455 lines
31 KiB
Markdown
455 lines
31 KiB
Markdown
# Mesh Beacon Module - Function, Settings, and Client Interface Spec
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Status: draft, tracks firmware branch `feat/mesh-beacon`.
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Audience: firmware reviewers (Part 1) and client-app developers - Android / Apple / Web / Python (Part 2).
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The Mesh Beacon module lets a node periodically **advertise the existence of a mesh** to
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nodes that are not yet on it - broadcasting a short human-readable message plus an optional
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"join offer" (a channel, region, and modem preset). It is the mechanism behind invitations
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like _"Join us on NarrowSlow"_: a node sitting on one preset/region can shout an invitation
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that listeners on other presets/regions can hear and surface to their user.
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The module is deliberately **advisory**. The firmware never auto-joins an advertised
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channel or auto-switches preset/region in response to a received beacon - it delivers the
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information to the client app and stops there. All "should I act on this?" decisions belong
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to the client and, ultimately, the user.
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---
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## Part 1 - Function and settings choices
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### 1.1 Two roles in one module
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| Role | Class | Active when | What it does |
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| --------------- | --------------------------- | ---------------------------- | ------------------------------------------------------------------------------------------------------------------------- |
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| **Broadcaster** | `MeshBeaconBroadcastModule` | `FLAG_BROADCAST_ENABLED` set | Periodically transmits `MESH_BEACON_APP` packets on the configured radio settings. |
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| **Listener** | `MeshBeaconListenerModule` | `FLAG_LISTEN_ENABLED` set | Receives `MESH_BEACON_APP` packets and caches the offer for the client (the packet itself flows to the client unchanged). |
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The boolean toggles live in a single `flags` bitfield (see [§1.8](#18-settings-reference-moduleconfigmeshbeaconconfig-tag-17)) - broadcasting and
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listening can be enabled independently on the same node. The whole module compiles out under the
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`MESHTASTIC_EXCLUDE_BEACON` build flag.
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### 1.2 Wire message
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Beacons travel on a dedicated port number:
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```protobuf
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MESH_BEACON_APP = 37 // meshtastic/portnums.proto
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ENCODING: protobuf (meshtastic.MeshBeacon)
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```
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```protobuf
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message MeshBeacon {
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string message = 1; // human-readable text, max 100 bytes (buffer 101)
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ChannelSettings offer_channel = 2; // optional advertised channel (name + PSK + slot)
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Config.LoRaConfig.RegionCode offer_region = 3; // optional advertised region (UNSET = none)
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optional Config.LoRaConfig.ModemPreset offer_preset = 4; // optional advertised preset
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}
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```
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`.options` size caps (enforced at generation and on send):
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`message ≤ 100`, `offer_channel.name ≤ 12`, `offer_channel.psk ≤ 32`.
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The three `offer_*` fields together describe _"there is a reachable mesh on this
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region+preset, here is the channel to use."_ Any subset may be present; an empty message with
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a populated offer (or vice-versa) is valid.
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### 1.3 Transmission behaviour
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Every outgoing beacon packet is stamped uniformly (`sendBeacon` → `stampPacket`):
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- `to = NODENUM_BROADCAST`
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- `from = local node` (see [§1.6](#16-broadcast_send_as_node-currently-disabled) for the disabled spoof path)
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- **`hop_limit = 0`** - beacons are **zero-hop**. They are never rebroadcast by the mesh; only
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direct RF neighbours hear them. This is the primary spam-control mechanism. (`hop_start` is
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normally `0` too, but `FLAG_LEGACY_SPLIT` raises it to `1` for old-firmware compatibility - see
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[§1.5](#15-legacy-split-flag_legacy_split).)
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- `priority = BACKGROUND`, `want_ack = false`.
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Broadcasting is additionally gated at runtime by:
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- airtime utilisation (`isTxAllowedAirUtil()`), and
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- device role - **`CLIENT_HIDDEN` never broadcasts**.
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#### Interval
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`broadcast_interval_secs` controls cadence. The floor is **3600 s (1 hour)**
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(`default_mesh_beacon_min_broadcast_interval_secs`); `0` means "use default". Values below the
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floor are silently raised, both at config-set time (AdminModule) and at runtime.
