aws-kcl/lib/kcl/checkpointer.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
 * Allows you to make checkpoint requests. A checkpoint marks a point in a shard until which all records are processed
 * successfully. If this MultiLangDaemon KCL application instance shuts down for whatever reason, then another instance
 * of the same KCL application resumes processing for this shard after the most recent checkpoint.
 */

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


/**
 * Creates an instance of the checkpointer.
 * @class Checkpointer
 * @param {KCLManager} kclManager - Main KCL manager instance that keeps track of current state and dispatches all
 *                                  processing functions.
 */
function Checkpointer(kclManager) {
  this._kclManager = kclManager;
  this._callback  = null;
}

/**
 * Checkpoints at a given sequence number. If the sequence number is not provided, the checkpoint will be at the end of
 * the most recently-delivered list of records.
 * @param {string} [sequenceNumber] - Sequence number of the record to checkpoint; if this value is not provided, the
 *                                    latest retrieved record is checkpointed.
 * @param {callback} callback - Function that is invoked after the checkpoint operation completes.
 */
Checkpointer.prototype.checkpoint = function(sequenceNumber, callback) {
  if (typeof sequenceNumber === 'function') {
    callback = sequenceNumber;
    sequenceNumber = null;
  }

  if (this._callback) {
    callback('Cannot checkpoint while another checkpoint is already in progress.');
    return;
  }
  this._callback = callback;
  this._kclManager.checkpoint(sequenceNumber);
};

/**
 * Gets called by the KCL manager when an outstanding checkpoint request completes either successfully or with
 * an error. This function then invokes the callback passed by the user when the checkpoint was requested.
 * @param {string} err - Error message if the checkpoint request was unsuccessful.
 * @param {string} sequenceNumber - Sequence number for which the checkpoint response is received.
 * @ignore
 */
Checkpointer.prototype.onCheckpointerResponse = function(err, sequenceNumber) {
  var callback = this._callback;
  this._callback = null;
  callback(err, sequenceNumber);
};

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