miharekar/Prevent email sending in Rails.md

## Prevent email sending in Rails.md

      
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              Prevent email sending in Rails.md
            
          
    #rails #actionmailer #callbacks
Callbacks for mailers are implemented using AbstractController::Callbacks.
This has a terminator lambda: https://github.com/rails/rails/blob/6af9cba73db6296ab9aec7dbeae1e193ea69f09f/actionpack/lib/abstract_controller/callbacks.rb#L34
AbstractController::Base defines performed? as: return response_body https://github.com/rails/rails/blob/6af9cba73db6296ab9aec7dbeae1e193ea69f09f/actionpack/lib/abstract_controller/base.rb#L188
So - as soon as we set any response body, no other callbacks or actions will occur.
Simple implementation:
class ApplicationMailer < ActionMailer::Base
  before_action :check_subscription

  private

  def check_subscription
    return unless params[:user].is_a?(User)

    prefix = self.class.name.sub(/Mailer$/, "").underscore.to_sym
    return unless User::ALL_EMAIL_SUBSCRIPTIONS.fetch(prefix, []).include?(action_name.to_sym)

    subscription = "#{prefix}_#{action_name}"
    self.response_body = :do_not_deliver unless params[:user].subscribed_to?(subscription)
  end
end