SmartThings-Local

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SmartThings-Local

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Local control of Samsung SmartThings appliances over cert-authenticated CoAP-DTLS. No cloud! Python library + Home Assistant MQTT bridge demo.

// repository documentation

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# SmartThings-Local

**`smartthings-local` is a Python library for local, cloud-free control of newer-generation Samsung connected appliances over cert-authenticated CoAP-DTLS.** It gives you the DTLS-CoAP transport, a tiered polling + OBSERVE state layer, and one-command identity-cert minting. That covers everything needed to read state from and write commands to a Samsung dryer, oven, fridge, etc. on your LAN, with no SmartThings cloud round-trip.

The repo also ships a self-contained **reference bridge demo** (`mqtt_demo/`) that turns the library into auto-discovered Home Assistant entities over MQTT. One process supervises multiple appliances, each on its own DTLS session.

> **Just want to control your Samsung appliance from Home Assistant?**
> Use [localthings](https://github.com/mbillow/localthings), a Home
> Assistant custom component built on the `smartthings-local` package.
> This repo is the protocol research project, the library itself, and a
> self-contained MQTT bridge demo; new appliance support (capability
> mappings, HA entities) should go to localthings, not here.

## Quick start (library)

`smartthings-local` is on PyPI:

```sh
pip install smartthings-local
```

Mint a client cert once (see [Part 2](#part-2--auth-get-the-identity-cert)), then drive a session directly:

```python
import cbor2
from smartthings_local.protocol.dtls_session import DtlsCoapSession

sess = DtlsCoapSession(
    "192.168.1.100", 49154,
    cert_path="certs/client_fullchain.pem",
    key_path="certs/client.key",
)
sess.connect()
sess.start_reader()

code, body = sess.get(["device", "0"])                       # Block2-aware read
code, _    = sess.post(["mode", "vs", "0"], cbor2.dumps({}))  # write
sess.subscribe(["operational", "state", "vs", "0"],          # OBSERVE
               on_notification=lambda href, payload: ...)
sess.close()
```

If the cert/key are minted at runtime and never written to disk (e.g. inside an HA config flow), pass them in memory instead of by path:

```python
sess = DtlsCoapSession("192.168.1.100", 49154, cert_pem=cert_pem, key_pem=key_pem)
```

For a full worked integration, the higher-level `smartthings_local.ocf` layer (`StateCache`, `PollScheduler`, `KeepaliveTask`, `ObserveRefreshTask`) coordinates tiered polling and OBSERVE on top of a session. The MQTT bridge demo below wires all of it together.

### What the demo bridge gives you

- **Multi-appliance, one container:** single Docker service holds N DTLS sessions in parallel, one per appliance, sharing one MQTT client. Adding an appliance class is ~150 lines and one descriptor file.
- **Bounded state latency:** hot-tier resources (job state, door, operational state) refresh on a sub-second cadence regardless of whether the appliance has internet. Worst-case lag is the tier interval (≤1s idle, ≤500ms during an active cycle on the dryer).
- **Writes that work:** dryer Start/Pause/Stop, course selection, wrinkle prevent; oven lamp (light entity), sound, fast preheat, setpoint slider, mode select, stop.
- **Optimistic publish + verify:** HA sees the new value the instant the device 2.04-confirms the write; the PollScheduler verifies on its next tier tick (after a 4s defer past Samsung's fetchback-revert window).
- **HA Energy Dashboard ready** (dryer): live watts + cumulative kWh as `total_increasing`.
- **Bridge logs tagged per-appliance** with `<class>.<serial>` once each device's serial is read on connect: `dryer.<serial>` and `oven.<serial>` interleave in the same log stream, easy to grep.
- **Zero HA YAML:** every entity is auto-discovered via MQTT discovery.
- **Your state stays on your LAN:** bridge → broker → HA. Samsung's cloud sees nothing from HA. *(The appliance still maintains its own TLS session to Samsung. That's the appliance's design, not ours.)*
- **A few controls the cloud HA integration doesn't offer.** Talking to the appliance directly surfaces some writes the official SmartThings integration doesn't currently expose for these models: dryer course selection ([HA core #162501](https://github.com/home-assistant/core/issues/162501)) and the oven temperature setpoint (where the cloud integration provides a read-only sensor). It's not a strict superset (the cloud integration still covers surfaces this doesn't), but the reverse-engineered write set is broad.

