controllers: refactor rate limits.

Refactor controllers so that endpoint rate limits are declared locally,
with the endpoint, instead of globally, in a single method in ApplicationController.

This way an endpoint's rate limit is declared in the same file as the
endpoint itself.

This is so we can add fine-grained rate limits for certain GET requests.
Before rate limits were only for non-GET requests.

app/controllers/application_controller.rb

@@ -8,7 +8,7 @@ class ApplicationController < ActionController::Base
   before_action :reset_current_user
   before_action :set_current_user
   before_action :normalize_search
-  before_action :check_rate_limit
+  before_action :check_default_rate_limit
   before_action :ip_ban_check
   before_action :set_variant
   before_action :add_headers
@@ -25,6 +25,23 @@ class ApplicationController < ActionController::Base
     end
   end
 
+  # Define a rate limit for the given controller action.
+  #
+  # @example
+  #   rate_limit :index, 1.0/1.minute, 50, if: -> { request.format.atom? }
+  def self.rate_limit(action, rate:, burst:, key: "#{controller_name}:#{action}", if: nil)
+    if_proc = binding.local_variable_get(:if)
+
+    before_action(only: action, if: if_proc) do
+      key = "#{controller_name}:#{action}"
+      rate_limiter = RateLimiter.build(action: key, rate: rate, burst: burst, user: CurrentUser.user, ip_addr: CurrentUser.ip_addr)
+      headers["X-Rate-Limit"] = rate_limiter.to_json
+      rate_limiter.limit!
+    end
+
+    skip_before_action :check_default_rate_limit, only: action, if: if_proc
+  end
+
   private
 
   def respond_with(subject, *args, model: model_name, **options, &block)
@@ -69,12 +86,20 @@ class ApplicationController < ActionController::Base
     response.headers["X-Git-Hash"] = Rails.application.config.x.git_hash
   end
 
-  def check_rate_limit
+  # Apply the default rate limit to all update actions (POST, PUT, or DELETE), unless the
+  # endpoint already declared a more specific rate limit using the `rate_limit` macro above.
+  def check_default_rate_limit
     return if request.get? || request.head?
 
-    rate_limiter = RateLimiter.for_action(controller_name, action_name, CurrentUser.user, CurrentUser.ip_addr)
-    headers["X-Rate-Limit"] = rate_limiter.to_json
+    rate_limiter = RateLimiter.build(
+      action: "#{controller_name}:#{action_name}",
+      rate: CurrentUser.user.api_regen_multiplier,
+      burst: 200,
+      user: CurrentUser.user,
+      ip_addr: CurrentUser.ip_addr,
+    )
 
+    headers["X-Rate-Limit"] = rate_limiter.to_json
     rate_limiter.limit!
   end
 

app/controllers/comment_votes_controller.rb

@@ -1,6 +1,9 @@
 class CommentVotesController < ApplicationController
   respond_to :js, :json, :xml, :html
 
+  rate_limit :create,  rate: 1.0/1.second, burst: 200
+  rate_limit :destroy, rate: 1.0/1.second, burst: 200
+
   def index
     @comment_votes = authorize CommentVote.visible(CurrentUser.user).paginated_search(params, count_pages: true)
     @comment_votes = @comment_votes.includes(:user, comment: [:creator, { post: [:uploader, :media_asset] }]) if request.format.html?

app/controllers/comments_controller.rb

@@ -2,6 +2,8 @@ class CommentsController < ApplicationController
   respond_to :html, :xml, :json, :atom
   respond_to :js, only: [:new, :update, :destroy, :undelete]
 
+  rate_limit :create, rate: 1.0/1.minute, burst: 50
+
   def index
     params[:group_by] ||= "comment" if params[:search].present?
 

app/controllers/dmails_controller.rb

@@ -1,6 +1,8 @@
 class DmailsController < ApplicationController
   respond_to :html, :xml, :js, :json
 
+  rate_limit :create, rate: 1.0/1.minute, burst: 50
+
   def new
     if params[:respond_to_id]
       parent = authorize Dmail.find(params[:respond_to_id]), :show?

app/controllers/emails_controller.rb

@@ -2,6 +2,8 @@ class EmailsController < ApplicationController
   before_action :requires_reauthentication, only: [:edit, :update]
   respond_to :html, :xml, :json
 
+  rate_limit :update, rate: 1.0/1.minute, burst: 10
+
   def index
     @email_addresses = authorize EmailAddress.visible(CurrentUser.user).paginated_search(params, count_pages: true)
     @email_addresses = @email_addresses.includes(:user)

app/controllers/favorites_controller.rb

@@ -1,6 +1,9 @@
 class FavoritesController < ApplicationController
   respond_to :js, :json, :html, :xml
 
+  rate_limit :create,  rate: 1.0/1.second, burst: 200
+  rate_limit :destroy, rate: 1.0/1.second, burst: 200
+
   def index
     post_id = params[:post_id] || params[:search][:post_id]
     user_id = params[:user_id] || params[:search][:user_id]

app/controllers/forum_posts_controller.rb

@@ -1,6 +1,8 @@
 class ForumPostsController < ApplicationController
   respond_to :html, :xml, :json, :js
 
