throw error on counts/posts endpoint during a timeout (#2170)

app/controllers/counts_controller.rb

@@ -1,7 +1,8 @@
 class CountsController < ApplicationController
   respond_to :xml, :json
+  rescue_from Post::TimeoutError, with: :rescue_exception
 
   def posts
-    @count = Post.fast_count(params[:tags])
+    @count = Post.fast_count(params[:tags], raise_on_timeout: true)
   end
 end

app/models/post.rb

@@ -7,6 +7,7 @@ class Post < ApplicationRecord
   class RevertError < Exception ; end
   class SearchError < Exception ; end
   class DeletionError < Exception ; end
+  class TimeoutError < Exception ; end
 
   # Tags to copy when copying notes.
   NOTE_COPY_TAGS = %w[translated partially_translated check_translation translation_request reverse_translation]
@@ -1202,6 +1203,10 @@ class Post < ApplicationRecord
 
       if count.nil?
         # give up
+        if options[:raise_on_timeout]
+          raise TimeoutError.new("timed out")
+        end
+
         count = Danbooru.config.blank_tag_search_fast_count
       else
         set_count_in_cache(tags, count)

test/functional/counts_controller_test.rb

@@ -7,6 +7,12 @@ class CountsControllerTest < ActionDispatch::IntegrationTest
         get posts_counts_path
         assert_response :success
       end
+
+      should "render an error during a timeout" do
+        Post.stubs(:fast_count).raises(Post::TimeoutError.new)
+        get posts_counts_path
+        assert_response :error
+      end
     end
   end
 end