### Under the hood

Each appliance runs an independent bridge built around three coordinated pieces over one persistent DTLS session: a `StateCache` (single source of truth for all reps), a `PollScheduler` (tiered adaptive polling: hot/warm/cold plus a periodic `/device/0` sweep), and a `KeepaliveTask` (CoAP empty-CON ping for DTLS-layer liveness, with consecutive-failure detection for MQTT availability). Tier cadences are descriptor-declared and were calibrated against the empirically-measured per-firmware ceilings: dryer ~14 req/s, oven ~8 req/s. OBSERVE registrations (RFC 7641) are kept as an opportunistic freshness accelerator: when the appliance has internet and emits notifications, the cache absorbs them and the next-poll timer is reset for that resource; when it's air-gapped, polling alone carries the UX with no other code change. Token-stable Block2 (RFC 7959) handles multi-block reads. Writes are optimistically merged into the cache the moment the device 2.04-confirms, with the scheduler deferring that resource's next poll past the fetchback-revert window. Reconnect with exponential backoff on session errors, gated by a stateless DTLS ClientHello pre-flight (`smartthings_local/protocol/dtls_probe.py`) so a silent/rebooting device or wrong port drops into backoff in ~1 RTT instead of eating the full handshake timeout; when `OCF_PORT` is unset the same probe auto-discovers the live port across the OCF band.

Authentication uses a client cert keyed to the UUID published in Samsung's own wildcard cloud TLS cert. Every Samsung Tizen/RT-OCF appliance's factory ACL grants that UUID `perm=31` (full CRUDN) on `href=*`, so a single cert chain works across the whole fleet. Setup is one Python script.

---

## Part 1 — Is your appliance compatible?

Check before anything else; if it's older firmware, this project doesn't target it.

```sh
# UDP scan for DTLS-CoAP ports
nmap -Pn -sU -p 49152-49160 "$APPLIANCE_IP"
```

Read the result:

- **`49154/udp` (or similar 4915x) open|filtered with a DTLS handshake responding** → newer firmware (Tizen RT 3.x with DAWIT 3.0). This is what the bridge talks to.
- **Only `8888/tcp` open (token-based HTTPS)** → older firmware (~2018–2022). **Not supported here.**

nmap's `open|filtered` can't tell a real DTLS server from a silent UDP port. Confirm which of the candidate ports actually speaks DTLS with the ClientHello probe, which sends one ClientHello and reports back per port:

```sh
# Stateless liveness check: one ClientHello round trip, leaves no state on the device
python -m smartthings_local.protocol.dtls_probe "$APPLIANCE_IP" 49153 49154 49155 49156 --stateless
```

`live` means a DTLS server answered its `HelloVerifyRequest` (that's your control port); `dead` means silent / not DTLS. Once you have the client cert (Part 2), drop `--stateless` to run the default *diagnostic* drive, which reports `completed` (cert accepted) or `rejected` with the server's fatal alert. An `unsupported_certificate` / `unknown_ca` alert is the signature of a newer OCF-PKI device that won't accept the AC14K_M cert. The same probe gates the bridge's own reconnect loop and auto-discovers the port when `OCF_PORT` is unset.

### Tested combinations

| Appliance class | Model family | Confirmed |
|---|---|---|
| Washer | WW11DG (`DA_WM_TP2_20_COMMON`, `mnid=0AJT`) | All entities. Contributed by [@indykoning](https://github.com/indykoning) (PR #13); tested via [`mbillow/localthings`](https://github.com/mbillow/localthings) |
| Dryer | DV5000T (`DA_WM_TP2_20_COMMON`, `mnid=0AJT`); DV90T (same `mnid=0AJT`) | All entities, ≤1s hot-tier poll (OBSERVE accelerates when online) |
| Oven | NV7000BS-class (`TP1X_DA-KS-OVEN-0107X`, `mnid=0AJT`) | All entities; hot-tier poll covers door + operational state regardless of cloud reachability |
| Fridge | ARTIK051_REF_17K (`DA-REF-ART-COMMON-1_20201124`) | Contributed by [@aminorjourney](https://github.com/aminorjourney) (PR #1). Older firmware family; port 49155, minimal `/oic/res` with full tree under `/device/0` |

Other appliances on the same firmware family (dishwashers, AC units) almost certainly speak the same protocol: the auth path and read primitives are common, and a washer on the shared `DA_WM_TP2_20_COMMON` controller is already confirmed above. You'd write one new descriptor for the `localthings` registry.

