Coverage improvement and concern extraction for rate limit headers in API controller (#3625)

* Coverage for rate limit headers

* Move rate limit headers methods to concern

* Move throttle check to condition on before_action

* Move match_data variable into method

* Move utc timestamp to separate method

* Move header setting into smaller methods

* specs cleanup

2 files changed, 59 insertions, 13 deletions

diff --git a/app/controllers/api_controller.rb b/app/controllers/api_controller.rb
index 1e72549bd..42b85865e 100644
--- a/app/controllers/api_controller.rb
+++ b/app/controllers/api_controller.rb
@@ -4,11 +4,11 @@ class ApiController < ApplicationController
   DEFAULT_STATUSES_LIMIT = 20
   DEFAULT_ACCOUNTS_LIMIT = 40
 
+  include RateLimitHeaders
+
   skip_before_action :verify_authenticity_token
   skip_before_action :store_current_location
 
-  before_action :set_rate_limit_headers
-
   rescue_from ActiveRecord::RecordInvalid, Mastodon::ValidationError do |e|
     render json: { error: e.to_s }, status: 422
   end
@@ -43,17 +43,6 @@ class ApiController < ApplicationController
 
   protected
 
-  def set_rate_limit_headers
-    return if request.env['rack.attack.throttle_data'].nil?
-
-    now        = Time.now.utc
-    match_data = request.env['rack.attack.throttle_data']['api']
-
-    response.headers['X-RateLimit-Limit']     = match_data[:limit].to_s
-    response.headers['X-RateLimit-Remaining'] = (match_data[:limit] - match_data[:count]).to_s
-    response.headers['X-RateLimit-Reset']     = (now + (match_data[:period] - now.to_i % match_data[:period])).iso8601(6)
-  end
-
   def set_pagination_headers(next_path = nil, prev_path = nil)
     links = []
     links << [next_path, [%w(rel next)]] if next_path
diff --git a/app/controllers/concerns/rate_limit_headers.rb b/app/controllers/concerns/rate_limit_headers.rb
new file mode 100644
index 000000000..36cb91075
--- /dev/null
+++ b/app/controllers/concerns/rate_limit_headers.rb
@@ -0,0 +1,57 @@
+# frozen_string_literal: true
+
+module RateLimitHeaders
+  extend ActiveSupport::Concern
+
+  included do
+    before_action :set_rate_limit_headers, if: :rate_limited_request?
+  end
+
+  private
+
+  def set_rate_limit_headers
+    apply_header_limit
+    apply_header_remaining
+    apply_header_reset
+  end
+
+  def rate_limited_request?
+    !request.env['rack.attack.throttle_data'].nil?
+  end
+
+  def apply_header_limit
+    response.headers['X-RateLimit-Limit'] = rate_limit_limit
+  end
+
+  def rate_limit_limit
+    api_throttle_data[:limit].to_s
+  end
+
+  def apply_header_remaining
+    response.headers['X-RateLimit-Remaining'] = rate_limit_remaining
+  end
+
+  def rate_limit_remaining
+    (api_throttle_data[:limit] - api_throttle_data[:count]).to_s
+  end
+
+  def apply_header_reset
+    response.headers['X-RateLimit-Reset'] = rate_limit_reset
+  end
+
+  def rate_limit_reset
+    (request_time + reset_period_offset).iso8601(6)
+  end
+
+  def api_throttle_data
+    request.env['rack.attack.throttle_data']['api']
+  end
+
+  def request_time
+    @_request_time ||= Time.now.utc
+  end
+
+  def reset_period_offset
+    api_throttle_data[:period] - request_time.to_i % api_throttle_data[:period]
+  end
+end