mastodon/app/services/update_remote_profile_service.rb

class UpdateRemoteProfileService < BaseService
  def call(author_xml, account)
    if author_xml.at_xpath('./poco:displayName').nil?
      account.display_name = account.username
    else
      account.display_name = author_xml.at_xpath('./poco:displayName').content
    end

    unless author_xml.at_xpath('./poco:note').nil?
      account.note = author_xml.at_xpath('./poco:note').content
    end

    unless author_xml.at_xpath('./xmlns:link[@rel="avatar"]').nil?
      account.avatar_remote_url = author_xml.at_xpath('./xmlns:link[@rel="avatar"]').attribute('href').value
    end

    account.save!
  end
end