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| 1 | +module IqRdf |
| 2 | + class StreamingWriter |
| 3 | + |
| 4 | + FORMATS = %w[ttl nt xml].freeze |
| 5 | + |
| 6 | + def initialize(io, format, default_namespace: nil, lang: nil, config: {}) |
| 7 | + @io = io |
| 8 | + @format = format.to_s |
| 9 | + raise ArgumentError, "Unknown format '#{format}'. Must be one of: #{FORMATS.join(', ')}" unless FORMATS.include?(@format) |
| 10 | + @document_language = lang |
| 11 | + @config = config |
| 12 | + @namespaces = {} |
| 13 | + @header_written = false |
| 14 | + @blank_nodes = {} |
| 15 | + |
| 16 | + register_namespace(:rdf, URI.parse("http://www.w3.org/1999/02/22-rdf-syntax-ns#")) |
| 17 | + namespaces(default: default_namespace) if default_namespace |
| 18 | + end |
| 19 | + |
| 20 | + def namespaces(namespaces) |
| 21 | + raise ArgumentError, "Parameter 'namespaces' has to be a hash" unless namespaces.is_a?(Hash) |
| 22 | + namespaces.each do |name, uri_prefix| |
| 23 | + uri_prefix = ::URI.parse(uri_prefix) |
| 24 | + raise ArgumentError, "Parameter 'namespaces' must be in the form {Symbol => URIString, ...}" unless name.is_a?(Symbol) |
| 25 | + register_namespace(name, uri_prefix) |
| 26 | + end |
| 27 | + self |
| 28 | + end |
| 29 | + |
| 30 | + def <<(node) |
| 31 | + return if node.nil? |
| 32 | + raise ArgumentError, "Node must be an IqRdf::Uri and a Subject!" unless node.is_a?(IqRdf::Uri) && node.is_subject? |
| 33 | + write_header unless @header_written |
| 34 | + serialize_node(node) |
| 35 | + end |
| 36 | + |
| 37 | + def close |
| 38 | + write_xml_footer if @format == 'xml' && @header_written |
| 39 | + end |
| 40 | + |
| 41 | + def self.open(io, format, **opts) |
| 42 | + writer = new(io, format, **opts) |
| 43 | + yield writer |
| 44 | + ensure |
| 45 | + writer&.close |
| 46 | + end |
| 47 | + |
| 48 | + private |
| 49 | + |
| 50 | + def register_namespace(name, uri_prefix) |
| 51 | + @namespaces[name] = IqRdf::Namespace.create(name, uri_prefix) |
| 52 | + end |
| 53 | + |
| 54 | + def write_header |
| 55 | + case @format |
| 56 | + when 'ttl' then write_turtle_header |
| 57 | + when 'xml' then write_xml_header |
| 58 | + end |
| 59 | + @header_written = true |
| 60 | + end |
| 61 | + |
| 62 | + def serialize_node(subject) |
| 63 | + case @format |
| 64 | + when 'ttl' then serialize_turtle(subject) |
| 65 | + when 'nt' then serialize_ntriples(subject) |
| 66 | + when 'xml' then serialize_xml(subject) |
| 67 | + end |
| 68 | + end |
| 69 | + |
| 70 | + # --- Turtle --- |
| 71 | + |
| 72 | + def write_turtle_header |
| 73 | + @namespaces.values.sort_by(&:turtle_token).each do |namespace| |
| 74 | + @io.write("@prefix #{namespace.turtle_token}: <#{namespace.uri_prefix}>.\n") |
| 75 | + end |
| 76 | + @io.write("\n") |
| 77 | + end |
| 78 | + |
| 79 | + def serialize_turtle(subject) |
| 80 | + pref = subject.to_s |
| 81 | + indent = "".ljust(pref.length) |
| 82 | + |
| 83 | + if subject.rdf_type |
| 84 | + @io.write("#{pref} a #{subject.rdf_type}") |
| 85 | + pref = ";\n" + indent |
| 86 | + end |
| 87 | + |
| 88 | + subject.nodes.each do |predicate| |
| 89 | + objects = predicate.nodes.map { |object| |
| 90 | + object.to_s(indent: indent, lang: predicate.lang || subject.lang || @document_language) |
| 91 | + }.join(", ") |
| 92 | + @io.write("#{pref} #{predicate} #{objects}") |
| 93 | + pref = ";\n" + indent |
| 94 | + end |
| 95 | + @io.write(".\n") |
| 96 | + @io.write("\n") if @config[:empty_line_between_triples] |
| 97 | + end |
| 98 | + |
| 99 | + # --- N-Triples --- |
| 100 | + |
| 101 | + def serialize_ntriples(sbj) |
| 102 | + nt_process_subject(sbj) do |triple| |
