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;
	}
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