Feature: URI drerfrencement content negotiation

controllers/dereference_resource_controller.rb

@@ -1,5 +1,6 @@
 require_relative '../test/test_case'
 
+use Rack::ContentNegotiation
 
 class DereferenceResourceController < ApplicationController
   namespace "/ontologies" do
@@ -11,7 +12,8 @@
         error 500, "Usage: ontologies/:acronym/resolve/:uri?output_format= OR POST: acronym, uri, output_format parameters"
       end
 
-      output_format = params[:output_format].presence || 'jsonld'
+      output_format = env["format"].presence || params[:output_format].presence || 'application/n-triples'
+
       process_request(acronym, uri, output_format)
     end
 
@@ -28,25 +30,19 @@
 
       r = Resource.new(sub.id, uri)
       case output_format
-      when 'jsonld'
-        content_type 'application/json'
-        reply  JSON.parse(r.to_json)
-      when 'json'
-        content_type 'application/json'
-        reply JSON.parse(r.to_json)
-      when 'xml'
-        content_type 'application/xml'
-        reply r.to_xml
-      when 'turtle'
-        content_type 'text/turtle'
-        reply r.to_turtle
-      when 'ntriples'
-        content_type 'application/n-triples'
-        reply r.to_ntriples
+      when 'application/ld+json', 'application/json'
+          r.to_json
+      when 'application/rdf+xml', 'application/xml'
+          r.to_xml
+      when 'text/turtle'
+          r.to_turtle
+      when 'application/n-triples'
+          r.to_ntriples
       else
-        error 500, "Invalid output format"
+          error 500, "Invalid output format, valid format are: application/json, application/ld+json,  application/xml, application/rdf+xml, text/turtle and application/n-triples"
       end
 
+
     end
 
     def valid_url?(url)

lib/rack/content_negotiation.rb

@@ -0,0 +1,131 @@
+module Rack
+  class ContentNegotiation
+    DEFAULT_CONTENT_TYPE = "application/n-triples" # N-Triples
+    VARY = { 'Vary' => 'Accept' }.freeze
+    ENDPOINTS_FILTER = %r{^/ontologies/[^/]+/resolve/[^/]+$} # Accepted API endpoints to apply content negotiation
+
+    # @return [#call]
+    attr_reader :app
+
+    # @return [Hash{Symbol => String}]
+    attr_reader :options
+
+    ##
+    # @param  [#call]                  app
+    # @param  [Hash{Symbol => Object}] options
+    #   Other options passed to writer.
+    # @option options [String] :default (DEFAULT_CONTENT_TYPE) Specific content type
+    # @option options [RDF::Format, #to_sym] :format Specific RDF writer format to use
+    def initialize(app, options = {})
+      @app, @options = app, options
+      @options[:default] = (@options[:default] || DEFAULT_CONTENT_TYPE).to_s
+    end
+
+    ##
+    # Handles a Rack protocol request.
+    # Parses Accept header to find appropriate mime-type and sets content_type accordingly.
+    #
+    # Inserts ordered content types into the environment as `ORDERED_CONTENT_TYPES` if an Accept header is present
+    #
+    # @param  [Hash{String => String}] env
+    # @return [Array(Integer, Hash, #each)] Status, Headers and Body
+    # @see    https://rubydoc.info/github/rack/rack/file/SPEC
+    def call(env)
+      if env['PATH_INFO'].match?(ENDPOINTS_FILTER)
+        if env.has_key?('HTTP_ACCEPT')
+          accepted_types = parse_accept_header(env['HTTP_ACCEPT'])
+          if !accepted_types.empty?
+            env["format"] = accepted_types.first
+            add_content_type_header(app.call(env), env["format"])
+          else
+            not_acceptable
+          end
+        else
+          env["format"] = options[:default]
+          add_content_type_header(app.call(env), env["format"])
+        end
+      else
+        app.call(env)
+      end
+    end
+
+    protected
+
+    # Parses an HTTP `Accept` header, returning an array of MIME content types ordered by precedence rules.
+    #
+    # @param  [String, #to_s] header
+    # @return [Array<String>] Array of content types sorted by precedence
+    # @see    https://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1
+    def parse_accept_header(header)
+      entries = header.to_s.split(',')
+      parsed_entries = entries.map { |entry| parse_accept_entry(entry) }
+      sorted_entries = parsed_entries.sort_by { |entry| entry.quality }.reverse
+      content_types = sorted_entries.map { |entry| entry.content_type }
+      content_types.flatten.compact
+    end
+
+
+
+    # Parses an individual entry from the Accept header.
+    #
+    # @param [String] entry An entry from the Accept header
+    # @return [Entry] An object representing the parsed entry
+    def parse_accept_entry(entry)
+      # Represents an entry parsed from the Accept header
+      entry_struct = Struct.new(:content_type, :quality, :wildcard_count, :param_count)
+      content_type, *params = entry.split(';').map(&:strip)
+      quality = 1.0 # Default quality
+      params.reject! do |param|
+        if param.start_with?('q=')
+          quality = param[2..-1].to_f
+          true
+        end
+      end
+      wildcard_count = content_type.count('*')
+      entry_struct.new(content_type, quality, wildcard_count, params.size)
+    end
+
+
+    ##
+    # Returns a content type appropriate for the given `media_range`,
+    # returns `nil` if `media_range` contains a wildcard subtype
+    # that is not mapped.
+    #
+    # @param  [String, #to_s] media_range
+    # @return [String, nil]
+    def find_content_type_for_media_range(media_range)
+      case media_range.to_s
+      when '*/*', 'text/*'
+        options[:default]
+      when 'application/n-triples'
+        'application/n-triples'
+      when 'text/turtle'
+        'text/turtle'
+      when 'application/json', 'application/ld+json', 'application/*'
+        'application/ld+json'
+      when 'text/xml', 'text/rdf+xml',  'application/rdf+xml', 'application/xml'
+        'application/rdf+xml'
+      else
+        nil
+      end
+    end
+
+    ##
+    # Outputs an HTTP `406 Not Acceptable` response.
+    #
+    # @param  [String, #to_s] message
+    # @return [Array(Integer, Hash, #each)]
+    def not_acceptable(message = nil)
+      code = 406
+      http_status =  [code, Rack::Utils::HTTP_STATUS_CODES[code]].join(' ')
+      message = http_status + (message.nil? ? "\n" : " (#{message})\n")
+      [code, { 'Content-Type' => "text/plain" }.merge(VARY), [message]]
+    end
+
+    def add_content_type_header(response, type)
+      response[1] = response[1].merge(VARY).merge('Content-Type' => type)
+      response
+    end
+
+  end
+end

