swaitsandClaude Opus 4.7
9232c16f7c
A frozen spec is only meaningful if it's paired with the corpus that was current at release time — otherwise a v0.1.0 reader follows "see corpus/payloads/ack/" and lands on a file whose test vectors may have changed since v0.1.0 was cut. Three changes: 1. `cut-version` now copies BOTH src/ AND corpus/ into the snapshot directory. A release is the pair, not just the text. 2. The corpus URL rewriting in cut-version now retargets /tree/main/corpus -> /tree/main/versions/<v>/corpus (and the blob variant). This lets the link resolve on GitHub from main alone — no git tag required, since the frozen copy is a real path under main. Downgrades the "tag is REQUIRED" message from last commit back to "optionally tag the commit". 3. The frozen corpus's spec_ref fields get rewritten too: from `src/04-payload-ack.md` to `versions/<v>/04-payload-ack.md`, so a reader following a test vector lands on the spec text the vector was paired with at release time. versions/v0.1.0/ regenerated from scratch via `just cut-version v0.1.0` to pick up the corpus snapshot + the new sed patterns. The release is now self-consistent: v0.1.0 spec links go to v0.1.0 corpus, which links back to v0.1.0 spec. Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
124 lines
4.9 KiB
Markdown
124 lines
4.9 KiB
Markdown
# MeshCore Protocol Specification
|
||
|
||
## Section 5: Payload — Advertisement
|
||
|
||
### Overview
|
||
|
||
The advertisement payload allows a node to announce its identity to the mesh. It
|
||
contains the node's Ed25519 public key, a timestamp, a signature proving
|
||
ownership of the key, and optional application data describing the node's type,
|
||
location, features, and name.
|
||
|
||
### Payload Type
|
||
|
||
Header payload type field: `0x04` (ADVERT)
|
||
|
||
### Wire Format
|
||
|
||
```
|
||
0 31
|
||
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
||
| |
|
||
| Ed25519 Public Key (32 bytes) |
|
||
| |
|
||
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
||
| Timestamp (uint32_le) |
|
||
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
||
| |
|
||
| Ed25519 Signature (64 bytes) |
|
||
| |
|
||
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
||
| App Data (0-32 bytes) |
|
||
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|
||
```
|
||
|
||
### Fields
|
||
|
||
| Field | Offset | Size | Type | Description |
|
||
|-------|--------|------|------|-------------|
|
||
| pub_key | 0 | 32 bytes | raw | Ed25519 public key of the advertising node |
|
||
| timestamp | 32 | 4 bytes | uint32_le | Unix epoch timestamp of advertisement creation |
|
||
| signature | 36 | 64 bytes | raw | Ed25519 signature (see Signature section below) |
|
||
| app_data | 100 | 0-32 bytes | structured | Optional application data (see App Data section below) |
|
||
|
||
### Minimum and Maximum Sizes
|
||
|
||
- Minimum payload: 100 bytes (pub_key + timestamp + signature, no app_data)
|
||
- Maximum payload: 132 bytes (100 + MAX_ADVERT_DATA_SIZE of 32)
|
||
|
||
### Signature
|
||
|
||
The signature is computed over the concatenation of:
|
||
|
||
```
|
||
message = pub_key(32) || timestamp_le(4) || app_data(0-32)
|
||
```
|
||
|
||
The node signs this message using its Ed25519 private key. Receivers MUST verify
|
||
the signature using the public key from the payload. Packets with invalid
|
||
signatures MUST be discarded.
|
||
|
||
### App Data Format
|
||
|
||
When present (payload_len > 100), app_data is a structured field beginning with
|
||
a flags byte:
|
||
|
||
```
|
||
Bit: 7 6 5 4 3 2 1 0
|
||
+-------+-------+-------+-------+---+---+---+---+
|
||
|has_ |has_ |has_ |has_ | Node Type |
|
||
|name |feat2 |feat1 |loc | (4 bits) |
|
||
+-------+-------+-------+-------+---+---+---+---+
|
||
```
|
||
|
||
| Field | Offset | Size | Condition | Type | Description |
|
||
|-------|--------|------|-----------|------|-------------|
|
||
| flags | 0 | 1 byte | Always | uint8 | See bit layout above |
|
||
| latitude | 1 | 4 bytes | flags bit 4 set | int32_le | Latitude × 1,000,000 |
|
||
| longitude | 5 | 4 bytes | flags bit 4 set | int32_le | Longitude × 1,000,000 |
|
||
| feat1 | varies | 2 bytes | flags bit 5 set | uint16_le | Feature field 1 |
|
||
| feat2 | varies | 2 bytes | flags bit 6 set | uint16_le | Feature field 2 |
|
||
| name | varies | remaining | flags bit 7 set | UTF-8 | Node name (no null terminator) |
|
||
|
||
Fields appear in the order listed. The offset of each field depends on which
|
||
preceding optional fields are present.
|
||
|
||
### Node Types (flags bits 0-3)
|
||
|
||
| Value | Name | Description |
|
||
|-------|------|-------------|
|
||
| 0 | None | Unspecified |
|
||
| 1 | Chat | Chat client node |
|
||
| 2 | Repeater | Mesh repeater node |
|
||
| 3 | Room | Room server node |
|
||
| 4 | Sensor | Sensor node |
|
||
|
||
### Decoding Algorithm
|
||
|
||
1. Read 32 bytes as pub_key.
|
||
2. Read 4 bytes as timestamp (uint32_le).
|
||
3. Read 64 bytes as signature.
|
||
4. If offset (100) > payload_len, the packet is INVALID (incomplete).
|
||
5. If offset (100) == payload_len, there is no app_data. Done.
|
||
6. Read remaining bytes as app_data (up to MAX_ADVERT_DATA_SIZE = 32 bytes).
|
||
If more than 32 bytes remain, implementations MUST truncate to 32.
|
||
7. Construct the signature verification message: pub_key || timestamp_le || app_data.
|
||
8. Verify the Ed25519 signature. If invalid, the receiver MUST discard the packet.
|
||
9. Parse app_data:
|
||
a. Read 1 byte as flags.
|
||
b. If flags bit 4 set: read 4 bytes latitude (int32_le), 4 bytes longitude (int32_le).
|
||
c. If flags bit 5 set: read 2 bytes feat1 (uint16_le).
|
||
d. If flags bit 6 set: read 2 bytes feat2 (uint16_le).
|
||
e. If flags bit 7 set: read remaining bytes as UTF-8 name.
|
||
|
||
### Cross-References
|
||
|
||
- [Section 15: Identity](15-identity.md) — Ed25519 key management
|
||
- [Section 14: Cryptography](14-crypto.md) — Signature operations
|
||
- Test vectors: [`corpus/payloads/advert/`](https://github.com/swaits/meshcore-spec/tree/main/versions/v0.1.0/corpus/payloads/advert/)
|
||
|
||
### Reference Implementation
|
||
|
||
- `Mesh::createAdvert()` in `src/Mesh.cpp` — Encoding
|
||
- `Mesh::onRecvPacket()`, case `PAYLOAD_TYPE_ADVERT` in `src/Mesh.cpp` — Decoding and verification
|