swaits/meshcore-spec

0 Fork 0

Files

T

swaits a031c6e266

mdBook / build (push) Canceled after 0s

Details

mdBook / deploy (push) Canceled after 0s

Details

chore: repoint remaining links at git.swaits.com

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.

2026-08-31 18:32:21 -06:00

2.0 KiB

Raw Blame History

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

2.0 KiB Raw Blame History