mastodon/app/validators/html_validator.rb

# frozen_string_literal: true

class HtmlValidator < ActiveModel::EachValidator
  def validate_each(record, attribute, value)
    return if value.blank?
    record.errors.add(attribute, I18n.t('html_validator.invalid_markup')) unless valid_html?(value)
  end

  private

  def valid_html?(str)
    Nokogiri::HTML.fragment(str).to_s == str
  end
end