### Firmware families: a limitation

Descriptors are firmware-family-specific. Each descriptor hardcodes the resource layout of one firmware family: which hrefs it polls, which fields it reads, which write surfaces it exposes. There's no runtime feature detection. The three sample descriptors here (`mqtt_demo/samples/`) are frozen references.

**What this means in practice:** if you set `APPLIANCE_<n>_CLASS=fridge` on a fridge that speaks a different firmware family than the one this descriptor was built for, the bridge will start and connect fine, but many sensors will publish as unknown and some controls won't work. Nothing catastrophic. You just get a half-broken HA device card.

If your appliance model doesn't match a row in the tested table above, it may still work if it's on the same firmware family; otherwise you'd write a new descriptor (see "Adding a new appliance class" below). The ARTIK051 fridge and the newer RF9000B-class fridge, for example, expose different resource models (collection-resource vs per-instance-resource) and can't share a descriptor even though they're both "fridges".

---

## How the app keeps in sync with the appliance

There are two parallel paths between the appliance and the app over the local CoAP-DTLS socket:

- **Push (OBSERVE).** When the appliance can reach Samsung's cloud, it emits a CoAP OBSERVE notification on the LAN socket within ~100ms of any state change: cycle start, door open, mode flip. The notification travels over the LAN; nothing about the push itself routes via Samsung. **But** the appliance's decision to emit it at all is gated inside its cloud-publish thread. Block the appliance from the internet and the LAN OBSERVE pushes stop, even though the LAN path itself is unaffected and the appliance still answers reads + accepts writes normally.
- **Polling.** The app always polls a small tier of hot resources (operational state, door, etc.) on a sub-second cadence, a warmer tier (mode, kidslock, alarms, …) every 15–30 s, and a full `/device/0` sweep every 5 minutes. This carries the UX regardless of whether OBSERVE is firing.

In normal operation both happen at once: an OBSERVE notification arrives first, the cache absorbs it, and the next-poll timer for that resource is reset. In an air-gapped LAN the app keeps working. Only the worst-case freshness changes (from ~100 ms with push to ≤1 s on hot-tier resources via polling). Reads, writes, and HA entities behave identically.

Which path is doing the work is visible in Home Assistant. The bridge publishes per-appliance diagnostic entities including **Push Active** (on while OBSERVE is firing), **Last Update Source** (`observe` / `poll` / `sweep` / `optimistic`), **Last OBSERVE Age**, **Poll Max RTT**, **Slow Polls (window)**, **Poll Errors (window)**, and **Stalest Resource Age**, all under each device's Diagnostic section.

---

## Part 2 — Auth: get the identity cert

The bridge authenticates with a **client cert** signed by `AC14K_M`, an intermediate CA that has been public for years and remains in current firmware trust stores. The cert's Subject DN carries a UUID that the on-device ACL grants full access to.

You can read the UUID yourself out of the relevant server cert:

```sh
openssl s_client -connect <samsung-host>:443 -servername <samsung-host> \
                 -showcerts < /dev/null 2>/dev/null \
  | openssl x509 -noout -subject
# subject=C=KR, O=Samsung Electronics, OU=uuid:<UUID>, CN=*.samsungiotcloud.com
```

The UUID lives in `OU=uuid:<UUID>`. The server cert is currently valid through **2035-04-09**.

This README doesn't pin the literal UUID: the setup script extracts it live each run, so it self-updates if upstream rotates.

### Why this works

- Every Samsung Tizen/RT-OCF appliance has a **factory-baked ACE** in `/oic/sec/acl` granting this UUID `perm=31` on `href=*`.
- TizenRT iotivity derives peerId from `memmem(subject_dn, "uuid:")`, which is RDN-agnostic. A cert with the UUID in CN authenticates the same as one with it in OU.
- We don't need the matching private key from the original keyholder. We mint our own key and have `AC14K_M` sign our leaf. Different key, same identity, same access.

