Split the session, gate optional parameters on the peer version, own the SMPP version in defs

src/link-timers.ts

@@ -0,0 +1,50 @@
+import type { LogInt } from '@larvit/log';
+
+export type LinkTimersOptions = {
+	/** How long between enquire_link probes. Undefined or 0 never probes. */
+	enquireLinkInterval?: number | undefined;
+	/** How long a silent peer is kept. Undefined or 0 keeps it forever. */
+	idleTimeout?: number | undefined;
+	log: LogInt;
+	onEnquireLink: () => void;
+	onIdle: () => void;
+};
+
+/** Keeps a quiet connection honest: probes the peer, and gives up on one that stays silent. */
+export class LinkTimers {
+	private readonly options: LinkTimersOptions;
+	private enquireLink: NodeJS.Timeout | undefined;
+	private idle: NodeJS.Timeout | undefined;
+
+	constructor(options: LinkTimersOptions) {
+		this.options = options;
+	}
+
+	/** Starts both timers over, which every sign of life from the peer should do. */
+	reset(): void {
+		const { enquireLinkInterval, idleTimeout, log, onEnquireLink, onIdle } = this.options;
+
+		this.clear();
+
+		if (enquireLinkInterval !== undefined && enquireLinkInterval > 0) {
+			this.enquireLink = setTimeout(onEnquireLink, enquireLinkInterval);
+			this.enquireLink.unref();
+		}
+
+		if (idleTimeout !== undefined && idleTimeout > 0) {
+			this.idle = setTimeout(() => {
+				log.info('linkTimers - closing an idle peer', { idleTimeout });
+				onIdle();
+			}, idleTimeout);
+			this.idle.unref();
+		}
+	}
+
+	clear(): void {
+		if (this.enquireLink) clearTimeout(this.enquireLink);
+		if (this.idle) clearTimeout(this.idle);
+
+		this.enquireLink = undefined;
+		this.idle = undefined;
+	}
+}