Add route information to lograge structured logging

changelogs/unreleased/an-api-route-logger.yml

+---
+title: Add route information to lograge structured logging for API logs
+merge_request: 21487
+author:
+type: other

lib/api/api.rb

@@ -15,6 +15,7 @@ module API
                   include: [
                     GrapeLogging::Loggers::FilterParameters.new,
                     GrapeLogging::Loggers::ClientEnv.new,
+                    Gitlab::GrapeLogging::Loggers::RouteLogger.new,
                     Gitlab::GrapeLogging::Loggers::UserLogger.new,
                     Gitlab::GrapeLogging::Loggers::QueueDurationLogger.new,
                     Gitlab::GrapeLogging::Loggers::PerfLogger.new

lib/gitlab/grape_logging/loggers/route_logger.rb

+# frozen_string_literal: true
+
+# This grape_logging module (https://github.com/aserafin/grape_logging) makes it
+# possible to log the details of the action
+module Gitlab
+  module GrapeLogging
+    module Loggers
+      class RouteLogger < ::GrapeLogging::Loggers::Base
+        def parameters(request, _)
+          endpoint = request.env[Grape::Env::API_ENDPOINT]
+          route = endpoint&.route&.pattern&.origin
+
+          return {} unless route
+
+          { route: route }
+        rescue
+          # endpoint.route calls env[Grape::Env::GRAPE_ROUTING_ARGS][:route_info]
+          # but env[Grape::Env::GRAPE_ROUTING_ARGS] is nil in the case of a 405 response
+          # so we're rescuing exceptions and bailing out
+          {}
+        end
+      end
+    end
+  end
+end