Upstream RNS enforces two requirements in code that SPEC.md left implicit;
both caused silent message loss in a clean-room Go LXMF service against
upstream Python rns 1.2.4 / lxmf 0.9.7.
§6.4.2 LRRTT — initiator's link-activation packet
- HEADER_1, DATA, dest_type=LINK (0x03), ctx=0xfe; body is
`umsgpack.packb(rtt_seconds)` encrypted with the link's session keys.
- The responder transitions HANDSHAKE→ACTIVE only on LRRTT receipt
(Link.py:534-553), which is also what fires the link_established
callback. LXMF's set_resource_strategy(ACCEPT_APP) is installed
from that callback; without it, every RESOURCE_ADV the initiator
sends hits the silent ACCEPT_NONE branch at Link.py:1087.
§6.4.3 Header type for post-handshake DATA and Resource
- Link-addressed packets are routed via link_table, which forwards
header bytes verbatim (Transport.py:1587-1622). HEADER_2 with a
relay's transport_id therefore arrives at the destination intact
and is dropped by packet_filter (Transport.py:1283-1285) as
"for another transport instance".
- Mandates HEADER_1 with no transport_id for all post-handshake
link DATA / Resource / control packets regardless of hop count.
- Asymmetry with LINKREQUEST (which IS path_table-routed and so
HEADER_2-eligible) is spelled out.
Companion changes:
- §6.4 renamed to "Session keys and link activation"; existing
HKDF content moved into §6.4.1.
- §2.5 LRRTT context-byte entry points at §6.4.2.
- §12.5.2 (Link DATA forwarding) cross-references §6.4.3.
- §14 failure-modes table: two new entries for the silent-drop
chains documented above.
- flows/send-link-lxmf.md step 4 strengthened (LRRTT is mandatory,
not informational); step 6 corrected (Transport.outbound does NOT
apply HEADER_1→HEADER_2 for link DATA — that conversion is
path_table-keyed, link DATA is link_table-keyed).
- test-vectors/links.json extended with an LRRTT entry: pinned
rtt_seconds=0.05 + pinned 16-byte IV produces deterministic
wire bytes for the encrypted body.
- tools/regen_links.py drives the LRRTT generation with an
os.urandom patch for the Token IV.
- tools/verify_link_lrrtt.py (new) locks the wire claims:
HEADER_1, ctx=0xfe, dest=link_id, body decrypts under
derived_key to msgpack float64 matching rtt_seconds.
Citations all verified against installed RNS 1.2.4 / LXMF 0.9.7.
All 14 verifiers PASS.
