mastodon/app/services/follow_remote_account_service.rb

class FollowRemoteAccountService < BaseService
  include OStatus2::MagicKey

  DFRN_NS = 'http://purl.org/macgirvin/dfrn/1.0'.freeze

  # Find or create a local account for a remote user.
  # When creating, look up the user's webfinger and fetch all
  # important information from their feed
  # @param [String] uri User URI in the form of username@domain
  # @return [Account]
  def call(uri)
    username, domain = uri.split('@')

    return Account.find_local(username) if TagManager.instance.local_domain?(domain)
    return nil if DomainBlock.blocked?(domain)

    account = Account.find_remote(username, domain)

    return account unless account.nil?

    Rails.logger.debug "Creating new remote account for #{uri}"
    account = Account.new(username: username, domain: domain)

    data = Goldfinger.finger("acct:#{uri}")

    raise Goldfinger::Error, 'Missing resource links' if data.link('http://schemas.google.com/g/2010#updates-from').nil? || data.link('salmon').nil? || data.link('http://webfinger.net/rel/profile-page').nil? || data.link('magic-public-key').nil?

    account.remote_url  = data.link('http://schemas.google.com/g/2010#updates-from').href
    account.salmon_url  = data.link('salmon').href
    account.url         = data.link('http://webfinger.net/rel/profile-page').href
    account.public_key  = magic_key_to_pem(data.link('magic-public-key').href)
    account.private_key = nil

    xml  = get_feed(account.remote_url)
    hubs = get_hubs(xml)

    account.uri     = get_account_uri(xml)
    account.hub_url = hubs.first.attribute('href').value

    get_profile(xml, account)
    account.save!

    return account
  end

  private

  def get_feed(url)
    response = http_client.get(Addressable::URI.parse(url))
    Nokogiri::XML(response)
  end

  def get_hubs(xml)
    hubs = xml.xpath('//xmlns:link[@rel="hub"]')
    raise Goldfinger::Error, 'No PubSubHubbub hubs found' if hubs.empty? || hubs.first.attribute('href').nil?
    hubs
  end

  def get_account_uri(xml)
    author_uri = xml.at_xpath('/xmlns:feed/xmlns:author/xmlns:uri')

    if author_uri.nil?
      owner = xml.at_xpath('/xmlns:feed').at_xpath('./dfrn:owner', dfrn: DFRN_NS)
      author_uri = owner.at_xpath('./xmlns:uri') unless owner.nil?
    end

    raise Goldfinger::Error, 'Author URI could not be found' if author_uri.nil?
    author_uri.content
  end

  def get_profile(xml, account)
    author = xml.at_xpath('/xmlns:feed/xmlns:author') || xml.at_xpath('/xmlns:feed').at_xpath('./dfrn:owner', dfrn: DFRN_NS)
    update_remote_profile_service.call(author, account)
  end

  def update_remote_profile_service
    @update_remote_profile_service ||= UpdateRemoteProfileService.new
  end

  def http_client
    HTTP.timeout(:per_operation, write: 20, connect: 20, read: 50)
  end
end