release: prepare ArduinoHA v3.2.0

feat: merge Home Assistant MQTT compatibility release

.github/workflows/ci.yml

@@ -18,7 +18,18 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
+      - run: bash -n scripts/*.sh
       - run: ./scripts/check-docs.sh
+  native-core-tests:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.11'
+      - run: python -m pip install --upgrade platformio==6.1.19
+      - run: pio test -e native --filter test_native_core
+
   compile-tests:
     runs-on: ubuntu-latest
     strategy:
@@ -32,3 +43,4 @@ jobs:
           python-version: '3.11'
       - run: python -m pip install --upgrade platformio==6.1.19
       - run: ./scripts/test.sh compile --platform ${{ matrix.platform }}
+      - run: ./scripts/test.sh examples --platform ${{ matrix.platform }}

.github/workflows/ha-test-harness.yml

@@ -0,0 +1,43 @@
+name: Home Assistant MQTT test harness
+
+on:
+  workflow_dispatch:
+  schedule:
+    - cron: "17 3 * * 1"
+
+permissions:
+  contents: read
+
+jobs:
+  test_harness:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - home_assistant: "2024.11.3"
+            expect_disabled_cleanup: "0"
+          - home_assistant: stable
+            expect_disabled_cleanup: "0"
+          - home_assistant: dev
+            expect_disabled_cleanup: "1"
+    env:
+      HA_VERSION: ${{ matrix.home_assistant }}
+      TEST_HARNESS_EXPECT_DISABLED_CLEANUP: ${{ matrix.expect_disabled_cleanup }}
+      COMPOSE_FILE: tests/ha-test-harness/compose.yaml
+    steps:
+      - uses: actions/checkout@v4
+      - name: Start broker and Home Assistant
+        run: docker compose up -d mqtt homeassistant
+      - name: Check single-to-device migration
+        run: docker compose run --rm tests
+      - name: Restart Home Assistant from retained data
+        run: docker compose restart homeassistant
+      - name: Check retained discovery after restart
+        run: docker compose run --rm -e TEST_HARNESS_MODE=retained-restart tests
+      - name: Collect Home Assistant logs on failure
+        if: failure()
+        run: docker compose logs --no-color homeassistant mqtt
+      - name: Remove test harness volumes
+        if: always()
+        run: docker compose down -v

.github/workflows/release.yml

@@ -9,8 +9,37 @@ permissions:
   contents: write
 
 jobs:
+  test_harness:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - home_assistant: "2024.11.3"
+          - home_assistant: stable
+    env:
+      HA_VERSION: ${{ matrix.home_assistant }}
+      TEST_HARNESS_EXPECT_DISABLED_CLEANUP: "0"
+      COMPOSE_FILE: tests/ha-test-harness/compose.yaml
+    steps:
+      - uses: actions/checkout@v4
+      - name: Start broker and Home Assistant
+        run: docker compose up -d mqtt homeassistant
+      - name: Check single-to-device migration
+        run: docker compose run --rm tests
+      - name: Restart Home Assistant from retained data
+        run: docker compose restart homeassistant
+      - name: Check retained discovery after restart
+        run: docker compose run --rm -e TEST_HARNESS_MODE=retained-restart tests
+      - name: Collect Home Assistant logs on failure
+        if: failure()
+        run: docker compose logs --no-color homeassistant mqtt
+      - name: Remove test harness volumes
+        if: always()
+        run: docker compose down -v
   publish:
     runs-on: ubuntu-latest
+    needs: test_harness
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-python@v5
@@ -18,7 +47,10 @@ jobs:
           python-version: '3.11'
       - run: python -m pip install --upgrade platformio==6.1.19
       - run: ./scripts/test.sh compile --platform esp8266
+      - run: ./scripts/test.sh examples --platform esp8266
+      - run: pio test -e native --filter test_native_core
       - run: ./scripts/test.sh compile --platform esp32
+      - run: ./scripts/test.sh examples --platform esp32
       - run: ./scripts/check-docs.sh
       - run: ./scripts/prepare-release.sh "$GITHUB_REF_NAME"
       - run: ./scripts/release-notes.sh "$GITHUB_REF_NAME" > "$RUNNER_TEMP/release-notes.md"

.gitignore

@@ -1,6 +1,10 @@
 .DS_Store
 tmp/
 
+# Python test tooling
+__pycache__/
+*.py[cod]
+
 # PlatformIO build output
 .pio/
 

CHANGELOG.md

@@ -1,9 +1,39 @@
 # Changelog
 
+## 3.2.0
+
+**Discovery publication and resilience:**
+
+- Batch direct MQTT discovery writes into bounded 128-byte chunks, avoiding hundreds of tiny TCP writes while preserving streaming payload generation.
+- Treat allocation or streaming failure as a failed discovery publication, discard the unfinished payload, and reconnect before the next retained update.
+- Allocate device-discovery component serializers only for sizing and emission, reducing peak heap use; make serializer allocation failure safe.
+
+**Compatibility, tests, and documentation:**
+
+- Add the reusable, Docker-based HA/MQTT testkit and run ArduinoHA migration and retained-restart checks against Home Assistant 2024.11.3, stable, and dev.
+- Make the fixed baseline and current stable test-harness lanes release gates; keep the rolling dev lane scheduled/manual.
+- Add maintained, credential-free PlatformIO ESP8266/ESP32 example projects and compile them in CI.
+
+## 3.1.0
+
+**Home Assistant MQTT compatibility:**
+
+- Add an explicit, retry-safe single-component to device-discovery migration sequence: retained `migrate_discovery` markers, device config, then legacy-topic cleanup.
+- Match Home Assistant device-component removal semantics with a platform-only tombstone followed by a compacted payload; `republishDiscovery()` re-adds a removed component.
+- Stop serializing removed `obj_id`; keep `setObjectId()` source-compatible and use `setDefaultEntityId()` for new entities.
+
+**Reliability and maintenance:**
+
+- Reject invalid discovery topic tokens, escape dynamic JSON values, and fail discovery publication on partial writes or missing device IDs.
+- Register entities safely regardless of whether they are constructed before or after `HAMqtt`, diagnose entity-limit drops, and make explicit disconnect callbacks observable.
+- Make `HAText` own its current state and bounded command copy; align device-discovery origin version with the package version.
+- Add native AddressSanitizer/UndefinedBehaviorSanitizer core regression coverage and release-script version consistency checks.
+
 ## 3.0.2
 
 - Align the Arduino IDE `library.properties` version with `library.json` so both package formats identify the same release.
 
+
 ## 3.0.1
 
 - Build and test against the Arduino 3-compatible pioarduino ESP32 platform.
@@ -31,8 +61,8 @@
 **Migration notes:**
 * Unit tests now live under `test/` as PlatformIO Unity suites (`pio test`). The legacy `tests/` tree (AUnit, EpoxyDuino, Make, AUniter) has been removed.
 * Home Assistant deprecated MQTT `object_id` in favor of `default_entity_id`, and newer Home Assistant versions may warn on or remove `object_id` handling in discovery payloads.
-* Existing code using `setObjectId()` remains supported as a legacy fallback, but new projects should migrate to `setDefaultEntityId()`.
-* If you enable device discovery mode, avoid publishing per-entity discovery topics manually. Use `republishDiscovery()` when a runtime config change needs to refresh discovery state.
+* `setObjectId()` remains source-compatible but no longer serializes the removed `obj_id` discovery property; new projects should use `setDefaultEntityId()`.
+* Existing single-component devices must use the staged migration API before device discovery; use `republishDiscovery()` when a runtime config change needs to refresh discovery state.
 
 ## 2.1.0
 

README.md

@@ -3,15 +3,7 @@
 [![](https://img.shields.io/github/v/release/alexhopeoconnor/arduino-home-assistant?label=Version)](https://github.com/alexhopeoconnor/arduino-home-assistant/releases)
 [![](https://img.shields.io/badge/Documentation-40BC13)](docs/README.md)
 
-ArduinoHA is the maintained MQTT-discovery library behind compact Arduino, ESP8266, and ESP32 integrations with Home Assistant. It uses Arduino's standard network `Client` API and is continuously compile-tested on ESP8266 and ESP32.
-
-## Why use it
-
-- **Home Assistant discovery:** entities appear automatically from retained MQTT discovery payloads.
-- **Two-way entities:** report local state and receive Home Assistant commands with a small, explicit API.
-- **One physical device:** group multiple entities, metadata, shared availability, and MQTT Last Will under `HADevice`.
-- **Control the footprint:** compile out entity implementations a firmware does not use.
-- **Two discovery shapes:** start with one payload per entity or opt into a single device-discovery payload.
+ArduinoHA lets an Arduino, ESP8266, or ESP32 application publish MQTT discovery data that Home Assistant understands. Give it a connected Arduino `Client`, declare entities, and Home Assistant creates the controls and telemetry automatically.
 
 ## Start with a sensor
 
@@ -29,9 +21,7 @@ void setup() {
     WiFi.macAddress(mac);
     device.setUniqueId(mac, sizeof(mac));
 
-    WiFi.begin("SSID", "password");
-    while (WiFi.status() != WL_CONNECTED) delay(500);
-
+    // Your application connects Wi-Fi before MQTT begins.
     temperature.setName("Temperature");
     temperature.setUnitOfMeasurement("°C");
     mqtt.begin("mqtt.local", "mqtt_user", "mqtt_password");
@@ -43,36 +33,33 @@ void loop() {
 }
 ```
 
-Read [Getting started](docs/getting-started.md) before copying this into production: it explains object lifetime, MQTT lifecycle, ESP32 includes, and install routes.
+Build [ESP Sensor](examples/01-esp-sensor/) for a complete ESP8266/ESP32 project. It clearly marks the network and broker values you must provide without committing credentials.
+
+## What you can build
+
+- **Automatic Home Assistant discovery:** retained MQTT discovery messages create entities without hand-written Home Assistant YAML.
+- **Two-way controls:** sensors publish state while switches, lights, covers, and other writable entities receive explicit callbacks.
+- **One physical device:** `HADevice` groups metadata, multiple entities, shared availability, and MQTT Last Will.
+- **Device discovery:** publish one compact discovery document for a new multi-entity device, or keep traditional per-entity discovery.
+- **Small footprint:** exclude entity implementations your firmware does not use.
+
+## Choose an example
+
+| Example | Learn how to… |
+| --- | --- |
+| [ESP Sensor](examples/01-esp-sensor/) | connect an ESP application and publish changing numeric telemetry |
+| [Switch Callback](examples/02-switch-callback/) | reflect Home Assistant commands in a physical output and report state back |
+| [Multi-entity Device](examples/03-multi-entity-device/) | group controls and telemetry with shared availability and Last Will |
+| [Device Discovery](examples/04-device-discovery/) | publish one Home Assistant device-discovery document for a new device |
+| [Entity recipes](examples/README.md#entity-recipes) | find the existing focused Arduino sketches for each supported entity |
 
 ## Install
 
