swaits
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Rewrites lingering github.com / *.sr.ht references to this Gitea instance, translating GitHub and Sourcehut URL shapes to Gitea's (/blob/<ref>/ and sr.ht /tree/<ref>/item/ -> /src/branch/<ref>/, /tree/<tag> -> /src/tag/<tag>, /actions/workflows/X -> /actions?workflow=X, /edit/ -> /_edit/). Left pointing at the old hosts on purpose: pull-request links (PRs were not migrated), forks that were never migrated, and GitHub-only surfaces Gitea lacks. OpenPGP identity proofs are untouched by design.
69 lines
2.0 KiB
Markdown
69 lines
2.0 KiB
Markdown
# MeshCore Protocol Specification
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## Section 12: Payload — Control
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### Overview
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The CONTROL payload carries control and discovery data. Control packets are raw
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byte payloads whose structure is determined by the first byte. A subset of
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control packets (those with bit 7 of the first byte set) are restricted to
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zero-hop delivery only.
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### Payload Type
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Header payload type field: `0x0B` (CONTROL)
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### Wire Format
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```
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0
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Control Byte | Data... |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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```
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### Fields
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| Field | Offset | Size | Type | Description |
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|-------|--------|------|------|-------------|
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| control_byte | 0 | 1 byte | uint8 | Control type identifier |
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| data | 1 | variable | raw | Control-specific data |
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### Zero-Hop Restriction
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When bit 7 (`0x80`) of the control byte is set, the packet is restricted to
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zero-hop delivery only. The reference implementation enforces this:
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- If `(payload[0] & 0x80) != 0` AND the packet is direct-routed:
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- It is processed only if `getPathHashCount() == 0`.
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- It is NOT forwarded to other nodes.
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### Discovery Protocols
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Control packets are commonly used for node discovery. The specific sub-protocol
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formats are application-defined, but typically include:
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- **Discovery Request**: Sent zero-hop to find nearby nodes
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- **Discovery Response**: Contains node type, name, SNR, and other metadata
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### Encoding
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1. Construct the raw control data bytes.
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2. If the control packet should be zero-hop only, set bit 7 of the first byte.
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3. Copy data to payload, set payload_len.
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### Constraints
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- Payload MUST be at least 1 byte (the control byte).
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- Maximum payload: 184 bytes (MAX_PACKET_PAYLOAD).
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### Cross-References
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- [Section 17: Routing](17-routing.md) — Zero-hop delivery
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- Test vectors: [`corpus/payloads/control/`](https://git.swaits.com/swaits/meshcore-spec/src/branch/main/versions/v0.1.0/corpus/payloads/control/)
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### Reference Implementation
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- `Mesh::createControlData()` in `src/Mesh.cpp` — Encoding
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- `Mesh::onRecvPacket()`, CONTROL handling — Zero-hop check and delivery
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