def _get_task_host():
  """Get the Host header value for all mr tasks.

  Task Host header determines which instance this task would be routed to.

  Current version id format is: v7.368834058928280579
  Current module id is just the module's name. It could be "default"
  Default version hostname is app_id.appspot.com

  Returns:
    A complete host name is of format version.module.app_id.appspot.com
  If module is the default module, just version.app_id.appspot.com. The reason
  is if an app doesn't have modules enabled and the url is
  "version.default.app_id", "version" is ignored and "default" is used as
  version. If "default" version doesn't exist, the url is routed to the
  default version.
  """
  version = os.environ["CURRENT_VERSION_ID"].split(".")[0]
  default_host = os.environ["DEFAULT_VERSION_HOSTNAME"]
  module = os.environ["CURRENT_MODULE_ID"]
  if os.environ["CURRENT_MODULE_ID"] == "default":
    return "%s.%s" % (version, default_host)
  return "%s.%s.%s" % (version, module, default_host)
Get the Host header value for all mr tasks.

  Task Host header determines which instance this task would be routed to.

  Current version id format is: v7.368834058928280579
  Current module id is just the module's name. It could be "default"
  Default version hostname is app_id.appspot.com

  Returns:
    A complete host name is of format version.module.app_id.appspot.com
  If module is the default module, just version.app_id.appspot.com. The reason
  is if an app doesn't have modules enabled and the url is
  "version.default.app_id", "version" is ignored and "default" is used as
  version. If "default" version doesn't exist, the url is routed to the
  default version.