rate-limit/index.js

"use strict";

const Promise = require("bluebird");
const ms = require("ms");
const promiseDelayEvery = require("@joepie91/promise-delay-every");
const propagateAbort = require("@promistream/propagate-abort");
const propagatePeek = require("@promistream/propagate-peek");
const debug = require("debug")("promistream:rate-limit");

function makeClonableInstance(interval) {
	let intervalInMilliseconds = (typeof interval === "number")
		? interval
		: ms(interval);

	debug(`Creating clonable with interval of ${intervalInMilliseconds}ms`);

	let delayer = promiseDelayEvery(intervalInMilliseconds);

	return function createClone	() {
		debug("Creating clone");

		return {
			_promistreamVersion: 0,
			description: `rate-limited stream (1 per ${interval})`,
			read: (source) => {
				return Promise.try(() => {
					debug("Attempted read");
					return delayer();
				}).then(() => {
					debug("Delay passed, completing read");
					return source.read();
				});
			},
			peek: propagatePeek,
			abort: propagateAbort
		};
	};
}

module.exports = function rateLimitedStream(... args) {
	// Internally, we treat a non-clonable stream as a clonable stream that will only ever have one clone - this makes implementation much simpler
	let createClone = makeClonableInstance(... args);

	return createClone();
};

module.exports.clonable = makeClonableInstance;