edgefirst-schemas 3.4.3

Zero-copy CDR message types for EdgeFirst Perception (ROS 2 + Foxglove + custom)

edgefirst-schemas (Python)

Zero-copy CDR message types for EdgeFirst Perception. Wraps the edgefirst-schemas Rust crate via PyO3.

pip install edgefirst-schemas

The wheel ships as cp311-abi3 (Python 3.11+, single wheel per OS/arch). For an older Python floor, build from source with --no-default-features --features abi3-py38 — see Build from source.

Quick start

from edgefirst.schemas.builtin_interfaces import Time
from edgefirst.schemas.std_msgs import Header
from edgefirst.schemas.sensor_msgs import Image
import numpy as np

pixels = np.zeros((720, 1280, 3), dtype=np.uint8)
img = Image(
    header=Header(stamp=Time(sec=1, nanosec=0), frame_id="cam"),
    height=720, width=1280, encoding="rgb8",
    is_bigendian=0, step=1280 * 3,
    data=pixels,  # any contiguous buffer-protocol object
)

# Zero-copy view of the pixel data — `np.frombuffer` aliases the same
# bytes the message was constructed with, no copy.
arr = np.frombuffer(img.data, dtype=np.uint8).reshape(720, 1280, 3)

# Wire bytes for transport:
buf = img.to_bytes()
img2 = Image.from_cdr(buf)
assert img2.width == 1280

Forwarding raw CDR bytes without a copy

For publish paths where you want to hand the wire bytes straight to a transport (Zenoh, raw socket, mcap writer), cdr_view() exposes the full CDR buffer (header + payload) as a zero-copy BorrowedBuf:

transport.publish(memoryview(img.cdr_view()))   # zero-copy

to_bytes() is the explicit-copy alternative when the consumer wants an owned bytes value.

Zero-copy contract — BorrowedBuf

Every bulk byte payload (Image.data, Mask.mask, RadarCube.cube, PointCloud2.data, CompressedVideo.data, CompressedImage.data) returns a BorrowedBuf view that aliases the parent message's bytes — not a copy. The BorrowedBuf holds a strong reference to the parent, so it's safe to keep it (or a memoryview derived from it) live after the original message reference is dropped.

Method	Returns	Cost
borrowed_buf itself	wraps the bytes	zero-copy, O(1)
np.frombuffer(borrowed_buf, dtype=...)	numpy ndarray aliasing the bytes	zero-copy, O(1) (Py 3.11+)
memoryview(borrowed_buf)	parent-anchored memoryview	zero-copy, O(1) (Py 3.11+)
borrowed_buf.tobytes()	owned bytes	one memcpy
borrowed_buf.view()	memoryview (Py 3.11+) / bytes (abi3-py38)	zero-copy / one memcpy

Migrating from the pycdr2-backed edgefirst.schemas

This release replaces the pure-Python pycdr2 codec with a Rust-backed pyo3 binding. Wire-format bytes are unchanged — anything encoded by the previous pycdr2 module decodes through from_cdr() and vice-versa — but the Python API surface is narrower and stricter.

What changed at the call site

# pycdr2-backed (old)                    # pyo3-backed (new)
img = Image()                            img = Image(
img.height = 720                             header=Header(stamp=Time(1, 0)),
img.width = 1280                             height=720, width=1280,
img.encoding = "rgb8"                        encoding="rgb8", is_bigendian=0,
img.data = pixels                            step=1280 * 3, data=pixels,
buf = img.serialize()                    )
img2 = Image.deserialize(buf)            buf = img.to_bytes()
                                         img2 = Image.from_cdr(buf)

pycdr2 pattern	pyo3 replacement
Foo() then field assignment	Foo(field=value, …) constructor only — pyclasses are frozen
.serialize()	.to_bytes()
Foo.deserialize(buf)	Foo.from_cdr(buf)
msg.data returning bytes	msg.data returning BorrowedBuf (zero-copy view); use .tobytes() for the old shape
from_schema(), decode_pcd(), colormap(), registry helpers	removed — the legacy module survives only at benches/python/legacy/ for benchmark parity
std_msgs.{String, Int32, Float64, …} primitive wrappers	removed — these were pycdr2-generated single-value wrappers; pass raw Python values instead
Mutable dataclass-style instances	Frozen pyclasses; rebuild instead of mutate

What stays the same

• All field names and types match the ROS 2 / Foxglove / EdgeFirst schemas verbatim.
• Wire-format CDR1 LE bytes are byte-equivalent across versions.
• The edgefirst.schemas.<submodule> import paths (sensor_msgs.Image, std_msgs.Header, etc.) are preserved.

abi3-py38 builds — typed numpy caveats

The default wheel is cp311-abi3, where the buffer protocol is in the limited API and typed numpy arrays (np.uint16, np.float32, …) work zero-copy as constructor inputs. On the opt-in abi3-py38 build the buffer protocol isn't available; pass arr.tobytes() for typed arrays, and BorrowedBuf.view() returns bytes (one copy) instead of a parent-anchored memoryview. Plain bytes / bytearray / np.uint8 arrays work on either build.

shape = np.array([2, 128, 12, 128], dtype=np.uint16)

# Default cp311-abi3 wheel — works directly:
RadarCube(..., shape=shape, ...)

# abi3-py38 build — pass bytes:
RadarCube(..., shape=shape.tobytes(), ...)

Build from source

Default (cp311-abi3 wheel for Python 3.11+):

maturin develop --release --manifest-path crates/python/Cargo.toml

abi3-py38 wheel (for embedded targets pinning an older Python):

maturin build --release \
  --manifest-path crates/python/Cargo.toml \
  --no-default-features --features abi3-py38

Cross-compile manylinux2014 wheels via zig:

maturin build --release --zig --compatibility manylinux2014 \
  --target aarch64-unknown-linux-gnu \
  --manifest-path crates/python/Cargo.toml