Extra 2 bytes at the beginning of payload

[agolovchuk]

Hi!

It seems that the QoS level in PUBLISH packets is currently hardcoded to 0, which creates a minor mismatch with the MQTT protocol (specifically section 3.3.2.2). According to the spec, the Packet Identifier field should only be present if the QoS level is 1 or 2. Because of this, there’s a small artifact in the message.

tinymqtt/src/lib.rs

Line 74 in f57d8c8

writer.write_u16(0); // Packet identifier