+  rate_limit :create, rate: 1.0/1.minute, burst: 50
+
   def new
     @forum_post = authorize ForumPost.new_reply(params)
     respond_with(@forum_post)

app/controllers/forum_topics_controller.rb

@@ -3,6 +3,8 @@ class ForumTopicsController < ApplicationController
   respond_to :atom, only: [:index, :show]
   before_action :normalize_search, :only => :index
 
+  rate_limit :create, rate: 1.0/1.minute, burst: 50
+
   def new
     @forum_topic = authorize ForumTopic.new
     @forum_topic.original_post = ForumPost.new

app/controllers/moderation_reports_controller.rb

@@ -1,6 +1,8 @@
 class ModerationReportsController < ApplicationController
   respond_to :html, :xml, :json, :js
 
+  rate_limit :create, rate: 1.0/1.minute, burst: 10
+
   def new
     @moderation_report = authorize ModerationReport.new(permitted_attributes(ModerationReport))
     respond_with(@moderation_report)

app/controllers/post_disapprovals_controller.rb

@@ -1,6 +1,8 @@
 class PostDisapprovalsController < ApplicationController
   respond_to :js, :html, :json, :xml
 
+  rate_limit :destroy, rate: 1.0/1.second, burst: 200
+
   def create
     @post_disapproval = authorize PostDisapproval.new(user: CurrentUser.user, **permitted_attributes(PostDisapproval))
     @post_disapproval.save

app/controllers/post_votes_controller.rb

@@ -1,6 +1,9 @@
 class PostVotesController < ApplicationController
   respond_to :js, :json, :xml, :html
 
+  rate_limit :create,  rate: 1.0/1.second, burst: 200
+  rate_limit :destroy, rate: 1.0/1.second, burst: 200
+
   def index
     @post_votes = authorize PostVote.visible(CurrentUser.user).paginated_search(params)
     @post_votes = @post_votes.includes(:user, post: [:uploader, :media_asset]) if request.format.html?

app/controllers/sessions_controller.rb

@@ -2,6 +2,8 @@ class SessionsController < ApplicationController
   respond_to :html, :json
   skip_forgery_protection only: :create, if: -> { !request.format.html? }
 
+  rate_limit :create, rate: 1.0/1.minute, burst: 10
+
   def new
     @user = User.new
   end

app/controllers/users_controller.rb

@@ -1,6 +1,8 @@
 class UsersController < ApplicationController
   respond_to :html, :xml, :json
 
+  rate_limit :create, rate: 1.0/5.minutes, burst: 10
+
   def new
     @user = authorize User.new
     @user.email_address = EmailAddress.new

app/logical/rate_limiter.rb

@@ -21,34 +21,19 @@ class RateLimiter
     @burst = burst
   end
 
-  # Create a RateLimiter object for the current controller, action, user, and
-  # IP. A RateLimiter usually has two RateLimits, one for the user and one for
-  # their IP. The action is limited if either the user or their IP are limited.
+  # Create a RateLimiter object for the given action. A RateLimiter usually has
+  # two RateLimits, one for the user and one for their IP. The action is
+  # limited if either the user or their IP are limited.
   #
-  # @param controller_name [String] the current controller
-  # @param action_name [String] the current controller action
-  # @param user [User] the current user
-  # @param ip_addr [String] the user's IP address
-  # @return [RateLimit] the rate limit for the action
-  def self.for_action(controller_name, action_name, user, ip_addr)
-    action = "#{controller_name}:#{action_name}"
+  # @param action [String] An identifier for the action being rate limited.
+  # @param rate [Float] The rate limit, in actions per second.
+  # @param burst [Float] The burst limit (the maximum number of actions you can
+  #   perform in one burst before being rate limited).
+  # @param user [User] The current user.
+  # @param ip_addr [String] The user's IP address.
+  # @return [RateLimit] The rate limit for the action.
+  def self.build(action:, rate:, burst:, user:, ip_addr:)
     keys = [(user.cache_key unless user.is_anonymous?), "ip/#{ip_addr.to_s}"].compact
-
-    case action
-    when "users:create"
-      rate, burst = 1.0 / 5.minutes, 10
-    when "emails:update", "sessions:create", "moderation_reports:create"
-      rate, burst = 1.0 / 1.minute, 10
-    when "dmails:create", "comments:create", "forum_posts:create", "forum_topics:create"
-      rate, burst = 1.0 / 1.minute, 50
-    when "comment_votes:create", "comment_votes:destroy", "post_votes:create",
-         "post_votes:destroy", "favorites:create", "favorites:destroy", "post_disapprovals:create"
-      rate, burst = 1.0 / 1.second, 200
-    else
-      rate = user.api_regen_multiplier
-      burst = 200
-    end
-
     RateLimiter.new(action, keys, rate: rate, burst: burst)
   end