CXXCBC-419: ensure that MCBP protocol parser starts with clean state

[avsej]

No description provided.

[thejcfactor]

LGTM 👍

[brett19]

@avsej Can you explain where I've made an error in the following thinking for understanding why this reset call is neccessary? The mcbp_parser instance (_parser) is itself actually part of the mcbp_session object. That mcbp_session appears to be one-time use, and you are calling reset() in on_connect, which is inherently invoked only once, and always prior to the on_read's which ultimately feed data to the parser and pull packets off. Additionally, reset() doesn't appear to have any useful behaviour except clearing the buffer inside the parser, which would already be empty since it's a new object I would think.

[avsej]

no, it is not a one time object, and we reuse it if it cannot bootstrap, we just reopen the underlying TCP socket. Yes it is rather a design flaw, and this bug proves the weakness of reusing the session during retrying bootstrap.