rumqttc: value returned by `v4::Connect.write` doesn't match reality

[Devdutt Shenoi]

let connect = v4::Connect {
  protocol: Protocol::V4,
  keep_alive: u16::MAX,
  client_id: "".to_owned(),
  clean_session: true,
  last_will: Some(LastWill::new(
    "".to_owned(),
    Bytes::new(),
    QoS::AtLeastOnce,
    true,
  )),
  login: Some(Login::new("", "")),
};
let mut buf = BytesMut::new();
let written = connect.write(&mut buf);
        
assert_eq!(written, Ok(buf.len()));

Expected Behavior

written should be equal to 18

Current Behavior

It is equal to 16

Failure Information (for bugs)

This part of the code evaluates written as len, which doesn't account for the length of header fields of the packet, i.e. 1 + count.

[Swanand Mulay]

I think the len() method on any packet doesn't account for FixedHeader ( which is 2 bytes as per standards ).

But in write(), as we write along with FixedHeader, we are seeing that deviation.

this brings the question of whether len() should return length of Connect struct, or the actual Connect packet that will get sent.

i.e. 1 + count

can you please explain this a bit?

[Devdutt Shenoi]

I believe len() accounts for the size of payload, while size of serialized packets we account for with size()

[Swanand Mulay]

we have fixed it in rumqttc with PR #818 , but this issue is also observed in rumqttd as well, will close this once it is fixed there.

[Swanand Mulay]

done with PR #819 🚀 !