generate function cannot handle zero-length client identifiers

[janniswarnat]

Hi all,

thank you for providing this very helpful package :-).

The MQTT standard version 5 allows clients to connect using a zero-length client identifier. Yet the generate function seems not to be able to handle this:

const mqtt = require('mqtt-packet');
const opts = {protocolVersion: 5};
const parser = mqtt.parser(opts);

parser.on('packet', (packet) => {
    console.log("packet event emitted on noopParser", packet);
});

parser.on('error', (error) => {
    console.log("error event emitted on noopParser", error.message);
});

let packet = {
    cmd: "connect",
    protocolId: "MQTT",
    protocolVersion: 5,
    clean: true,
    keepalive: 60,
    properties:
        {
            receiveMaximum: 20
        },
    clientId:""
};

let generatedBuffer = mqtt.generate(packet, opts);
console.log('generatedBuffer',generatedBuffer);
parser.parse(generatedBuffer);

This will give error message "Packet too short" when parsing the generated buffer.

Thanks in advance for your feedback and best regards

Jannis