Add middleware to record queue time (#34172)

lib/mastodon/middleware/prometheus_queue_time.rb

@@ -0,0 +1,26 @@
+# frozen_string_literal: true
+
+module Mastodon
+  module Middleware
+    class PrometheusQueueTime < ::PrometheusExporter::Middleware
+      # Overwrite to only collect the queue time metric
+      def call(env)
+        queue_time = measure_queue_time(env)
+
+        result = @app.call(env)
+
+        result
+      ensure
+        obj = {
+          type: 'web',
+          queue_time: queue_time,
+          default_labels: default_labels(env, result),
+        }
+        labels = custom_labels(env)
+        obj = obj.merge(custom_labels: labels) if labels
+
+        @client.send_json(obj)
+      end
+    end
+  end
+end