test/controllers/test_dereference_resource_controller.rb

@@ -20,7 +20,8 @@ def self.before_suite
   end
 
   def test_dereference_resource_controller_json
-    get "/ontologies/#{@@graph}/resolve/#{@@uri}?output_format=json"
+    header 'Accept', 'application/json'
+    get "/ontologies/#{@@graph}/resolve/#{@@uri}"
     assert last_response.ok?
 
     result = last_response.body
@@ -73,7 +74,8 @@ def test_dereference_resource_controller_json
   end
 
   def test_dereference_resource_controller_xml
-    get "/ontologies/#{@@graph}/resolve/#{@@uri}?output_format=xml"
+    header 'Accept', 'application/xml'
+    get "/ontologies/#{@@graph}/resolve/#{@@uri}"
     assert last_response.ok?
 
     result = last_response.body
@@ -124,7 +126,8 @@ def test_dereference_resource_controller_xml
   end
 
   def test_dereference_resource_controller_ntriples
-    get "/ontologies/#{@@graph}/resolve/#{@@uri}?output_format=ntriples"
+    header 'Accept', 'application/n-triples'
+    get "/ontologies/#{@@graph}/resolve/#{@@uri}"
     assert last_response.ok?
 
     result = last_response.body
@@ -135,16 +138,17 @@ def test_dereference_resource_controller_ntriples
           <http://opendata.inrae.fr/thesaurusINRAE/c_6496> <http://www.w3.org/2004/02/skos/core#topConceptOf> <http://opendata.inrae.fr/thesaurusINRAE/mt_65> .
           <http://opendata.inrae.fr/thesaurusINRAE/c_6496> <http://www.w3.org/2004/02/skos/core#inScheme> <http://opendata.inrae.fr/thesaurusINRAE/thesaurusINRAE> .
           <http://opendata.inrae.fr/thesaurusINRAE/c_6496> <http://www.w3.org/2004/02/skos/core#inScheme> <http://opendata.inrae.fr/thesaurusINRAE/mt_65> .
-          <http://opendata.inrae.fr/thesaurusINRAE/c_6496> <http://www.w3.org/2004/02/skos/core#prefLabel> "alt\\\\u00E9rationdel'ADN"@fr .
+          <http://opendata.inrae.fr/thesaurusINRAE/c_6496> <http://www.w3.org/2004/02/skos/core#prefLabel> "alt\\u00E9rationdel'ADN"@fr .
           <http://opendata.inrae.fr/thesaurusINRAE/mt_65> <http://www.w3.org/2004/02/skos/core#hasTopConcept> <http://opendata.inrae.fr/thesaurusINRAE/c_6496> .
     NTRIPLES
-    a = result.gsub('\\"', '"').gsub(' ', '')[1..-2].split("\\n").reject(&:empty?)
+    a = result.gsub(' ', '').split("\n").reject(&:empty?)
     b = expected_result.gsub(' ', '').split("\n").reject(&:empty?)
     assert_equal b.sort, a.sort
   end
 
   def test_dereference_resource_controller_turtle
-    get "/ontologies/#{@@graph}/resolve/#{@@uri}?output_format=turtle"
+    header 'Accept', 'text/turtle'
+    get "/ontologies/#{@@graph}/resolve/#{@@uri}"
     assert last_response.ok?
 
     result = last_response.body
@@ -164,7 +168,7 @@ def test_dereference_resource_controller_turtle
           ns0:mt_65
               skos:hasTopConcept ns0:c_6496 .
     TURTLE
-    a = result.gsub('\\"', '"').gsub(' ', '')[1..-2].split("\\n").reject(&:empty?)
+    a = result.gsub(' ', '').split("\n").reject(&:empty?)
     b = expected_result.gsub(' ', '').split("\n").reject(&:empty?)
 
     assert_equal b.sort, a.sort