Check for env[Grape::Env::GRAPE_ROUTING_ARGS] instead of endpoint.route

`endpoint.route` is calling `env[Grape::Env::GRAPE_ROUTING_ARGS][:route_info]`
but `env[Grape::Env::GRAPE_ROUTING_ARGS]` is `nil` in the case of a 405 response
Signed-off-by: Rémy Coutable <remy@rymai.me>

changelogs/unreleased/26587-metrics-middleware-endpoint-is-nil.yml

+---
+title: Check for env[Grape::Env::GRAPE_ROUTING_ARGS] instead of endpoint.route
+merge_request: 8544
+author:

lib/gitlab/metrics/rack_middleware.rb

@@ -71,10 +71,17 @@ module Gitlab
       def tag_endpoint(trans, env)
         endpoint = env[ENDPOINT_KEY]
 
-        # endpoint.route is nil in the case of a 405 response
-        if endpoint.route
-          path = endpoint_paths_cache[endpoint.route.request_method][endpoint.route.path]
-          trans.action = "Grape##{endpoint.route.request_method} #{path}"
+        begin
+          route = endpoint.route
+        rescue
+          # endpoint.route is calling 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
+
+        if route
+          path = endpoint_paths_cache[route.request_method][route.path]
+          trans.action = "Grape##{route.request_method} #{path}"
         end
       end
 

spec/lib/gitlab/metrics/rack_middleware_spec.rb

@@ -126,5 +126,16 @@ describe Gitlab::Metrics::RackMiddleware do
 
       expect(transaction.action).to eq('Grape#GET /projects/:id/archive')
     end
+
+    it 'does not tag a transaction if route infos are missing' do
+      endpoint = double(:endpoint)
+      allow(endpoint).to receive(:route).and_raise
+
+      env['api.endpoint'] = endpoint
+
+      middleware.tag_endpoint(transaction, env)
+
+      expect(transaction.action).to be_nil
+    end
   end
 end