Module codec 

Pure LLDP (IEEE 802.1AB) frame codec.

Everything in this file is a pure function over plain values: it opens no socket, reads no configuration and touches no global state. That is deliberate. The LLDP transport is raw Ethernet and needs CAP_NET_RAW / /dev/bpf*, which no test in this repository has, so the transport can never be executed here — but the frame format can be, and is, checked against literal bytes from the specification and from a real capture (tests/server/lldp/codec_test.rs).

This is the bluetooth_ble_beacon split the root CLAUDE.md describes: payload construction is pure and exhaustively tested; the platform transport is a thin layer over it that has never run. metadata().notes says both.

Frame layout

| dst MAC (6) | src MAC (6) | 0x88CC (2) | LLDPDU ... |

An LLDPDU is a sequence of TLVs. Each TLV starts with two octets holding a 7-bit type and a 9-bit length:

 0                   1
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|     type (7)  |   length (9)  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IEEE 802.1AB-2016 §8.5 requires the first three TLVs, in this order: Chassis ID (1), Port ID (2), Time To Live (3). Optional TLVs follow, and End Of LLDPDU (type 0, length 0) terminates. Chassis ID and Port ID each carry a leading subtype octet that decides how the rest of the value is read — a MAC address, a network address or text — and getting that wrong is the classic way to produce a frame a neighbour silently discards.

No bytes cross the LLM boundary

Every identifier is carried in and out of here as a string in its natural notation — "00:01:30:f9:ad:a0" for a MAC, "192.0.2.1" for an address, "1/1" for an interface name — and every subtype and capability as a name. Models cannot reliably produce or read a TLV blob, and a tlv_hex parameter would defeat the entire point of the protocol (see the action & event design rules in the root CLAUDE.md).

Structs

AdvertisementRequest

What a send_lldp_advertisement action asks for, once validated.

LldpFrame

A full LLDP Ethernet frame, decoded.

Lldpdu

A decoded LLDPDU: the three mandatory TLVs plus whichever optional ones were present.

ManagementAddress

One management address, as carried by TLV type 8.

Enums

IdKind

Which side of the frame an identifier belongs to. The two use different subtype numbers for the same thing, so the value encoder has to know which table it is reading.

Constants

CHASSIS_ID_SUBTYPES

Chassis ID subtypes, 802.1AB-2016 Table 8-2.

ETHERNET_HEADER_LEN

Destination MAC | source MAC | EtherType.

LLDP_ETHERTYPE

EtherType assigned to LLDP (IEEE 802.1AB §8.1).

LLDP_MULTICAST_MAC

The nearest-bridge group address every LLDP agent transmits to (802.1AB Table 7-1).

PORT_ID_SUBTYPES

Port ID subtypes, 802.1AB-2016 Table 8-3. Not the same numbering as Chassis ID — a MAC address is 4 for a chassis and 3 for a port, which is the single easiest thing to get wrong in this protocol.

SYSTEM_CAPABILITIES

System capability bits, 802.1AB-2016 Table 8-4.

TLV_CHASSIS_ID

TLV_END_OF_LLDPDU

TLV_MANAGEMENT_ADDRESS

TLV_PORT_DESCRIPTION

TLV_PORT_ID

TLV_SYSTEM_CAPABILITIES

TLV_SYSTEM_DESCRIPTION

TLV_SYSTEM_NAME

TLV_TIME_TO_LIVE

Functions

capability_bits

Turn capability names back into a bitmask. An unrecognised name is an error, not a silently dropped bit: a model that asks to advertise "swtich" must be told, or it will believe it claimed to be a bridge.

capability_names

Split a capability bitmask into names. Bits with no assigned meaning are reported as reserved_bit_<n> rather than dropped — a neighbour that sets one is telling us something, even if the spec has not named it yet.

decode_frame

Parse an Ethernet frame carrying an LLDPDU.

encode_frame

Wrap an LLDPDU in its Ethernet header.

format_mac

Render six octets as lowercase colon-separated hex.

parse_mac

Parse aa:bb:cc:dd:ee:ff (or the -/.-free spellings) into six octets.

subtype_code

Look a subtype name up in the relevant table.

subtype_name

Render a subtype number as its name, or "reserved_<n>" for one the spec does not define.