Add a cleaner shutdown routine (hopefully, but it is still buggy)

Author: chrisspiegl

beforeShutdown.js

@@ -0,0 +1,92 @@
+// Inspired by: https://stackoverflow.com/a/64028857/975333
+
+import process from 'node:process';
+
+/**
+ * @callback BeforeShutdownListener
+ * @param {string} [signalOrEvent] The exit signal or event name received on the process.
+ */
+
+/**
+ * System signals the app will listen to initiate shutdown.
+ * @const {string[]}
+ */
+const SHUTDOWN_SIGNALS = ['SIGINT', 'SIGTERM', 'SIGUSR1', 'SIGUSR2'];
+
+/**
+ * Time in milliseconds to wait before forcing shutdown.
+ * @const {number}
+ */
+const SHUTDOWN_TIMEOUT = 15_000;
+
+/**
+ * A queue of listener callbacks to execute before shutting
+ * down the process.
+ * @type {BeforeShutdownListener[]}
+ */
+const shutdownListeners = [];
+
+/**
+ * Listen for signals and execute given `fn` function once.
+ * @param  {string[]} signals System signals to listen to.
+ * @param  {function(string)} fn Function to execute on shutdown.
+ */
+const processOnce = (signals, fn) => {
+	for (const sig of signals) {
+		process.once(sig, fn);
+	}
+};
+
+/**
+ * Sets a forced shutdown mechanism that will exit the process after `timeout` milliseconds.
+ * @param {number} timeout Time to wait before forcing shutdown (milliseconds)
+ */
+const forceExitAfter = timeout => () => {
+	setTimeout(() => {
+		// Force shutdown after timeout
+		console.warn(`Could not close resources gracefully after ${timeout}ms: forcing shutdown`);
+		return process.exit(1);
+	}, timeout).unref();
+};
+
+/**
+ * Main process shutdown handler. Will invoke every previously registered async shutdown listener
+ * in the queue and exit with a code of `0`. Any `Promise` rejections from any listener will
+ * be logged out as a warning, but won't prevent other callbacks from executing.
+ * @param {string} signalOrEvent The exit signal or event name received on the process.
+ */
+async function shutdownHandler(signalOrEvent) {
+	console.warn(`Shutting down: received [${signalOrEvent}] signal`);
+
+	for (const listener of shutdownListeners) {
+		try {
+			await listener(signalOrEvent);
+		} catch (error) {
+			console.warn(`A shutdown handler failed before completing with: ${error.message || error}`);
+		}
+	}
+
+	return process.exit(0);
+}
+
+/**
+ * Registers a new shutdown listener to be invoked before exiting
+ * the main process. Listener handlers are guaranteed to be called in the order
+ * they were registered.
+ * @param {BeforeShutdownListener} listener The shutdown listener to register.
+ * @returns {BeforeShutdownListener} Echoes back the supplied `listener`.
+ */
+function beforeShutdown(listener) {
+	shutdownListeners.push(listener);
+	return listener;
+}
+
+// Register shutdown callback that kills the process after `SHUTDOWN_TIMEOUT` milliseconds
+// This prevents custom shutdown handlers from hanging the process indefinitely
+processOnce(SHUTDOWN_SIGNALS, forceExitAfter(SHUTDOWN_TIMEOUT));
+
+// Register process shutdown callback
+// Will listen to incoming signal events and execute all registered handlers in the stack
+processOnce(SHUTDOWN_SIGNALS, shutdownHandler);
+
+export default beforeShutdown;