/usr/lib/ruby/vendor_ruby/ffi/tools/const_generator.rb is in ruby-ffi 1.9.6debian-2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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require 'open3'
module FFI
# ConstGenerator turns C constants into ruby values.
#
# @example a simple example for stdio
# cg = FFI::ConstGenerator.new('stdio') do |gen|
# gen.const(:SEEK_SET)
# gen.const('SEEK_CUR')
# gen.const('seek_end') # this constant does not exist
# end # #calculate called automatically at the end of the block
#
# cg['SEEK_SET'] # => 0
# cg['SEEK_CUR'] # => 1
# cg['seek_end'] # => nil
# cg.to_ruby # => "SEEK_SET = 0\nSEEK_CUR = 1\n# seek_end not available"
class ConstGenerator
@options = {}
attr_reader :constants
# Creates a new constant generator that uses +prefix+ as a name, and an
# options hash.
#
# The only option is +:required+, which if set to +true+ raises an error if a
# constant you have requested was not found.
#
# @param [#to_s] prefix
# @param [Hash] options
# @return
# @option options [Boolean] :required
# @overload initialize(prefix, options)
# @overload initialize(prefix, options) { |gen| ... }
# @yieldparam [ConstGenerator] gen new generator is passed to the block
# When passed a block, {#calculate} is automatically called at the end of
# the block, otherwise you must call it yourself.
def initialize(prefix = nil, options = {})
@includes = ['stdio.h', 'stddef.h']
@constants = {}
@prefix = prefix
@required = options[:required]
@options = options
if block_given? then
yield self
calculate self.class.options.merge(options)
end
end
# Set class options
# These options are merged with {#initialize} options when it is called with a block.
# @param [Hash] options
# @return [Hash] class options
def self.options=(options)
@options = options
end
# Get class options.
# @return [Hash] class options
def self.options
@options
end
# @param [String] name
# @return constant value (converted if a +converter+ was defined).
# Access a constant by name.
def [](name)
@constants[name].converted_value
end
# Request the value for C constant +name+.
#
# @param [#to_s] name C constant name
# @param [String] format a printf format string to print the value out
# @param [String] cast a C cast for the value
# @param ruby_name alternate ruby name for {#to_ruby}
#
# @overload const(name, format=nil, cast='', ruby_name=nil, converter=nil)
# +converter+ is a Method or a Proc.
# @param [#call] converter convert the value from a string to the appropriate
# type for {#to_ruby}.
# @overload const(name, format=nil, cast='', ruby_name=nil) { |value| ... }
# Use a converter block. This block convert the value from a string to the
# appropriate type for {#to_ruby}.
# @yieldparam value constant value
def const(name, format = nil, cast = '', ruby_name = nil, converter = nil,
&converter_proc)
format ||= '%d'
cast ||= ''
if converter_proc and converter then
raise ArgumentError, "Supply only converter or converter block"
end
converter = converter_proc if converter.nil?
const = Constant.new name, format, cast, ruby_name, converter
@constants[name.to_s] = const
return const
end
# Calculate constants values.
# @param [Hash] options
# @option options [String] :cppflags flags for C compiler
# @return [nil]
# @raise if a constant is missing and +:required+ was set to +true+ (see {#initialize})
def calculate(options = {})
binary = File.join Dir.tmpdir, "rb_const_gen_bin_#{Process.pid}"
Tempfile.open("#{@prefix}.const_generator") do |f|
@includes.each do |inc|
f.puts "#include <#{inc}>"
end
f.puts "\nint main(int argc, char **argv)\n{"
@constants.each_value do |const|
f.puts <<-EOF
#ifdef #{const.name}
printf("#{const.name} #{const.format}\\n", #{const.cast}#{const.name});
#endif
EOF
end
f.puts "\n\treturn 0;\n}"
f.flush
output = `gcc #{options[:cppflags]} -D_DARWIN_USE_64_BIT_INODE -D_LARGEFILE_SOURCE -D_FILE_OFFSET_BITS=64 -x c -Wall -Werror #{f.path} -o #{binary} 2>&1`
unless $?.success? then
output = output.split("\n").map { |l| "\t#{l}" }.join "\n"
raise "Compilation error generating constants #{@prefix}:\n#{output}"
end
end
output = `#{binary}`
File.unlink(binary + (FFI::Platform.windows? ? ".exe" : ""))
output.each_line do |line|
line =~ /^(\S+)\s(.*)$/
const = @constants[$1]
const.value = $2
end
missing_constants = @constants.select do |name, constant|
constant.value.nil?
end.map { |name,| name }
if @required and not missing_constants.empty? then
raise "Missing required constants for #{@prefix}: #{missing_constants.join ', '}"
end
end
# Dump constants to +io+.
# @param [#puts] io
# @return [nil]
def dump_constants(io)
@constants.each do |name, constant|
name = [@prefix, name].join '.' if @prefix
io.puts "#{name} = #{constant.converted_value}"
end
end
# Outputs values for discovered constants. If the constant's value was
# not discovered it is not omitted.
# @return [String]
def to_ruby
@constants.sort_by { |name,| name }.map do |name, constant|
if constant.value.nil? then
"# #{name} not available"
else
constant.to_ruby
end
end.join "\n"
end
# Add additional C include file(s) to calculate constants from.
# @note +stdio.h+ and +stddef.h+ automatically included
# @param [List<String>, Array<String>] i include file(s)
# @return [Array<String>] array of include files
def include(*i)
@includes |= i.flatten
end
end
# This class hold constants for {ConstGenerator}
class ConstGenerator::Constant
attr_reader :name, :format, :cast
attr_accessor :value
# @param [#to_s] name
# @param [String] format a printf format string to print the value out
# @param [String] cast a C cast for the value
# @param ruby_name alternate ruby name for {#to_ruby}
# @param [#call] converter convert the value from a string to the appropriate
# type for {#to_ruby}.
def initialize(name, format, cast, ruby_name = nil, converter=nil)
@name = name
@format = format
@cast = cast
@ruby_name = ruby_name
@converter = converter
@value = nil
end
# Return constant value (converted if a +converter+ was defined).
# @return constant value.
def converted_value
if @converter
@converter.call(@value)
else
@value
end
end
# get constant ruby name
# @return [String]
def ruby_name
@ruby_name || @name
end
# Get an evaluable string from constant.
# @return [String]
def to_ruby
"#{ruby_name} = #{converted_value}"
end
end
end
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