code: def protocol(alias_name, default=None, allow_none=False):
      
      warnings.warn('Will be removed in v1.0', DeprecationWarning, stacklevel=2)
      try:
          return _split_docker_link(alias_name)[0]
      except KeyError as err:
          if default or allow_none:
              return default
          else:
              raise err
docs: Get the protocol from the docker link alias or return the default.
  
      Args:
          alias_name: The docker link alias
          default: The default value if the link isn't available
          allow_none: If the return value can be `None` (i.e. optional)
  
      Examples:
          Assuming a Docker link was created with ``docker --link postgres:db``
          and the resulting environment variable is ``DB_PORT=tcp://172.17.0.82:5432``.
  
          >>> envitro.docker.protocol('DB')
          tcp