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The cadence is **reboot-safe**. Each broadcast's time is persisted to flash via `TransmitHistory`
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(keyed by `MESH_BEACON_APP`), and the broadcaster reads it back on boot - so a node that reboots
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(or crash-loops) won't re-broadcast until a full interval has elapsed since its last real send,
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rather than firing ~30 s after every boot. The timestamp is written **before** the transmit, so a
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brown-out during the high-current LoRa TX still counts as "sent." This mirrors `NodeInfoModule` /
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`PositionModule`.
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#### Radio switching for TX
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A beacon's whole point is often to reach a mesh on a _different_ preset/region/channel than the
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broadcaster currently runs. Before transmitting a beacon tagged with target radio settings, the
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module temporarily reconfigures the radio (`reconfigureForBeaconTX`), sends, then restores the
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prior config. Per-packet target settings are held in an 8-entry **sidecar table** keyed by packet
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ID - chosen so the `MeshPacket` proto carries no extra per-packet radio fields, and normal
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(non-beacon) traffic is never touched.
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Two safety guards run before any radio switch (`beaconTxConfigInvalid`):
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1. **An unlicensed node never keys up on a licensed-only (ham) region.** (The reverse - a licensed
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node operating in a non-ham region - is allowed. The switch only touches preset/region/channel,
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never `owner.is_licensed`.)
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2. **The preset must be valid for the target region** (`validateConfigLora`).
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If either fails, the radio is **not** switched and the radio driver **drops** the packet rather
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than letting it fall through onto the current config.
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#### Channel encryption on an override channel
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Encryption keys off the **primary** channel slot, and the radio-thread channel switch happens
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_after_ encryption. So when a beacon goes out on an override channel (different name/PSK), the
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module installs the beacon channel into the primary slot for the synchronous duration of
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`send()`, then restores it (`sendBeaconPacket`). This guarantees the packet is encrypted with the
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beacon channel's key and stamped with its hash - not the primary's. Meshtastic threading is
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cooperative, so there is no preemption between swap and restore.
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### 1.4 Where beacons are sent: single-target and multi-target
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The broadcaster can send to one set of radio settings or to several. **Single- and multi-target
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are equal options - neither is preferred and neither is legacy.** Pick whichever matches the
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deployment.
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- **Single-target:** the scalar `broadcast_on_preset` / `broadcast_on_region` /
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`broadcast_on_channel` fields describe one destination. Used when `broadcast_targets` is empty.
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- **Multi-target:** `broadcast_targets` (repeated `BroadcastTarget`) describes several. When
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non-empty it takes over from the scalar `broadcast_on_*` fields, and the broadcaster sends **one
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beacon copy per entry**. Each `BroadcastTarget` is `{ optional preset, region, optional channel_index }`,
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where `channel_index` references a slot in the node's own channel table (the channel must already be
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configured locally - its key is needed to encrypt the beacon). Within one cycle, targets that
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resolve to the **same** effective preset/region/channel are de-duplicated - only the first is
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transmitted - so an accidentally repeated entry costs no extra airtime.
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#### Same-settings vs. other-settings
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Independent of single/multi, each destination can either reuse the node's **own current radio
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settings** or specify **different** ones:
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- **Same-settings ("message of the day"):** leave the preset / region / channel unset. They fall
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back to the running config, so the beacon goes out on the node's current mesh with **no radio
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switch** - a plain periodic broadcast to whoever is already on this preset/region.
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- **Other-settings (cross-mesh invite):** set a preset / region / channel that differs from the
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running config. The radio is temporarily switched for that copy's TX, then restored (see
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[§1.3](#radio-switching-for-tx)).
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Both modes support both styles: a single-target beacon with no `broadcast_on_*` overrides is a
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message-of-the-day on the current mesh; a multi-target list can mix one entry on the current
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settings with others on different presets/regions.
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### 1.5 Legacy split (`FLAG_LEGACY_SPLIT`)
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This one flag controls **two** independent legacy-compatibility behaviours. Both are about making
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beacons usable by firmware that predates this module.
