expire-unused-keys/index.js

Who wants to keep track of what's not being used? This guy!

var EventEmitter = require('events').EventEmitter

function onlyLetOneTaskRunAtATime(fnTask) {
	var running = false

	function done() {
		running = false
	}

	return function run() {
		if (!running) {
			running = true
			fnTask(done)
		}
	}
}

function noop() {}

module.exports = function Expirer(timeoutMs, db, checkIntervalMs) {
	var repeatExpirations = false

	if (typeof timeoutMs === 'object') { // options mode
		db = timeoutMs.db
		checkIntervalMs = timeoutMs.checkIntervalMs
		repeatExpirations = timeoutMs.repeatExpirations
		timeoutMs = timeoutMs.timeoutMs
	}
	var expirer = new EventEmitter()

	var forgotten = []

	function filterForgotten(keys) {
		return keys.filter(function(key) {
			return forgotten.indexOf(key) === -1
		})
	}

	var checkForExpiredKeys = onlyLetOneTaskRunAtATime(function check(done) {
		var now = new Date().getTime()
		var batchKeys = []
		db.createReadStream().on('data', function(data) {
			if (parseInt(data.value) + timeoutMs < now) {
				batchKeys.push(data.key)
			}
		}).on('end', function() {
			// Need to make sure that none of these keys were "forgotten" since we opened the read stream
			var expiringNow = filterForgotten(batchKeys)
			var batchObjects = expiringNow.map(function(key) {
				if (repeatExpirations) {
					return { type: 'put', key: key, value: new Date().getTime() }
				} else {
					return { type: 'del', key: key }
				}
			})

			db.batch(batchObjects, function(err) {
				if (!err) {
					filterForgotten(expiringNow).forEach(function (key) { expirer.emit('expire', key) })
				}
				forgotten = []
				done(err)
			})
		})
	})

	expirer.on('touch', function touch(key) {
		db.put(key, new Date().getTime())
	})

	function forget(key, cb) {
		forgotten.push(key)
		db.del(key, cb)
	}

	expirer.on('forget', forget)

	var interval = setInterval(checkForExpiredKeys, checkIntervalMs || 1000)
	interval.unref && interval.unref()

	expirer.touch = expirer.emit.bind(expirer, 'touch')
	expirer.forget = expirer.emit.bind(expirer, 'forget')
	expirer.createIfNotExists = function createIfNotExists(key) {
		db.get(key, function (err, value) {
			if (err && err.notFound) {
				expirer.emit('touch', key)
			}
		})
	}
	expirer.stop = function stop() {
		clearInterval(interval)
	}

	process.nextTick(checkForExpiredKeys)

	return expirer
}