add rate limit

app/controllers/api/api_base_controller.rb

@@ -19,6 +19,12 @@ module Api
       render json: { error: e.message }, status: :unprocessable_entity
     end
 
+    rescue_from RateLimit::LimitApproached do |e|
+      Rollbar.error(e) if defined?(Rollbar)
+
+      render json: { error: 'Too many requests' }, status: :too_many_requests
+    end
+
     if Rails.env.production?
       rescue_from CanCan::AccessDenied do |e|
         Rollbar.warning(e) if defined?(Rollbar)

app/controllers/application_controller.rb

@@ -22,6 +22,12 @@ class ApplicationController < ActionController::Base
     redirect_to request.path
   end
 
+  rescue_from RateLimit::LimitApproached do |e|
+    Rollbar.error(e) if defined?(Rollbar)
+
+    redirect_to request.referer, alert: 'Too many requests', status: :too_many_requests
+  end
+
   if Rails.env.production?
     rescue_from CanCan::AccessDenied do |e|
       Rollbar.warning(e) if defined?(Rollbar)

app/controllers/send_submission_email_controller.rb

@@ -21,6 +21,8 @@ class SendSubmissionEmailController < ApplicationController
         Submitter.find_by!(slug: params[:submitter_slug])
       end
 
+    RateLimit.call("send-email-#{@submitter.id}", limit: 2, ttl: 5.minutes)
+
     SubmitterMailer.documents_copy_email(@submitter, sig: true).deliver_later!
 
     respond_to do |f|

lib/rate_limit.rb

@@ -0,0 +1,19 @@
+# frozen_string_literal: true
+
+module RateLimit
+  LimitApproached = Class.new(StandardError)
+
+  STORE = ActiveSupport::Cache::MemoryStore.new
+
+  module_function
+
+  def call(key, limit:, ttl:, enabled: Docuseal.multitenant?)
+    return true unless enabled
+
+    value = STORE.increment(key, 1, expires_in: ttl)
+
+    raise LimitApproached if value > limit
+
+    true
+  end
+end