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**(a) Text/offer packet split.** A combined `MESH_BEACON_APP` packet carries both the text and the
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offer, but old firmware only decodes `TEXT_MESSAGE_APP` and would never show the text. When
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`FLAG_LEGACY_SPLIT` is set **and both text and offer content are present**, the broadcaster
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emits **two** packets on the same beacon radio settings instead of one:
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- **Packet A** - `MESH_BEACON_APP` carrying the **offer only** (no text).
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- **Packet B** - `TEXT_MESSAGE_APP` carrying the **text only**.
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This is an independent two-packet decision, not an either/or: offer-only and text-only payloads
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still go out as a single packet in their respective cases; only the both-present case splits.
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**(b) `hop_start = 1` override.** When `FLAG_LEGACY_SPLIT` is set, **every** beacon packet it sends
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(combined, split-A, or split-B; even same-settings ones) is stamped with `hop_start = 1` while
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`hop_limit` stays `0`. Pre-2.7.20 firmware drops `hop_start == 0` packets in a pre-decryption check
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before it can read the bitfield, so `hop_start = 1` lets those nodes accept the beacon - and it
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remains genuinely zero-hop (`hop_limit = 0` still prevents any rebroadcast).
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> **Side effect for clients:** with `hop_start = 1, hop_limit = 0`, receivers compute
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> `hops_away = hop_start − hop_limit = 1`, so a legacy-split beacon reads as **1 hop away** even
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> though it arrived over direct RF. Without legacy-split it reads as direct (0). Don't treat a
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> beacon's `hops_away` as a reliable distance signal.
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### 1.6 `broadcast_send_as_node` (currently disabled)
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The schema reserves `broadcast_send_as_node` (field 3) to send beacons _as_ another node ID. **The
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firmware application of this field is currently commented out pending review**, so beacons always
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go out as the local node today. The access-control rule is, however, already enforced in
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AdminModule and should be treated as canonical:
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> A remote admin may only set `broadcast_send_as_node` to **their own** node ID
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> (`mp.from`). Any other value is rejected and reset to the stored value.
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Design note for when it is re-enabled: it is a _node-ID_ spoof only - it rewrites `from` but forges
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no signature. Once `from` is not us, the packet is no longer `isFromUs()`, so the router skips
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XEdDSA signing and receivers get an unsigned packet attributed to another node.
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### 1.7 Reception behaviour (listener)
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When `FLAG_LISTEN_ENABLED` is **off**, the router drops incoming `MESH_BEACON_APP` packets up front
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(`Router::handleReceived`, same pattern as a disabled NeighborInfo module) - so they reach neither
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the modules nor the phone. When it is **on**, the packet flows normally and the listener's
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`wantPacket` accepts it (`has_mesh_beacon` + `FLAG_LISTEN_ENABLED` + `portnum == MESH_BEACON_APP`).
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On a valid beacon (`handleReceivedProtobuf`):
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1. **Offer → cache.** Any offer (`offer_channel` / `offer_region` / `offer_preset`) is stored in
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the static `lastReceivedOffer` (sender, channel, region, preset, `received_at`). `received_at`
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is `0` if the node has no RTC fix yet - **consumers must not treat `0` as a valid timestamp.**
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2. **Never auto-applied.** The firmware does not switch channel/preset/region from a received
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offer. Acting on it is the client app's job.
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3. The handler returns `CONTINUE` (not `STOP`), so the original `MESH_BEACON_APP` packet **flows to
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the client unchanged** through the normal FromRadio path (see Part 2). The client reads the
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`message` field directly from that packet - there is no separate copy.
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The firmware deliberately does **not** unwrap a combined beacon's text into a synthesized
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`TEXT_MESSAGE_APP`, and does **not** fire `EVENT_RECEIVED_MSG`: a beacon is an advisory broadcast,
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not a personal message, so it must not duplicate the text or wake the device from sleep. If a
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broadcaster needs non-beacon-aware clients to see the text, it uses `FLAG_LEGACY_SPLIT`, which sends
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a real `TEXT_MESSAGE_APP` over RF (see [§1.5](#15-legacy-split-flag_legacy_split)).
