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

Code before:
            port: monitor.port || '161',
            retries: monitor.maxretries,
            timeout: 1000,
            version: getKey(snmp.Version, monitor.snmpVersion) || snmp.Version2c,
        };

        function getKey(obj, value) {
            return Object.keys(obj).find(key => obj[key] === value) || null;
        }

        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", `SNMP: ${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)}, Value: ${varbinds[0].value}`); // Log the received varbinds for debugging
                        resolve(varbinds);
                    }
                });
            });

            if (varbinds.length === 0 || getKey(snmp.ObjectType, varbinds[0].type) === 'NoSuchInstance') {
                throw new Error(`No varbinds returned from SNMP session (OID: ${monitor.snmpOid})`);
            } else {
                const value = varbinds[0].value;
                const numericValue = parseInt(value);
                const stringValue = value.toString('ascii');

                switch (monitor.snmpCondition) {
                    case '>':
                        heartbeat.status = numericValue > monitor.snmpControlValue ? UP : DOWN;
                        break;
                    case '>=':
                        heartbeat.status = numericValue >= monitor.snmpControlValue ? UP : DOWN;
                        break;
                    case '<':
                        heartbeat.status = numericValue < monitor.snmpControlValue ? UP : DOWN;
                        break;
                    case '<=':
                        heartbeat.status = numericValue <= monitor.snmpControlValue ? UP : DOWN;
                        break;

Review comment (bug):
Think this might be clearer

```suggestion
                        log.debug("monitor", `SNMP: Received varbinds (Type=${getKey(snmp.ObjectType, varbinds[0].type)}): ${varbinds[0].value}`);
```

Code after:
            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})`);
            }
        } finally {
            if (session) {
                session.close();
            }
        }
    }
}

module.exports = {
    SNMPMonitorType,
};