class Rack::SPARQL::ContentNegotiation
Rack
middleware for SPARQL
content negotiation.
Uses HTTP Content Negotiation to find an appropriate RDF
format to serialize any result with a body being `RDF::Enumerable`.
Override content negotiation by setting the :format option to {Rack::SPARQL#initialize}.
This endpoint also serves the fuction of Rack::LinkedData, as it will serialize SPARQL
results, which may be RDF
Graphs
Constants
- VARY
Attributes
@!attribute [r] app @return [#call]
@!attribute [r] options @return [Hash{Symbol => Object}]
Public Class Methods
@param [#call] app @param [Hash{Symbol => Object}] options
Other options passed to writer.
@option options [RDF::Format, to_sym] :format Specific RDF
writer format to use
# File lib/rack/sparql/conneg.rb, line 32 def initialize(app, options = {}) @app, @options = app, options end
Public Instance Methods
Handles a Rack
protocol request. Parses Accept header to find appropriate mime-type and sets content_type accordingly.
If result is `RDF::Literal::Boolean`, `RDF::Query::Results`, or `RDF::Enumerable` The result is serialized using {SPARQL::Results}
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)] @see www.rubydoc.info/github/rack/rack/Rack/Runtime#call-instance_method
# File lib/rack/sparql/conneg.rb, line 47 def call(env) env['ORDERED_CONTENT_TYPES'] = parse_accept_header(env['HTTP_ACCEPT']) if env.has_key?('HTTP_ACCEPT') response = app.call(env) body = response[2].respond_to?(:body) ? response[2].body : response[2] case body when RDF::Enumerable, RDF::Query::Solutions, RDF::Literal::Boolean response[2] = body # Put it back in the response, it might have been a proxy serialize(env, *response) else response end end
Serializes a SPARQL
query result into a Rack
protocol response using HTTP content negotiation rules or a specified Content-Type.
@param [Hash{String => String}] env @param [Integer] status @param [Hash{String => Object}] headers @param [RDF::Enumerable] body @return [Array(Integer, Hash
, each)] @raise [RDF::WriterError] when no results are generated
# File lib/rack/sparql/conneg.rb, line 69 def serialize(env, status, headers, body) begin serialize_options = {} serialize_options[:content_types] = env['ORDERED_CONTENT_TYPES'] if env['ORDERED_CONTENT_TYPES'] serialize_options.merge!(@options) results = ::SPARQL.serialize_results(body, **serialize_options) raise RDF::WriterError, "can't serialize results" unless results headers = headers.merge(VARY).merge('Content-Type' => results.content_type) # FIXME: don't overwrite existing Vary headers [status, headers, [results]] rescue RDF::WriterError => e # Use this instead of not_acceptable so that headers are not lost. http_error(406, e.message, headers.merge(VARY)) end end
Protected Instance Methods
# File lib/rack/sparql/conneg.rb, line 98 def accept_entry(entry) type, *options = entry.delete(' ').split(';') quality = 0 # we sort smallest first options.delete_if { |e| quality = 1 - e[2..-1].to_f if e.start_with? 'q=' } [type, [quality, type.count('*'), 1 - options.size]] end
Outputs an HTTP `4xx` or `5xx` response.
@param [Integer, to_i] code @param [String, to_s] message @param [Hash{String => String}] headers @return [Array(Integer, Hash
, each)]
# File lib/rack/sparql/conneg.rb, line 121 def http_error(code, message = nil, headers = {}) message = http_status(code) + (message.nil? ? "\n" : " (#{message})\n") [code, {'Content-Type' => 'text/plain; charset=utf-8'}.merge(headers), [message]] end
Returns the standard HTTP status message for the given status `code`.
@param [Integer, to_i] code @return [String]
# File lib/rack/sparql/conneg.rb, line 131 def http_status(code) [code, Rack::Utils::HTTP_STATUS_CODES[code]].join(' ') end
Outputs an HTTP `406 Not Acceptable` response.
@param [String, to_s] message @return [Array(Integer, Hash
, each)]
# File lib/rack/sparql/conneg.rb, line 110 def not_acceptable(message = nil) http_error(406, message, VARY) end
Parses an HTTP `Accept` header, returning an array of MIME content types ordered by the precedence rules defined in HTTP/1.1 Section 14.1.
@param [String, to_s] header @return [Array<String>] @see www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.1
# File lib/rack/sparql/conneg.rb, line 93 def parse_accept_header(header) entries = header.to_s.split(',') entries.map { |e| accept_entry(e) }.sort_by(&:last).map(&:first) end