 ```ini
 lib_deps =
-    home-assistant-integration=https://github.com/alexhopeoconnor/arduino-home-assistant.git#v3.0.2
+    home-assistant-integration=https://github.com/alexhopeoconnor/arduino-home-assistant.git#v3.2.0
 ```
 
-PlatformIO clones the Git repository and checks out the ref after `#`; that ref is a release tag, not a GitHub Release asset. Arduino IDE is supported through the included [`library.properties`](library.properties); see [Getting started](docs/getting-started.md#install-the-library).
+PlatformIO clones the Git repository and checks out the ref after `#`; that ref is a release tag, not a GitHub Release asset. Arduino IDE is supported through the included [`library.properties`](library.properties).
 
-## Documentation
-
-The [documentation map](docs/README.md) is the starting point:
-
-- [Getting started](docs/getting-started.md): connection lifecycle and minimal sketches.
-- [Device and discovery](docs/device-and-discovery.md): device metadata, discovery modes, and runtime refresh.
-- [MQTT usage](docs/mqtt-usage.md): callbacks, availability, custom MQTT, logging, and footprint flags.
-- [Entity guide](docs/entities.md): supported entity types and the best matching example.
-- [Examples](examples/README.md): curated entry points and the full example index.
-
-## Development and releases
-
-```bash
-./scripts/test.sh compile --platform esp8266
-./scripts/test.sh compile --platform esp32
-./scripts/check-docs.sh
-./scripts/prepare-release.sh vMAJOR.MINOR.PATCH --tag
-```
-
-The release preflight validates both package manifests and the matching changelog section. A pushed tag repeats the board-free compile checks and creates a GitHub Release from that section; it does not publish to the PlatformIO Registry or deploy firmware.
-
-See the [changelog](CHANGELOG.md) and [licence](LICENSE).
+See [getting started](docs/getting-started.md), the [documentation map](docs/README.md), [examples](examples/README.md), [release history](CHANGELOG.md), and [licence](LICENSE).

docs/README.md

@@ -1,13 +1,12 @@
-# Documentation
-
-User-facing notes for this library. API details live in the headers under [`src/`](../src/).
+# ArduinoHA documentation
 
 | Topic | What it covers |
 | ----- | ---------------- |
-| [Getting started](getting-started.md) | Prerequisites, installing the library, minimal sketches |
-| [Device & discovery](device-and-discovery.md) | `HADevice`, MQTT connection, discovery prefixes, entity IDs |
-| [MQTT usage](mqtt-usage.md) | Callbacks, custom topics, availability, compiler flags |
-| [Entities](entities.md) | Supported Home Assistant entity classes and example selection |
-| [Examples](../examples/README.md) | Curated paths through the standalone sketches |
+| [Getting started](getting-started.md) | Connecting a `Client`, installing the library, and the first MQTT lifecycle |
+| [Device & discovery](device-and-discovery.md) | `HADevice`, discovery modes, metadata, identifiers, and migration |
+| [MQTT usage](mqtt-usage.md) | Callbacks, custom topics, availability, logging, and footprint flags |
+| [Entities](entities.md) | Supported Home Assistant entity classes and the best matching example |
+| [Examples](../examples/README.md) | Guided PlatformIO projects and focused entity recipes |
+| [Compatibility baseline](compatibility.md) | Supported Home Assistant capabilities and fork-specific compatibility notes |
 
 Class-level API details live in headers under [`src/`](../src/). Return to the [project overview](../README.md).

docs/compatibility.md

@@ -0,0 +1,40 @@
+# Compatibility baseline
+
+This maintenance line begins from fork commit `84cc0037b1c0` (release `v3.0.2`).
+It intentionally tracks Home Assistant's MQTT discovery test harness without merging
+upstream development wholesale.
+
+| Reference | Audited revision / target |
+| --- | --- |
+| Fork baseline | `84cc0037b1c0` (`v3.0.2`) |
+| Upstream main | `1d333ab229b2` (`v2.1.0`) |
+| Upstream develop | `a7039fad810b` (unreleased WIP 2.2.0) |
+| Device discovery minimum | Home Assistant `2024.11.0` |
+| Test harness matrix | `2024.11.3`, current `stable`, current `dev` |
+
+The only imported upstream code fix is the four missing-device-ID guards from
+upstream commit `9c9d074`. Device discovery migration, JSON validation,
+lifecycle handling, and tests are fork-native changes.
+
+## Deliberate exclusions
+
+- No merge or wholesale cherry-pick of upstream `develop` / WIP 2.2.0.
+- No `obj_id` serialization: Home Assistant removed that discovery field. Use
+  `setDefaultEntityId()` for new code.
+- No binary-sensor `state_class`: it is not valid in the current HA MQTT binary
+  sensor schema.
+- No upstream IMqttClient abstraction or unreviewed entity-type feature PRs.
+
+## Ongoing audit routine
+
+The `upstream` remote has no usable push URL. Fetch and compare explicitly:
+
+```bash
+git fetch --prune upstream
+git log --oneline main..upstream/develop
+git diff --stat main...upstream/develop
+```
+
+Port only independently reviewed changes with regression tests; treat open
+upstream pull requests as proposals, not release inputs. Run the native,
+board-compile, and HA test harness gates before publishing a new release.

docs/device-and-discovery.md

@@ -22,7 +22,13 @@ String setters take **pointers whose contents are not copied** — use literals
 
 When MQTT connects, the library publishes Home Assistant **MQTT discovery** payloads so entities appear automatically.
 
-**Rule:** construct entity objects **after** `HAMqtt` so they can register with it.
+Entities can be constructed either before or after `HAMqtt`. Entities which already
+exist when `HAMqtt` is constructed are registered then; entities constructed later
+register immediately. Both the device, MQTT object, and entities must have a lifetime
+that outlasts `mqtt.loop()`.
+
+`HAMqtt` has a configurable entity limit (24 by default). Check
+`getRegisteredDeviceTypeCount()`, `getDeviceTypeLimit()`, and `getDeviceTypeRegistrationFailures()` in firmware diagnostics: registrations above the limit are rejected and logged rather than silently disappearing from discovery.
 
 ### Topic prefixes
 
@@ -41,7 +47,51 @@ mqtt.setDataPrefix("myDataPrefix");
 ### Single-component vs device discovery
 
 - **Default:** one retained discovery topic per entity (single-component discovery).
-- **Optional:** call `HAMqtt::enableDeviceDiscovery()` to publish a single **device** discovery payload with components under `cmps` (see project README for migration notes).
+- **Device discovery:** `HAMqtt::enableDeviceDiscovery()` publishes one retained device payload with components under `cmps`.
+
+Both formats remain supported by Home Assistant. Device discovery requires Home Assistant **2024.11.0 or newer**. Use `enableDeviceDiscovery()` only for a new device which has never published this library's single-component discovery topics.
+
+### Migrating an existing device to device discovery
+
+Do not switch an existing device by calling `enableDeviceDiscovery()` alone. Home Assistant derives an entity's discovery identity from the topic, and a direct switch causes retained-topic conflicts. The migration deliberately publishes, in order:
+
+1. `{"migrate_discovery":true}` to every old retained component config topic;
+2. the retained `/device/<deviceId>/config` payload; and only then
+3. an empty retained payload to every old component config topic.
+
+Keep the device ID and each entity ID unchanged. They preserve the mapping from the old `<component>/<deviceId>/<entityId>/config` topic to `cmps[entityId]` in the new device payload.
+
+Start migration once during setup, then advance *one stage per loop iteration* after the MQTT connection is available. Each method is retry-safe: do not advance if it returns `false`.
+
+```cpp
+bool migrationStarted = false;
+
+void setup() {
+    // Create device, mqtt, and entities; keep their IDs unchanged.
+    migrationStarted = mqtt.beginDeviceDiscoveryMigration();
+    mqtt.begin("192.168.1.50", "user", "password");
+}
+
+void loop() {
+    mqtt.loop();
+
+    switch (mqtt.getDeviceDiscoveryMigrationState()) {
+    case HAMqtt::DeviceDiscoveryMigrationMarkersPending:
+        mqtt.publishDeviceDiscoveryMigrationMarkers();
+        break;
+    case HAMqtt::DeviceDiscoveryMigrationMarkersPublished:
+        mqtt.publishDeviceDiscoveryMigrationConfig();
+        break;
+    case HAMqtt::DeviceDiscoveryMigrationDevicePublished:
+        mqtt.completeDeviceDiscoveryMigration();
+        break;
+    default:
+        break;
+    }
+}
+```
+
+The migration stage is held in RAM. If the board reboots before completion, start the same migration again; the retained marker/config/cleanup publishes are idempotent. If you must abandon a started migration while connected, call `rollbackDeviceDiscoveryMigration()`. Once a device config has been published, it first writes `{"migrate_discovery":true}` to the device discovery topic, restores the legacy configs, then clears the device config and returns to single-component mode. A failed rollback remains pending and suppresses automatic device-bundle publication until retried successfully. Run all publishing stages from `loop()`, not inside an inbound MQTT callback.
 
 Device discovery can also publish richer origin/device metadata, for example:
 
@@ -56,6 +106,7 @@ mqtt.setOriginSupportUrl("https://example.com/device-help");
 ```
 
 For entity identifiers in Home Assistant, prefer **`setDefaultEntityId()`** over legacy **`setObjectId()`**.
+`setObjectId()` remains source-compatible but no longer serializes the removed MQTT `obj_id` property. `setDefaultEntityId()` influences Home Assistant's entity ID only when it first creates the entity; existing users can retain a customized entity ID in the entity registry.
 
 Common entity discovery metadata can be configured on most entity types via:
 
@@ -70,9 +121,15 @@ Common entity discovery metadata can be configured on most entity types via:
 After changing discovery-related settings at runtime:
 
 - `HABaseDeviceType::republishDiscovery()` to refresh discovery.
-- `HABaseDeviceType::removeFromDiscovery()` to clear retained discovery for one entity.
+- `HABaseDeviceType::removeFromDiscovery()` to remove one entity from discovery.
 
-If device discovery mode is enabled, the library clears stale per-entity configs when refreshing.
+In single-component mode, removal clears that entity's retained config topic. In device discovery mode, Home Assistant requires a platform-only component marker (`{"p":"sensor"}`, for example), followed by a compacted device bundle that omits the component. ArduinoHA performs both publishes. Call `republishDiscovery()` on that entity to add it back.
+
+## Identifier and lifetime checklist
+
+- Give `HADevice` a stable, non-empty unique ID and each entity a stable, topic-safe ID (`A-Z`, `a-z`, `0-9`, `_`, `-`).
+- Use `enableExtendedUniqueIds()` when multiple devices could otherwise reuse the same entity IDs.
+- Metadata setters store pointers; retain their backing strings. `HAText` copies the current state and command text it receives, so its state does not borrow a transient MQTT buffer.
 
 ## Trimming flash (optional)
 

docs/entities.md

@@ -26,7 +26,7 @@ The library does not currently implement alarm control panels, events, humidifie
 
 ## Common lifecycle
 
-Create `HADevice`, `HAMqtt`, then entities in that order; create them before `mqtt.begin(...)`. Call `mqtt.loop()` regularly. Read [Getting started](getting-started.md) for the connection flow and [device discovery](device-and-discovery.md) for discovery settings.
+Create long-lived `HADevice`, `HAMqtt`, and entity objects, then call `mqtt.begin(...)` once and `mqtt.loop()` regularly. Entities may be constructed before or after `HAMqtt`; both orders register safely. Read [Getting started](getting-started.md) for the connection flow and [device discovery](device-and-discovery.md) for discovery settings.
 
 For shared online/offline state, use `device.enableSharedAvailability()` and `device.enableLastWill()` before connecting. The [availability examples](../examples/availability/) show the simplest setup, while [advanced availability](../examples/advanced-availability/) covers custom payloads and Last Will behaviour.
 

docs/getting-started.md

@@ -11,7 +11,7 @@ ArduinoHA talks to Home Assistant over **MQTT** (TCP). You need an MQTT broker r
 
 ```ini
 lib_deps =
-    home-assistant-integration=https://github.com/alexhopeoconnor/arduino-home-assistant.git#v3.0.2
+    home-assistant-integration=https://github.com/alexhopeoconnor/arduino-home-assistant.git#v3.2.0
 ```
 
 **Arduino IDE:** this fork is not indexed by Library Manager. Download the
@@ -26,7 +26,7 @@ Arduino networking API.
 1. Create **`HADevice`** and **`HAMqtt`** once (global or inside a long-lived object).
 2. Call **`HAMqtt::begin(...)`** once, at the **end** of `setup()` — it only stores broker settings; the actual connection runs during **`HAMqtt::loop()`**.
 3. Call **`mqtt.loop()`** regularly in `loop()` (not necessarily every iteration).
-4. Construct **entity classes** (sensors, switches, …) **after** `HAMqtt`, and register them before `begin()` where the API requires it.
+4. Construct **entity classes** (sensors, switches, …) before or after `HAMqtt`; ArduinoHA registers both orders. Keep all objects alive for the whole MQTT lifetime and configure discovery before the first connection.
 
