code: function populateHostPrefix(request)  {
    var enabled = request.service.config.hostPrefixEnabled;
    if (!enabled) return request;
    var operationModel = request.service.api.operations[request.operation];
    //don't marshal host prefix when operation has endpoint discovery traits
    if (hasEndpointDiscover(request)) return request;
    if (operationModel.endpoint && operationModel.endpoint.hostPrefix) {
      var hostPrefixNotation = operationModel.endpoint.hostPrefix;
      var hostPrefix = expandHostPrefix(hostPrefixNotation, request.params, operationModel.input);
      prependEndpointPrefix(request.httpRequest.endpoint, hostPrefix);
      validateHostname(request.httpRequest.endpoint.hostname);
    }
    return request;
  }
docs: Prepend prefix defined by API model to endpoint that's already
  constructed. This feature does not apply to operations using
  endpoint discovery and can be disabled.
  @api private