aws-kcl/lib/kcl/io_handler.js

Kinesis Client Libray (KCL) in Node.js.

/***
Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
SPDX-License-Identifier: Apache-2.0
***/

'use strict';

/**
 * @fileoverview
 * Communicates with the MultiLangDaemon through the input and output files.
 */

var EventEmitter = require('events').EventEmitter;
var readline = require('readline');
var util = require('util');

/**
 * Creates an instance of the I/O handler.
 * @class IOHandler
 * @param {file} inputFile - A file to read input lines from.
 * @param {file} outputFile - A file to write output lines to.
 * @param {file} errorFile - A file to write error lines to.
 */
function IOHandler(inputFile, outputFile, errorFile) {
  this._inputFile = inputFile;
  this._outputFile = outputFile;
  this._errorFile = errorFile;

  this._readlineInterface = readline.createInterface(this._inputFile, this._outputFile);
  this._onInputLineCallback = this._onInputLine.bind(this);
  this._onInputCloseCallback = this._onInputClose.bind(this);
  this._readlineInterface.on('line', this._onInputLineCallback);
  this._readlineInterface.on('close', this._onInputCloseCallback);
}

/** @extends EventEmitter */
util.inherits(IOHandler, EventEmitter);

/**
 * Frees up any resources held by this instance.
 */
IOHandler.prototype.destroy = function() {
  this._readlineInterface.removeListener('line', this._onInputLineCallback);
  this._readlineInterface.removeListener('close', this._onInputCloseCallback);
  this._readlineInterface.close();
};

/**
 * Sends the string message to the MultiLangDaemon using the output stream.
 * @param {string} line - Line to send to the MultiLangDaemon.
 * @param {callback} callback - Callback that gets invoked on completion.
 */
IOHandler.prototype.writeLine = function(line, callback) {
  var result = this._outputFile.write(util.format('\n%s\n', line), 'utf8', callback);
  if (!result) {
    callback(util.format('Unable to write %s to file.', line));
  }
};

/**
 * Logs an error.
 * @param {string} error - Error to log.
 */
IOHandler.prototype.writeError = function(error) {
  this._errorFile.write(util.format('%s\n', error));
};

/**
 * Event handler for when a new line is received from the MultiLangDaemon through the input stream.
 @ @param {string} line - New line received.
 * @private
 */
IOHandler.prototype._onInputLine = function(line) {
  this.emit('line', line);
};

/**
 * Event handler for when the input stream is closed.
 * @private
 */
IOHandler.prototype._onInputClose = function() {
  this.emit('close');
};

/** @exports kcl/IOHandler */
module.exports = IOHandler;