Slightly reduce RAM usage (#7301)

* No need to re-require sidekiq plugins, they are required via Gemfile

* Add derailed_benchmarks tool, no need to require TTY gems in Gemfile

* Replace ruby-oembed with FetchOEmbedService

Reduce startup by 45382 allocated objects

* Remove preloaded JSON-LD in favour of caching HTTP responses

Reduce boot RAM by about 6 MiB

* Fix tests

* Fix test suite by stubbing out JSON-LD contexts

1 files changed, 16 insertions, 1 deletions

diff --git a/app/helpers/jsonld_helper.rb b/app/helpers/jsonld_helper.rb
index a3cfdadb8..e9056166c 100644
--- a/app/helpers/jsonld_helper.rb
+++ b/app/helpers/jsonld_helper.rb
@@ -48,7 +48,7 @@ module JsonLdHelper
   end
 
   def canonicalize(json)
-    graph = RDF::Graph.new << JSON::LD::API.toRdf(json)
+    graph = RDF::Graph.new << JSON::LD::API.toRdf(json, documentLoader: method(:load_jsonld_context))
     graph.dump(:normalize)
   end
 
@@ -90,4 +90,19 @@ module JsonLdHelper
     request.add_headers('Accept' => 'application/activity+json, application/ld+json')
     request
   end
+
+  def load_jsonld_context(url, _options = {}, &_block)
+    json = Rails.cache.fetch("jsonld:context:#{url}", expires_in: 30.days, raw: true) do
+      request = Request.new(:get, url)
+      request.add_headers('Accept' => 'application/ld+json')
+
+      request.perform do |res|
+        raise JSON::LD::JsonLdError::LoadingDocumentFailed unless res.code == 200 && res.mime_type == 'application/ld+json'
+        res.body_with_limit
+      end
+    end
+
+    doc = JSON::LD::API::RemoteDocument.new(url, json)
+    block_given? ? yield(doc) : doc
+  end
 end