v0.1.2

.eslintrc.cjs

@@ -1,17 +0,0 @@
-module.exports = {
-	root: true,
-	env: {
-		node: true,
-		es2021: true,
-	},
-	parser: '@typescript-eslint/parser',
-	plugins: ['@typescript-eslint', 'prettier'],
-	extends: [
-		'eslint:recommended',
-		'plugin:@typescript-eslint/recommended',
-		'plugin:prettier/recommended',
-	],
-	rules: {
-		'prettier/prettier': 'error',
-	},
-};

node-health/.eslintrc.cjs

@@ -1,10 +0,0 @@
-module.exports = {
-	root: true,
-	extends: ['../../.eslintrc.cjs'],
-	parserOptions: {
-		project: './tsconfig.json',
-	},
-	rules: {
-		// package-level overrides
-	},
-};

node-health/eslint.config.mts

@@ -0,0 +1,14 @@
+import js from '@eslint/js';
+import globals from 'globals';
+import tseslint from 'typescript-eslint';
+import { defineConfig } from 'eslint/config';
+
+export default defineConfig([
+	{
+		files: ['**/*.{js,mjs,cjs,ts,mts,cts}'],
+		plugins: { js },
+		extends: ['js/recommended'],
+		languageOptions: { globals: globals.browser },
+	},
+	tseslint.configs.recommended,
+]);

node-health/package.json

@@ -1,7 +1,14 @@
 {
-	"name": "@health/node",
+	"name": "@end/node-health",
-	"version": "0.1.0",
+	"repository": {
-	"private": true,
+		"type": "git",
+		"url": "https://gitea.auvem.com/end/health.git"
+	},
+	"publishConfig": {
+		"registry": "https://gitea.auvem.com/api/packages/end/npm/"
+	},
+	"version": "0.1.2",
+	"license": "MIT",
 	"main": "dist/index.js",
 	"types": "dist/index.d.ts",
 	"files": [
@@ -14,6 +21,13 @@
 		"test": "echo \"No tests configured\" && exit 0",
 		"check": "npm run lint && npm run build"
 	},
-	"dependencies": {},
+	"devDependencies": {
-	"devDependencies": {}
+		"@eslint/js": "^9.39.2",
+		"@types/node": "^25.0.3",
+		"eslint": "^9.39.2",
+		"globals": "^16.5.0",
+		"jiti": "^2.6.1",
+		"typescript": "^5.9.3",
+		"typescript-eslint": "^8.50.1"
+	}
 }

node-health/src/checks.ts

@@ -0,0 +1,40 @@
+import { monitorEventLoopDelay } from 'node:perf_hooks';
+import { ReadinessCheck, ReadinessFunctionReturn, ReadinessStatus } from './readiness';
+
+/**
+ * Builds a readiness check function that monitors event loop lag.
+ * @param options - Configuration options for the event loop lag check.
+ * @param options.degradedMs - Threshold in milliseconds for degraded status (default: 200).
+ * @param options.failMs - Threshold in milliseconds for error status (default: 1000).
+ * @param options.histResetMs - Interval in milliseconds to reset the histogram (default: 60000).
+ * @param options.percentile - Percentile to monitor (default: 50).
+ * @returns A ReadinessFunction that checks event loop lag.
+ */
+export const buildEventLoopLagCheck = (options: {
+	degradedMs?: number;
+	failMs?: number;
+	histResetMs?: number;
+	percentile?: number;
+}): ReadinessCheck => {
+	const { degradedMs = 200, failMs = 1000, histResetMs = 60000, percentile = 50 } = options;
+
+	const hist = monitorEventLoopDelay({ resolution: 10 });
+	hist.enable();
+
+	setInterval(() => {
+		hist.reset();
+	}, histResetMs).unref();
+
+	return {
+		name: 'event-loop-lag',
+		fn: async (): Promise<ReadinessFunctionReturn> => {
+			const lag = hist.percentile(percentile) / 1e6; // Convert from nanoseconds to milliseconds
+			const status: ReadinessStatus = lag < degradedMs ? 'ok' : lag < failMs ? 'degraded' : 'error';
+			return {
+				status,
+				message: `Event loop lag is ${lag.toFixed(2)} ms`,
+			};
+		},
+		timeout: 500,
+	};
+};

node-health/src/index.ts

@@ -1,30 +1,3 @@
-/**
+export * from './liveness';
- * Simple liveness & readiness helpers
+export * from './readiness';
- */
+export * from './checks';
-
-export type ReadinessResult = {
-  ok: boolean;
-  details: { name: string; ok: boolean; error?: string }[];
-};
-
-export function liveness() {
-  return {
-    status: 'ok',
-    timestamp: Date.now(),
-  };
-}
-
-export async function readiness(
-  checks: Array<{ name: string; fn: () => Promise<boolean> | boolean }>
-): Promise<ReadinessResult> {
-  const results: ReadinessResult['details'] = [];
-  for (const c of checks) {
-    try {
-      const r = await Promise.resolve(c.fn());
-      results.push({ name: c.name, ok: !!r });
-    } catch (err: any) {
-      results.push({ name: c.name, ok: false, error: err?.message ?? String(err) });
-    }
-  }
-  return { ok: results.every((r) => r.ok), details: results };
-}

