Preload context to avoid remote loading

Loading a local version of the context is recommended for several reasons.

* It reduces test run time from 53 seconds to less than a second.
* It ensures that our hard-coded URIs are in sync with the used context.
* It guards us against network errors and downtime of the DFC website.

src/org/datafoodconsortium/connector/codegen/ruby/static/lib/datafoodconsortium/connector/connector.rb

@@ -21,6 +21,7 @@
 # SOFTWARE.
 
 require 'singleton'
+require 'datafoodconsortium/connector/context'
 require 'datafoodconsortium/connector/json_ld_serializer'
 
 class DataFoodConsortium::Connector::Connector

src/org/datafoodconsortium/connector/codegen/ruby/static/lib/datafoodconsortium/connector/context.rb

@@ -0,0 +1,67 @@
+# frozen_string_literal: true
+
+require 'json/ld'
+
+# Preload the DFC context.
+#
+# Similar to: https://github.com/ruby-rdf/json-ld-preloaded/
+module DataFoodConsortium
+  module Connector
+    class Context < JSON::LD::Context
+      VERSION_1_8 = JSON.parse <<~JSON
+        {
+          "rdfs": "http://www.w3.org/2000/01/rdf-schema#",
+          "skos" : "http://www.w3.org/2004/02/skos/core#",
+          "dfc": "https://github.com/datafoodconsortium/ontology/releases/latest/download/DFC_FullModel.owl#",
+          "dc": "http://purl.org/dc/elements/1.1/#",
+          "dfc-b": "https://github.com/datafoodconsortium/ontology/releases/latest/download/DFC_BusinessOntology.owl#",
+          "dfc-p": "https://github.com/datafoodconsortium/ontology/releases/latest/download/DFC_ProductGlossary.owl#",
+          "dfc-t": "https://github.com/datafoodconsortium/ontology/releases/latest/download/DFC_TechnicalOntology.owl#",
+          "dfc-m": "https://github.com/datafoodconsortium/taxonomies/releases/latest/download/measures.rdf#",
+          "dfc-pt": "https://github.com/datafoodconsortium/taxonomies/releases/latest/download/productTypes.rdf#",
+          "dfc-f": "https://github.com/datafoodconsortium/taxonomies/releases/latest/download/facets.rdf#",
+          "ontosec": "http://www.semanticweb.org/ontologies/2008/11/OntologySecurity.owl#",
+          "dfc-p:hasUnit":{ "@type":"@id" },
+          "dfc-b:hasUnit":{ "@type":"@id" },
+          "dfc-b:hasQuantity":{ "@type":"@id" },
+          "dfc-p:hasType":{ "@type":"@id" },
+          "dfc-b:hasType":{ "@type":"@id" },
+          "dfc-b:references":{ "@type":"@id" },
+          "dfc-b:referencedBy":{ "@type":"@id" },
+          "dfc-b:offeres":{ "@type":"@id" },
+          "dfc-b:supplies":{ "@type":"@id" },
+          "dfc-b:defines":{ "@type":"@id" },
+          "dfc-b:affiliates":{ "@type":"@id" },
+          "dfc-b:hasCertification":{ "@type":"@id" },
+          "dfc-b:manages":{ "@type":"@id" },
+          "dfc-b:offeredThrough":{ "@type":"@id" },
+          "dfc-b:hasBrand":{ "@type":"@id" },
+          "dfc-b:hasGeographicalOrigin":{ "@type":"@id" },
+          "dfc-b:hasClaim":{ "@type":"@id" },
+          "dfc-b:hasAllergenDimension":{ "@type":"@id" },
+          "dfc-b:hasNutrientDimension":{ "@type":"@id" },
+          "dfc-b:hasPhysicalDimension":{ "@type":"@id" },
+          "dfc:owner":{ "@type":"@id" },
+          "dfc-t:hostedBy":{ "@type":"@id" },
+          "dfc-t:hasPivot":{ "@type":"@id" },
+          "dfc-t:represent":{ "@type":"@id" }
+        }
+      JSON
+
+      add_preloaded("http://www.datafoodconsortium.org/") { parse(VERSION_1_8) }
+
+      # This is the actual file the DFC website refers to in a link header.
+      alias_preloaded(
+        "https://www.datafoodconsortium.org/wp-content/plugins/wordpress-context-jsonld/context.jsonld",
+        "http://www.datafoodconsortium.org/"
+      )
+
+      # This is the old URL that's not online anymore.
+      # Keep it for compatiblity with all versions before 1.8.
+      alias_preloaded(
+        "http://static.datafoodconsortium.org/ontologies/context.json",
+        "http://www.datafoodconsortium.org/"
+      )
+    end
+  end
+end