Function output payload

General
2

Firstly, is there a reason you are not using node-red-node-snmp?

Secondly, as you are running async code, you cannot return msg you need to use node.send

e.g....

// NPM module exposed as variable, npm_module
const session = snmp.createSession ("192.168.10.250", "public");
const oids = ["1.3.6.1.2.1.1.1.0"];

session.get (oids, function (error, varbinds) {
    if (error) {
        node.error(error, msg);
    } else {
        for (let i = 0; i < varbinds.length; i++) {
            const e = snmp.varbindError(varbinds[i]);
            if (e) {
                node.error(e, msg);
            } else {
                msg.payload = varbinds[i].value;
                msg.topic = varbinds[i].oid;
                node.send(msg)
            }
        }
    }
    session.close ();
});

/// return msg;  << delete this