Net::FTP#start_tls_session

# File tmp/rubies/ruby-3.0.5/lib/net/ftp.rb, line 357
def start_tls_session(sock)
  ssl_sock = SSLSocket.new(sock, @ssl_context)
  ssl_sock.sync_close = true
  ssl_sock.hostname = @host if ssl_sock.respond_to? :hostname=
  if @ssl_session &&
      Process.clock_gettime(Process::CLOCK_REALTIME) < @ssl_session.time.to_f + @ssl_session.timeout
    # ProFTPD returns 425 for data connections if session is not reused.
    ssl_sock.session = @ssl_session
  end
  ssl_socket_connect(ssl_sock, @ssl_handshake_timeout || @open_timeout)
  if @ssl_context.verify_mode != VERIFY_NONE
    ssl_sock.post_connection_check(@host)
  end
  return ssl_sock
end