 ### Ethernet (example)
 
@@ -87,6 +87,10 @@ All are valid; pick one. Hostnames work instead of IP addresses.
 - `mqtt.begin("192.168.1.50", "user", "pass")` — credentials, port 1883  
 - `mqtt.begin("192.168.1.50", 8888, "user", "pass")` — credentials + custom port  
 
+`begin()` is intentionally a one-time configuration call. Reconnects are owned by `mqtt.loop()`, which uses the configured reconnect interval. Do not call `begin()` in a reconnect timer. `mqtt.disconnect()` now also produces the registered disconnected and state-change callbacks, making an explicit shutdown observable in the same way as a transport loss.
+
+Use Home Assistant **2024.11.0 or newer** when opting into device discovery. See [Device & discovery](device-and-discovery.md) for the required staged migration from an existing single-component device.
+
 ## Security note
 
 Credentials go over **plain TCP** unless you use a TLS-capable stack and broker setup. On a trusted LAN this is often acceptable; treat untrusted networks accordingly.

docs/mqtt-usage.md

@@ -114,6 +114,11 @@ myButton.setPayloadPress("PRESS");
 
 Defined in `ArduinoHADefines.h` or via build flags.
 
+- **`ARDUINOHA_DISABLE_STDFUNCTION`** — disables the default capturing-lambda and
+  `std::bind` overloads on entity command APIs. Use it on targets without a complete
+  `std::function` implementation or where code size/RAM matters (constrained AVR
+  builds are the usual case). ESP8266/ESP32 support the overloads. `HAMqtt`
+  lifecycle callbacks remain ordinary function pointers.
 - **`ARDUINOHA_DEBUG`** — enables ArduinoHA logging by default and sets the initial maximum verbosity to `Debug`. Without this flag, structured logs are compiled in but remain disabled until you call `arduinoHASetLogEnabled(true)`.
 
