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spec: link corpus references to GitHub, version-aware

Every "Test vectors: \`corpus/...\`" mention in the spec is now a
markdown link pointing at the corresponding file or directory on
GitHub. Each version build resolves its links to the correct git
ref:

  - /latest/ -> https://github.com/swaits/meshcore-spec/tree/main/corpus/...
  - /v0.1.0/ -> https://github.com/swaits/meshcore-spec/tree/v0.1.0/corpus/...
  - future /vX.Y.Z/ -> /tree/vX.Y.Z/corpus/...

Two changes:

1. src/*.md (18 files): the inline-code corpus paths in each
   "Cross-References" section are now markdown links. Directories
   point at /tree/main/corpus/..., individual .json files point at
   /blob/main/corpus/.... CHANGELOG and other non-corpus main links
   are intentionally left pointing at main — the canonical history
   lives there regardless of which version you're reading.

2. justfile: `cut-version` now also runs a sed over the snapshot's
   *.md files replacing /tree/main/corpus -> /tree/<VERSION>/corpus
   and /blob/main/corpus -> /blob/<VERSION>/corpus. So a freshly-cut
   version is self-consistent.

versions/v0.1.0/* regenerated by re-running
`just cut-version v0.1.0` after the new src/ links + recipe sed
landed.

Tagging the release commit (`git tag v0.1.0`) is now REQUIRED — not
"optional" — because the rendered /v0.1.0/ pages reference
/tree/v0.1.0/corpus/... on GitHub. Without the tag the links 404.
cut-version's output now says so.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-05-12 10:35:09 -06:00

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MeshCore Protocol Specification

Section 12: Payload — Control

Overview

The CONTROL payload carries control and discovery data. Control packets are raw byte payloads whose structure is determined by the first byte. A subset of control packets (those with bit 7 of the first byte set) are restricted to zero-hop delivery only.

Payload Type

Header payload type field: 0x0B (CONTROL)

Wire Format

 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Control Byte |  Data...      |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Fields

Field	Offset	Size	Type	Description
control_byte	0	1 byte	uint8	Control type identifier
data	1	variable	raw	Control-specific data

Zero-Hop Restriction

When bit 7 (0x80) of the control byte is set, the packet is restricted to zero-hop delivery only. The reference implementation enforces this:

If (payload[0] & 0x80) != 0 AND the packet is direct-routed:
- It is processed only if getPathHashCount() == 0.
- It is NOT forwarded to other nodes.

Discovery Protocols

Control packets are commonly used for node discovery. The specific sub-protocol formats are application-defined, but typically include:

Discovery Request: Sent zero-hop to find nearby nodes
Discovery Response: Contains node type, name, SNR, and other metadata

Encoding

Construct the raw control data bytes.
If the control packet should be zero-hop only, set bit 7 of the first byte.
Copy data to payload, set payload_len.

Constraints

Payload MUST be at least 1 byte (the control byte).
Maximum payload: 184 bytes (MAX_PACKET_PAYLOAD).

Cross-References

Section 17: Routing — Zero-hop delivery
Test vectors: corpus/payloads/control/

Reference Implementation

Mesh::createControlData() in src/Mesh.cpp — Encoding
Mesh::onRecvPacket(), CONTROL handling — Zero-hop check and delivery

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