Currently all lines in parameters list have two parameters - key and value. Value is the parsed script name from the HTTP request resolved to the local absolute pathname. It isn't parsed in any way and isn't null-terminated. No data, message means that the response for some HTTP request with provided ID is finished. Server doesn't parse the data.
Message enables instance selection.
Message disables instance selection. No data, message means that the response for some HTTP request with provided ID is finished and client should be disconnected from the server. Requests are sent until the number of requests, sent to the instance and not completely answered by it reaches the queue limit, and if the queue limit is 1, only one requests can be sent to the instance at a time. Instance selection fhttpd can allow multiple instances of the same application to run simultaneously on one or several hosts. Since instance selection is done in the server, some mechanism should determine situations, where such requests handling is necessary and give the server the data, by which instances will be selected.