Reading extra bytes when server returns connection error

[tannaurus]

Something I observed as a result of Reqwest using this crate under the hood. I'm interested in hearing the maintainer's thoughts on this, because I feel as though the spec isn't very specific here.

receive_reply reads 4 bytes with tcp.read_exact, but it's my interpretation of the spec that the server only needs to respond with 2 bytes: VER and REP. Only if REP is X'00' succeeded should the client anticipate RSV and ATYP.

Is my interpretation incorrect?

[sticnarf]

The spec doesn't say that RSV and ATYP can be optional on failure. So, to my understanding, if the server strictly follows the spec, it should not omit any of the fields even if there's a failure.

But I do understand that implementations may omit those useless fields because it makes more sense.