docs: def start_xenon_server(port=50051, disable_tls=False):
      """Start the server."""
      jar_file = find_xenon_grpc_jar()
      if not jar_file:
          raise RuntimeError("Could not find 'xenon-grpc' jar file.")
  
      cmd = ['java', '-jar', jar_file, '-p', str(port)]
  
      if not disable_tls:
          crt_file, key_file = create_self_signed_cert()
  
          cmd.extend([
              '--server-cert-chain', str(crt_file),
              '--server-private-key', str(key_file),
              '--client-cert-chain', str(crt_file)])
      else:
          crt_file = key_file = None
  
      process = subprocess.Popen(
          cmd,
          bufsize=1,
          universal_newlines=True,
          stdout=subprocess.PIPE,
          stderr=subprocess.PIPE)
      return process, crt_file, key_file