rack_honeypot.rb

# When a spammer wants to attack your site, they'll likely send an automated bot
# that will blindly fill out any forms it encounters. The idea of a "honeypot" is that
# you place a hidden field in a form. That's the honeypot. If this field is filled in, then 
# it's almost certain to be a spammer (since a normal user wouldn't have even seen the 
# field), and the contents of the form can safely be discarded. 

# Normally, you would implement a "honeypot" in a Rails app with some combination of a 
# special field in a particular form, and then some logic in the corresponding controller that 
# would check for content in the "honeypot" field. This is somewhat of an inefficient 
# approach, because it requires special code (not DRY), and bots are still going through an 
# entire request/response cycle with all of the normal action/controller overhead. 

# Using a Rack middleware strategy, you have a very low impact solution, both in terms of 
# code needed, and in terms of impact on your servers. All you need to do is to enable the 
# middleware and place a honeypot field in whatever forms you want to protect. Then, the middleware 
# will return a blank 200 OK response for any form posts that include a value for the honeypot field. 

# config/environment.rb

HONEYPOT_FIELD_NAME = 'something_unique_to_your_app'
config.middleware.use "Rack::Honeypot", HONEYPOT_FIELD_NAME

# lib/rack/honeypot.rb

module Rack
  class Honeypot

    def initialize(app, field_name)
      @app = app
      @field_name = field_name
    end

    def call(env)
      form_hash = env["rack.request.form_hash"]

      if form_hash && form_hash[@field_name] =~ /\S/
        [200, {'Content-Type' => 'text/html', "Content-Length" => "0"}, []]
      else
        @app.call(env)
      end
    end
    
  end
end

# app/views/posts/new.html.erb

<% form_for Post.new do |f| %>

  <%= f.text_area :body %>

  <div class="something_unique_to_your_app">
    <%= label_tag HONEYPOT_FIELD_NAME, 'Please leave this field empty:' %>
    <%= text_field_tag HONEYPOT_FIELD_NAME %>
  </div>

  <%= submit_tag 'Submit' %>

<% end %>

# public/stylesheets/application.css

# Replace HONEYPOT_FIELD_NAME with the name of your honeypot, as set in config/environment.rb

.HONEYPOT_FIELD_NAME { display: none; }

# That's it!