| 103 | + nt_process_blank_nodes(triple, sbj) |
| 104 | + end |
| 105 | + end |
| 106 | + |
| 107 | + def nt_process_subject(sbj, &block) |
| 108 | + rdf_type = IqRdf::Rdf::build_uri("type") |
| 109 | + |
| 110 | + if (sbj.rdf_type rescue false) |
| 111 | + lang = sbj.lang || @document_language |
| 112 | + nt_write_triple([sbj, rdf_type, sbj.rdf_type], lang) |
| 113 | + end |
| 114 | + |
| 115 | + sbj.nodes.each do |prd| |
| 116 | + lang = prd.lang || sbj.lang || @document_language |
| 117 | + prd.nodes.each do |obj| |
| 118 | + triple = [sbj, prd, obj] |
| 119 | + nt_write_triple(triple, lang) |
| 120 | + block.call(triple) if block |
| 121 | + end |
| 122 | + end |
| 123 | + end |
| 124 | + |
| 125 | + def nt_process_blank_nodes(triple, current_res) |
| 126 | + sbj, _prd, obj = triple |
| 127 | + [sbj, obj].select { |res| res.is_a?(IqRdf::BlankNode) && res != current_res }.each do |res| |
| 128 | + nt_process_subject(res) do |inner_triple| |
| 129 | + nt_process_blank_nodes(inner_triple, res) |
| 130 | + end |
| 131 | + end |
| 132 | + end |
| 133 | + |
| 134 | + def nt_write_triple(triple, lang) |
| 135 | + parts = triple.map { |res| nt_resource(res, lang) } |
| 136 | + @io.write("#{parts.join(' ')} .\n") |
| 137 | + end |
| 138 | + |
| 139 | + def nt_resource(res, lang) |
| 140 | + if res.is_a?(IqRdf::Literal) |
| 141 | + res.to_ntriples(lang) |
| 142 | + elsif res.is_a?(IqRdf::BlankNode) |
| 143 | + nt_blank_node(res) |
| 144 | + elsif res.is_a?(IqRdf::Collection) |
| 145 | + nt_collection(res) |
| 146 | + else |
| 147 | + "<#{res.full_uri}>" |
| 148 | + end |
| 149 | + end |
| 150 | + |
| 151 | + def nt_blank_node(res) |
| 152 | + @blank_nodes[res] ||= @blank_nodes.size + 1 |
| 153 | + "_:b#{@blank_nodes[res]}" |
| 154 | + end |
| 155 | + |
| 156 | + def nt_collection(res) |
| 157 | + nt_blank_node(res) # register collection object (matches original side-effect) |
| 158 | + list = IqRdf::BlankNode.new |
| 159 | + sublist = list |
| 160 | + total = res.elements.length |
| 161 | + res.elements.each_with_index do |current_element, i| |
| 162 | + last = i + 1 == total |
| 163 | + sublist::rdf.build_predicate("type", IqRdf::Rdf::build_uri("List")) |
| 164 | + sublist::rdf.first(current_element) |
| 165 | + if last |
| 166 | + sublist::rdf.rest(IqRdf::Rdf::build_uri("nil")) |
| 167 | + else |
| 168 | + new_sublist = IqRdf::BlankNode.new |
| 169 | + sublist::rdf.rest(new_sublist) |
| 170 | + end |
| 171 | + nt_process_subject(sublist) { |triple| nt_process_blank_nodes(triple, sublist) } |
| 172 | + sublist = new_sublist unless last |
| 173 | + end |
| 174 | + nt_blank_node(list) |
| 175 | + end |
| 176 | + |
| 177 | + # --- XML --- |
| 178 | + |
| 179 | + def write_xml_header |
| 180 | + @xml = Builder::XmlMarkup.new(target: @io, indent: 2) |
| 181 | + @xml.instruct! |
| 182 | + opts = {} |
| 183 | + @namespaces.values.each do |namespace| |
| 184 | + opts[namespace.token == :default ? "xmlns" : "xmlns:#{namespace.token}"] = namespace.uri_prefix |
| 185 | + end |
| 186 | + opts["xml:lang"] = @document_language if @document_language |
| 187 | + # Fiber pausiert den Builder-Block nach dem öffnenden Tag, so dass |
| 188 | + # Builder die Einrückungstiefe korrekt trackt während Nodes gestreamt werden. |
| 189 | + @xml_fiber = Fiber.new { @xml.rdf(:RDF, opts) { Fiber.yield } } |
| 190 | + @xml_fiber.resume |
| 191 | + end |
| 192 | + |
| 193 | + def serialize_xml(node) |
| 194 | + node.build_xml(@xml) |
| 195 | + end |
| 196 | + |
| 197 | + def write_xml_footer |
| 198 | + @xml_fiber.resume if @xml_fiber&.alive? |
| 199 | + end |
| 200 | + |
| 201 | + end |
| 202 | +end |
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