domotz-remote-pawn/src/discovery/snmp/snmp_overlay_db.js

Domotz Agent

/** This file is part of Domotz Agent.
 * Copyright (C) 2021  Domotz Ltd
 *
 * Domotz Agent is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Domotz Agent is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Domotz Agent.  If not, see <http://www.gnu.org/licenses/>.
 *
 *
 * Created by Fausto Lelli <fausto@domotz.com>
 */

var path = require('path');
var os = require('os');

const OID_DB_REMOTE_ENDPOINT = '/overlay/catalog';
const OVERLAY_DB_SEMAPHORE = 'SNMP_OVERLAY_DB_SEMAPHORE';
const OID_DB_FILE = path.join(os.tmpdir(), 'overlay_db.json');

var snmpOverlayDBFactory = function (resourceLocator) {
    'use strict';

    var fileUtils = resourceLocator.utils.file;
    var crypto = resourceLocator.crypto;
    var mutex = resourceLocator.utils.mutex;
    var engineRequest = resourceLocator.engineRequest;

    var myConsole = resourceLocator.log.decorateLogs();

    // the following variables must be invalidated
    var currentMD5 = null;
    var overlayMap = {};

    var lockDiscovery = function () {
        return mutex.lock(OVERLAY_DB_SEMAPHORE, 1);
    };

    var unlockDiscovery = function () {
        mutex.safeUnlock(OVERLAY_DB_SEMAPHORE, 1);
    };

    function getOverlay(overlayId) {
        if (overlayMap.hasOwnProperty(overlayId)) {
            return overlayMap[overlayId];
        }

        var content = getOverlayDB();
        if (content && content.hasOwnProperty('overlays')) {
            var overlays = content.overlays;

            var min = 0;
            var max = overlays.length - 1;
            var guess;

            while (min <= max) {
                guess = Math.floor((max + min) / 2);

                if (overlays[guess].id === overlayId) {
                    overlayMap[overlayId] = overlays[guess];
                    return overlays[guess];
                } else if (overlays[guess].id < overlayId) {
                    min = guess + 1;
                } else {
                    max = guess - 1;
                }
            }

            return null;
        } else {
            return null;
        }
    }

    function getOverlayDB() {
        var content = fileUtils.readFile(OID_DB_FILE);
        if (content) {
            try {
                return JSON.parse(content);
            } catch (e) {
                myConsole.info('Can not parse db file: %s', e);
            }
        }
        return null;
    }

    function saveOverlayDB(db) {
        fileUtils.writeFileSafe(OID_DB_FILE, db);
        currentMD5 = null;
        overlayMap = {};
        getOverlayMD5();
    }

    function computeSingleOverlayMD5(overlay) {
        var overlayContent = overlay.id;

        var oidScalar = Object.keys(overlay.oid_scalar);
        if (oidScalar && oidScalar.length > 0) {
            oidScalar.sort();
            for (var iScalar = 0; iScalar < oidScalar.length; iScalar++) {
                overlayContent += oidScalar[iScalar];
            }
        }
        var oidColumn = Object.keys(overlay.oid_column);
        if (oidColumn && oidColumn.length > 0) {
            oidColumn.sort();
            for (var iColumn = 0; iColumn < oidColumn.length; iColumn++) {
                overlayContent += oidColumn[iColumn];
            }
        }
        return crypto.createHash('md5').update(overlayContent).digest('hex');
    }

    function getOverlayMD5() {
        if (currentMD5) {
            return currentMD5;
        }

        var content = getOverlayDB();
        if (content && content.hasOwnProperty('overlays')) {
            var overlays = content.overlays;
            var contentMD5 = '';

            for (var i = 0; i < overlays.length; i++) {
                contentMD5 += computeSingleOverlayMD5(overlays[i]);
            }

            currentMD5 = crypto.createHash('md5').update(contentMD5).digest('hex');
            myConsole.info('New MD5 computed: %s', currentMD5);
            return currentMD5;
        } else {
            return null;
        }
    }

    function invalidate() {
        myConsole.info('Force check of Overlay DB cache');
        currentMD5 = null;
        checkOverlayDB();
    }

    function checkOverlayDB() {
        if (!lockDiscovery()) {
            myConsole.warn('WARNING: SNMP Overlay DB Check already in progress, ignoring the call');
            return;
        }

        var currentMD5 = getOverlayMD5();

        var url = OID_DB_REMOTE_ENDPOINT;
        if (currentMD5 !== null) {
            url = OID_DB_REMOTE_ENDPOINT + '?md5=' + currentMD5;
        }
        myConsole.info('Check MIB Overlay DB, url: %s', url);

        engineRequest
            .sendWithPromise(url, 'GET', null, function (response) {
                myConsole.debug('Received response code : %s', response.statusCode);
                if (response.statusCode === 304) {
                    myConsole.info('MIB Overlay DB is unchanged, using cached info ');
                } else {
                    myConsole.info('Writing MIB Overlay DB to filesystem');
                    saveOverlayDB(response.body);
                }
            })
            .catch(function (err) {
                myConsole.error('Can not retrieve MIB Overlay DB %s', err);
            })
            .finally(function () {
                unlockDiscovery();
            });
    }

    return {
        getOverlay: function (overlayId) {
            return getOverlay(overlayId);
        },
        getOverlayMD5: getOverlayMD5,
        checkOverlayDB: checkOverlayDB,
        invalidate: invalidate,
    };
};

module.exports.factory = snmpOverlayDBFactory;