@metrics/client/lib/client.js

A streaming metric producer. Allows producing counters, gauges, histograms and summaries in a way that is independent of your metrics system.

"use strict";

/* eslint prefer-rest-params: "off" */

const timeSpan = require("time-span");
const stream = require("readable-stream");
const crypto = require("crypto");
const Metric = require("@metrics/metric");

const Counter = require("./counter");
const Gauge = require("./gauge");
const Summary = require("./summary");
const Histogram = require("./histogram");

const push = Symbol("metrics:client:push");

const MetricsClient = class MetricsClient extends stream.Transform {
	constructor({ id } = {}) {
		super(
			Object.assign(
				{
					objectMode: true,
				},
				...arguments,
			),
		);

		Object.defineProperty(this, "id", {
			value: id || crypto.randomBytes(3 * 4).toString("base64"),
			enumerable: true,
		});

		// Avoid hitting the max listeners limit when multiple
		// streams is piped into the same stream.
		this.on("pipe", () => {
			this.setMaxListeners(this.getMaxListeners() + 1);
		});

		this.on("unpipe", () => {
			this.setMaxListeners(this.getMaxListeners() - 1);
		});
	}

	get [Symbol.toStringTag]() {
		return "MetricsClient";
	}

	[push](metric) {
		const met = metric;
		met.source = this.id;

		if (this._readableState.flowing) {
			this.push(met);
			return;
		}
		this.emit("drop", met);
	}

	counter(options) {
		const counter = new Counter(options);
		counter.on("metric", (metric) => {
			this[push](metric);
		});
		return counter;
	}

	gauge(options) {
		const gauge = new Gauge(options);
		gauge.on("metric", (metric) => {
			this[push](metric);
		});
		return gauge;
	}

	summary(options) {
		const summary = new Summary(options);
		summary.on("metric", (metric) => {
			this[push](metric);
		});
		return summary;
	}

	histogram(options) {
		const histogram = new Histogram(options);
		histogram.on("metric", (metric) => {
			this[push](metric);
		});
		return histogram;
	}

	timer(options = {}) {
		const end = timeSpan();
		return (opts = {}) => {
			const meta = { ...options.meta, ...opts.meta };
			const time = end.seconds();
			const metric = new Metric({
				type: 5,
				value: time,
				...options,
				...opts,
				meta,
			});
			this[push](metric);
		};
	}

	metric(options) {
		const metric = new Metric(options);
		this[push](metric);
	}

	_transform(metric, enc, next) {
		if (metric.source === this.id) {
			this.emit("drop", metric);
			next(null);
			return;
		}
		next(null, metric);
	}
};

module.exports = MetricsClient;