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### 1.8 Settings reference (`ModuleConfig.MeshBeaconConfig`, tag 17)
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| # | Field | Type | Meaning / constraints |
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| --- | ------------------------- | ------------------------ | ------------------------------------------------------------------------------------------------------ |
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| 1 | `flags` | uint32 (bitfield) | Bitwise-OR of `Flags` values (listen / broadcast / legacy-split toggles). See enum below. |
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| 3 | `broadcast_send_as_node` | uint32 | Send-as node ID. **Application disabled in firmware.** Remote admin may only set to own node ID. |
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| 4 | `broadcast_message` | string | Text in each broadcast. **Hard-capped at 100 bytes.** |
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| 5 | `broadcast_offer_channel` | ChannelSettings | Channel advertised in `offer_channel`. |
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| 6 | `broadcast_offer_region` | RegionCode | Region advertised in `offer_region`. Must be a known region or it is cleared. |
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| 7 | `broadcast_offer_preset` | optional ModemPreset | Preset advertised in `offer_preset`. Validated against offer region (else cleared). |
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| 8 | `broadcast_on_channel` | ChannelSettings | Channel to transmit on (single-target). Empty name → preset display name. |
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| 9 | `broadcast_on_region` | RegionCode | Region to transmit on (single-target). |
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| 10 | `broadcast_on_preset` | optional ModemPreset | Preset to transmit on (single-target). Validated against on-region (else this + `on_channel` cleared). |
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| 11 | `broadcast_interval_secs` | uint32 | Cadence. **Min 3600**, default 3600; `0` = default. |
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| 13 | `broadcast_targets` | repeated BroadcastTarget | Multi-target list; when non-empty overrides the single-target `broadcast_on_*` fields. |
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> The three boolean toggles were folded into the `flags` bitfield; field tags 2 and 12 are now
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> unused (the branch is unreleased, so the old tags are left as gaps rather than reserved).
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**`Flags` enum** (nested in `MeshBeaconConfig`; OR the values into `flags`):
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| Bit value | Name | Meaning |
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| --------- | ------------------------ | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ |
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| 0 | `FLAG_NONE` | No options enabled. |
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| 1 | `FLAG_LISTEN_ENABLED` | Receive beacons; cache the offer. The packet flows to the client, which reads `message` directly. |
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| 2 | `FLAG_BROADCAST_ENABLED` | Periodically broadcast beacons from this node. |
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| 4 | `FLAG_LEGACY_SPLIT` | Legacy compatibility: (a) split text+offer into separate `TEXT_MESSAGE_APP` + `MESH_BEACON_APP` packets, and (b) stamp `hop_start = 1` on every beacon so pre-2.7.20 firmware accepts it (see [§1.5](#15-legacy-split-flag_legacy_split)). |
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`BroadcastTarget`: `1 preset` (optional, falls back to running config), `2 region` (`UNSET` = running config), `4 channel_index` (optional `uint32`, index into the node's channel table; if unset, the default channel for the preset is used). Tag `3` is an unused gap - it previously held an embedded `ChannelSettings`, dropped to keep `ModuleConfig` within the BLE `FromRadio` size budget.
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---
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## Part 2 - Client interface specification
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This section is what a client app needs to integrate with the beacon module. Everything goes
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through the **standard admin / ToRadio / FromRadio protocol** - there is no bespoke transport.
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### 2.1 Capability detection
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The module is build-flag optional. Treat it as present when the node's `LocalModuleConfig`
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contains a `mesh_beacon` sub-message (`LocalModuleConfig.mesh_beacon`, tag 18). If absent, the
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firmware was built with `MESHTASTIC_EXCLUDE_BEACON` - hide the beacon UI.
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### 2.2 Reading and writing configuration
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Standard module-config flow - no new admin messages:
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- **Read:** `AdminMessage.get_module_config_request = ModuleConfig.MeshBeaconConfig` (variant 17).
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Reply is `get_module_config_response` with the `mesh_beacon` payload.
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- **Write:** `AdminMessage.set_module_config { mesh_beacon = … }`.