### One-command setup

```sh
pip install -r requirements-bootstrap.txt
TARGET_IP=$APPLIANCE_IP python setup_cert.py --test
```

What it does:

1. Fetches the AC14K_M signing CA + private key + upstream chain (RemoteAccessCA → CECA → ROOTCA) from a public mirror.
2. Fetches the relevant server cert and extracts the current UUID from its subject DN.
3. Sanity-checks that the AC14K_M cert and key actually pair (modulus match) before signing anything.
4. Generates a fresh RSA-2048 key pair you own.
5. Builds a CSR with the UUID in OU + CN + SAN and signs it with `AC14K_M` (SHA-1, matching the on-device trust hierarchy).
6. Concatenates `leaf + AC14K_M + 3 upstream CAs` into the fullchain PEM.
7. With `--test`: opens a DTLS handshake against `$TARGET_IP:$TARGET_PORT` (default `49154`) and GETs `/oic/sec/acl`; a `2.05` reply proves the cert authenticated (anonymous peers get `4.01`).

Output in `./certs/`: `client_fullchain.pem` + `client.key`.

Neither the UUID nor the AC14K_M bundle is hardcoded in this repo; both are fetched live each run, so the script self-updates if upstream rotates. If either fetch fails, the script prints an inline workaround: supply the UUID via `UUID=<uuid>` env, or supply the AC14K_M bundle via `AC14K_M_CERT_BUNDLE=/path/to/cert.pem`. `BRAYSTORM_URL=<mirror>` points at a different bundle source.

On Fedora/RHEL (and other hardened OpenSSL 3.x builds) the default crypto policy blocks SHA-1 signing, which step 5 needs. The script detects this, retries the signing step once with SHA-1 force-enabled for just that command, and only fails if the retry also fails. If it does, it prints the remedy: `sudo update-crypto-policies --set DEFAULT:SHA1` (undo afterward with `sudo update-crypto-policies --set DEFAULT`).

### How durable is this?

Rotating the published UUID would require Samsung to re-issue TLS certs across their IoT cloud, push new ACLs to every device in the field, and update the on-device daemon identity: a multi-quarter change with a long backwards-compat tail. `AC14K_M` has been public for years and is still in 2026 firmware trust stores. Local access via this path is roughly as durable as cloud control of these appliances.

> **Legacy path:** earlier versions used a per-hub-UUID cert via an anonymous `/oic/sec/doxm` read escalation. That still works on the dryer-family firmware but isn't necessary: the cert minted here authenticates against every appliance and survives device resets. The old `bootstrap.py` for the legacy flow was removed when the package was renamed; see git history if you need it.

---

## Part 3 — Configure your appliances

Copy `.env.example` to `.env` and fill in.

### Layered envs

The bridge config splits into:

- **Shared keys** (one per process): MQTT broker + creds, HA discovery prefix, cert paths, timer intervals.
- **Per-appliance keys** (one block per appliance) under `APPLIANCE_<n>_*` (1-indexed).

`APPLIANCE_COUNT` tells the bridge how many indexed blocks to read. Bump it as you add appliances.

```bash
APPLIANCE_COUNT=2

# Appliance 1 — dryer
APPLIANCE_1_CLASS=dryer
APPLIANCE_1_IP=192.168.1.100
APPLIANCE_1_OCF_PORT=             # blank → auto-discover across the OCF band (dryer=49155)
APPLIANCE_1_TOPIC=samsung_dryer
APPLIANCE_1_NAME=Samsung Dryer

# Appliance 2 — oven
APPLIANCE_2_CLASS=oven
APPLIANCE_2_IP=192.168.1.101
APPLIANCE_2_OCF_PORT=             # blank → auto-discover across the OCF band (oven=49154)
APPLIANCE_2_TOPIC=samsung_oven
APPLIANCE_2_NAME=Samsung Oven
```

Each `APPLIANCE_<n>_CLASS` must match a descriptor key in `mqtt_demo/samples/__init__.py::DESCRIPTORS`: currently `dryer`, `oven`, and `fridge`.

---

## Part 4 — Run it

### Docker (the real deployment)

```sh
docker compose up -d --build
docker compose logs -f
```

Container name `smartthings-local`. Outbound-only; no ports exposed. Needs egress to each appliance's IP/port (UDP) and to your MQTT broker. The certs in `./certs/` (or whatever `APPDATA_DIR` points to via the volume mount) are read-only mounted at `/config`.

### Deploying to a remote Linux host (Unraid, etc.)

```sh
# Once: upload the cert + key onto the remote.
ssh "$SSH_HOST" mkdir -p "$APPDATA_DIR"
scp certs/client_fullchain.pem certs/client.key "$SSH_HOST:$APPDATA_DIR/"

# Each deploy: ship source + .env, rebuild container on the host.
./deploy.sh
```

Set `SSH_HOST`, `REMOTE_DIR`, `APPDATA_DIR` in `.env`. `deploy.sh` extracts those three keys via `grep` rather than `source .env`, so values containing spaces (like `APPLIANCE_1_NAME=Samsung Dryer`) don't break it.

