Glossary

The words the VRPC documentation uses, each in one meaning. The protocol specification defines the ones the wire depends on.

Term	Meaning
Adapter	The part of an agent that holds the registered classes and their instances, and executes calls on them (VrpcAdapter).
Agent	A program, or the part of one, that offers its classes to clients over the broker (VrpcAgent). Has a name unique in its domain.
Agent info	What an agent publishes about itself, retained: online or offline, its host, its version, its protocol version.
Answer	An agent's reply to a request: a result or an error.
Broker	The MQTT broker every agent and client connects to.
callAll	One call of a member function on every shared instance of a class, or on those a selection names; answers one entry per instance.
Callback	A function passed as an argument, which the agent calls back into the caller - once, or a few times during the call.
Class info	What an agent publishes about each class, retained: its static and member functions, its shared instances and, in full, their documentation.
Client	A program, or the part of one, that calls agents (VrpcClient).
Connection id	The name of one client connection, <domain>/<mqttClientId>/<secret>. Answers, callbacks and events for that connection travel on topics under it.
Context	What a request addresses: an instance, or a class for its static functions.
Declare	To subscribe: a call of an event function that carries a subscription id.
Delete	To end an instance for good; it releases what it runs.
Domain	A name that groups agents and clients; they see and reach each other within one domain only.
End	A decided stop of a registration: its source ended it, or somebody did on purpose. Its subscribers are told.
Event function	A function that calls a handler again and again until it is released, such as onReading(handler).
Greeting	What a registration hands every new subscriber first, usually its current state.
Heal	To restore a lost subscription by declaring it again once its agent is back.
Instance	A named object of a class, kept by an agent. Shared instances are visible to every client; isolated ones belong to the connection that created them.
Loss	A stop nobody decided: the agent went offline, or the instance went away. Heals when the agent is back.
Owner	The connection that created an isolated instance; the only one that may use it.
Presence	A client connection's last will, offline, on <connectionId>/__clientInfo__. Agents watch it to clean up after a connection.
Protocol version	The version of the VRPC protocol a peer speaks (v); currently 4.
Proxy	The object a client hands out for an instance or a class; its functions call the real ones remotely.
Registration	The one call of an event function on one instance (or class) with one set of arguments, shared by every subscription that asks for the same. The agent owns it.
Registration object	What an event function returns: how to undo its call, and optionally how to greet, when it ended and what to answer.
Release	To undo a registration once its last subscription left.
Request	A client's message asking an agent to call a function.
Selection	The instances a callAll calls: a name pattern (* matches any run of characters) or a list of names and patterns.
Subscription	One listener's wish to receive the events of a registration. The client owns it.
Subscription id	The name of a subscription, __e__<connectionId>/<topicId>; events travel to the topic it names. A secret of its connection.
Will	The message the broker publishes for a peer whose connection breaks: an agent's agent info offline, a client's presence.
Withdraw	To end a subscription on purpose.