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The on/off toggles (listen, broadcast, legacy-split) are bits in the `flags` field, not separate
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booleans - read/write them with the `MeshBeaconConfig.Flags` values
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(`FLAG_LISTEN_ENABLED = 1`, `FLAG_BROADCAST_ENABLED = 2`, `FLAG_LEGACY_SPLIT = 4`). To toggle one
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bit, read the current `flags`, set/clear the bit, and write the whole config back.
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The firmware **sanitises on write** - your value may be silently adjusted. Mirror these rules
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client-side so the UI doesn't disagree with the device:
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| Rule | Firmware behaviour |
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| --------------------------------------------------------------------------- | ------------------------------------------------------------------------------- |
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| `broadcast_message` length | Truncated to 100 bytes. |
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| `broadcast_interval_secs` | If non-zero and `< 3600`, raised to 3600. |
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| `broadcast_on_preset` invalid for `broadcast_on_region` (or current region) | Cleared, **and `broadcast_on_channel` cleared too.** |
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| `broadcast_offer_preset` invalid for offer/current region | Cleared. |
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| `broadcast_offer_region` not a known region | Cleared to `UNSET`. |
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| `broadcast_targets[i].region` not a known region | That entry's region cleared to `UNSET` (TX falls back to running config). |
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| `broadcast_targets[i].preset` invalid for that entry's region | That entry's `preset` and `channel_index` cleared. |
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| `broadcast_targets[i].channel_index` ≥ `MAX_NUM_CHANNELS` (8) | That entry's `channel_index` cleared (existence is **not** checked - see §2.5). |
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| `broadcast_send_as_node` ≠ sender's node ID (remote admin) | Rejected, reset to stored value. |
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Setting beacon config does **not** trigger a reboot (`shouldReboot = false`); changes take effect
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on the next broadcast cycle. After a successful write, **re-read** the config to display the
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effective (sanitised) values.
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### 2.3 Receiving beacons
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A received beacon reaches the client as a normal `FromRadio.packet` (`MeshPacket`) - the listener
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returns `CONTINUE`, so the packet is **not** consumed on-device. The client must:
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1. Subscribe to the FromRadio packet stream as usual.
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2. For packets with `decoded.portnum == MESH_BEACON_APP (37)`, decode `decoded.payload` as a
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`meshtastic.MeshBeacon`.
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3. Read `message`, `offer_channel`, `offer_region`, `offer_preset` (presence-checked).
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4. `packet.from` is the **originating beaconer** (the firmware preserves it).
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> **Requires `FLAG_LISTEN_ENABLED` set in `flags`.** With listening disabled the firmware drops
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> received `MESH_BEACON_APP` packets in the router - before they reach the phone or any on-device
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> handler - the same way it drops a disabled module's packets (e.g. NeighborInfo). The node still
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> physically receives the RF, but the client will not see beacons over the FromRadio stream until
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> listening is enabled.
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#### Reading the text - no duplication
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For a beacon-aware client the text is **simply the `message` field of the `MESH_BEACON_APP`
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packet** you already decode for the offer (step 3 above). One packet, one field - the firmware does
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**not** inject a separate `TEXT_MESSAGE_APP` copy, so there is nothing to deduplicate.
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The only time a beacon's text arrives as a separate `TEXT_MESSAGE_APP` is when the broadcaster set
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`FLAG_LEGACY_SPLIT`: in that mode the `MESH_BEACON_APP` carries the **offer only** (empty `message`)
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and the text is sent as a normal `TEXT_MESSAGE_APP` over RF, so legacy/non-beacon-aware clients can
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display it. These two cases are mutually exclusive - a given beacon's text appears exactly once,
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either in `MESH_BEACON_APP.message` (combined) or as a `TEXT_MESSAGE_APP` (legacy-split) - so a
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client never needs to dedup. Render whichever it receives.
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### 2.4 Acting on an offer (the core client responsibility)
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When a `MESH_BEACON_APP` carries offer content, present it to the user as an **invitation** -
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e.g. _"Node ⟨from⟩ invites you to join '⟨offer_channel.name⟩' on ⟨preset⟩/⟨region⟩."_ Then, only on
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explicit user confirmation, apply it by writing normal config:
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- `offer_channel` → add/replace a `Channel` (`set_channel`), typically as a secondary channel.
