lib/rdf/ntriples/writer.rb
# -*- encoding: utf-8 -*-
module RDF::NTriples
##
# N-Triples serializer.
#
# Output is serialized for UTF-8, to serialize as ASCII
# (with) unicode escapes, set encoding: Encoding::ASCII as
# an option to {RDF::NTriples::Writer#initialize}.
#
# @example Obtaining an NTriples writer class
# RDF::Writer.for(:ntriples) #=> RDF::NTriples::Writer
# RDF::Writer.for("etc/test.nt")
# RDF::Writer.for(file_name: "etc/test.nt")
# RDF::Writer.for(file_extension: "nt")
# RDF::Writer.for(content_type: "application/n-triples")
#
# @example Serializing RDF statements into an NTriples file
# RDF::NTriples::Writer.open("etc/test.nt") do |writer|
# graph.each_statement do |statement|
# writer << statement
# end
# end
#
# @example Serializing RDF statements into an NTriples string
# RDF::NTriples::Writer.buffer do |writer|
# graph.each_statement do |statement|
# writer << statement
# end
# end
#
# @example Serializing RDF statements into an NTriples string with escaped UTF-8
# RDF::NTriples::Writer.buffer(encoding: Encoding::ASCII) do |writer|
# graph.each_statement do |statement|
# writer << statement
# end
# end
#
# @see http://www.w3.org/TR/rdf-testcases/#ntriples
# @see http://www.w3.org/TR/n-triples/
class Writer < RDF::Writer
include RDF::Util::Logger
format RDF::NTriples::Format
# @see http://www.w3.org/TR/rdf-testcases/#ntrip_strings
ESCAPE_PLAIN = /\A[\x20-\x21\x23-\x26\x28#{Regexp.escape '['}#{Regexp.escape ']'}-\x7E]*\z/m.freeze
ESCAPE_PLAIN_U = /\A(?:#{Reader::IRI_RANGE}|#{Reader::UCHAR})*\z/.freeze
##
# Escape Literal and URI content. If encoding is ASCII, all unicode
# is escaped, otherwise only ASCII characters that must be escaped are
# escaped.
#
# @param [String] string
# @param [Encoding] encoding
# @return [String]
# @see http://www.w3.org/TR/rdf-testcases/#ntrip_strings
def self.escape(string, encoding = nil)
ret = case
when string.match?(ESCAPE_PLAIN) # a shortcut for the simple case
string
when string.ascii_only?
StringIO.open do |buffer|
buffer.set_encoding(Encoding::ASCII)
string.each_byte { |u| buffer << escape_ascii(u, encoding) }
buffer.string
end
when encoding && encoding != Encoding::ASCII
# Not encoding UTF-8 characters
StringIO.open do |buffer|
buffer.set_encoding(encoding)
string.each_char do |u|
buffer << case u.ord
when (0x00..0x7F)
escape_ascii(u, encoding)
else
u
end
end
buffer.string
end
else
# Encode ASCII && UTF-8 characters
StringIO.open do |buffer|
buffer.set_encoding(Encoding::ASCII)
string.each_codepoint { |u| buffer << escape_unicode(u, encoding) }
buffer.string
end
end
encoding ? ret.encode(encoding) : ret
end
##
# Escape ascii and unicode characters.
# If encoding is UTF_8, only ascii characters are escaped.
#
# @param [Integer, #ord] u
# @param [Encoding] encoding
# @return [String]
# @raise [ArgumentError] if `u` is not a valid Unicode codepoint
# @see http://www.w3.org/TR/rdf-testcases/#ntrip_strings
def self.escape_unicode(u, encoding)
case (u = u.ord)
when (0x00..0x7F) # ASCII 7-bit
escape_ascii(u, encoding)
when (0x80..0xFFFF) # Unicode BMP
escape_utf16(u)
when (0x10000..0x10FFFF) # Unicode
escape_utf32(u)
else
raise ArgumentError.new("expected a Unicode codepoint in (0x00..0x10FFFF), but got 0x#{u.to_s(16)}")
end
end
##
# Standard ASCII escape sequences. If encoding is ASCII, use Test-Cases
# sequences, otherwise, assume the test-cases escape sequences. Otherwise,
# the N-Triples recommendation includes `\b` and `\f` escape sequences.
#
# Within STRING_LITERAL_QUOTE, only the characters `U+0022`, `U+005C`, `U+000A`, `U+000D` are encoded using `ECHAR`. `ECHAR` must not be used for characters that are allowed directly in STRING_LITERAL_QUOTE.
#
# @param [Integer, #ord] u
# @return [String]
# @raise [ArgumentError] if `u` is not a valid Unicode codepoint
# @see http://www.w3.org/TR/rdf-testcases/#ntrip_strings
# @see http://www.w3.org/TR/n-triples/
def self.escape_ascii(u, encoding)
case (u = u.ord)
when (0x08) then "\\b"
when (0x09) then "\\t"
when (0x0A) then "\\n"
when (0x0C) then "\\f"
when (0x0D) then "\\r"
when (0x22) then "\\\""
when (0x5C) then "\\\\"
when (0x00..0x1F) then escape_utf16(u)
when (0x7F) then escape_utf16(u)
when (0x20..0x7E) then u.chr
else
raise ArgumentError.new("expected an ASCII character in (0x00..0x7F), but got 0x#{u.to_s(16)}")
end
end
##
# @param [Integer, #ord] u
# @return [String]
# @see http://www.w3.org/TR/rdf-testcases/#ntrip_strings
def self.escape_utf16(u)
sprintf("\\u%04X", u.ord)
end
##
# @param [Integer, #ord] u
# @return [String]
# @see http://www.w3.org/TR/rdf-testcases/#ntrip_strings
def self.escape_utf32(u)
sprintf("\\U%08X", u.ord)
