Upstream irtt 0.9.1 always emits both midpoint timestamp fields (wall,
then monotonic) in an ECHO reply for single-clock StampAt::Midpoint
negotiations, even though only one clock was negotiated, so its header is
one timestamp longer than the negotiated header.
The resulting datagram length is not simply negotiated_len + 8. Both
forms are max(negotiated_length, header), so the extra field lengthens
the datagram only while the larger header still exceeds the negotiated
length, and displaces payload beyond that; the difference is 8, then
7..1, then 0.
decode_echo_reply now accepts the compatibility length wherever it is
strictly longer than the negotiated length, parsing both wire fields and
exposing only the negotiated clock's value. Where the two lengths
coincide the forms are indistinguishable from the packet alone, so the
reply is accepted with normal negotiated parsing rather than a heuristic
- a monotonic-only midpoint negotiation therefore cannot always be
corrected, which is documented and tested. Every other length stays
strictly rejected.
Echo request decoding and encode_echo_reply are unchanged: the encoder
must keep emitting the sane negotiated layout.
Nils Andreas Svee