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- `offer_region` / `offer_preset` → `set_config { lora = … }` (`use_preset = true`, set
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`modem_preset` and `region`). **Note this changes the node's own radio and will drop it off its
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current mesh** - make that consequence explicit in the UI.
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**The firmware will never do any of this for the user. No silent auto-apply.** The on-device
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`lastReceivedOffer` cache is a firmware-internal convenience and is **not** currently exposed via
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an admin message - clients should source offers from the live `MESH_BEACON_APP` packet stream
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(§2.3), not expect a "get last offer" RPC.
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#### Offer trust model - read before applying
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- **The advertised PSK is not a secret.** `offer_channel.psk` is a public join token sent in the
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clear inside a broadcast; it is a convenience, not a security boundary. An operator who wants a
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genuinely private channel must distribute the PSK out-of-band and leave `offer_channel` unset.
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Surface offered channels as **public/open** to the user.
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- **Validate before applying.** Reject or warn if `offer_preset` is not valid for `offer_region`,
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and **never** apply a licensed-only (ham) region for a user who is not a licensed operator -
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mirror the firmware's own guard.
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- Beacons are **unsigned** when sent as another node (the disabled send-as path), and even normal
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beacons assert nothing about the sender's authority. Treat `from` as informational.
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||
### 2.5 Configuring this node as a broadcaster
|
||
|
||
To make a node advertise a mesh, write `MeshBeaconConfig` with `FLAG_BROADCAST_ENABLED` set in
|
||
`flags` and at least one of: a non-empty `broadcast_message`, or offer content
|
||
(`broadcast_offer_*`). With neither, the broadcaster has nothing to send and stays silent.
|
||
|
||
Typical multi-region invite beacon:
|
||
|
||
```text
|
||
flags = FLAG_BROADCAST_ENABLED | FLAG_LEGACY_SPLIT // broadcast on; split so legacy nodes still see the text
|
||
broadcast_message = "Join us on NarrowSlow!"
|
||
broadcast_offer_preset = NARROW_SLOW
|
||
broadcast_offer_region = EU_N_868
|
||
broadcast_offer_channel = { name: "MyChannel", psk: <32-byte key> }
|
||
broadcast_interval_secs = 3600
|
||
// channel_index points at slots in THIS node's channel table - configure those channels first.
|
||
broadcast_targets = [
|
||
{ preset: LONG_FAST, region: EU_868, channel_index: 0 },
|
||
{ preset: NARROW_SLOW, region: EU_N_868, channel_index: 1 },
|
||
]
|
||
```
|
||
|
||
The same fields can be baked in at build time via `userPrefs.jsonc`
|
||
(`USERPREFS_MESH_BEACON_*`) - see that file for the full list, including
|
||
`USERPREFS_MESH_BEACON_TARGET_<n>_*` for multi-target entries.
|
||
|
||
#### Single-target vs. multi-target - equal options, different channel representation
|
||
|
||
Single-target and multi-target are **equal, first-class options**. Neither is preferred,
|
||
deprecated, or a "legacy" fallback - pick whichever matches the deployment (a single-target
|
||
beacon with no overrides is a plain message-of-the-day; a multi-target list reaches several
|
||
preset/region/channel combinations). The broadcaster uses `broadcast_targets` when it is
|
||
non-empty and the scalar `broadcast_on_*` fields when it is empty.
|
||
|
||
The one **subtle implementation difference** is how each names its TX channel:
|
||
|
||
| Path | TX channel is specified by | Channel name/PSK live… |
|
||
| ------------- | ------------------------------------------------------- | ----------------------------------------- |
|
||
| Single-target | `broadcast_on_channel` - an embedded `ChannelSettings` | …inline in the beacon config |
|
||
| Multi-target | `broadcast_targets[i].channel_index` - a `uint32` index | …in the node's channel table (referenced) |
|
||
|
||
This asymmetry is deliberate: embedding a full `ChannelSettings` in every one of the (up to
|
||
four) targets would push `ModuleConfig` past the BLE `FromRadio` size limit, so a target
|
||
references an already-configured channel-table slot instead. `broadcast_offer_channel` (the
|
||
advertised join token) is **always** inline regardless of path - it is the advertisement payload
|
||
and must carry the actual name/PSK.
