mastodon/app/services/resolve_account_service.rb

# frozen_string_literal: true

class ResolveAccountService < BaseService
  include JsonLdHelper
  include DomainControlHelper
  include WebfingerHelper

  # Find or create an account record for a remote user. When creating,
  # look up the user's webfinger and fetch ActivityPub data
  # @param [String, Account] uri URI in the username@domain format or account record
  # @param [Hash] options
  # @option options [Boolean] :redirected Do not follow further Webfinger redirects
  # @option options [Boolean] :skip_webfinger Do not attempt any webfinger query or refreshing account data
  # @return [Account]
  def call(uri, options = {})
    return if uri.blank?

    process_options!(uri, options)

    # First of all we want to check if we've got the account
    # record with the URI already, and if so, we can exit early

    return if domain_not_allowed?(@domain)

    @account ||= Account.find_remote(@username, @domain)

    return @account if @account&.local? || @domain.nil? || !webfinger_update_due?

    # At this point we are in need of a Webfinger query, which may
    # yield us a different username/domain through a redirect
    process_webfinger!(@uri)
    @domain = nil if TagManager.instance.local_domain?(@domain)

    # Because the username/domain pair may be different than what
    # we already checked, we need to check if we've already got
    # the record with that URI, again

    return if domain_not_allowed?(@domain)

    @account ||= Account.find_remote(@username, @domain)

    if gone_from_origin? && not_yet_deleted?
      queue_deletion!
      return
    end

    return @account if @account&.local? || gone_from_origin? || !webfinger_update_due?

    # Now it is certain, it is definitely a remote account, and it
    # either needs to be created, or updated from fresh data

    fetch_account!
  rescue Webfinger::Error, Oj::ParseError => e
    Rails.logger.debug "Webfinger query for #{@uri} failed: #{e}"
    nil
  end

  private

  def process_options!(uri, options)
    @options = options

    if uri.is_a?(Account)
      @account  = uri
      @username = @account.username
      @domain   = @account.domain
    else
      @username, @domain = uri.split('@')
    end

    @domain = begin
      if TagManager.instance.local_domain?(@domain)
        nil
      else
        TagManager.instance.normalize_domain(@domain)
      end
    end

    @uri = [@username, @domain].compact.join('@')
  end

  def process_webfinger!(uri)
    @webfinger                           = webfinger!("acct:#{uri}")
    confirmed_username, confirmed_domain = split_acct(@webfinger.subject)

    if confirmed_username.casecmp(@username).zero? && confirmed_domain.casecmp(@domain).zero?
      @username = confirmed_username
      @domain   = confirmed_domain
      return
    end

    # Account doesn't match, so it may have been redirected
    @webfinger         = webfinger!("acct:#{confirmed_username}@#{confirmed_domain}")
    @username, @domain = split_acct(@webfinger.subject)

    unless confirmed_username.casecmp(@username).zero? && confirmed_domain.casecmp(@domain).zero?
      raise Webfinger::RedirectError, "The URI #{uri} tries to hijack #{@username}@#{@domain}"
    end
  rescue Webfinger::GoneError
    @gone = true
  end

  def split_acct(acct)
    acct.gsub(/\Aacct:/, '').split('@')
  end

  def fetch_account!
    return unless activitypub_ready?

    RedisLock.acquire(lock_options) do |lock|
      if lock.acquired?
        @account = ActivityPub::FetchRemoteAccountService.new.call(actor_url)
      else
        raise Mastodon::RaceConditionError
      end
    end

    @account
  end

  def webfinger_update_due?
    return false if @options[:check_delivery_availability] && !DeliveryFailureTracker.available?(@domain)
    return false if @options[:skip_webfinger]

    @account.nil? || @account.possibly_stale?
  end

  def activitypub_ready?
    ['application/activity+json', 'application/ld+json; profile="https://www.w3.org/ns/activitystreams"'].include?(@webfinger.link('self', 'type'))
  end

  def actor_url
    @actor_url ||= @webfinger.link('self', 'href')
  end

  def gone_from_origin?
    @gone
  end

  def not_yet_deleted?
    @account.present? && !@account.local?
  end

  def queue_deletion!
    AccountDeletionWorker.perform_async(@account.id, reserve_username: false, skip_activitypub: true)
  end

  def lock_options
    { redis: Redis.current, key: "resolve:#{@username}@#{@domain}" }
  end
end