feat(core): Add Gossiper helper

This helper provides a class that can be used to implement simple gossip
behavior, where a node is picked at random at a certain interval. This
can be used to broadcast certain messages, such as requests or updates
of data in a way where it eventually reaches the entire group.

packages/core/src/Gossiper.ts

@@ -0,0 +1,36 @@
+import { Group } from './Group';
+import { Node } from './Node';
+
+export interface GossiperOptions<V extends object> {
+	/**
+	 * The interval to gossip with.
+	 */
+	intervalInMs: number;
+
+	gossip: (node: Node<V>) => void;
+}
+
+export class Gossiper<V extends object> {
+	private readonly group: Group<V>;
+	private readonly timer: any;
+
+	private readonly gossip: (node: Node<V>) => void;
+
+	public constructor(group: Group<V>, options: GossiperOptions<V>) {
+		this.group = group;
+		this.timer = setInterval(this.findAndGossip.bind(this), options.intervalInMs);
+		this.gossip = options.gossip;
+	}
+
+	public destroy(): void {
+		clearInterval(this.timer);
+	}
+
+	private findAndGossip() {
+		const nodes = this.group.nodes;
+		const idx = Math.floor(Math.random() * nodes.length);
+
+		const node = nodes[idx];
+		this.gossip(node);
+	}
+}

packages/core/src/index.ts

@@ -67,4 +67,5 @@ export * from './Group';
 export * from './group/NamedGroup';
 export * from './RequestReplyHelper';
 
+export * from './Gossiper';
 export * from './SynchronizedValues';