Repairing a unicode string that contains invalid characters

demo.rb

# encoding: utf-8

s = "Blah \xe9 blah 헌글"

puts "BEFORE"
puts "encoding: #{s.encoding}"
puts "valid   : #{s.valid_encoding?}"
puts "text    : #{s}"

s = s.
  encode('utf-16le', 'utf-8',
    :invalid => :replace,
    :undef => :replace,
    :replace => "#").
  encode('utf-8')

puts "\nAFTER"
puts "encoding: #{s.encoding}"
puts "valid   : #{s.valid_encoding?}"
puts "text    : #{s}"