### Bare metal (first test / debugging)

```sh
python3 -m venv .venv
.venv/bin/pip install -r mqtt_demo/requirements.txt
.venv/bin/python -m mqtt_demo
```

### Expected first-run logs

```
14:08:42  INFO   mqtt_demo                SmartThings-Local Bridge starting (2 appliances)
14:08:42  INFO   mqtt_demo                  broker = <broker-ip>:1883 (user=<mqtt-user>)
14:08:42  INFO   mqtt_demo                  [1] dryer @ <dryer-ip>:49155? (DTLS, auto-discover) → topic samsung_dryer/*
14:08:42  INFO   mqtt_demo                  [2] oven  @ <oven-ip>:49154? (DTLS, auto-discover) → topic samsung_oven/*
14:08:42  INFO   mqtt_demo                MQTT connected → <broker-ip>:1883
14:08:43  INFO   dryer                    discovered DTLS port 49155
14:08:43  INFO   oven                     discovered DTLS port 49154
14:08:43  INFO   dryer                    DTLS connected — subscribing 11 paths
14:08:44  INFO   dryer.<dryer-serial>     identified — serial=…
14:08:44  INFO   dryer.<dryer-serial>     seeded → 25 links; sensors live
14:08:44  INFO   oven                     DTLS connected — subscribing 11 paths
14:08:46  INFO   oven.<oven-serial>       identified — serial=…
14:08:46  INFO   oven.<oven-serial>       seeded → 16 links; sensors live
```

In HA: **Settings → Devices & Services → MQTT** should show both devices populated.

---

## Per-appliance notes

### Dryer

| Capability | Works? | Notes |
|---|---|---|
| Read all state | ✅ | Machine state, job state, energy (W + kWh), course, dry level, completion time, remote control, child lock, alarms |
| Wrinkle Prevent toggle | ✅ | Persists |
| Start / Pause / Stop | ✅ | Via `/operational/state/vs/0`; needs Remote Control on |
| Change course | ✅ | Via `/st/dryercourse/vs/0`; needs Remote Control on. **Not exposed by the SmartThings cloud HA integration.** |
| Power on/off | ❌ | Accepted (2.04) but reverts within seconds; hardware-mirrored |
| Child Lock / Remote Control toggle | ❌ | Same; hardware-mirrored physical buttons |

The dryer's `/operational/state/vs/0` is on the bridge's hot poll tier (1s idle / 0.5s while a cycle is active) and also accepts OBSERVE registration. When the appliance has internet it pushes notifications within ~100ms of any state change and the cache absorbs them as fast freshness; when air-gapped the hot-tier poll carries the same UX with worst-case lag of one tier interval.

### Oven

| Capability | Works? | Notes |
|---|---|---|
| Read state | ✅ | Cavity state, current/target temp, door, mode, alarms, firmware-update-available |
| Lamp (light entity) | ✅ | Binary On/Off only; High/Low/Dim values are accepted (2.04) but silently coerced back. Works regardless of Remote Control. |
| Sound, Fast preheat | ⚠️ | Wired but untested RC-gated. |
| Setpoint slider | ⚠️ | Wired but untested RC-gated. |
| Mode select | ⚠️ | Wired but untested RC-gated. |
| Stop button | ✅ |  |
| **Kitchen timer (`⏲` icon)** | ❌ | **The oven's panel kitchen timer is not exposed via CoAP at all.** Confirmed by full `/device/0` dump: `UpperTimer*` fields in `/mode/vs/0` only populate when set via the API, not from the panel. |

**The oven doesn't push OBSERVE on `/mode/vs/0` writes** (the dryer does). The bridge handles this transparently because state freshness comes from polling rather than from OBSERVE:
1. **Optimistic publish** — the moment a POST returns 2.04, the bridge merges the write body into the cache and publishes to MQTT. HA reflects the new value instantly.
2. **Scheduler reconciliation** — the PollScheduler defers polling the just-written resource for ~4s (past Samsung's fetchback-revert window), then refreshes it on its tier cadence. If the device silently coerced the value, the corrected state is republished and HA reverts.
3. **Periodic `/device/0` sweep** — every 5 minutes the scheduler's sweep tier re-fetches the whole device tree, bounding worst-case drift on any resource the per-tier polls don't cover.