end
##
# Returns the serialized N-Triples representation of the given RDF
# value.
#
# @param [RDF::Value] value
# @return [String]
# @raise [ArgumentError] if `value` is not an `RDF::Statement` or `RDF::Term`
def self.serialize(value)
writer = (@serialize_writer_memo ||= self.new)
case value
when nil then nil
when FalseClass then value.to_s
when RDF::Statement
writer.format_statement(value) + "\n"
when RDF::Term
writer.format_term(value)
else
raise ArgumentError, "expected an RDF::Statement or RDF::Term, but got #{value.inspect}"
end
end
##
# Initializes the writer.
#
# @param [IO, File] output
# the output stream
# @param [Boolean] validate (true)
# whether to validate terms when serializing
# @param [Hash{Symbol => Object}] options ({})
# any additional options. See {RDF::Writer#initialize}
# @yield [writer] `self`
# @yieldparam [RDF::Writer] writer
# @yieldreturn [void]
def initialize(output = $stdout, validate: true, **options, &block)
super
end
##
# Outputs an N-Triples comment line.
#
# @param [String] text
# @return [void]
def write_comment(text)
puts "# #{text.chomp}" # TODO: correctly output multi-line comments
end
##
# Outputs the N-Triples representation of a triple.
#
# @param [RDF::Resource] subject
# @param [RDF::URI] predicate
# @param [RDF::Term] object
# @return [void]
def write_triple(subject, predicate, object)
puts format_triple(subject, predicate, object, **@options)
end
##
# Returns the N-Triples representation of a statement.
#
# @param [RDF::Statement] statement
# @param [Hash{Symbol => Object}] options ({})
# @return [String]
def format_statement(statement, **options)
format_triple(*statement.to_triple, **options)
end
##
# Returns the N-Triples representation of an RDF-star quoted triple.
#
# @param [RDF::Statement] statement
# @param [Hash{Symbol => Object}] options ({})
# @return [String]
def format_quotedTriple(statement, **options)
"<<%s %s %s>>" % statement.to_a.map { |value| format_term(value, **options) }
end
##
# Returns the N-Triples representation of a triple.
#
# @param [RDF::Resource] subject
# @param [RDF::URI] predicate
# @param [RDF::Term] object
# @param [Hash{Symbol => Object}] options ({})
# @return [String]
def format_triple(subject, predicate, object, **options)
"%s %s %s ." % [subject, predicate, object].map { |value| format_term(value, **options) }
end
##
# Returns the N-Triples representation of a blank node.
#
# @param [RDF::Node] node
# @param [Boolean] unique_bnodes (false)
# Serialize node using unique identifier, rather than any used to create the node.
# @param [Hash{Symbol => Object}] options ({})
# @return [String]
def format_node(node, unique_bnodes: false, **options)
unique_bnodes ? node.to_unique_base : node.to_s
end
##
# Returns the N-Triples representation of a URI reference using write encoding.
#
# @param [RDF::URI] uri
# @param [Hash{Symbol => Object}] options ({})
# @return [String]
def format_uri(uri, **options)
string = uri.to_s
iriref = case
when string.match?(ESCAPE_PLAIN_U) # a shortcut for the simple case
string
when string.ascii_only? || (encoding && encoding != Encoding::ASCII)
StringIO.open do |buffer|
buffer.set_encoding(encoding)
string.each_char do |u|
buffer << case u.ord
when (0x00..0x20) then self.class.escape_utf16(u)
when 0x22, 0x3c, 0x3e, 0x5c, 0x5e, 0x60, 0x7b, 0x7c, 0x7d # "<>\^`{|}
self.class.escape_utf16(u)
else u
end
end
buffer.string
end
else
# Encode ASCII && UTF-8/16 characters
StringIO.open do |buffer|
buffer.set_encoding(Encoding::ASCII)
string.each_byte do |u|
buffer << case u
when (0x00..0x20) then self.class.escape_utf16(u)
when 0x22, 0x3c, 0x3e, 0x5c, 0x5e, 0x60, 0x7b, 0x7c, 0x7d # "<>\^`{|}
self.class.escape_utf16(u)
when (0x80..0xFFFF) then self.class.escape_utf16(u)
when (0x10000..0x10FFFF) then self.class.escape_utf32(u)
else u
end
end
buffer.string
end
end
encoding ? "<#{iriref}>".encode(encoding) : "<#{iriref}>"
end
##
# Returns the N-Triples representation of a literal.
#
# @param [RDF::Literal, String, #to_s] literal
# @param [Hash{Symbol => Object}] options ({})
# @return [String]
def format_literal(literal, **options)
case literal
when RDF::Literal
# Note, escaping here is more robust than in Term
text = quoted(escaped(literal.value))
text << "@#{literal.language}" if literal.language?
text << "--#{literal.direction}" if literal.direction?
text << "^^<#{uri_for(literal.datatype)}>" if literal.datatype?
text
else
quoted(escaped(literal.to_s))
end
end
##
# @private
def escaped(string)
self.class.escape(string, encoding)
end
end
end