AvoidBomInUTF8FromCSV.rb

class BomUtf8CSV
  attr_reader :has_bom
  UTF_8_BOM = "\xEF\xBB\xBF".b
  def initialize(io)
    io.rewind if io.respond_to?(:rewind)
    @has_bom = io.read(UTF_8_BOM.length) == UTF_8_BOM
    io.rewind unless @has_bom
    @io = io
    @csv = CSV.new(@io, { headers: true })
  end

  def headers
    @csv.rewind
    @io.read(UTF_8_BOM.length) if @has_bom

    CSV.new(@io, { headers: false }).shift
  end
end

require 'csv'

input = StringIO.new.tap(&:binmode)
input.write "\xEF\xBB\xBF"
input.puts "num,bar,baz"
input.puts "123,aaa,1.1"
input.puts "234,bbb,2.2"

puts "CSV::VERSION: #{CSV::VERSION}"
csv = BomUtf8CSV.new(input)
puts csv.headers == %w|num bar baz|


# when csv <= 3.0.1 #=> true
# when csv > 3.0.1 #=> false