### Fridge (ARTIK051)

Contributed by [@aminorjourney](https://github.com/aminorjourney) in PR #1, verified against an `ARTIK051_REF_17K` fridge-freezer on firmware `DA-REF-ART-COMMON-1_20201124`. First public documentation of this firmware's local resource layout.

| Capability | Works? | Notes |
|---|---|---|
| Read temperatures | ✅ | Fridge + freezer current + setpoint via `/temperatures/vs/0` |
| Read doors | ✅ | Fridge, freezer, convertible zone via `/doors/vs/0` items array; plus an "any door open" binary sensor |
| Energy monitoring | ✅ | Instantaneous W + cumulative Wh via `/energy/consumption/vs/0` |
| Water filter | ✅ | Usage % + status via `/filter/waterfilter/vs/0` |
| Ice maker | ✅ | State + ice-making status via `/icemaker/one/vs/0` |
| Setpoint slider (fridge / freezer) | ✅ | Fridge 1–7°C, freezer -23 to -15°C |
| Power Cool, Power Freeze, Sabbath, Ice Maker switches | ✅ | |
| Active modes | ✅ | Read-only sensor of the fridge's mode list |

Notes specific to this firmware family:
- **Port 49155**, not the 49154 the oven defaults to.
- `/oic/res` only advertises 15 paths; the full resource tree lives at `/device/0` (32 links). The bridge's periodic `/device/0` sweep handles this transparently; no descriptor change needed.
- `/hass/state/vs/0` and `/hass/command/vs/0` return `4.04`. They're vestigial paths from an earlier firmware and are ignored.
- Doors are exposed as a Samsung-plural collection resource (`/doors/vs/0` with an `items[]` array keyed by `x.com.samsung.da.description`), not as per-room OCF resources like the newer RF9000B-class fridges use. This is one of the concrete divergences behind the "Firmware families" caveat in Part 1.

---

## Reference

### Config keys

| Key | Meaning |
|---|---|
| `APPLIANCE_COUNT` | Number of `APPLIANCE_<n>_*` blocks to read (1-indexed) |
| `APPLIANCE_<n>_CLASS` | Descriptor name: `dryer`, `oven`, `fridge` |
| `APPLIANCE_<n>_IP` | LAN IP of the appliance |
| `APPLIANCE_<n>_OCF_PORT` | Optional. Blank → auto-discover the DTLS port across the OCF band 49153–49156 (via a stateless ClientHello probe); set it to pin a specific port and skip discovery (dryer=49155, oven=49154, fridge=49155) |
| `APPLIANCE_<n>_TOPIC` | MQTT topic prefix (also the HA device identifier; changing it re-keys the device) |
| `APPLIANCE_<n>_NAME` | Friendly name on the HA device card |
| `MQTT_BROKER` / `MQTT_PORT` / `MQTT_USER` / `MQTT_PASS` | Broker config |
| `HA_DISCOVERY_PREFIX` | HA discovery topic root (default `homeassistant`) |
| `CERT_PATH` / `KEY_PATH` | Override cert lookup (auto-detects `/config/` then `./certs/`) |
| `HEALTH_INTERVAL_S` | Seconds between `<prefix>/bridge/health` publishes (default 60) |
| `PING_INTERVAL_S` | CoAP empty-CON ping cadence; three consecutive failures publish `availability=offline` (default 25). Tier polling cadences are descriptor-declared, not env-tunable. |
| `SSH_HOST` / `REMOTE_DIR` / `APPDATA_DIR` | Used by `deploy.sh` only |

### MQTT topics — outgoing (bridge → broker)

Per appliance, where `<prefix>` is its `APPLIANCE_<n>_TOPIC`.

| Topic | Retain | When |
|---|---|---|
| `<prefix>/availability` | ✓ | `online` after seed; `offline` on disconnect (LWT for appliance #1) |
| `<prefix>/remote_available` | ✓ | `online` iff bridge is up AND Remote Control on the appliance is on. Gates the control entities. |
| `<prefix>/state` | ✓ | JSON sensor dict; published only when sensors actually diff |
| `<prefix>/bridge/health` | ✓ | Every `HEALTH_INTERVAL_S`: connect_count, error_count, notif_count, poll_count, poll_error_count, ping_count, ping_fail_count, reachable, last_change_age_s, last_seed_age_s, session_age_s, stalest_href, stalest_age_s, serial |
| `<ha_prefix>/{sensor,binary_sensor,switch,light,number,select,button}/<prefix>/.../config` | ✓ | HA MQTT discovery, republished on every MQTT (re)connect |

### MQTT topics — incoming (bridge subscribes)

`<prefix>/cmd/#`. **The MQTT user must have READ permission on this subtree.** Without it the broker silently drops the TCP connection shortly after SUBSCRIBE. Check broker logs if writes never land.