node-health/src/liveness.ts

@@ -0,0 +1,31 @@
+/**
+ * Type representing the result of a liveness check.
+ */
+export type LivenessResult = {
+	/** Status of the service (always 'ok'). */
+	status: 'ok';
+	/** Timestamp of the liveness check in milliseconds since the Unix epoch. */
+	timestamp: number;
+};
+
+/**
+ * Liveness check - indicates if the service is running.
+ * @returns A LivenessResult object.
+ */
+export function liveness() {
+	return {
+		status: 'ok',
+		timestamp: Date.now(),
+	} as LivenessResult;
+}
+
+/**
+ * Handler for liveness HTTP requests.
+ * @returns A Response object with LivenessResult in JSON format and status 200.
+ */
+export const handleLiveness = (): Response => {
+	return new Response(JSON.stringify(liveness()), {
+		status: 200,
+		headers: { 'Content-Type': 'application/json' },
+	});
+};

node-health/src/readiness.ts

@@ -0,0 +1,251 @@
+/** Return type of a readiness check function */
+export type ReadinessFunctionReturn = {
+	/** Status of the readiness check */
+	status: ReadinessStatus;
+	/** Optional message providing additional information about the readiness check */
+	message?: string;
+};
+
+/** Function that performs a readiness check */
+export type ReadinessFunction = (check: ReadinessCheck) => Promise<ReadinessFunctionReturn>;
+
+/** Status of a readiness check */
+export type ReadinessStatus = 'ok' | 'error' | 'degraded';
+
+const aggregateStatus = (statuses: ReadinessStatus[]): ReadinessStatus => {
+	if (statuses.includes('error')) return 'error';
+	if (statuses.includes('degraded')) return 'degraded';
+	return 'ok';
+};
+
+/** Represents a readiness check with an optional timeout */
+export type ReadinessCheck = {
+	/** Name of the readiness check */
+	name: string;
+	/** Function that performs the readiness check */
+	fn: ReadinessFunction;
+	/** Timeout in milliseconds for the readiness check (default: 5000) */
+	timeout?: number;
+};
+
+/** Result of a system readiness check */
+export type ReadinessResult = {
+	/**
+	 * Status of the system readiness check, aggregated as the worst status
+	 * among individual checks. 'unknown' is a special case indicating that
+	 * no checks were performed, used by ScheduledReadiness before the first run.
+	 * */
+	status: ReadinessStatus | 'unknown';
+	/** Start time of the system readiness check in milliseconds since the Unix epoch */
+	start: number;
+	/** Duration of the system readiness check in milliseconds */
+	duration: number;
+	/** Details of individual readiness checks */
+	details: ReadinessDetail[];
+};
+
+/** Detail of an individual readiness check */
+export type ReadinessDetail = {
+	/** Name of the readiness check */
+	name: string;
+	/** Status of the readiness check */
+	status: ReadinessStatus;
+	/** Duration of the readiness check in milliseconds */
+	duration: number;
+	/** Message providing additional information about the readiness check */
+	message?: string;
+};
+
+/**
+ * Performs a readiness check by executing the provided readiness functions.
+ * @param checks - An array of readiness functions to execute.
+ * @returns A Promise that resolves to a ReadinessResult object.
+ */
+export const readiness = async (checks: ReadinessCheck[]): Promise<ReadinessResult> => {
+	const start = Date.now();
+	const t0 = performance.now();
+	const details: ReadinessDetail[] = [];
+
+	for (const check of checks) {
+		const checkt0 = performance.now();
+		try {
+			const result = await withTimeout(
+				check.fn(check),
+				check.timeout ?? 5000,
+				`Readiness check '${check.name}' timed out after ${check.timeout ?? 5000} ms`,
+			);
+			details.push({
+				name: check.name,
+				status: result.status,
+				message: result.message,
+				duration: performance.now() - checkt0,
+			});
+		} catch (err) {
+			details.push({
+				name: check.name,
+				status: 'error',
+				message: err instanceof Error ? err.message : String(err),
+				duration: performance.now() - checkt0,
+			});
+		}
+	}
+
+	const duration = performance.now() - t0;
+
+	return {
+		status: aggregateStatus(details.map((d) => d.status)),
+		start,
+		duration,
+		details,
+	};
+};
+
+/**
+ * Creates a handler function for readiness HTTP requests. Warning: this runs all
+ * checks on each request and may be slow.
+ * @param checks - An array of readiness functions to execute.
+ * @returns A function that returns a Response object with ReadinessResult in JSON format.
+ */
+export const createReadinessHandler = (checks: ReadinessCheck[]): (() => Promise<Response>) => {
+	return async () => {
+		const result = await readiness(checks);
+		return respondWithResult(result);
+	};
+};
+
+/**
+ * Class that schedules periodic readiness checks.
