Repository: louislam/uptime-kuma
File: server/monitor-types/snmp.js (JavaScript)

Code before:
const { UP, DOWN, log, getKey } = require("../../src/util");
const snmp = require("net-snmp");

class SNMPMonitorType extends MonitorType {
    name = "snmp";

    /**
     * @inheritdoc
     */
    async check(monitor, heartbeat, _server) {

        const options = {
            port: monitor.port || "161",
            retries: monitor.maxretries,
            timeout: monitor.timeout * 1000,

            // Resolve the net-snmp version identifier from monitor.snmpVersion using the `getKey` method (see utils.ts).
            // If the specified version exists, use it; otherwise, default to SNMP version 2c.
            version: getKey(snmp.Version, monitor.snmpVersion) || snmp.Version2c,
        };

        try {
            const session = snmp.createSession(monitor.hostname, monitor.snmpCommunityString, options);

            // Handle errors during session creation
            session.on("error", (error) => {
                heartbeat.status = DOWN;
                heartbeat.msg = `SNMP: Error creating SNMP session: ${error.message}`;
                log.debug("monitor", heartbeat.msg);
            });

            const varbinds = await new Promise((resolve, reject) => {
                session.get([ monitor.snmpOid ], (error, varbinds) => {
                    if (error) {
                        reject(error);
                    } else {
                        log.debug("monitor", `SNMP: Received varbinds (Type=${getKey(snmp.ObjectType, varbinds[0].type)}): ${varbinds[0].value}`);
                        resolve(varbinds);
                    }
                });
            });

            // Verify if any varbinds were returned from the SNMP session or if the varbind type indicates a non-existent instance.
            // The `getKey` method retrieves the key associated with the varbind type from the snmp.ObjectType object.
            if (varbinds.length === 0 || getKey(snmp.ObjectType, varbinds[0].type) === "NoSuchInstance") {
                throw new Error(`No varbinds returned from SNMP session (OID: ${monitor.snmpOid})`);

            // Varbinds succesfully returned
            } else {

                const value = varbinds[0].value;

Review comment (bug):
What is the output here for somebody who can't debug this:
We only ever look at `varbinds[0]` after this point.
What can the other indexes be?

(would using the json-query code be a better fit?)

Code after:
const { UP, log, evaluateJsonQuery } = require("../../src/util");
const snmp = require("net-snmp");

class SNMPMonitorType extends MonitorType {
    name = "snmp";

    /**
     * @inheritdoc
     */
    async check(monitor, heartbeat, _server) {
        let session;
        try {
            const sessionOptions = {
                port: monitor.port || "161",
                retries: monitor.maxretries,
                timeout: monitor.timeout * 1000,
                version: snmp.Version[monitor.snmpVersion],
            };
            session = snmp.createSession(monitor.hostname, monitor.radiusPassword, sessionOptions);

            // Handle errors during session creation
            session.on("error", (error) => {
                throw new Error(`Error creating SNMP session: ${error.message}`);
            });

            const varbinds = await new Promise((resolve, reject) => {
                session.get([ monitor.snmpOid ], (error, varbinds) => {
                    error ? reject(error) : resolve(varbinds);
                });
            });
            log.debug("monitor", `SNMP: Received varbinds (Type: ${snmp.ObjectType[varbinds[0].type]} Value: ${varbinds[0].value})`);

            if (varbinds.length === 0) {
                throw new Error(`No varbinds returned from SNMP session (OID: ${monitor.snmpOid})`);
            }

            if (varbinds[0].type === snmp.ObjectType.NoSuchInstance) {
                throw new Error(`The SNMP query returned that no instance exists for OID ${monitor.snmpOid}`);
            }

            // We restrict querying to one OID per monitor, therefore `varbinds[0]` will always contain the value we're interested in.
            const value = varbinds[0].value;

            const { status, response } = await evaluateJsonQuery(value, monitor.jsonPath, monitor.jsonPathOperator, monitor.expectedValue);

            if (status) {
                heartbeat.status = UP;
                heartbeat.msg = `JSON query passes (comparing ${response} ${monitor.jsonPathOperator} ${monitor.expectedValue})`;
            } else {
                throw new Error(`JSON query does not pass (comparing ${response} ${monitor.jsonPathOperator} ${monitor.expectedValue})`);
            }