readline-responsive/readlineResponsive.js

Responsive version of readline, pause() and resume() method work immediately.

/**
 * readlineResponsive
 * pause() and resume() method work immediately.
 *
 * params :
 * @ (stream) inputStream
 * @ (string) filePath
 *
 * methods :
 * - resume
 * - pause
 * - close
 *
 * events :
 * - line
 * - resume
 * - pause
 * - close
 */
const readline = require("readline"),
	fs = require("fs"),
	stream = require("stream"),
	events = require("events");

const readlineResponsive = function (input) {
	/**
	 * Declare variables
	 */
	const buffer = [],
		returnObj = new events.EventEmitter();

	const STREAMING = 0,
		PAUSED = 1,
		CLOSED = 2;

	let rStream,
		status,
		srcStreamClosed = false;

	init();
	function init () {
		if (typeof(input) === 'string') input = fs.createReadStream(input);

		//check input stream
		if (!(input instanceof stream.Readable)) throw "Initialize Failed. Invalid inputStream.";

		//create readline object
		rStream = readline.createInterface({
			input
		});
		status = STREAMING;

		rStream.on('line', line => {
			//Already closed
			if (status === CLOSED) return;

			buffer.push(line);

			if (status === STREAMING && buffer.length === 1) {
				_consumeBuffer();
			}
		});

		rStream.on('close', () => {
			srcStreamClosed = true;
			if (buffer.length === 0 && status === STREAMING) {
				status = CLOSED;
				returnObj.emit('close');
			}
		});

	}

	function resume () {
		if (status === CLOSED) return;

		status = STREAMING;
		_consumeBuffer();

		if (status === STREAMING) rStream.resume();
	}

	function pause () {
		status = PAUSED;
		rStream.pause();
	}

	function close () {
		status = CLOSED;
		rStream.close();
	}


	/**
	 * private functions
	 */
	function _consumeBuffer () {
		while(status === STREAMING && buffer.length) {
			returnObj.emit('line', buffer.shift());
		}

		if (srcStreamClosed && buffer.length === 0) {
			status = CLOSED;
			returnObj.emit('close');
		}
	}


	returnObj.resume = resume;
	returnObj.pause = pause;
	returnObj.close = close;

	return returnObj;
};

module.exports = readlineResponsive;