+ */
+export class ScheduledReadiness {
+	private checks: ReadinessCheck[];
+	private interval: number;
+	private started: boolean = false;
+	private timer: NodeJS.Timeout | null = null;
+	private latestResult: ReadinessResult | null = null;
+	private nextResult: Promise<ReadinessResult> | null = null;
+
+	/**
+	 * Creates an instance of ScheduledReadiness.
+	 * @param checks - An array of readiness functions to execute.
+	 * @param interval - Interval in milliseconds between readiness checks.
+	 */
+	constructor(checks: ReadinessCheck[], interval: number) {
+		this.checks = checks;
+		this.interval = interval;
+	}
+
+	/** Starts the scheduled readiness checks */
+	async start() {
+		if (this.started) return; // Already started
+		this.started = true;
+
+		const runCheck = async () => {
+			// Prevent concurrent runs
+			if (this.nextResult) return;
+
+			this.nextResult = readiness(this.checks);
+			try {
+				this.latestResult = await this.nextResult;
+			} finally {
+				this.nextResult = null;
+			}
+		};
+
+		await runCheck(); // Initial run
+		this.timer = setInterval(runCheck, this.interval);
+	}
+
+	/** Stops the scheduled readiness checks */
+	stop() {
+		if (this.timer) {
+			clearInterval(this.timer);
+			this.timer = null;
+		}
+		this.started = false;
+	}
+
+	/** Gets the next readiness result, waiting if a check is in progress */
+	async getNextResult(): Promise<ReadinessResult | null> {
+		if (this.nextResult) {
+			return await this.nextResult;
+		}
+		return this.latestResult;
+	}
+
+	/** Gets the latest readiness result without waiting */
+	getResult(): ReadinessResult | null {
+		return this.latestResult;
+	}
+
+	/**
+	 * Sets the interval for readiness checks and restarts the timer if already started.
+	 * @param ms - Interval in milliseconds.
+	 */
+	setInterval(ms: number) {
+		this.interval = ms;
+		if (this.timer) {
+			this.stop();
+			this.start();
+		}
+	}
+
+	/**
+	 * Creates a handler function for readiness HTTP requests using the latest scheduled result.
+	 * Scheduled handler always returns the most recent result, or 'unknown' if no checks have run yet.
+	 * @returns A function that returns a Response object with ReadinessResult in JSON format.
+	 */
+	createHandler(): () => Promise<Response> {
+		return async () => {
+			const result = this.getResult();
+			if (!result) {
+				return new Response(
+					JSON.stringify({
+						status: 'unknown',
+						start: Date.now(),
+						duration: 0,
+						details: [],
+					} as ReadinessResult),
+					{
+						status: httpStatusFromReadiness('unknown'),
+						headers: { 'Content-Type': 'application/json' },
+					},
+				);
+			}
+
+			return respondWithResult(result);
+		};
+	}
+}
+
+/** Returns a Response object with the given ReadinessResult in JSON format */
+const respondWithResult = (result: ReadinessResult) => {
+	return new Response(JSON.stringify(result), {
+		status: httpStatusFromReadiness(result.status),
+		headers: { 'Content-Type': 'application/json' },
+	});
+};
+
+/** Returns the HTTP status code corresponding to a given readiness status */
+const httpStatusFromReadiness = (status: ReadinessStatus | 'unknown'): number => {
+	if (status === 'ok') return 200;
+	if (status === 'degraded') return 200; // 206 could also be suitable, but let's avoid false alarms
+	if (status === 'error') return 503;
+	return 200; // unknown, treat as ok to avoid false alarms
+};
+
+const withTimeout = async <T>(
+	promise: Promise<T>,
+	ms: number,
+	timeoutMessage: string,
+): Promise<T> => {
+	let timeoutHandle: NodeJS.Timeout;
+	const timeoutPromise = new Promise<never>((_, reject) => {
+		timeoutHandle = setTimeout(() => {
+			reject(new Error(timeoutMessage));
+		}, ms);
+	});
+
+	return Promise.race([promise, timeoutPromise]).finally(() => {
+		clearTimeout(timeoutHandle);
+	});
+};

node-health/tsconfig.json

@@ -1,6 +1,16 @@
 {
-	"extends": "../tsconfig.base.json",
 	"compilerOptions": {
+		"lib": ["es2023"],
+		"target": "es2023",
+		"module": "node20",
+		"declaration": true,
+		"declarationMap": true,
+		"sourceMap": true,
+		"strict": true,
+		"esModuleInterop": true,
+		"skipLibCheck": true,
+		"forceConsistentCasingInFileNames": true,
+		"resolveJsonModule": true,
 		"rootDir": "src",
 		"outDir": "dist",
 		"composite": false

tsconfig.base.json

@@ -1,15 +0,0 @@
-{
-  "compilerOptions": {
-    "target": "ES2021",
-    "module": "ES2020",
-    "moduleResolution": "node",
-    "declaration": true,
-    "declarationMap": true,
-    "sourceMap": true,
-    "strict": true,
-    "esModuleInterop": true,
-    "skipLibCheck": true,
-    "forceConsistentCasingInFileNames": true,
-    "resolveJsonModule": true
-  }
-}