 Structured logging is available through:
@@ -135,9 +140,9 @@ public:
 };
 ```
 
-`arduinoHALog(...)` and `arduinoHALogf(...)` support subsystem-tagged messages such as `mqtt`, `discovery`, `availability`, `serializer`, `entity`, and `device`. `DeviceFramework` installs a structured sink so ArduinoHA messages follow the same main log stream as the rest of the firmware.
+`arduinoHALog(...)` and `arduinoHALogf(...)` support subsystem-tagged messages such as `mqtt`, `discovery`, `availability`, `serializer`, `entity`, and `device`. Install a sink when you want those messages to join your application’s normal serial or structured log stream.
 
-Optional transport context for diagnostics (registered automatically by **DeviceFramework**): **`arduinoHASetNetworkStatusFn`** (for example returning `WiFi.status()` so publish failure lines can include `wifi=`).
+Applications that use Wi-Fi can register **`arduinoHASetNetworkStatusFn`** with a callback returning `WiFi.status()`. Publish failure diagnostics can then include the current Wi-Fi status without coupling ArduinoHA to a particular network library.
 
 **Exclude unused device types** (saves flash from vtables), e.g.:
 

examples/01-esp-sensor/README.md

@@ -0,0 +1,9 @@
+# ESP Sensor
+
+This is the first complete ArduinoHA project for an ESP8266 D1 mini or ESP32 development board. It connects Wi-Fi, derives a stable device ID from the board MAC address, and publishes a changing **Uptime** sensor to Home Assistant.
+
+Before uploading, replace the `EXAMPLE_*` values in `include/ExampleNetwork.h`, or provide them as PlatformIO build flags. The header contains safe placeholders and must not contain real credentials when committed.
+
+After MQTT connects, Home Assistant discovers **ArduinoHA sensor example** and its Uptime entity. Rebooting the board keeps the same Home Assistant identity because its MAC address is stable.
+
+See [getting started](../../docs/getting-started.md) and the shared [examples guide](../README.md).

examples/01-esp-sensor/include/ExampleNetwork.h

@@ -0,0 +1,37 @@
+#pragma once
+#if defined(ESP32)
+#include <Network.h>
+#include <WiFi.h>
+#else
+#include <ESP8266WiFi.h>
+#endif
+
+#ifndef EXAMPLE_WIFI_SSID
+#define EXAMPLE_WIFI_SSID "replace-with-wifi-name"
+#endif
+#ifndef EXAMPLE_WIFI_PASSWORD
+#define EXAMPLE_WIFI_PASSWORD "replace-with-wifi-password"
+#endif
+#ifndef EXAMPLE_MQTT_HOST
+#define EXAMPLE_MQTT_HOST "replace-with-mqtt-host"
+#endif
+#ifndef EXAMPLE_MQTT_USER
+#define EXAMPLE_MQTT_USER ""
+#endif
+#ifndef EXAMPLE_MQTT_PASSWORD
+#define EXAMPLE_MQTT_PASSWORD ""
+#endif
+
+inline void connectExampleWiFi() {
+    WiFi.mode(WIFI_STA);
+    WiFi.begin(EXAMPLE_WIFI_SSID, EXAMPLE_WIFI_PASSWORD);
+    while (WiFi.status() != WL_CONNECTED) {
+        delay(250);
+    }
+}
+
+inline void setExampleUniqueId(HADevice& device) {
+    uint8_t mac[6];
+    WiFi.macAddress(mac);
+    device.setUniqueId(mac, sizeof(mac));
+}

examples/01-esp-sensor/platformio.ini

@@ -0,0 +1,24 @@
+[platformio]
+default_envs = esp8266
+
+[common]
+framework = arduino
+lib_ldf_mode = deep+
+lib_deps =
+    home-assistant-integration=symlink://../..
+
+[env:esp8266]
+extends = common
+platform = espressif8266
+board = d1_mini
+platform_packages =
+    platformio/framework-arduinoespressif8266 @ https://github.com/esp8266/Arduino.git#521ae60a89e64bb0d1eb7a0b7addf620ced5cad3
+
+[env:esp32]
+extends = common
+platform = https://github.com/pioarduino/platform-espressif32/releases/download/51.03.05/platform-espressif32.zip
+board = esp32dev
+build_unflags = -std=gnu++11
+build_flags =
+    -std=gnu++14
+    -I${platformio.packages_dir}/framework-arduinoespressif32/libraries/Network/src

examples/01-esp-sensor/src/main.cpp

@@ -0,0 +1,30 @@
+#include <Arduino.h>
+#include <ArduinoHA.h>
+#include "ExampleNetwork.h"
+
+WiFiClient client;
+HADevice device;
+HAMqtt mqtt(client, device);
+HASensorNumber uptime("uptime");
+
+void setup() {
+    Serial.begin(115200);
+    connectExampleWiFi();
+    setExampleUniqueId(device);
+
+    device.setName("ArduinoHA sensor example");
+    device.setSoftwareVersion("1.0.0");
+    uptime.setName("Uptime");
+    uptime.setUnitOfMeasurement("s");
+    mqtt.begin(EXAMPLE_MQTT_HOST, EXAMPLE_MQTT_USER, EXAMPLE_MQTT_PASSWORD);
+}
+
+void loop() {
+    mqtt.loop();
+
+    static unsigned long lastUpdate = 0;
+    if (millis() - lastUpdate >= 1000) {
+        uptime.setValue(static_cast<uint32_t>(millis() / 1000));
+        lastUpdate = millis();
+    }
+}

examples/02-switch-callback/README.md

@@ -0,0 +1,9 @@
+# Switch Callback
+
+This example creates one writable Home Assistant switch. When Home Assistant sends a command, `onOutputCommand()` changes the local output and immediately reports the resulting state back through the supplied `HASwitch`.
+
+The ESP8266 build uses `LED_BUILTIN`; the ESP32 build uses GPIO 2. Confirm your board’s LED polarity before treating that output as a real load.
+
+Set the Wi-Fi and MQTT placeholders in `include/ExampleNetwork.h`, flash the board, then toggle **Example output** in Home Assistant.
+
+See [MQTT usage](../../docs/mqtt-usage.md) and the shared [examples guide](../README.md).

examples/02-switch-callback/include/ExampleNetwork.h

@@ -0,0 +1,37 @@
+#pragma once
+#if defined(ESP32)
+#include <Network.h>
+#include <WiFi.h>
+#else
+#include <ESP8266WiFi.h>
+#endif
+
+#ifndef EXAMPLE_WIFI_SSID
+#define EXAMPLE_WIFI_SSID "replace-with-wifi-name"
+#endif
+#ifndef EXAMPLE_WIFI_PASSWORD
+#define EXAMPLE_WIFI_PASSWORD "replace-with-wifi-password"
+#endif
+#ifndef EXAMPLE_MQTT_HOST
+#define EXAMPLE_MQTT_HOST "replace-with-mqtt-host"
+#endif
+#ifndef EXAMPLE_MQTT_USER
+#define EXAMPLE_MQTT_USER ""
+#endif
+#ifndef EXAMPLE_MQTT_PASSWORD
+#define EXAMPLE_MQTT_PASSWORD ""
+#endif
+
+inline void connectExampleWiFi() {
+    WiFi.mode(WIFI_STA);
+    WiFi.begin(EXAMPLE_WIFI_SSID, EXAMPLE_WIFI_PASSWORD);
+    while (WiFi.status() != WL_CONNECTED) {
+        delay(250);
+    }
+}
+
+inline void setExampleUniqueId(HADevice& device) {
+    uint8_t mac[6];
+    WiFi.macAddress(mac);
+    device.setUniqueId(mac, sizeof(mac));
+}

examples/02-switch-callback/platformio.ini

@@ -0,0 +1,24 @@
+[platformio]
+default_envs = esp8266
+
+[common]
+framework = arduino
+lib_ldf_mode = deep+
+lib_deps =
+    home-assistant-integration=symlink://../..
+
+[env:esp8266]
+extends = common
+platform = espressif8266
+board = d1_mini
+platform_packages =
+    platformio/framework-arduinoespressif8266 @ https://github.com/esp8266/Arduino.git#521ae60a89e64bb0d1eb7a0b7addf620ced5cad3
+
+[env:esp32]
+extends = common
+platform = https://github.com/pioarduino/platform-espressif32/releases/download/51.03.05/platform-espressif32.zip
+board = esp32dev
+build_unflags = -std=gnu++11
+build_flags =
+    -std=gnu++14
+    -I${platformio.packages_dir}/framework-arduinoespressif32/libraries/Network/src

examples/02-switch-callback/src/main.cpp

@@ -0,0 +1,36 @@
+#include <Arduino.h>
+#include <ArduinoHA.h>
+#include "ExampleNetwork.h"
+
+#if defined(ESP32)
+constexpr uint8_t kOutputPin = 2;
+#else
+constexpr uint8_t kOutputPin = LED_BUILTIN;
+#endif
+
+WiFiClient client;
+HADevice device;
+HAMqtt mqtt(client, device);
+HASwitch output("output");
+
+void onOutputCommand(bool state, HASwitch* sender) {
+    digitalWrite(kOutputPin, state ? HIGH : LOW);
+    sender->setState(state);
+}
+
+void setup() {
+    Serial.begin(115200);
+    pinMode(kOutputPin, OUTPUT);
+    digitalWrite(kOutputPin, LOW);
+    connectExampleWiFi();
+    setExampleUniqueId(device);
+
+    device.setName("ArduinoHA switch example");
+    output.setName("Example output");
+    output.onCommand(onOutputCommand);
+    mqtt.begin(EXAMPLE_MQTT_HOST, EXAMPLE_MQTT_USER, EXAMPLE_MQTT_PASSWORD);
+}
+
+void loop() {
+    mqtt.loop();
+}

examples/03-multi-entity-device/README.md

@@ -0,0 +1,9 @@
+# Multi-entity Device
+
+This example groups an Uptime sensor and writable output under one `HADevice`. It adds common metadata, one shared availability topic, and MQTT Last Will so Home Assistant marks the complete device unavailable if its network connection disappears.
+
+Configure `include/ExampleNetwork.h`, flash the selected target, and inspect the device page in Home Assistant. Both entities belong to **ArduinoHA multi-entity example** and share its availability state.
+
+Use this shape when one physical board exposes several related controls or sensors.
+
+See [device and discovery](../../docs/device-and-discovery.md) and [MQTT usage](../../docs/mqtt-usage.md).

examples/03-multi-entity-device/include/ExampleNetwork.h

@@ -0,0 +1,37 @@
+#pragma once
+#if defined(ESP32)
+#include <Network.h>
+#include <WiFi.h>
+#else
+#include <ESP8266WiFi.h>
+#endif
+
+#ifndef EXAMPLE_WIFI_SSID
+#define EXAMPLE_WIFI_SSID "replace-with-wifi-name"
+#endif
+#ifndef EXAMPLE_WIFI_PASSWORD
+#define EXAMPLE_WIFI_PASSWORD "replace-with-wifi-password"
+#endif
+#ifndef EXAMPLE_MQTT_HOST
+#define EXAMPLE_MQTT_HOST "replace-with-mqtt-host"
+#endif
+#ifndef EXAMPLE_MQTT_USER
+#define EXAMPLE_MQTT_USER ""
+#endif
+#ifndef EXAMPLE_MQTT_PASSWORD
+#define EXAMPLE_MQTT_PASSWORD ""
+#endif
+
+inline void connectExampleWiFi() {
+    WiFi.mode(WIFI_STA);
+    WiFi.begin(EXAMPLE_WIFI_SSID, EXAMPLE_WIFI_PASSWORD);
+    while (WiFi.status() != WL_CONNECTED) {
+        delay(250);
+    }
+}
+
+inline void setExampleUniqueId(HADevice& device) {
+    uint8_t mac[6];
+    WiFi.macAddress(mac);
+    device.setUniqueId(mac, sizeof(mac));
+}

examples/03-multi-entity-device/platformio.ini

@@ -0,0 +1,24 @@
+[platformio]
+default_envs = esp8266
+
+[common]
+framework = arduino
+lib_ldf_mode = deep+
+lib_deps =
+    home-assistant-integration=symlink://../..
+
+[env:esp8266]
+extends = common
+platform = espressif8266
+board = d1_mini
+platform_packages =
+    platformio/framework-arduinoespressif8266 @ https://github.com/esp8266/Arduino.git#521ae60a89e64bb0d1eb7a0b7addf620ced5cad3
+
+[env:esp32]
+extends = common
+platform = https://github.com/pioarduino/platform-espressif32/releases/download/51.03.05/platform-espressif32.zip
+board = esp32dev
+build_unflags = -std=gnu++11
+build_flags =
+    -std=gnu++14
+    -I${platformio.packages_dir}/framework-arduinoespressif32/libraries/Network/src

examples/03-multi-entity-device/src/main.cpp

@@ -0,0 +1,48 @@
+#include <Arduino.h>
+#include <ArduinoHA.h>
+#include "ExampleNetwork.h"
+
+#if defined(ESP32)
+constexpr uint8_t kOutputPin = 2;
+#else
+constexpr uint8_t kOutputPin = LED_BUILTIN;
+#endif
+
+WiFiClient client;
+HADevice device;
+HAMqtt mqtt(client, device);
+HASensorNumber uptime("uptime");
+HASwitch output("output");
+
+void onOutputCommand(bool state, HASwitch* sender) {
+    digitalWrite(kOutputPin, state ? HIGH : LOW);
+    sender->setState(state);
+}
+
+void setup() {
+    Serial.begin(115200);
+    pinMode(kOutputPin, OUTPUT);
+    connectExampleWiFi();
+    setExampleUniqueId(device);
+
+    device.setName("ArduinoHA multi-entity example");
+    device.setManufacturer("Example Devices");
+    device.setSoftwareVersion("1.0.0");
+    device.enableSharedAvailability();
+    device.enableLastWill();
+
+    uptime.setName("Uptime");
+    uptime.setUnitOfMeasurement("s");
+    output.setName("Example output");
+    output.onCommand(onOutputCommand);
+    mqtt.begin(EXAMPLE_MQTT_HOST, EXAMPLE_MQTT_USER, EXAMPLE_MQTT_PASSWORD);
+}
+
+void loop() {
+    mqtt.loop();
+    static unsigned long lastUpdate = 0;
+    if (millis() - lastUpdate >= 1000) {
+        uptime.setValue(static_cast<uint32_t>(millis() / 1000));
+        lastUpdate = millis();
+    }
+}

examples/04-device-discovery/README.md

@@ -0,0 +1,9 @@
+# Device Discovery
+
+This example opts into Home Assistant MQTT device discovery. Instead of one retained discovery document per entity, ArduinoHA publishes one device document containing the component definitions and richer board metadata.
+
+Use device discovery for a **new** device on Home Assistant 2024.11.0 or newer. Do not enable it on a device that has already published traditional single-component discovery without following the documented migration procedure.
+
+After configuring `include/ExampleNetwork.h` and flashing the board, Home Assistant discovers **ArduinoHA device discovery example** and its Uptime sensor.
+
