wiegand-encoder/lib/decode.js

Encode and decode 26, 34, or 38 bit Wiegand protocol credentials

"use strict";
//
//  src/decode.ts
//  Created by Jesse Youngblood on 02/02/20
//  Copyright (c) 2020 Jesse Youngblood. All rights reserved.
//
var __importDefault = (this && this.__importDefault) || function (mod) {
    return (mod && mod.__esModule) ? mod : { "default": mod };
};
Object.defineProperty(exports, "__esModule", { value: true });
const parity_1 = __importDefault(require("./parity"));
/**
 * Decode a Wiegand protocol message into a card number and facility code, after validating parity bits
 * @param {string} wiegand - Wiegand message
 * @param {number} [cardNumberLength] - How many bits the card number should be
 * @param {number} [facilityCodeLength] - How many bits the facility code should be
 * @param {boolean=true} [validateParity] - Whether to validate parity bits on the message or not
 * @throws
 * @returns {{cardNumber: string, facilityCode: string}}
 */
function decode(string, cardNumberLength, facilityCodeLength, validateParity = true) {
    if (typeof string !== 'string') {
        throw new Error(`Invalid Wiegand credential. Received: "${string}"`);
    }
    if (cardNumberLength === undefined || facilityCodeLength === undefined) {
        // Use the message length to infer the facility code length and the card length
        // If the input length is 26, this will resolve to 8 & 16
        // This enables automatically decoding 26, 34, or 38 bit credentials without specifying element length
        facilityCodeLength = Math.floor((string.length - 2) / 3);
        cardNumberLength = (string.length - 2) - facilityCodeLength;
    }
    if (Number.isInteger(cardNumberLength) === false || cardNumberLength < 0) {
        throw new Error(`Card number length must be a positive integer. Received "${cardNumberLength}"`);
    }
    if (Number.isInteger(facilityCodeLength) === false || facilityCodeLength < 0) {
        throw new Error(`Facility code length must be a positive integer. Received "${facilityCodeLength}"`);
    }
    if (string.length !== facilityCodeLength + cardNumberLength + 2) {
        throw new Error(`Invalid credential length. Expected ${facilityCodeLength + cardNumberLength + 2} bits, recieved ${string.length}.`);
    }
    // Confirm the input characters are binary
    if (string.split('').filter(char => ['0', '1'].includes(char) === false).length > 0) {
        throw new Error(`Invalid Wiegand credential. Expected binary string, received "${string}"`);
    }
    // Confirm the parity bits
    if (validateParity === true) {
        parity_1.default.validate(string);
    }
    // Extract facility code and card number
    const contents = string.substring(1, string.length - 1);
    const facilityCodeBinary = contents.substring(0, facilityCodeLength);
    const cardNumberBinary = contents.substring(facilityCodeLength);
    // Cast the binary numbers into integers
    const facilityCode = parseInt(facilityCodeBinary, 2);
    const cardNumber = parseInt(cardNumberBinary, 2);
    return { cardNumber, facilityCode };
}
exports.default = decode;