Dryer:

| Suffix | Payloads | Effect |
|---|---|---|
| `cmd/wrinkle_prevent` | `On`, `Off` | POST `/washer/vs/0` |
| `cmd/operational_state` | `Run`, `Pause`, `Ready` | POST `/operational/state/vs/0`; requires RC |
| `cmd/dryer_mode` | Course name (e.g. `Cotton`) | Translated to `Course_HH` then POST `/st/dryercourse/vs/0`; requires RC |

Oven:

| Suffix | Payloads | Effect |
|---|---|---|
| `cmd/lamp` | `On`, `Off` | RMW of `/mode/vs/0 .options[UpperLamp_*]` |
| `cmd/sound` | `On`, `Off` | RMW of `/mode/vs/0 .options[Sound_*]` |
| `cmd/fastpreheat` | `On`, `Off` | RMW of `/mode/vs/0 .options[fastpreheat_*]` |
| `cmd/setpoint` | Integer °C (30–270, step 5) | RMW of `/temperatures/vs/0 .items[0].desired`; requires RC |
| `cmd/mode` | Mode name (e.g. `Convection`, `LargeGrill`) | POST `/mode/vs/0 {modes: [<name>]}`; requires RC |
| `cmd/stop` | (button press) | POST `/operational/state/vs/0 {state: Ready}` |

### Entity counts (approximate, per appliance)

| Type | Dryer | Oven |
|---|---|---|
| `sensor` | 17 | 17 |
| `binary_sensor` | 4 | 7 |
| `switch` | 1 (wrinkle) | 2 (sound, fastpreheat) |
| `light` | — | 1 (lamp) |
| `number` | — | 1 (setpoint slider) |
| `select` | 1 (course) | 1 (mode) |
| `button` | 3 (start/pause/stop) | 1 (stop) |

Gated control entities use HA's `availability_mode: all` against `<prefix>/availability` AND `<prefix>/remote_available`. Flip Remote Control on the appliance's front panel and those entities un-grey in HA.

### Repo layout

```
smartthings_local/                   The installable library — `pip install smartthings-local`
  __init__.py
  protocol/                          DTLS-CoAP transport (reusable by any consumer, not just MQTT)
    __init__.py
    coap.py                          CoAP wire protocol: message encode/decode, token handling
    dtls_session.py                  DTLS session: handshake, client-cert auth (file or in-memory PEM), Block2, liveness
    dtls_probe.py                    DTLS ClientHello liveness probe (stateless gate + diagnostic mode)
    ocf_root_ca.pem                  Samsung OCF root CA, bundled for handshake verification
  ocf/                               OCF resource + state layer (reusable)
    __init__.py
    state_cache.py                   StateCache — single source of truth for appliance state
    poll_scheduler.py                Tiered adaptive polling (hot/warm/cold + sweep)
    keepalive.py                     CoAP liveness checks (empty-CON pings)
    observe_refresh.py               OBSERVE registration management
mqtt_demo/                           MQTT bridge demo (consumes smartthings_local)
  __init__.py
  __main__.py                        Entry point — loads config, spawns one bridge per appliance
  config.py                          SharedConfig + ApplianceConfig dataclasses
  logger.py                          Tagged logger helpers
  bridge.py                          Bridge — one DTLS session per appliance, descriptor-driven
  descriptor.py                      ApplianceDescriptor dataclass + HA discovery helpers
  samples/
    __init__.py                      Sample DESCRIPTORS registry (frozen reference implementations)
    dryer.py                         Dryer descriptor (paths, flatten, discovery, commands)
    oven.py                          Oven descriptor
    fridge.py                        Fridge descriptor (ARTIK051 firmware family)
  Dockerfile                         Container build (python:3.11-slim + 3 deps)
  docker-compose.yml                 One service: smartthings-local
  deploy.sh                          tar + ssh + docker compose up --build
  requirements.txt                   Python dependencies for the bridge
  .env.example                       Template — copy to .env, fill in
setup_cert.py                        One-shot cert minting script (live-fetches AC14K_M + UUID)
pyproject.toml                       Packaging — PyPI dist `smartthings-local`, hatch-vcs versioning
tests/                               pytest suite (CoAP wire, state cache, import isolation, cert loading, DTLS probe, bridge port resolution, cert signing)
.github/workflows/publish.yml        Build + PyPI Trusted Publishing on `v*` tags
```

