Config Server Communication

The configuration server is accessible through a TCP connection, with optional TLS v1.2 encryption and authentication support. Clients connect to the server and can then send commands and receive data back.

All communication to and from the configuration server is done using Flatbuffers, a schema-based serialization protocol originally developed by Google. The following schema is used:

namespace dv;

enum ConfigAction : int8 {
	CFG_ERROR          = 0,
	NODE_EXISTS        = 1,
	ATTR_EXISTS        = 2,
	GET_CHILDREN       = 3,
	GET_ATTRIBUTES     = 4,
	GET_TYPE           = 5,
	GET_RANGES         = 6,
	GET_FLAGS          = 7,
	GET_DESCRIPTION    = 8,
	GET                = 9,
	PUT                = 10,
	ADD_MODULE         = 11,
	REMOVE_MODULE      = 12,
	ADD_PUSH_CLIENT    = 13,
	REMOVE_PUSH_CLIENT = 14,
	PUSH_MESSAGE_NODE  = 15,
	PUSH_MESSAGE_ATTR  = 16,
	DUMP_TREE          = 17,
	DUMP_TREE_NODE     = 18,
	DUMP_TREE_ATTR     = 19,
	GET_CLIENT_ID      = 20
}

enum ConfigType : int8 {
	UNKNOWN = -1,
	BOOL    = 0,
	INT     = 1,
	LONG    = 2,
	FLOAT   = 3,
	DOUBLE  = 4,
	STRING  = 5
}

enum ConfigNodeEvents : int8 {
	NODE_ADDED   = 0,
	NODE_REMOVED = 1
}

enum ConfigAttributeEvents : int8 {
	ATTRIBUTE_ADDED           = 0,
	ATTRIBUTE_MODIFIED        = 1,
	ATTRIBUTE_REMOVED         = 2,
	ATTRIBUTE_MODIFIED_CREATE = 3
}

table ConfigActionData {
	action: ConfigAction = CFG_ERROR;
	nodeEvents: ConfigNodeEvents; // Node related.
	attrEvents: ConfigAttributeEvents; // Attribute related.
	id: uint64;
	node: string;
	key: string;
	type: ConfigType = UNKNOWN;
	value: string;
	// On attribute create() only.
	ranges: string;
	flags: int32;
	description: string;
}

root_type ConfigActionData;

The buffer content is defined in ConfigActionData. The ‘action’ member is the only one that’s required to be always set. The ConfigType, ConfigNodeEvents and ConfigAttributeEvents enums reflect the values found in the main dv::Config namespace, adapted for the Flatbuffer schema here. The ConfigAction enum defines all possible action that the configuration server can execute or respond with. The following table goes into detail of what data the client needs to send or what data he can expect back, based on the ConfigAction sent. On success, the response message will have the same action value, with possibly other additional data members set (see ‘Server to Client Response’); on failure, CFG_ERROR is returned with a string explaining the problem.

ConfigAction	Client to Server Message	Server to Client Response
CFG_ERROR	N/A (only from server due to errors).	Sent whenever an error occours. Error message is contained in member ‘value’.
NODE_EXISTS	Check if a given ‘node’ exists.	Member ‘value’ either “true” or “false”.
ATTR_EXISTS	Check if a given ‘key’ (with optional ‘type’) exists for the given ‘node’.	Member ‘value’ either “true” or “false”.
GET_CHILDREN	Get the names of all children of a ‘node’.	Member ‘value’ contains all child node names, separated by ‘|’.
GET_ATTRIBUTES	Get the names of all attribute keys of a ‘node’.	Member ‘value’ contains all attribute key names, separated by ‘|’.
GET (_TYPE,_RANGES,_FLAGS,_DESCRIPTION)	Get all information for the ‘key’ (with optional ‘type’) of ‘node’.	All members are filled with information on key.
PUT	Update the value for the ‘key’ (with optional ‘type’) of ‘node’, using the string member ‘value’.	No additional return value.
ADD_MODULE	Create a new module with name of ‘node’ and library of ‘key’.	No additional return value.
REMOVE_MODULE	Remove the module with name of ‘node’.	No additional return value.
ADD_PUSH_CLIENT	Add this client to the list of clients that shall receive push notifications on configuration changes. No input values.	Client ID formatted as string in ‘value’.
REMOVE_PUSH_CLIENT	Remove this client from the list of clients that shall receive push notifications on configuration changes. No input values.	No additional return value.
PUSH_MESSAGE_NODE	N/A (only from server after ADD_PUSH_CLIENT).	Detected change on a node. ‘id’ contains the ID of the change originator (0=runtime, 1-N=connected client), ‘nodeEvents’ the kind of change, ‘node’ the path of the node that changed.
PUSH_MESSAGE_ATTR	N/A (only from server after ADD_PUSH_CLIENT).	Detected change on an attribute. ‘id’ contains the ID of the change originator (0=runtime, 1-N=connected client), ‘attrEvents’ the kind of change, ‘node’ the path of the node where the attribute resides, ‘key’ the name of the attribute key, ‘type’ the type of the attribute, ‘value’ the new value. On attribute addition (attrEvents=ATTRIBUTE_ADDED), the following members are also set: ‘flags’ to the current flags value, ‘ranges’ to the min/max ranges and ‘description’ to the current description (help text).
DUMP_TREE	Send a full dump of the current configuration tree. No input values.	No additional return value. Confirmation means dump is complete.
DUMP_TREE_NODE	N/A (only from server in response to DUMP_TREE).	Next node encountered in full configuration dump. Contains node path in member ‘node’.
DUMP_TREE_ATTR	N/A (only from server in response to DUMP_TREE).	Next attribute encountered in full configuration dump. Contains node path in member ‘node’, attribute key name in ‘key’, key type in ‘type’, current value in ‘value’, current flags in ‘flags’, min/max ranges in ‘ranges’ and description (help text) in ‘description’.
GET_CLIENT_ID	Get the ID of this client. No input values.	Member ‘id’ contains the 64bit numeric ID of this client.