+See [device discovery](../../docs/device-and-discovery.md#single-component-vs-device-discovery) and the shared [examples guide](../README.md).

examples/04-device-discovery/include/ExampleNetwork.h

@@ -0,0 +1,37 @@
+#pragma once
+#if defined(ESP32)
+#include <Network.h>
+#include <WiFi.h>
+#else
+#include <ESP8266WiFi.h>
+#endif
+
+#ifndef EXAMPLE_WIFI_SSID
+#define EXAMPLE_WIFI_SSID "replace-with-wifi-name"
+#endif
+#ifndef EXAMPLE_WIFI_PASSWORD
+#define EXAMPLE_WIFI_PASSWORD "replace-with-wifi-password"
+#endif
+#ifndef EXAMPLE_MQTT_HOST
+#define EXAMPLE_MQTT_HOST "replace-with-mqtt-host"
+#endif
+#ifndef EXAMPLE_MQTT_USER
+#define EXAMPLE_MQTT_USER ""
+#endif
+#ifndef EXAMPLE_MQTT_PASSWORD
+#define EXAMPLE_MQTT_PASSWORD ""
+#endif
+
+inline void connectExampleWiFi() {
+    WiFi.mode(WIFI_STA);
+    WiFi.begin(EXAMPLE_WIFI_SSID, EXAMPLE_WIFI_PASSWORD);
+    while (WiFi.status() != WL_CONNECTED) {
+        delay(250);
+    }
+}
+
+inline void setExampleUniqueId(HADevice& device) {
+    uint8_t mac[6];
+    WiFi.macAddress(mac);
+    device.setUniqueId(mac, sizeof(mac));
+}

examples/04-device-discovery/platformio.ini

@@ -0,0 +1,24 @@
+[platformio]
+default_envs = esp8266
+
+[common]
+framework = arduino
+lib_ldf_mode = deep+
+lib_deps =
+    home-assistant-integration=symlink://../..
+
+[env:esp8266]
+extends = common
+platform = espressif8266
+board = d1_mini
+platform_packages =
+    platformio/framework-arduinoespressif8266 @ https://github.com/esp8266/Arduino.git#521ae60a89e64bb0d1eb7a0b7addf620ced5cad3
+
+[env:esp32]
+extends = common
+platform = https://github.com/pioarduino/platform-espressif32/releases/download/51.03.05/platform-espressif32.zip
+board = esp32dev
+build_unflags = -std=gnu++11
+build_flags =
+    -std=gnu++14
+    -I${platformio.packages_dir}/framework-arduinoespressif32/libraries/Network/src

examples/04-device-discovery/src/main.cpp

@@ -0,0 +1,33 @@
+#include <Arduino.h>
+#include <ArduinoHA.h>
+#include "ExampleNetwork.h"
+
+WiFiClient client;
+HADevice device;
+HAMqtt mqtt(client, device);
+HASensorNumber uptime("uptime");
+
+void setup() {
+    Serial.begin(115200);
+    connectExampleWiFi();
+    setExampleUniqueId(device);
+
+    device.setName("ArduinoHA device discovery example");
+    device.setManufacturer("Example Devices");
+    device.setModel("ESP example");
+    device.setSoftwareVersion("1.0.0");
+    uptime.setName("Uptime");
+    uptime.setUnitOfMeasurement("s");
+
+    mqtt.enableDeviceDiscovery();
+    mqtt.begin(EXAMPLE_MQTT_HOST, EXAMPLE_MQTT_USER, EXAMPLE_MQTT_PASSWORD);
+}
+
+void loop() {
+    mqtt.loop();
+    static unsigned long lastUpdate = 0;
+    if (millis() - lastUpdate >= 1000) {
+        uptime.setValue(static_cast<uint32_t>(millis() / 1000));
+        lastUpdate = millis();
+    }
+}

examples/README.md

@@ -1,19 +1,24 @@
 # ArduinoHA examples
 
-Each directory is an Arduino sketch. Start with the network example matching your board, then pick an entity example from the table. Copy credentials into your local development configuration; do not commit them in a sketch.
+Start with a guided PlatformIO project when you are new to the library. Each one builds for ESP8266 and ESP32, contains safe placeholder credentials, and explains the Home Assistant result you should see.
 
-| Starting point | Use it for |
+```bash
+pio run -d examples/01-esp-sensor -e esp8266
+pio run -d examples/01-esp-sensor -e esp8266 -t upload
+```
+
+| Guided example | What it demonstrates |
 | --- | --- |
-| [nodemcu](nodemcu/nodemcu.ino) | Basic ESP8266 Wi-Fi and MQTT connection |
-| [nano33iot](nano33iot/nano33iot.ino) | Basic Arduino Nano 33 IoT connection |
-| [mqtt-with-credentials](mqtt-with-credentials/mqtt-with-credentials.ino) | MQTT authentication |
-| [mqtt-advanced](mqtt-advanced/mqtt-advanced.ino) | Custom MQTT subscriptions and publishing |
-| [availability](availability/availability.ino) | Per-entity availability |
-| [advanced-availability](advanced-availability/advanced-availability.ino) | Shared availability and MQTT Last Will |
+| [ESP Sensor](01-esp-sensor/) | Wi-Fi application wiring, a unique device ID, and changing numeric telemetry |
+| [Switch Callback](02-switch-callback/) | A Home Assistant command callback and local state acknowledgement |
+| [Multi-entity Device](03-multi-entity-device/) | Multiple entities, shared availability, and MQTT Last Will |
+| [Device Discovery](04-device-discovery/) | One device-discovery document for a newly deployed device |
 
-## Entity examples
+## Entity recipes
 
-| Example | Home Assistant behaviour |
+The original focused sketches remain useful as short API recipes. They are intentionally transport-specific Arduino sketches, rather than full product firmware.
+
+| Recipe | Home Assistant behaviour |
 | --- | --- |
 | [binary-sensor](binary-sensor/binary-sensor.ino) | Door/contact-style binary state |
 | [button](button/button.ino) | Press action |
@@ -34,6 +39,4 @@ Each directory is an Arduino sketch. Start with the network example matching you
 | [sensor-integer](sensor-integer/sensor-integer.ino) | Integer uptime measurement |
 | [tag-scanner](tag-scanner/tag-scanner.ino) | RFID tag reporting |
 
-The examples are intentionally small, not production firmware frameworks. For reusable Wi-Fi configuration, MQTT wiring, profiles, OTA, and migrations, use [DeviceFramework](https://github.com/alexhopeoconnor/DeviceFramework) in a consuming firmware.
-
 See the [entity guide](../docs/entities.md) and [project overview](../README.md).

library.json

@@ -1,6 +1,6 @@
 {
   "name": "home-assistant-integration",
-  "version": "3.0.2",
+  "version": "3.2.0",
   "description": "Maintained Home Assistant MQTT discovery and entity integration for Arduino and ESP devices.",
   "keywords": [
     "mqtt",
@@ -23,7 +23,7 @@
       "maintainer": true
     }
   ],
-  "license": "MIT",
+  "license": "AGPL-3.0",
   "homepage": "https://github.com/alexhopeoconnor/arduino-home-assistant",
   "repository": {
     "type": "git",

library.properties

@@ -1,5 +1,5 @@
 name=home-assistant-integration
-version=3.0.2
+version=3.2.0
 author=Dawid Chyrzynski <dev@chyrzynski.pl>, Alex Hope-O'Connor <alex.hope.oconnor@pomonaqld.au>
 maintainer=Alex Hope-O'Connor <alex.hope.oconnor@pomonaqld.au>
 sentence=Home Assistant MQTT integration for Arduino

platformio.ini

@@ -27,12 +27,43 @@ lib_deps = knolleary/PubSubClient@2.8.0
 
 [env:esp8266]
 extends = common
+test_ignore = test_native_core
 platform = espressif8266
 board = d1_mini
 
 [env:esp32]
 extends = common
+test_ignore = test_native_core
 platform = https://github.com/pioarduino/platform-espressif32/releases/download/51.03.05/platform-espressif32.zip
 board = esp32dev
 build_unflags = -std=gnu++11
 build_flags = ${common.build_flags} -std=gnu++14
+
+; Host-only regression checks for serialization, topic validation, and the
+; PubSubClient mock path. The Arduino compatibility files live exclusively
+; under test/native and are never included in firmware environments.
+[env:native]
+platform = native
+test_framework = unity
+test_build_src = yes
+lib_deps = throwtheswitch/Unity@^2.6.1
+build_flags =
+    -DARDUINOHA_TEST
+    -Itest/native/include
+    -fsanitize=address,undefined
+    -fno-omit-frame-pointer
+build_src_filter =
+    -<*>
+    +<ArduinoHALog.cpp>
+    +<HADevice.cpp>
+    +<HAMqtt.cpp>
+    +<device-types/HABaseDeviceType.cpp>
+    +<device-types/HAText.cpp>
+    +<mocks/PubSubClientMock.cpp>
+    +<utils/HAAvailabilityConfig.cpp>
+    +<utils/HADictionary.cpp>
+    +<utils/HAJson.cpp>
+    +<utils/HANumeric.cpp>
+    +<utils/HASerializer.cpp>
+    +<utils/HASerializerArray.cpp>
+    +<utils/HAUtils.cpp>

scripts/bump-version.sh

@@ -0,0 +1,54 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+usage() {
+    echo "Usage: $0 vMAJOR.MINOR.PATCH" >&2
+    exit 2
+}
+
+tag="${1:-}"
+[[ "$tag" =~ ^v[0-9]+\.[0-9]+\.[0-9]+$ ]] || usage
+
+root="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
+version="${tag#v}"
+repo_url="https://github.com/alexhopeoconnor/arduino-home-assistant.git"
+reference_files=(README.md docs/getting-started.md)
+defines_file="$root/src/ArduinoHADefines.h"
+
+current_version="$(sed -n 's/.*"version": "\([^"]*\)".*/\1/p' "$root/library.json" | head -n 1)"
+[[ "$current_version" != "$version" ]] || {
+    echo "library.json already declares $version; choose a new version." >&2
+    exit 1
+}
+version_macro_count="$(grep -Ec '^#define ARDUINOHA_LIBRARY_VERSION "[0-9]+\.[0-9]+\.[0-9]+"$' "$defines_file" || true)"
+[[ "$version_macro_count" -eq 1 ]] || {
+    echo "src/ArduinoHADefines.h must contain exactly one ARDUINOHA_LIBRARY_VERSION macro." >&2
+    exit 1
+}
+grep -q "^## $version$" "$root/CHANGELOG.md" && {
+    echo "CHANGELOG.md already has a $version section; choose a new version." >&2
+    exit 1
+}
+
+sed -i -E '0,/"version": "[0-9]+\.[0-9]+\.[0-9]+"/s//"version": "'"$version"'"/' "$root/library.json"
+sed -i -E "s/^version=[0-9]+\.[0-9]+\.[0-9]+$/version=$version/" "$root/library.properties"
+sed -i -E "s/^#define ARDUINOHA_LIBRARY_VERSION \"[0-9]+\.[0-9]+\.[0-9]+\"$/#define ARDUINOHA_LIBRARY_VERSION \"$version\"/" "$defines_file"
+for file in "${reference_files[@]}"; do
+    sed -i -E "s|${repo_url}#v[0-9]+\.[0-9]+\.[0-9]+|${repo_url}#v${version}|g" "$root/$file"
+done
+
+temp_file="$(mktemp)"
+trap 'rm -f "$temp_file"' EXIT
+{
+    IFS= read -r changelog_heading < "$root/CHANGELOG.md"
+    [[ "$changelog_heading" == "# Changelog" ]] || {
+        echo "CHANGELOG.md must begin with # Changelog" >&2
+        exit 1
+    }
+    printf '%s\n\n## %s\n\n- TODO: Describe this release.\n' "$changelog_heading" "$version"
+    tail -n +2 "$root/CHANGELOG.md"
+} > "$temp_file"
+mv "$temp_file" "$root/CHANGELOG.md"
+
+echo "Updated ArduinoHA declarations and canonical install references to $tag."
+echo "Replace the generated changelog TODO with the release summary, then run scripts/check-docs.sh and scripts/prepare-release.sh $tag."

scripts/check-docs.sh

@@ -24,4 +24,14 @@ while IFS= read -r -d '' markdown; do
     done < <(sed -nE 's/.*\]\(([^ )]+)( "[^"]*")?\).*/\1/p' "$markdown")
 done < <(find "$root" -path "$root/.git" -prune -o -name '*.md' -type f -print0)
 
+while IFS= read -r example; do
+    for required in README.md platformio.ini; do
+        [[ -f "$example/$required" ]] || { echo "Incomplete guided example: ${example#$root/} is missing $required" >&2; exit 1; }
+    done
+    find "$example" -maxdepth 2 -type f \( -name '*.ino' -o -name '*.cpp' \) -print -quit | grep -q . || {
+        echo "Incomplete guided example: ${example#$root/} has no sketch source" >&2
+        exit 1
+    }
+done < <(find "$root/examples" -mindepth 1 -maxdepth 1 -type d -name '[0-9][0-9]-*' -print | sort)
+
 echo "Documentation links and required files passed"

scripts/prepare-release.sh

@@ -18,6 +18,18 @@ if [[ "$manifest_version" != "$version" ]]; then
     echo "library.json is $manifest_version; expected $version for $tag" >&2
     exit 1
 fi
+defines_file="$root/src/ArduinoHADefines.h"
+version_macro_count="$(grep -Ec '^#define ARDUINOHA_LIBRARY_VERSION "[0-9]+\.[0-9]+\.[0-9]+"$' "$defines_file" || true)"
+if [[ "$version_macro_count" -ne 1 ]]; then
+    echo "src/ArduinoHADefines.h must contain exactly one ARDUINOHA_LIBRARY_VERSION macro." >&2
+    exit 1
+fi
+
+defines_version="$(sed -n 's/^#define ARDUINOHA_LIBRARY_VERSION "\([^"]*\)"$/\1/p' "$defines_file")"
+if [[ "$defines_version" != "$version" ]]; then
+    echo "src/ArduinoHADefines.h is $defines_version; expected $version for $tag" >&2
+    exit 1
+fi
 
 if [[ -f "$root/library.properties" ]]; then
     properties_version="$(sed -n 's/^version=//p' "$root/library.properties" | head -n 1)"
@@ -32,12 +44,31 @@ if ! grep -q "^## ${version}$" "$root/CHANGELOG.md"; then
     exit 1
 fi
 
+if awk -v heading="## $version" '
+    $0 == heading { found = 1; next }
+    found && /^## / { exit }
+    found { print }
+' "$root/CHANGELOG.md" | grep -Fq 'TODO: Describe this release.'; then
+    echo "CHANGELOG.md still has the generated TODO for $version" >&2
+    exit 1
+fi
+repo_url="https://github.com/alexhopeoconnor/arduino-home-assistant.git"
+validate_reference() {
+    local file="$1"
+    local reference_count
+    reference_count="$(grep -F "$repo_url#v" "$root/$file" | wc -l)"