`certs/` is gitignored. Drop the privileged client cert + key there; the container mounts that directory read-only at `/config`. See [`localthings`](https://github.com/mbillow/localthings) for production HA integration.

---

## Adding appliance support

The three descriptors in `mqtt_demo/samples/` (dryer, oven, fridge) are
frozen reference implementations: enough to exercise both the newer
Tizen RT 3.x family and the older ARTIK051 family, proving the
`smartthings_local` library layers generalize across firmware generations.
They are not updated for new appliance models.

**To add support for a new appliance, submit it to
[localthings](https://github.com/mbillow/localthings)**, which owns
the capability registry and Home Assistant integration.

---

## Traps to avoid

These each looked like obvious improvements at some point. Each one broke something.

- **Don't add OBSERVE subscriptions on OCF-standard `/<x>/0` paths.** They register successfully but never push. Use the Samsung `/<x>/vs/0` siblings (which do).
- **Don't assume OBSERVE silence means the appliance is broken.** When the appliance can't reach Samsung's cloud, its OBSERVE notify dispatch goes quiet even though the local DTLS session, GETs, POSTs, and the cache continue to work normally (measured at `~14 req/s` dryer / `~8 req/s` oven with 200/200 GETs successful while firewalled). The polling tiers are the structural answer to this; treat OBSERVE strictly as an optional accelerator.
- **Don't touch `/oic/sec/*` (doxm, pstat, cred, acl).** The bridge doesn't, and you shouldn't from helper scripts either. Those resources have wedge/brick risk on Samsung's RT-OCF security stack. The bridge surfaces are strictly `/<x>/vs/0` and `/device/0`.
- **Don't run two clients against the same appliance simultaneously.** Samsung's RT-OCF DTLS allows one active session per peer; a second handshake will get the device to drop the new socket. If HA seems to flap, check whether you've got `python -m mqtt_demo` running locally AND the Docker container up.
- **Expect gaps in write coverage, but few are hard limits.** The local DTLS surface appears to expose every write Samsung's own app uses; the ceiling is per-surface reverse-engineering (finding the resource, field, and encoding), not an API boundary. A control that isn't wired yet usually just hasn't been mapped. Oven cavity remote-start is the marquee open example: it works today through Samsung's cloud, and locally the write is accepted (`2.04`) but the cavity never engages. That's a reverse-engineering problem we haven't cracked yet, not a dead end. The hard limits are the few surfaces Samsung gates in hardware/firmware (power, child lock, remote-control enable), which accept the write then snap back to the physical switch. That mirrors Samsung's own behaviour, not a shortfall of the local path: the SmartThings app can't flip those remotely either (Remote Control is a button you press on the appliance). The optimistic-publish-then-verify pattern absorbs the reverts transparently: HA briefly shows the new value, then the PollScheduler's next tier poll (deferred ~4s past Samsung's revert window) re-reads and republishes the actual state. (The bridge deliberately does **not** fetch-back right after a write; that GET is itself what triggers the revert.)

---

## Known DTLS flakiness

Samsung's RT-OCF DTLS stack occasionally closes sessions actively, usually right after a Block2 GET or in the seconds after a POST. The bridge handles this with exponential reconnect (1s → 30s) and a re-seed on each new session. From HA's perspective the entity briefly goes offline then comes back; from the bridge's perspective you'll see lines like:

```
oven.…  DTLS recv: Unexpected EOF
oven.…  reconnect in 1s
oven.…  DTLS connected — subscribing 11 paths
oven.…  seeded → 16 links; sensors live
```

If reconnects become persistent (e.g. >10 in a minute) something's wrong: check the appliance's Wi-Fi link first, then look for a competing DTLS client on the LAN.

---

## Contributing

If you submit a PR, please don't include real device UUIDs, MACs, serials, IPs, or bearer tokens. Use the placeholders from `.env.example`.

SmartThings-Local

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