|
||
|
||
#### Configuring a multi-target broadcaster (two-step)
|
||
|
||
Because a target's channel is a reference, configuring a multi-target broadcaster takes **two
|
||
admin writes**, in order:
|
||
|
||
1. **Create/define each channel in the node's channel table** with the normal channel admin flow
|
||
(the same `set_channel` your app already uses for adding channels):
|
||
|
||
```text
|
||
AdminMessage.set_channel { index: 1, role: SECONDARY,
|
||
settings: { name: "NarrowSlow", psk: <key>, channel_num: 0 } }
|
||
```
|
||
|
||
2. **Write the beacon config**, pointing each target at the slot index from step 1:
|
||
|
||
```text
|
||
AdminMessage.set_module_config { mesh_beacon: {
|
||
flags = FLAG_BROADCAST_ENABLED
|
||
broadcast_targets = [ { preset: NARROW_SLOW, region: EU_N_868, channel_index: 1 } ]
|
||
} }
|
||
```
|
||
|
||
Notes:
|
||
|
||
- A target may **only** reference a channel that already exists locally - the node needs that
|
||
channel's key to encrypt the beacon. A `channel_index` that is out of range, or points at a
|
||
blank/unconfigured slot, is not an error: the beacon falls back to the node's **current/primary
|
||
channel** (its name, PSK, and slot) on the target preset/region. The channel name only defaults
|
||
to the preset's display name (e.g. `LongFast`) when the primary channel itself is unnamed - so
|
||
the fallback is "broadcast on my home channel," **not** a freshly-synthesised default-PSK channel
|
||
for that preset.
|
||
- `channel_index` must be `< MAX_NUM_CHANNELS` (8); the firmware clears it on write otherwise (see
|
||
§2.2 sanitise rules). This is the **only** check on write - the firmware does **not** verify that
|
||
the referenced slot is actually populated, because you may legitimately write the beacon config
|
||
before creating the channel. **Validating that a referenced channel exists is the client app's
|
||
responsibility.** A dangling reference doesn't error; it silently falls back to the preset's
|
||
default channel - so without a client-side check, the user can believe they're advertising
|
||
channel _X_ while the node is really transmitting on the preset default. Before writing, confirm
|
||
each `channel_index` maps to a configured `Channel`, and warn the user otherwise.
|
||
- **No automatic deduplication of channels.** Neither the beacon config nor the channel table
|
||
dedups by content: two `broadcast_targets` may carry the same `channel_index`, or different
|
||
indices whose slots hold identical settings, and `set_channel` will happily store two slots with
|
||
the same name/PSK. The broadcaster _does_ skip transmitting a target whose effective
|
||
preset/region/channel duplicates an earlier one in the same cycle (so a duplicated entry wastes
|
||
no airtime), but it does not rewrite or reject your config - keeping the target list free of
|
||
redundant entries is up to the client.
|
||
- The single-target path needs no separate `set_channel` step - its `broadcast_on_channel` is
|
||
written inline in the same beacon-config message.
|
||
|
||
### 2.6 Quick reference
|
||
|
||
| Concern | Value |
|
||
| ---------------------- | ---------------------------------------------------------------------------------------- |
|
||
| Port number | `MESH_BEACON_APP = 37` |
|
||
| Wire message | `meshtastic.MeshBeacon` |
|
||
| Config message | `ModuleConfig.MeshBeaconConfig` (variant tag 17) |
|
||
| On/off toggles | `flags` bitfield (`MeshBeaconConfig.Flags`) |
|
||
| Local config presence | `LocalModuleConfig.mesh_beacon` (tag 18) |
|
||
| Min broadcast interval | 3600 s (1 h) |
|
||
| Message max length | 100 bytes |
|
||
| Hop behaviour | Zero-hop (`hop_limit = 0`), never rebroadcast; `hop_start = 1` under `FLAG_LEGACY_SPLIT` |
|
||
| Auto-apply offers? | **Never** - client + user decide |
|
||
| Offer PSK | Public join token, not a secret |
|
||
| Disabled today | `broadcast_send_as_node` application |
|