zephyr-cbor

Zephyr CBOR (zcbor)

Zephyr integrates the zcbor library for CBOR encoding/decoding.

⭐ Recommended: Code Generation from CDDL Schema

For any non-trivial message format, use zcbor's code generator instead of hand-writing zcbor calls. It generates type-safe C structs and encode/decode functions from a CDDL schema — less error-prone, easier to maintain, and handles unions/optionals automatically.

1. Write a CDDL schema

CDDL supports two container styles — choose based on whether field order matters:

• Group/tuple (...) — ordered sequence, no keys on wire (more compact)
• Map {...} — key-value pairs, order-independent (more flexible)

; my-api.cddl

; Integer constants for a discriminated union
cmd_get_status = 1
cmd_set_config = 2

command_id /= cmd_get_status
command_id /= cmd_set_config

; Enum values
status_idle   = 0
status_active = 1
status_error  = 2

device_status /= status_idle
device_status /= status_active
device_status /= status_error

; Tuple (ordered, compact — no keys on wire)
set_config_params = (
    threshold: uint .size 2,
    enabled:   bool,
)

; Map (key-value, order-independent)
status_response = {
    status_code: device_status,
    uptime_ms:   uint,
    ? error_msg: tstr,
}

; Top-level message with optional params
My_Command = (
    command_id: command_id,
    ? params:   set_config_params,
)

2. Generate C code

pip install zcbor

zcbor code --decode --encode \
  --short-names \
  -c my-api.cddl \
  -t My_Command \
     status_response \
  --output-c src/cbor/my-api.c \
  --output-h include/cbor/my-api.h \
  --output-h-types include/cbor/my-api_types.h \
  --include-prefix "cbor/" \
  --default-max-qty 3

Key flags:

Flag	Purpose
--decode / --encode	Generate decode and/or encode functions
-t <types>	Root types to generate entry-point functions for
--short-names	Shorten generated symbol names (avoids very long identifiers)
--output-c/h/h-types	Output paths for .c, .h, and _types.h
--include-prefix	Prefix added to #include paths inside generated .c files
--default-max-qty N	Max array/list entries (affects struct array sizes)
--file-header <file>	Prepend a custom copyright/license header to generated files