HID_scanner.js

HID_scanner.js

// USB Event Detection
const usbDetect = require('usb-detection');

// USB HID library used to interface with USB devices
const HID = require('node-hid');

class Scanner {
    constructor(config, socket) {
        this.socket = socket;
        this.device = null;
        this.config = config.get('scanner');
        this.station = '';
        this.scannerRequired = true;
        this.scanAvailable = false;

        /**
         * Map for converting bar code ints to proper characters
         */
        this.hidMap = {
            4: "A", 5: "B", 6: "C", 7: "D", 8: "E",
            9: "F", 10: "G", 11: "H", 12: "I", 13: "J",
            14: "K", 15: "L", 16: "M", 17: "N", 18: "O",
            19: "P", 20: "Q", 21: "R", 22: "S", 23: "T",
            24: "U", 25: "V", 26: "W", 27: "X", 28: "Y",
            29: "Z", 30: '1', 31: '2', 32: '3', 33: '4',
            34: '5', 35: '6', 36: '7', 37: '8', 38: '9',
            // enter - barcode escape char
            39: '0', 40: 'enter', 44: " ", 45: "-", 55: ".", 56: "/",
            85: "*", 87: "+"
        };
    }

    /**
     * Find the device we are expecting.  If found attach and start listening.
     */
    findDevice() {
        const self = this;

        // Check for existing device
        if (this.device) {
            return;
        }

        // Find and attach
        usbDetect.find(self.config.vendorId, self.config.productId, function (err, devices) {
        }).then(function (devices) {
            if ((devices.length > 0)) {
                self.attach(devices[0]);
            } else {
                // Send status message
                self.sendScannerStatus();
            }
        });
    }

    /**
     * Attach the passed device for scanning
     *
     * @param device
     */
    attach(device) {
        this.device = new HID.HID(device.vendorId, device.productId);
        this.scanAvailable = true;

        const hidMap = this.hidMap;
        // empty array for barcode bytes
        let bcodeBuff = [];
        // string variable to hold barcode string
        let barCode = "";

        const self = this;

        // When device receives a chunk of data from scanning handle it
        this.device.on("data", function (chunk) {
            // Second byte of buffer is all that contains data
            if (hidMap[chunk[2]]) {
                // Escape character (enter)
                if (chunk[2] === 40) {
                    barCode = bcodeBuff.join("");
                    bcodeBuff = [];

                    // Send code scan
                    self.scanned(barCode);

                } else {
                    // Add converted chunk
                    bcodeBuff.push(hidMap[chunk[2]]);
                }
            }
        });

        // Bind to device error, usually due to disconnected device (unplug)
        this.device.on('error', function (err) {
            console.error('Caught Device Error!', err, ". This is usually caused by unplugging the device being used.");
        });

        // Send status message
        this.sendScannerStatus();
    }

    /**
     * Attached device has been detached (unplugged)
     */
    detached() {
        this.device.close();
        this.device = null;
        this.scanAvailable = false;
        // Send status message
        this.sendScannerStatus();
    }

    /**
     * Handle code scan
     *
     * @param code
     */
    scanned(code) {
        console.debug('Scanned code:', code);
        // Check make sure we have something defined so we can offload
        if (typeof this.station.handleScan === 'function') {
            // Handle the scanned code
            this.station.handleScan(code);
        }
    }

    /**
     * Reset material creation station 
     *
     * @param code
     */
    resetStation() {
        // Check make sure we have something defined so we can offload
        if (typeof this.station.reset === 'function') {
            // Reset station
            this.station.reset();
        }
    }

    /**
     * Listen for USB device changes related to the defined scanner
     */
    deviceListeners() {
        const self = this;
        // Listen for attach
        usbDetect.on('add:' + this.config.vendorId + ':' + this.config.productId, function (device) {
            console.log('Device added', device);
            self.findDevice(device);

        });

        // Listen for detach
        usbDetect.on('remove:' + this.config.vendorId + ':' + this.config.productId, function (device) {
            console.log('Device removed', device);
            self.detached();
        });
    }

    /**
     * Send the scanner status as a socket event
     */
    sendScannerStatus() {
        let enabled = (this.device) ? true : false;
        this.socket.sendScannerStatus(enabled, this.scannerRequired);
    }
}

module.exports = Scanner;