2 => @operand2,
      :operator => @operator
    })
  end


  def question
    "#{@operand1} #{@operator.to_s} #{@operand2} = ?"
  end


  private


  def result
    @operand1.send @operator, @operand2
  end
end

Here we are dumping the variables into a string using YAML and then encrypt/decrypt.

Then in your Controller,

class ContactsController < ApplicationController


  def new
    @captcha = Captcha.new
  end


  def create
    @captcha = Captcha.decrypt(params[:captcha_secret])


    unless @captcha.correct?(params[:captcha])
      flash.now[:alert] = "Please make sure you entered correct value for captcha."
      # Here we need to initialize @captcha with new object in order to show
      # different captcha each time on form
      @captcha = Captcha.new
      render :new
    else
      ContactsMailer.notify(contact).deliver
      flash[:notice] = "Your message has been sent successfully"
      redirect_to root_path
    end
  end
end

In your view,

<div class="field">
  <%= hidden_field_tag :captcha_secret, @captcha.encrypt %>
  <%= label_tag :captcha, @captcha.question %>
  <%= text_field_tag :captcha, "" %>
</div>

That’s it. And it will look similar to this,

captcha