+    [[ "$reference_count" -eq 1 ]] || { echo "$file must contain exactly one canonical release reference" >&2; exit 1; }
+    grep -Fq "$repo_url#$tag" "$root/$file" || { echo "$file does not reference $tag" >&2; exit 1; }
+}
+validate_reference README.md
+validate_reference docs/getting-started.md
+
 git -C "$root" diff --check
 
 package_dir="$(mktemp -d)"
 trap 'rm -rf "$package_dir"' EXIT
 pio pkg pack "$root" --output "$package_dir/package.tar.gz" >/dev/null
-echo "Validated PlatformIO package for $tag"
+echo "Validated release metadata and PlatformIO package for $tag"
 
 if [[ "${2:-}" == "--tag" ]]; then
     git -C "$root" diff --quiet

scripts/test.sh

@@ -2,17 +2,31 @@
 set -euo pipefail
 
 usage() {
-    echo "Usage: $0 compile --platform esp8266|esp32" >&2
+    echo "Usage: $0 compile|examples --platform esp8266|esp32" >&2
     exit 2
 }
 
-[[ "${1:-}" == "compile" && "${2:-}" == "--platform" && $# -eq 3 ]] || usage
-
+[[ $# -eq 3 && ( "${1:-}" == "compile" || "${1:-}" == "examples" ) && "${2:-}" == "--platform" ]] || usage
 case "${3:-}" in
     esp8266|esp32) environment="${3}" ;;
     *) usage ;;
 esac
 
 root="$(cd "$(dirname "${BASH_SOURCE[0]}")/.." && pwd)"
-pio test -d "$root" -e "$environment" --without-uploading --without-testing
-echo "ArduinoHA compile check passed for ${3}"
+case "$1" in
+    compile)
+        pio test -d "$root" -e "$environment" --without-uploading --without-testing
+        echo "ArduinoHA compile check passed for $environment"
+        ;;
+    examples)
+        mapfile -t examples < <(find "$root/examples" -mindepth 1 -maxdepth 1 -type d -name '[0-9][0-9]-*' -print | sort)
+        if (( ${#examples[@]} == 0 )); then
+            echo "No example projects found" >&2
+            exit 1
+        fi
+        for example in "${examples[@]}"; do
+            pio run -d "$example" -e "$environment" </dev/null
+        done
+        echo "ArduinoHA examples compile check passed for $environment"
+        ;;
+esac

src/ArduinoHADefines.h

@@ -32,7 +32,7 @@
 #endif
 
 // Current library version used in discovery origin metadata.
-#define ARDUINOHA_LIBRARY_VERSION "2.1.0"
+#define ARDUINOHA_LIBRARY_VERSION "3.2.0"
 
 #if defined(ARDUINOHA_DEBUG)
     #include <Arduino.h>

src/HADevice.cpp

@@ -3,45 +3,136 @@
 #include "HAMqtt.h"
 #include "utils/HAUtils.h"
 #include "utils/HADictionary.h"
+#include "utils/HAJson.h"
 #include "utils/HASerializer.h"
 #include <string.h>
 
 static bool appendEscapedJsonString(char*& cursor, char* end, const char* value)
 {
-    if (!cursor || !value || cursor >= end) {
-        return false;
-    }
-
-    if (cursor + 1 >= end) {
-        return false;
-    }
-
-    *cursor++ = '"';
-    for (const char* p = value; *p != '\0'; p++) {
-        if ((*p == '"' || *p == '\\') && cursor + 2 >= end) {
-            return false;
-        }
-
-        if (*p == '"' || *p == '\\') {
-            *cursor++ = '\\';
-        }
-
-        if (cursor + 1 >= end) {
-            return false;
-        }
-
-        *cursor++ = *p;
-    }
-
-    if (cursor + 1 >= end) {
-        return false;
-    }
-
-    *cursor++ = '"';
-    *cursor = 0;
-    return true;
+    return HAJson::appendEscapedString(cursor, end, value);
 }
 
+namespace {
+void skipJsonWhitespace(const char*& cursor)
+{
+    while (*cursor == ' ' || *cursor == '\t' || *cursor == '\n' || *cursor == '\r') {
+        cursor++;
+    }
+}
+
+bool isHexDigit(const char value)
+{
+    return (value >= '0' && value <= '9') ||
+        (value >= 'a' && value <= 'f') ||
+        (value >= 'A' && value <= 'F');
+}
+
+bool parseJsonString(const char*& cursor)
+{
+    if (*cursor != '"') {
+        return false;
+    }
+
+    cursor++;
+    while (*cursor != '\0') {
+        const unsigned char value = static_cast<unsigned char>(*cursor++);
+        if (value == '"') {
+            return true;
+        }
+
+        if (value < 0x20) {
+            return false;
+        }
+
+        if (value != '\\') {
+            continue;
+        }
+
+        const char escape = *cursor++;
+        if (escape == '\0') {
+            return false;
+        }
+
+        if (escape == '"' || escape == '\\' || escape == '/' ||
+            escape == 'b' || escape == 'f' || escape == 'n' ||
+            escape == 'r' || escape == 't') {
+            continue;
+        }
+
+        if (escape != 'u') {
+            return false;
+        }
+
+        for (uint8_t i = 0; i < 4; i++) {
+            if (!isHexDigit(*cursor++)) {
+                return false;
+            }
+        }
+    }
+
+    return false;
+}
+
+bool isValidConnectionsJson(const char* value, const size_t maxLength)
+{
+    if (!value || value[0] == '\0' || strlen(value) >= maxLength) {
+        return false;
+    }
+
+    const char* cursor = value;
+    skipJsonWhitespace(cursor);
+    if (*cursor++ != '[') {
+        return false;
+    }
+
+    skipJsonWhitespace(cursor);
+    if (*cursor == ']') {
+        cursor++;
+        skipJsonWhitespace(cursor);
+        return *cursor == '\0';
+    }
+
+    while (true) {
+        if (*cursor++ != '[') {
+            return false;
+        }
+
+        skipJsonWhitespace(cursor);
+        if (!parseJsonString(cursor)) {
+            return false;
+        }
+
+        skipJsonWhitespace(cursor);
+        if (*cursor++ != ',') {
+            return false;
+        }
+
+        skipJsonWhitespace(cursor);
+        if (!parseJsonString(cursor)) {
+            return false;
+        }
+
+        skipJsonWhitespace(cursor);
+        if (*cursor++ != ']') {
+            return false;
+        }
+
+        skipJsonWhitespace(cursor);
+        if (*cursor == ']') {
+            cursor++;
+            skipJsonWhitespace(cursor);
+            return *cursor == '\0';
+        }
+
+        if (*cursor++ != ',') {
+            return false;
+        }
+
+        skipJsonWhitespace(cursor);
+    }
+}
+} // namespace
+
 #define HADEVICE_INIT \
     _ownsUniqueId(false), \
     _serializer(new HASerializer(nullptr, 16)), \
@@ -250,14 +341,13 @@ bool HADevice::addConnection(const char* type, const char* value)
     return true;
 }
 
-void HADevice::setConnectionsJson(const char* connectionsJson)
+bool HADevice::setConnectionsJson(const char* connectionsJson)
 {
-    if (!connectionsJson || connectionsJson[0] == '\0') {
-        return;
+    if (!isValidConnectionsJson(connectionsJson, MaxConnectionsJsonLength)) {
+        return false;
     }
 
-    strncpy(_connectionsJson, connectionsJson, MaxConnectionsJsonLength - 1);
-    _connectionsJson[MaxConnectionsJsonLength - 1] = 0;
+    strcpy(_connectionsJson, connectionsJson);
     _hasConnections = true;
 
     if (!_connectionsPropertyRegistered) {
@@ -268,6 +358,8 @@ void HADevice::setConnectionsJson(const char* connectionsJson)
         );
         _connectionsPropertyRegistered = true;
     }
+
+    return true;
 }
 
 void HADevice::setPayloadAvailable(const char* payload)

src/HADevice.h

@@ -41,6 +41,11 @@ public:
      */
     ~HADevice();
 
+    HADevice(const HADevice&) = delete;
+    HADevice& operator=(const HADevice&) = delete;
+    HADevice(HADevice&&) = delete;
+    HADevice& operator=(HADevice&&) = delete;
+
     /**
      * Returns pointer to the unique ID. It can be nullptr if the device has no ID assigned.
      */
@@ -147,9 +152,15 @@ public:
 
     /**
      * Sets the `connections` array as raw JSON (e.g. [[\"mac\",\"aa:bb:cc:dd:ee:ff\"]]).
-     * The payload is copied into an internal buffer.
+     *
+     * This legacy escape hatch accepts only a complete JSON array of two-string
+     * connection tuples and rejects an oversized or malformed value rather than
+     * truncating a retained discovery document. Prefer addConnection().
+     *
+     * @returns false when the value is malformed or does not fit in the
+     * internal discovery buffer.
      */
-    void setConnectionsJson(const char* connectionsJson);
+    bool setConnectionsJson(const char* connectionsJson);
 
     void setPayloadAvailable(const char* payload);
     void setPayloadNotAvailable(const char* payload);

src/HAMqtt.h

@@ -25,6 +25,7 @@ class PubSubClientMock;
 
 class HADevice;
 class HABaseDeviceType;
+class HASerializer;
 
 #if defined(ARDUINO_API_VERSION)
 using namespace arduino;
@@ -67,6 +68,19 @@ public:
         StateUnauthorized = 5
     };
 
+    /**
+     * Explicit stages for safely migrating retained single-component discovery
+     * to Home Assistant device discovery.
+     */
+    enum DeviceDiscoveryMigrationState : uint8_t {
+        DeviceDiscoveryMigrationIdle = 0,
+        DeviceDiscoveryMigrationMarkersPending,
+        DeviceDiscoveryMigrationMarkersPublished,
+        DeviceDiscoveryMigrationDevicePublished,
+        DeviceDiscoveryMigrationCompleted,
+        DeviceDiscoveryMigrationRollbackPending
+    };
+
     /**
      * Returns existing instance (singleton) of the HAMqtt class.
      * It may be a null pointer if the HAMqtt object was never constructed or it was destroyed.
@@ -100,6 +114,11 @@ public:
      * Removes singleton of the HAMqtt class.
      */
     ~HAMqtt();
+    HAMqtt(const HAMqtt&) = delete;
+    HAMqtt& operator=(const HAMqtt&) = delete;
+    HAMqtt(HAMqtt&&) = delete;
+    HAMqtt& operator=(HAMqtt&&) = delete;
+
 
     /**
      * Sets the prefix of the Home Assistant discovery topics.
@@ -146,6 +165,59 @@ public:
     inline bool isDeviceDiscoveryEnabled() const
         { return _deviceDiscoveryEnabled; }
 
+    /**
+     * Starts an explicit Home Assistant-safe migration from retained
+     * single-component discovery to device discovery.
+     *
+     * This method enables device discovery but does not publish anything. Call
+     * the subsequent migration methods after MQTT is connected, in order.
+     */
+    bool beginDeviceDiscoveryMigration();
+
+    /**
+     * Publishes retained migration markers to each legacy component config
+     * topic. The state advances only when every marker is published.
+     */
+    bool publishDeviceDiscoveryMigrationMarkers();
+
+    /**
+     * Publishes the retained device discovery config after all legacy markers
+     * have been published.
+     */
+    bool publishDeviceDiscoveryMigrationConfig();
+
+    /**
+     * Clears the retained legacy component config topics after the device
+     * config was published. The state advances only when every cleanup
+     * publish succeeds.
+     */
+    bool completeDeviceDiscoveryMigration();
+
+    /**
+     * Reverses a staged device discovery migration. A migration marker is
+     * published to the device discovery topic before legacy retained configs
+     * are restored and the device config is cleared.
+     * The method never runs automatically and returns to single-component
+     * discovery only after every required retained publish succeeds.
+     */
+    bool rollbackDeviceDiscoveryMigration();
+
+    /**
+     * Returns the current in-memory device discovery migration stage.
+     */
+    inline DeviceDiscoveryMigrationState getDeviceDiscoveryMigrationState() const
+        { return _deviceDiscoveryMigrationState; }
+
+    /**
+     * Returns true while an explicit device discovery migration awaits a
+     * marker, device config, or legacy-topic cleanup step.
+     */
+    inline bool isDeviceDiscoveryMigrationInProgress() const
+    {
+        return _deviceDiscoveryMigrationState != DeviceDiscoveryMigrationIdle &&
+            _deviceDiscoveryMigrationState != DeviceDiscoveryMigrationCompleted;
+    }
+
     /**
      * Republishes the current MQTT device discovery payload when device
      * discovery is enabled.
@@ -348,7 +420,31 @@ public:
      * @note The HAMqtt class doesn't take ownership of the given pointer.
      * @param deviceType Instance of the device's type (HASwitch, HABinarySensor, etc.).
      */
-    void addDeviceType(HABaseDeviceType* deviceType);
+    bool addDeviceType(HABaseDeviceType* deviceType);
+
+    /**
+     * Removes a destroyed entity from the connection registry.
+     * The MQTT instance does not own entity lifetimes.
+     */
+    bool removeDeviceType(HABaseDeviceType* deviceType);
+
+    /**
+     * Number of entities currently registered for connection callbacks.
+     */
+    inline uint8_t getRegisteredDeviceTypeCount() const
+        { return _devicesTypesNb; }
