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src/lib/backoff-wrapper.js

  1. import {EventEmitter} from 'events'
  2. import ExponentialBackoffStrategy from 'backoff/lib/strategy/exponential'
  3.  
  4. /*
  5. This is heavily based on:
  6. https://github.com/MathieuTurcotte/node-backoff/blob/master/lib/backoff.js
  7.  
  8. ...which holds the following 2-line copyright notice:
  9. Copyright (c) 2012 Mathieu Turcotte
  10. Licensed under the MIT license.
  11.  
  12. This is a very bare-bones version of the file above
  13. */
  14.  
  15. /**
  16.  * A wrapper over the ExponentialBackoffStrategy from the backoff module.
  17.  */
  18. export default class ExponentialBackoff extends EventEmitter {
  19. 	/**
  20. 	 * Constructor.
  21. 	 */
  22. 	constructor() {
  23. 		super()
  24.  
  25. 		/**
  26. 		 * ExponentialBackoffStrategy instance.
  27. 		 * @type {ExponentialBackoffStrategy}
  28. 		 */
  29. 		this._strategy = new ExponentialBackoffStrategy({
  30. 			randomisationFactor: 0.3,
  31. 			initialDelay: 1000,
  32. 			maxDelay: 60000
  33. 		})
  34.  
  35. 		/**
  36. 		 * Number of previous failed attempts.
  37. 		 * @type {Number}
  38. 		 */
  39. 		this._backoffNumber = 0
  40.  
  41. 		/**
  42. 		 * Backoff timeout ID.
  43. 		 * @type {TimeoutID}
  44. 		 */
  45. 		this._timeoutID = undefined
  46. 	}
  47.  
  48. 	/**
  49. 	 * Signals that we tried executing the protected routine and failed, or that we want to start the process.
  50. 	 * @emits backoff(_backoffNumber, delay) delay is how much time will pass before we try executing the routine.
  51. 	 */
  52. 	backoff() {
  53. 		// Backoff already in progress
  54. 		if (this._timeoutID) {
  55. 			return
  56. 		}
  57.  
  58. 		const delay = this._strategy.next()
  59. 		this._timeoutID = setTimeout(() => {
  60. 			this._timeoutID = undefined
  61. 			this.emit('retry', this._backoffNumber)
  62. 			this._backoffNumber++
  63. 		}, delay)
  64. 		this.emit('backoff', this._backoffNumber, delay)
  65. 	}
  66.  
  67. 	/**
  68. 	 * Resets failed attempt number and cancels a possible pending action (routine execution after backoff).
  69. 	 */
  70. 	reset() {
  71. 		// Reset number of backoffs
  72. 		this._backoffNumber = 0
  73.  
  74. 		// Reset strategy
  75. 		this._strategy.reset()
  76.  
  77. 		// Clear a possibly running timeout
  78. 		if (this._timeoutID !== undefined) {
  79. 			clearTimeout(this._timeoutID)
  80. 			this._timeoutID = undefined
  81. 		}
  82. 	}
  83.  
  84. 	/**
  85. 	 * Used to signal the routine was successful.
  86. 	 * This resets the wrapper.
  87. 	 * @emits success
  88. 	 * @see {@link reset}
  89. 	 */
  90. 	success() {
  91. 		// Reset state
  92. 		this.reset()
  93.  
  94. 		// Alert everyone we did it (for now at least)
  95. 		this.emit('success')
  96. 	}
  97. }