discourse/app/controllers/clicks_controller.rb

class ClicksController < ApplicationController

  skip_before_filter :check_xhr

  def track
    params = track_params.merge(ip: request.remote_ip)

    if params[:topic_id].present? || params[:post_id].present?
      params.merge!({ user_id: current_user.id }) if current_user.present?
      @redirect_url = TopicLinkClick.create_from(params)

      if @redirect_url.blank? && params[:url].index('?')
        # Check the url without query parameters
        params[:url].sub!(/\?.*$/, '')
        @redirect_url = TopicLinkClick.create_from(params)
      end
    end

    # Sometimes we want to record a link without a 302. Since XHR has to load the redirected
    # URL we want it to not return a 302 in those cases.
    if params[:redirect] == 'false' || @redirect_url.blank?
      render nothing: true
    else
      redirect_to(@redirect_url)
    end
  end

  private

    def track_params
      params.require(:url)
      params.permit(:url, :post_id, :topic_id, :redirect)
    end

end