Fix setting Gitlab metrics content types

The method "content_type" on a controller does not always return the
correct content type. On the other hand, the method "request_format"
does _and_ immediately returns a Symbol (e.g. :json) instead of a
mime-type name (e.g. application/json). With these changes metrics
should again report their action names correctly.

Fixes https://gitlab.com/gitlab-com/infrastructure/issues/3499

changelogs/unreleased/fix-metrics-content-types.yml

+---
+title: Fix setting Gitlab metrics content types
+merge_request:
+author:
+type: fixed

lib/gitlab/metrics/web_transaction.rb

@@ -4,18 +4,6 @@ module Gitlab
       CONTROLLER_KEY = 'action_controller.instance'.freeze
       ENDPOINT_KEY = 'api.endpoint'.freeze
 
-      CONTENT_TYPES = {
-        'text/html' => :html,
-        'text/plain' => :txt,
-        'application/json' => :json,
-        'text/js' => :js,
-        'application/atom+xml' => :atom,
-        'image/png' => :png,
-        'image/jpeg' => :jpeg,
-        'image/gif' => :gif,
-        'image/svg+xml' => :svg
-      }.freeze
-
       def initialize(env)
         super()
         @env = env
@@ -40,7 +28,7 @@ module Gitlab
         controller = @env[CONTROLLER_KEY]
 
         action = "#{controller.action_name}"
-        suffix = CONTENT_TYPES[controller.content_type]
+        suffix = controller.request_format
 
         if suffix && suffix != :html
           action += ".#{suffix}"

spec/lib/gitlab/metrics/web_transaction_spec.rb

@@ -180,11 +180,11 @@ describe Gitlab::Metrics::WebTransaction do
     end
 
     context 'when request goes to ActionController' do
-      let(:content_type) { 'text/html' }
+      let(:request_format) { :html }
 
       before do
         klass = double(:klass, name: 'TestController')
-        controller = double(:controller, class: klass, action_name: 'show', content_type: content_type)
+        controller = double(:controller, class: klass, action_name: 'show', request_format: request_format)
 
         env['action_controller.instance'] = controller
       end
@@ -195,7 +195,7 @@ describe Gitlab::Metrics::WebTransaction do
       end
 
       context 'when the response content type is not :html' do
-        let(:content_type) { 'application/json' }
+        let(:request_format) { :json }
 
         it 'appends the mime type to the transaction action' do
           expect(transaction.labels).to eq({ controller: 'TestController', action: 'show.json' })