+
+    /**
+     * Maximum number of entities that can be registered in this HAMqtt instance.
+     */
+    inline uint8_t getDeviceTypeLimit() const
+        { return _maxDevicesTypesNb; }
+
+    /**
+     * Number of registrations dropped because the configured entity limit was reached.
+     */
+    inline uint16_t getDeviceTypeRegistrationFailures() const
+        { return _deviceTypeRegistrationFailures; }
 
     /**
      * Publishes the MQTT message with given topic and payload.
@@ -383,7 +479,7 @@ public:
      * @param data The string to publish.
      * @param length Length of the data (bytes).
      */
-    void writePayload(const char* data, const uint16_t length);
+    bool writePayload(const char* data, const uint16_t length);
 
     /**
      * Writes given data to the TCP stream.
@@ -393,7 +489,7 @@ public:
      * @param data The data to publish.
      * @param length Length of the data (bytes).
      */
-    void writePayload(const uint8_t* data, const uint16_t length);
+    bool writePayload(const uint8_t* data, const uint16_t length);
 
     /**
      * Writes given progmem data to the TCP stream.
@@ -402,7 +498,7 @@ public:
      *
      * @param data Progmem data to publish.
      */
-    void writePayload(const __FlashStringHelper* data);
+    bool writePayload(const __FlashStringHelper* data);
 
     /**
      * Finishes publishing of a message.
@@ -512,6 +608,36 @@ private:
      */
     void onConnectedLogic();
 
+    bool publishDeviceDiscoveryPayload(HABaseDeviceType* removalType = nullptr);
+
+    HASerializer* buildDeviceDiscoveryComponentSerializer(
+        HABaseDeviceType* deviceType,
+        HABaseDeviceType* removalType
+    );
+
+    bool clearDeviceDiscoveryConfig();
+
+    bool publishDeviceDiscoveryMigrationMarker(HABaseDeviceType* deviceType);
+
+    /**
+     * Marks the retained device discovery config for Home Assistant's reverse
+     * migration protocol before restoring legacy component configs.
+     */
+    bool publishDeviceDiscoveryMigrationMarker();
+
+    /**
+     * Removes a component from a device discovery payload using Home
+     * Assistant's required platform-only marker, followed by a compacted
+     * bundle when another component remains.
+     */
+    bool removeDeviceDiscoveryComponent(HABaseDeviceType* deviceType);
+
+    /**
+     * Re-adds (or refreshes) a component in the current device discovery
+     * payload.
+     */
+    bool republishDeviceDiscoveryComponent(HABaseDeviceType* deviceType);
+
     /**
      * Sets the state of the MQTT connection.
      */
@@ -567,6 +693,15 @@ private:
      */
     String formatDirectPublishFailureDiagnostics(bool hamqttConnectedBefore, int pubsubStateBefore) const;
 
+    // Buffer direct MQTT streaming writes so serializers do not issue hundreds
+    // of tiny TCP writes while a PubSubClient publish is open.
+    static const uint16_t DirectPublishBufferSize = 128;
+    bool flushDirectPublishBuffer();
+    bool appendDirectPublishPayload(const uint8_t* data, uint16_t length);
+    bool appendDirectPublishProgmemPayload(const __FlashStringHelper* src);
+    void clearDirectPublishBuffer();
+    void abortDirectPublish();
+
 #ifdef ARDUINOHA_TEST
     PubSubClientMock* _mqtt;
 #else
@@ -577,6 +712,10 @@ private:
     PubSubClient* _mqtt;
 #endif
 
+    uint8_t _directPublishBuffer[DirectPublishBufferSize];
+    uint16_t _directPublishBufferLength;
+    bool _directPublishActive;
+
     /// Instance of the HADevice passed to the constructor.
     const HADevice& _device;
 
@@ -604,6 +743,9 @@ private:
     /// Enables MQTT device discovery mode when set to true.
     bool _deviceDiscoveryEnabled;
 
+    /// Current in-memory stage of an explicit device discovery migration.
+    DeviceDiscoveryMigrationState _deviceDiscoveryMigrationState;
+
     const char* _originSupportUrl;
 
     /// The username used for the authentication. It's set in the HAMqtt::begin method.
@@ -630,6 +772,9 @@ private:
     /// The last will topic set by HAMqtt::setLastWill
     const char* _lastWillTopic;
 
+    /// Count of entity registrations rejected because the configured cap was full.
+    uint16_t _deviceTypeRegistrationFailures;
+
     /// The last will message set by HAMqtt::setLastWill
     const char* _lastWillMessage;
 
@@ -659,6 +804,8 @@ private:
     bool _deferredFlushFailedForTest = false;
     uint8_t _lastDeferredFlushErrorForTest = 0;
 #endif
+
+    friend class HABaseDeviceType;
 };
 
 #endif

src/device-types/HABaseDeviceType.cpp

@@ -6,6 +6,15 @@
 #include "../utils/HASerializer.h"
 #include <string.h>
 
+HABaseDeviceType* HABaseDeviceType::_firstInstance = nullptr;
+
+void HABaseDeviceType::registerAllWith(HAMqtt& mqttInstance)
+{
+    for (HABaseDeviceType* entity = _firstInstance; entity; entity = entity->_nextInstance) {
+        mqttInstance.addDeviceType(entity);
+    }
+}
+
 HABaseDeviceType::HABaseDeviceType(
     const __FlashStringHelper* componentName,
     const char* uniqueId
@@ -27,15 +36,34 @@ HABaseDeviceType::HABaseDeviceType(
     _payloadNotAvailable(nullptr),
     _availabilityMode(nullptr),
     _availabilityList(),
-    _availability(AvailabilityDefault)
+    _deviceDiscoveryRemoved(false),
+    _availability(AvailabilityDefault),
+    _nextInstance(_firstInstance)
 {
-    if (mqtt()) {
-        mqtt()->addDeviceType(this);
+    _firstInstance = this;
+    if (HAMqtt* mqttInstance = mqtt()) {
+        mqttInstance->addDeviceType(this);
     }
 }
 
 HABaseDeviceType::~HABaseDeviceType()
 {
+    if (_firstInstance == this) {
+        _firstInstance = _nextInstance;
+    } else {
+        HABaseDeviceType* previous = _firstInstance;
+        while (previous && previous->_nextInstance != this) {
+            previous = previous->_nextInstance;
+        }
+        if (previous) {
+            previous->_nextInstance = _nextInstance;
+        }
+    }
+
+    if (HAMqtt* mqttInstance = mqtt()) {
+        mqttInstance->removeDeviceType(this);
+    }
+
     destroySerializer();
 }
 
@@ -47,6 +75,25 @@ void HABaseDeviceType::setAvailability(bool online)
 
 bool HABaseDeviceType::removeFromDiscovery()
 {
+    HAMqtt* mqttInstance = mqtt();
+    if (!mqttInstance) {
+        return false;
+    }
+
+    if (mqttInstance->isDeviceDiscoveryEnabled() && supportsDeviceDiscovery()) {
+        return mqttInstance->removeDeviceDiscoveryComponent(this);
+    }
+
+    return removeSingleComponentDiscovery();
+}
+
+bool HABaseDeviceType::removeSingleComponentDiscovery()
+{
+    HAMqtt* mqttInstance = mqtt();
+    if (!mqttInstance) {
+        return false;
+    }
+
     const uint16_t topicLength = HASerializer::calculateConfigTopicLength(
         componentName(),
         uniqueId()
@@ -61,11 +108,11 @@ bool HABaseDeviceType::removeFromDiscovery()
     }
 
     destroySerializer();
-    if (!mqtt()->beginPublish(topic, 0, true)) {
+    if (!mqttInstance->beginPublish(topic, 0, true)) {
         return false;
     }
 
-    return mqtt()->endPublish();
+    return mqttInstance->endPublish();
 }
 
 bool HABaseDeviceType::republishDiscovery()
@@ -79,10 +126,7 @@ bool HABaseDeviceType::republishDiscovery()
         return publishConfig();
     }
 
-    // Clear any stale per-entity retained config so device discovery remains
-    // the single source of truth for supported entities.
-    removeFromDiscovery();
-    return mqttInstance->publishDeviceDiscovery();
+    return mqttInstance->republishDeviceDiscoveryComponent(this);
 }
 
 HAMqtt* HABaseDeviceType::mqtt()
@@ -136,8 +180,12 @@ void HABaseDeviceType::destroySerializer()
 
 bool HABaseDeviceType::publishConfig()
 {
-    buildSerializer();
+    HAMqtt* mqttInstance = mqtt();
+    if (!mqttInstance) {
+        return false;
+    }
 
+    buildSerializer();
     if (_serializer == nullptr) {
         return false;
     }
@@ -151,15 +199,19 @@ bool HABaseDeviceType::publishConfig()
     bool published = false;
     if (topicLength > 0 && dataLength > 0) {
         char topic[topicLength];
-        HASerializer::generateConfigTopic(
+        if (!HASerializer::generateConfigTopic(
             topic,
             componentName(),
             uniqueId()
-        );
+        )) {
+            destroySerializer();
+            return false;
+        }
 
-        if (mqtt()->beginPublish(topic, dataLength, true)) {
-            _serializer->flush();
-            published = mqtt()->endPublish();
+        if (mqttInstance->beginPublish(topic, dataLength, true)) {
+            const bool flushed = _serializer->flush();
+            const bool ended = mqttInstance->endPublish();
+            published = flushed && ended;
         }
     }
 
@@ -169,7 +221,12 @@ bool HABaseDeviceType::publishConfig()
 
 void HABaseDeviceType::publishAvailability()
 {
-    const HADevice* device = mqtt()->getDevice();
+    HAMqtt* mqttInstance = mqtt();
+    if (!mqttInstance) {
+        return;
+    }
+
+    const HADevice* device = mqttInstance->getDevice();
     if (
         !device ||
         device->isSharedAvailabilityEnabled() ||
@@ -251,13 +308,15 @@ bool HABaseDeviceType::publishAbsolute(
         return false;
     }
 
+    HAMqtt* mqttInstance = mqtt();
     const uint16_t len = strlen(payload);
-    if (!mqtt()->beginPublish(fullTopic, len, retained)) {
+    if (!mqttInstance->beginPublish(fullTopic, len, retained)) {
         return false;
     }
 
-    mqtt()->writePayload(payload, len);
-    return mqtt()->endPublish();
+    const bool written = mqttInstance->writePayload(payload, len);
+    const bool ended = mqttInstance->endPublish();
+    return written && ended;
 }
 
 bool HABaseDeviceType::publishOnDataTopic(
@@ -305,7 +364,12 @@ bool HABaseDeviceType::publishOnDataTopic(
     bool isProgmemData
 )
 {
-    if (!payload) {
+    HAMqtt* mqttInstance = mqtt();
+    if (!payload || !mqttInstance) {
+        return false;
+    }
+
+    if (!topic) {
         return false;
     }
 
@@ -326,14 +390,16 @@ bool HABaseDeviceType::publishOnDataTopic(
         return false;
     }
 
-    if (mqtt()->beginPublish(fullTopic, length, retained)) {
+    if (mqttInstance->beginPublish(fullTopic, length, retained)) {
+        bool written = false;
         if (isProgmemData) {
-            mqtt()->writePayload(AHATOFSTR(payload));
+            written = mqttInstance->writePayload(AHATOFSTR(payload));
         } else {
-            mqtt()->writePayload(payload, length);
+            written = mqttInstance->writePayload(payload, length);
         }
 
-        return mqtt()->endPublish();
+        const bool ended = mqttInstance->endPublish();
+        return written && ended;
     }
 
     return false;
@@ -353,12 +419,6 @@ void HABaseDeviceType::setEntityIdProperty(HASerializer* serializer) const
     const char* defaultEntityId = nonEmptyString(_defaultEntityId);
     if (defaultEntityId) {
         serializer->set(AHATOFSTR(HADefaultEntityIdProperty), defaultEntityId);
-        return;
-    }
-
-    const char* objectId = nonEmptyString(_objectId);
-    if (objectId) {
-        serializer->set(AHATOFSTR(HAObjectIdProperty), objectId);
     }
 }
 

src/device-types/HABaseDeviceType.h

@@ -40,6 +40,11 @@ public:
     );
 
     virtual ~HABaseDeviceType();
+    HABaseDeviceType(const HABaseDeviceType&) = delete;
+    HABaseDeviceType& operator=(const HABaseDeviceType&) = delete;
+    HABaseDeviceType(HABaseDeviceType&&) = delete;
+    HABaseDeviceType& operator=(HABaseDeviceType&&) = delete;
+
 
     /**
      * Returns unique ID of the device type.
@@ -100,8 +105,12 @@ public:
         { return _defaultEntityId; }
 
     /**
-     * Legacy alias for the MQTT `object_id` discovery property.
-     * Prefer setDefaultEntityId() for new code.
+     * Legacy compatibility setter. Home Assistant no longer supports the MQTT
+     * discovery `obj_id` payload property, so this value is retained only for
+     * source compatibility and is not published.
+     *
+     * Use setDefaultEntityId("domain.entity_id") to suggest an entity ID on
+     * first discovery. It does not rename existing entities.
      *
      * @param objectId The object ID.
      */
@@ -171,12 +180,23 @@ public:
 
     /**
      * Removes this entity from MQTT discovery by publishing an empty retained
-     * payload on its config topic.
