can't comply with MQTT spec requirements about flag validation

The Server MUST validate that the reserved flag in the CONNECT Control Packet is set to zero and disconnect the Client if it is not zero [MQTT-3.1.2-3]

If I set that flag to 1, mqtt-packet still parses it just fine, but doesn't emit raw flag bits, so it's impossible for a server implementation to comply with this spec requirement using mqtt-packet.

> var parser = require('mqtt-packet').parser()
> parser.on('packet', console.log)
// the `3` in the following sets the reserved flag to 1
> parser.parse(Buffer.from('100c00044d515454040300000000', 'hex'))
Packet {
  cmd: 'connect',
  retain: false,
  qos: 0,
  dup: false,
  length: 12,
  topic: null,
  payload: null,
  protocolId: 'MQTT',
  protocolVersion: 4,
  clean: true,
  keepalive: 0,
  clientId: ''
}

This goes for many other packet types' flags as well...for example

Bits 3,2,1 and 0 of the fixed header in the PUBREL Control Packet are reserved and MUST be set to 0,0,1 and 0 respectively. The Server MUST treat any other value as malformed and close the Network Connection [MQTT-3.6.1-1].

mqtt-packet should either attach a raw buffer to the packet, or at least some fields that represent the raw flag values.

It might be sufficient to emit an error when any packet's flags are invalid; I think in all cases the server is just supposed to close the connection, but I'm not 100% sure.

mqttjs / mqtt-packet

can't comply with MQTT spec requirements about flag validation #111