rk_zenoh

Zenoh bindings for Dart: publish, subscribe and liveliness for a fleet of devices that spends part of its time disconnected.

Underneath the binding is a small Rust crate (rust/) over a stable subset of Zenoh 1.9. It is deliberately narrow: about thirty functions instead of eight hundred, one ownership rule instead of a hundred and twenty-six type definitions, and every enum crosses the boundary by name.

final session = await ZenohSession.open(ZenohConfig(
  mode: SessionMode.peer,
  connect: ['tcp/127.0.0.1:7447'],
));

final alive = await session.declareLiveliness('telepos/alive/till-17');
final orders = await session.subscribe('telepos/till/till-17/cmd');
orders.samples.listen((s) => print('${s.key}: ${s.text}'));

await session.put('telepos/shop/3/heartbeat', utf8.encode('ok'));

await alive.close();
await session.close();

No call runs on the caller's isolate: the package keeps a worker isolate of its own, and all of the native side lives there.

What is not here, and why you want to know that up front

Advanced Pub/Sub is absent. The publisher cache, history for late subscribers, gap detection and recovery — all of it sits behind Zenoh's unstable feature, and this package does not enable it. That is exactly the part people usually turn into "works offline", so it has to be built on top of the package: durable state lives in a database that replicates, and this fabric carries what is happening now. A subscriber that was not listening missed nothing — as far as it is concerned, the message never existed.

For the same reason there is no per-message reliability control (zenoh::qos::Reliability is unstable) and no liveliness history.

Zenoh does not traverse NAT. It finds neighbours by multicast within a single network and spreads what it learns by gossip once an entry point is known, but the addresses it is handed have to be routable. Reaching a till behind somebody else's router is a relay's job, not the fabric's.

A Zenoh ID is not an address

A recreated session gets a new Zenoh ID. Messages sent to the old one are accepted successfully and delivered nowhere — with no error. For a till that restarts on every update, that is an ordinary event, not an edge case.

The package makes you choose explicitly, through ZenohIdentity:

The refusal is not a formality: whoever claims a pinned ID first keeps it — measured. Without a certificate, any machine on the network can cut a till out of the fabric simply by booting earlier.

The numbers, and how they were obtained, are in doc/stale-zid.md. The edges of the stable subset are in doc/stable-subset.md.

Building the native side

cd rust && cargo build --release

The package is a Flutter FFI plugin: flutter build invokes cargo itself and puts the library into the application on Windows, Linux and Android. There is no hook/ directory here and there never will be — its mere presence breaks dart run, dart test and flutter build. The mechanism, the three different routes to cargo, and the order to check things in on a Mac are in doc/native-build.md.

Outside a built application the library is located by an explicit path, by the RK_ZENOH_LIBRARY environment variable, or next to the executable; the crate is a plain cdylib/staticlib with a C ABI.

Where the library actually arrives:

Licence

MIT, by Rob Kim. See LICENSE. Zenoh itself is Apache-2.0 or EPL-2.0.