utils.js

  1. /**
  2.  * Contains misc static utility methods.
  3.  */
  4. class Utils {
  6. 	/**
  7. 	 * Converts a single byte to a hex string.
  8. 	 * @param {number} byte
  9. 	 * @return {string}
  10. 	 */
  11. 	static byteToHex(byte) {
  12. 		// Ensure hex string always has two chars
  13. 		return ('0' + byte.toString(16)).slice(-2);
  14. 	}
  16. 	/**
  17. 	 * Converts an array of bytes to a hex string.
  18. 	 * @param {array} byteArray
  19. 	 * @return {string}
  20. 	 */
  21. 	static bytesToHex(byteArray) {
  22. 		var hex = [];
  23. 		byteArray.forEach(byte => hex.push(Utils.byteToHex(byte)));
  24. 		return hex.join('');
  25. 	}
  27. 	/**
  28. 	 * Converts a hex string to a number.
  29. 	 * @param {string} hexString
  30. 	 * @return {number}
  31. 	 */
  32. 	static hexToNumber(hexString) {
  33. 		return parseInt(hexString, 16);
  34. 	}
  36. 	/**
  37. 	 * Converts an array of bytes to a number.
  38. 	 * @param {array} byteArray
  39. 	 * @return {number}
  40. 	 */
  41. 	static bytesToNumber(byteArray) {
  42. 		return Utils.hexToNumber(Utils.bytesToHex(byteArray));
  43. 	}
  45. 	/**
  46. 	 * Converts an array of bytes to letters.
  47. 	 * @param {array} byteArray
  48. 	 * @return {string}
  49. 	 */
  50. 	static bytesToLetters(byteArray) {
  51. 		var letters = [];
  52. 		byteArray.forEach(byte => letters.push(String.fromCharCode(byte)));
  53. 		return letters.join('');
  54. 	}
  56. 	/**
  57. 	 * Converts a decimal to it's binary representation.
  58. 	 * @param {number} dec
  59. 	 * @return {string}
  60. 	 */
  61. 	static decToBinary(dec) {
  62.     	return (dec >>> 0).toString(2);
  63. 	}
  65. 	/**
  66. 	 * Determines the length in bytes of a variable length quaantity.  The first byte in given range is assumed to be beginning of var length quantity.
  67. 	 * @param {array} byteArray
  68. 	 * @return {number}
  69. 	 */
  70. 	static getVarIntLength(byteArray) {
  71. 		// Get byte count of delta VLV
  72. 		// http://www.ccarh.org/courses/253/handout/vlv/
  73. 		// If byte is greater or equal to 80h (128 decimal) then the next byte
  74. 	    // is also part of the VLV,
  75. 	   	// else byte is the last byte in a VLV.
  76. 	   	let currentByte = byteArray[0];
  77. 	   	let byteCount = 1;
  79. 		while (currentByte >= 128) {
  80. 			currentByte = byteArray[byteCount];
  81. 			byteCount++;
  82. 		}
  84. 		return byteCount;
  85. 	}
  87. 	/**
  88. 	 * Reads a variable length value.
  89. 	 * @param {array} byteArray
  90. 	 * @return {number}
  91. 	 */
  92. 	static readVarInt(byteArray) {
  93. 		var result = 0;
  94. 		byteArray.forEach(number => {
  95. 			var b = number;
  96. 			if (b & 0x80) {
  97. 				result += (b & 0x7f);
  98. 				result <<= 7;
  99. 			} else {
  100. 				/* b is the last byte */
  101. 				result += b;
  102. 			}
  103. 		});
  105. 		return result;
  106. 	}
  108. 	/**
  109. 	 * Decodes base-64 encoded string
  110. 	 * @param {string} string
  111. 	 * @return {string}
  112. 	 */
  113. 	static atob(string) {
  114. 		if (typeof atob === 'function') return atob(string);
  115. 		return Buffer.from(string, 'base64').toString('binary');
  116. 	}
  117. }
  119. export {Utils};