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

Code before:
                    case '==':
                        if (!isNaN(value) && !isNaN(monitor.snmpControlValue)) {
                            // Both values are numeric, parse them as numbers
                            heartbeat.status = parseFloat(value) === parseFloat(monitor.snmpControlValue) ? UP : DOWN;
                        } else {
                            // At least one of the values is not numeric, compare them as strings
                            heartbeat.status = value.toString() === monitor.snmpControlValue.toString() ? UP : DOWN;
                        }
                        break;
                    case 'contains':
                        heartbeat.status = stringValue.includes(monitor.snmpControlValue) ? UP : DOWN;
                        break;
                    default:
                        heartbeat.status = DOWN;
                        heartbeat.msg = `Invalid condition: ${monitor.snmpCondition}`;
                        break;
                }
                heartbeat.msg = `SNMP value ` + (heartbeat.status ? `passes` : `does not pass`) + ` comparison: ${value.toString('ascii')} ${monitor.snmpCondition} ${monitor.snmpControlValue}`;

            }
            session.close(); // Close the session after use

        } catch (err) {
            heartbeat.status = DOWN;
            heartbeat.msg = `SNMP Error: ${err.message}`;
            log.debug("monitor", `SNMP: ${heartbeat.msg}`);
        }
    }

}

module.exports = {
    SNMPMonitorType,
};


Review comment (bug):
no need to have `SNMP` twice.
Also unsure if this logging is needed/benefial. Are we not doing this in the general code? 

```suggestion
            log.debug("monitor", heartbeat.msg);
```

Code after:
const { MonitorType } = require("./monitor-type");
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})`);
            }
        } finally {
            if (session) {
                session.close();
            }
        }
    }
}

module.exports = {
    SNMPMonitorType,
};