Ensure no invalid UTF8 chars in user data

gistfile1.rb

class UTF8Validator

  class InvalidUTF8Character < Exception; end

  VALIDATE_ENV_KEYS = [
    "QUERY_STRING",
    "REQUEST_PATH",
    "REQUEST_URI",
    "rack.request.form_vars" # POST data
  ]

  def initialize(app)
    @app = app
  end

  def call(env)
    validate_env(env)
    @app.call(env)
  rescue InvalidUTF8Character
    Rails.logger.info 'Invalid UTF-8 character - return 400'
    [400, {'Content-Type' => 'text/html'}, ["400"]]
  end

  def validate_env(env)
    VALIDATE_ENV_KEYS.each do |key|
      next unless value = env[key]

      validate(URI.decode(value))
    end
  end

  def validate(string)
    return unless string.is_a? String

    utf8_string = string.dup.force_encoding('utf-8')
    raise InvalidUTF8Character unless utf8_string.valid_encoding?
  end

end