Announce application data

LXMF carries application data in Reticulum announces. There are two formats: the delivery announce (sent by a normal LXMF destination) and the propagation-node announce. Both are normative and proven by [VEC-ANN-DELIVERY] and [VEC-ANN-PROPAGATION].

Delivery announce

The delivery announce app_data is (LXMRouter.py:1034-1050):

msgpack([ display_name, stamp_cost, supported_functionality ])

display_name: the UTF-8 encoded display name as bin, or None (LXMRouter.py:1038-1040).
stamp_cost: an integer in (0, 255), or None (LXMRouter.py:1042-1045).
supported_functionality: a list of advertised feature codes. LXMF 1.0.1 emits [SF_COMPRESSION], where SF_COMPRESSION = 0x00 (LXMRouter.py:1047-1048; LXMF.py:140-142).

Format detection

The decoders distinguish this version-0.5.0+ format from the legacy format (a bare UTF-8 display name) by sniffing the first byte: it is the new format iff app_data[0] is in 0x90..0x9f (msgpack fixarray) or equals 0xdc (array16) (LXMF.py:151-200). An implementation MUST emit a msgpack array so this sniff succeeds; the current three-element array begins with 0x93.

For compatibility with earlier senders, the reference compression decoder treats a missing or non-list third element as compression support. When the third element is a list, compression is supported only if that list contains SF_COMPRESSION (LXMF.py:187-200).

Proof: `[VEC-ANN-DELIVERY]`

msgpack([b"Alice", 8, [SF_COMPRESSION]]) produces 93c405416c696365089100, with first_byte = 0x93. The genuine decoders recover display_name = "Alice", stamp_cost = 8, and compression support (LXMF.py:151-200).

Propagation-node announce

The propagation announce app_data is a 7-element list (LXMRouter.py:328-336):

msgpack([
  legacy_flag,              # 0: bool, legacy LXMF PN support
  timebase,                 # 1: int, int(time.time())
  propagation_enabled,      # 2: bool
  per_transfer_limit_kb,    # 3: int
  per_sync_limit_kb,        # 4: int
  [prop_cost, prop_flex, peering_cost],   # 5: list of three ints
  metadata,                 # 6: dict (PN_META_* keys)
])

Validity

pn_announce_data_is_valid (LXMF.py:224-250) requires: data decodes to a list of length >= 7; data[1] (timebase), data[3], data[4] are integer- coercible; data[2] is strictly True or False; data[5] is a list whose first three elements are integer-coercible; and data[6] is a dict. An implementation MUST satisfy all of these for its propagation announce to be accepted.

Metadata map (`LXMF.py:128-138`)

Keys: PN_META_VERSION (0x00), PN_META_NAME (0x01), PN_META_SYNC_STRATUM (0x02), PN_META_SYNC_THROTTLE (0x03), PN_META_AUTH_BAND (0x04), PN_META_UTIL_PRESSURE (0x05), PN_META_CUSTOM (0xFF). The node name is metadata[PN_META_NAME] as UTF-8 bytes (LXMRouter.py:321).

Proof: `[VEC-ANN-PROPAGATION]`

The vector builds the 7-element list with metadata = {PN_META_NAME: b"Node"}, stamp_costs = [16, 3, 18], and a fixed timebase, then proves with the genuine helpers: pn_announce_data_is_valid = true, pn_name_from_app_data = "Node" (LXMF.py:202-213), and pn_stamp_cost_from_app_data = 16 (LXMF.py:215-222). Field 1 (timebase) is int(time.time()) in the real protocol and is pinned to a constant in the vector.

leviculum-lxmf decodes this announce to discover a propagation node. Encoding is documented here as a wire-format requirement; the Rust crate does not host a propagation node or emit propagation-node announces.

Leviculum Documentation