swaits/meshcore-spec

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swaitsandClaude Opus 4.7 9232c16f7c

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feat(versioning): snapshot corpus per spec version

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>

2026-05-12 10:38:02 -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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