Interface RaftStateMachine

Users of the RaftController have to implement a RaftStateMachine and provide an instance of it in the RaftControllerOptions when bootstrapping the controller. The provided state machine will be used internally to describe the state shared between all agents with corresponding RaftControllers.

A call to RaftController.propose() will trigger this.processInput() after the input has been committed. After that the state is retrieved with this.getState() and then used to resolve the promise returned by the initial RaftController.propose() call.

A typical RaftStateMachine implementation keeps track of some form of state (e.g. a variable of type Map) and defines how inputs affect this state inside processInput(). getState() and setState() are used to access the tracked state.

An example RaftStateMachine implementation of a key value store looks like this:

class KVStateMachine implements RaftStateMachine {
   private _state = new Map<string, string>();

   processInput(input: RaftData) {
       if (input.type === "set") {
           // Add or update key value pair
           this._state.set(input.key, input.value);
       } else if (input.type === "delete") {
           // Delete key value pair
           this._state.delete(input.key);
       }
   }

   getState(): RaftData {
       // Convert from Map to JSON compatible object
       return Array.from(this._state);
   }

   setState(state: RaftData): void {
       // Convert from JSON compatible object to Map
       this._state = new Map(state);
   }
}

// Propose an input object of this type to set or update a key value pair
type KVSet = { type: "set"; key: string; value: string };

// Propose an input object of this type to delete a key value pair
type KVDelete = { type: "delete"; key: string };
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