+     * payload on its config topic in single-component mode. In device
+     * discovery mode, publishes Home Assistant's required component-removal
+     * marker and updates the retained device config.
      */
     bool removeFromDiscovery();
 
+    /**
+     * Returns true after this entity was removed from the retained device
+     * discovery payload and before it is republished.
+     */
+    inline bool isRemovedFromDeviceDiscovery() const
+        { return _deviceDiscoveryRemoved; }
+
     /**
      * Republishes MQTT discovery config for this entity.
+     * In device discovery mode, this also re-adds an entity previously removed
+     * from the retained device payload.
      */
     bool republishDiscovery();
 
@@ -318,8 +338,8 @@ protected:
 
     /**
      * Adds the preferred entity ID property to the serializer.
-     * `default_entity_id` takes precedence and the legacy `object_id` is only
-     * emitted when no default entity ID was configured.
+     * Only `default_entity_id` is emitted. The legacy `obj_id` field is not
+     * supported by current Home Assistant MQTT discovery schemas.
      */
     void setEntityIdProperty(HASerializer* serializer) const;
 
@@ -371,6 +391,13 @@ protected:
     const char* _availabilityMode;
     HAAvailabilityConfig _availabilityList;
 
+    /// Tracks an entity removed from the retained device discovery payload.
+    bool _deviceDiscoveryRemoved;
+
+    static void registerAllWith(HAMqtt& mqtt);
+
+    static HABaseDeviceType* _firstInstance;
+
 private:
     enum Availability {
         AvailabilityDefault = 0,
@@ -382,8 +409,13 @@ private:
     Availability _availability;
 
     const char* effectivePayloadAvailable() const;
+    /// Intrusive list entry used to register entities created before HAMqtt.
+    HABaseDeviceType* _nextInstance;
+
     const char* effectivePayloadNotAvailable() const;
 
+    bool removeSingleComponentDiscovery();
+
     friend class HAMqtt;
     friend class HASerializer;
 };

src/device-types/HAText.cpp

@@ -4,6 +4,8 @@
 #include "../HAMqtt.h"
 #include "../utils/HADictionary.h"
 #include "../utils/HASerializer.h"
+#include <new>
+#include <string.h>
 
 HAText::HAText(const char* uniqueId) :
     HABaseDeviceType(AHATOFSTR(HAComponentText), uniqueId),
@@ -25,6 +27,40 @@ HAText::HAText(const char* uniqueId) :
 
 }
 
+HAText::~HAText()
+{
+    delete[] _currentState;
+}
+
+void HAText::setCurrentState(const char* state)
+{
+    setCurrentStateInternal(state);
+}
+
+bool HAText::setCurrentStateInternal(const char* state)
+{
+    if (!state) {
+        delete[] _currentState;
+        _currentState = nullptr;
+        return true;
+    }
+
+    const size_t stateLength = strlen(state);
+    if (stateLength > MaxCommandLength) {
+        return false;
+    }
+
+    char* stateCopy = new (std::nothrow) char[stateLength + 1];
+    if (!stateCopy) {
+        return false;
+    }
+
+    memcpy(stateCopy, state, stateLength + 1);
+    delete[] _currentState;
+    _currentState = stateCopy;
+    return true;
+}
+
 void HAText::setValueTemplate(const char* valueTemplate)
 {
     _valueTemplate = valueTemplate;
@@ -49,9 +85,11 @@ bool HAText::setState(const char* state, const bool force)
         return true;
     }
 
-    const bool published = publishState(state);
-    _currentState = state;
-    return published;
+    if (!setCurrentStateInternal(state)) {
+        return false;
+    }
+
+    return publishState(_currentState);
 }
 
 void HAText::buildSerializer()
@@ -222,14 +260,26 @@ void HAText::onMqttMessage(
 #endif
     ;
 
-    if (hasCommandCallback && HASerializer::compareDataTopics(
-        topic,
-        uniqueId(),
-        AHATOFSTR(HACommandTopic)
-    )) {
-        char value[length + 1];
+    if (
+        hasCommandCallback &&
+        length <= MaxCommandLength &&
+        (length == 0 || payload) &&
+        HASerializer::compareDataTopics(
+            topic,
+            uniqueId(),
+            AHATOFSTR(HACommandTopic)
+        )
+    ) {
+        char* value = new (std::nothrow) char[static_cast<size_t>(length) + 1];
+        if (!value) {
+            return;
+        }
+
         value[length] = 0;
-        memcpy(value, payload, length);
+        if (length > 0) {
+            memcpy(value, payload, length);
+        }
+
         if (_commandCallback) {
             _commandCallback(value, this);
         }
@@ -238,6 +288,8 @@ void HAText::onMqttMessage(
             _commandStdCallback(value, this);
         }
 #endif
+
+        delete[] value;
     }
 }
 

src/device-types/HAText.h

@@ -28,11 +28,16 @@ public:
         ModePassword
     };
 
+    /// Maximum number of bytes accepted in a text command payload.
+    static const uint16_t MaxCommandLength = 255;
+
     /**
      * @param uniqueId The unique ID of the text entity. It needs to be unique in a scope of your device.
      */
     HAText(const char* uniqueId);
 
+    ~HAText() override;
+
     /**
      * Changes state of the text and publishes MQTT message.
      * Please note that if a new value is the same as previous one,
@@ -51,8 +56,7 @@ public:
      *
      * @param state New state of the text.
      */
-    inline void setCurrentState(const char* state)
-        { _currentState = state; }
+    void setCurrentState(const char* state);
 
     /**
      * Returns last known state of the text.
@@ -174,6 +178,14 @@ private:
      */
     bool publishState(const char* state);
 
+    /**
+     * Copies state into the owned current-state buffer, or clears it when state
+     * is nullptr.
+     *
+     * @returns Returns false when allocating the copy fails.
+     */
+    bool setCurrentStateInternal(const char* state);
+
     /**
      * Returns progmem string representing mode of the text.
      */
@@ -203,8 +215,8 @@ private:
     const char* _valueTemplate;
     const char* _commandTemplate;
 
-    /// The current state of the text. It can be nullptr if state wasn't set.
-    const char* _currentState;
+    /// Owned current state of the text. It can be nullptr if state wasn't set.
+    char* _currentState;
 
     /// The callback that will be called when command is received from the HA.
     HATEXT_CALLBACK(_commandCallback);

src/mocks/PubSubClientMock.cpp

@@ -2,6 +2,7 @@
 #ifdef ARDUINOHA_TEST
 
 #include "../ArduinoHADefines.h"
+#include <stdlib.h>
 
 PubSubClientMock::PubSubClientMock() :
     _pendingMessage(nullptr),
@@ -156,12 +157,25 @@ bool PubSubClientMock::beginPublish(
 
 size_t PubSubClientMock::write(const uint8_t *buffer, size_t size)
 {
-    if (!_pendingMessage || !_pendingMessage->buffer) {
+    if (!_pendingMessage || !_pendingMessage->buffer || !buffer) {
         return 0;
     }
 
-    strncat(_pendingMessage->buffer, (const char*)buffer, size);
-    return size;
+    const size_t capacity = _pendingMessage->bufferSize - 1;
+    if (_pendingMessage->writtenSize >= capacity) {
+        return 0;
+    }
+
+    const size_t available = capacity - _pendingMessage->writtenSize;
+    const size_t written = size < available ? size : available;
+    if (written == 0) {
+        return 0;
+    }
+
+    memcpy(_pendingMessage->buffer + _pendingMessage->writtenSize, buffer, written);
+    _pendingMessage->writtenSize += written;
+    _pendingMessage->buffer[_pendingMessage->writtenSize] = 0;
+    return written;
 }
 
 size_t PubSubClientMock::print(const __FlashStringHelper* buffer)
@@ -184,35 +198,46 @@ int PubSubClientMock::endPublish()
         return 0;
     }
 
-    size_t messageSize = _pendingMessage->bufferSize;
-    uint8_t index = _flushedMessagesNb;
+    if (_pendingMessage->writtenSize != _pendingMessage->bufferSize - 1 ||
+        _flushedMessagesNb == UINT8_MAX) {
+        return 0;
+    }
 
-    _flushedMessagesNb++;
-    _flushedMessages = static_cast<MqttMessage**>(
-        realloc(_flushedMessages, _flushedMessagesNb * sizeof(MqttMessage*))
+    MqttMessage** expanded = static_cast<MqttMessage**>(
+        realloc(_flushedMessages, (_flushedMessagesNb + 1) * sizeof(MqttMessage*))
     );
+    if (!expanded) {
+        return 0;
+    }
+
+    _flushedMessages = expanded;
+    _flushedMessages[_flushedMessagesNb++] = _pendingMessage;
 
-    _flushedMessages[index] = _pendingMessage; // handover memory responsibility
     _pendingMessage = nullptr; // do not call destructor
 
-    return messageSize;
+    return _flushedMessages[_flushedMessagesNb - 1]->bufferSize;
 }
 
 bool PubSubClientMock::subscribe(const char* topic)
 {
-    uint8_t index = _subscriptionsNb;
+    if (!topic || _subscriptionsNb == UINT8_MAX) {
+        return false;
+    }
 
-    _subscriptionsNb++;
-    _subscriptions = static_cast<MqttSubscription**>(
-        realloc(_subscriptions, _subscriptionsNb * sizeof(MqttSubscription*))
+    MqttSubscription** expanded = static_cast<MqttSubscription**>(
+        realloc(_subscriptions, (_subscriptionsNb + 1) * sizeof(MqttSubscription*))
     );
+    if (!expanded) {
+        return false;
+    }
 
     size_t topicSize = strlen(topic) + 1;
     MqttSubscription* subscription = new MqttSubscription();
     subscription->topic = new char[topicSize];
     memcpy(subscription->topic, topic, topicSize);
 
-    _subscriptions[index] = subscription;
+    _subscriptions = expanded;
+    _subscriptions[_subscriptionsNb++] = subscription;
     return true;
 }
 
@@ -223,7 +248,8 @@ void PubSubClientMock::clearFlushedMessages()
             delete _flushedMessages[i];
         }
 
-        delete _flushedMessages;
+        free(_flushedMessages);
+        _flushedMessages = nullptr;
     }
 
     _flushedMessagesNb = 0;
@@ -236,7 +262,8 @@ void PubSubClientMock::clearSubscriptions()
             delete _subscriptions[i];
         }
 
-        delete _subscriptions;
+        free(_subscriptions);
+        _subscriptions = nullptr;
     }
 
     _subscriptionsNb = 0;

src/mocks/PubSubClientMock.h

@@ -19,6 +19,7 @@ struct MqttMessage
     size_t topicSize;
     char* buffer;
     size_t bufferSize;
+    size_t writtenSize;
     bool retained;
 
     MqttMessage() :
@@ -26,6 +27,7 @@ struct MqttMessage
         topicSize(0),
         buffer(nullptr),
         bufferSize(0),
+        writtenSize(0),
         retained(false)
     {
 
@@ -34,11 +36,11 @@ struct MqttMessage
     ~MqttMessage()
     {
         if (topic) {
-            delete topic;
+            delete[] topic;
         }
 
         if (buffer) {
-            delete buffer;
+            delete[] buffer;
         }
     }
 };
@@ -55,7 +57,7 @@ struct MqttSubscription {
     ~MqttSubscription()
     {
         if (topic) {
-            delete topic;
+            delete[] topic;
         }
     }
 };

src/utils/HAAvailabilityConfig.cpp

@@ -2,20 +2,17 @@
 #include <string.h>
 #include "HAAvailabilityConfig.h"
 #include "HADictionary.h"
+#include "HAJson.h"
 
 static uint16_t jsonEscapedStringSize(const char* s)
 {
-    if (!s) {
-        return 0;
-    }
-    return 2 * strlen_P(HASerializerJsonEscapeChar) + strlen(s);
+    return HAJson::calculateEscapedStringSize(s);
 }
 
-static void appendEscapedString(char* buf, const char* s)
+static bool appendEscapedString(char* buf, char* end, const char* s)
 {
-    strcat_P(buf, HASerializerJsonEscapeChar);
-    strcat(buf, s);
-    strcat_P(buf, HASerializerJsonEscapeChar);
+    char* cursor = buf + strlen(buf);
+    return HAJson::appendEscapedString(cursor, end, s);
 }
 
 HAAvailabilityConfig::HAAvailabilityConfig() :
@@ -90,12 +87,12 @@ void HAAvailabilityConfig::clear()
 
 uint16_t HAAvailabilityConfig::calculateJsonSize() const
 {
-    uint16_t size =
+    uint32_t size =
         strlen_P(HASerializerJsonArrayPrefix) +
         strlen_P(HASerializerJsonArraySuffix);
 
     if (_count == 0) {
-        return size;
+        return static_cast<uint16_t>(size);
     }
 
     size += (_count - 1) * strlen_P(HASerializerJsonPropertiesSeparator);
@@ -107,39 +104,59 @@ uint16_t HAAvailabilityConfig::calculateJsonSize() const
         size += strlen_P(HASerializerJsonDataSuffix);
 
         // "t":"..."
+        const uint16_t topicSize = jsonEscapedStringSize(e.topic);
+        if (topicSize == 0) {
+            return 0;
+        }
         size +=
             strlen_P(HASerializerJsonPropertyPrefix) +
             strlen_P(HATopic) +
             strlen_P(HASerializerJsonPropertySuffix) +
-            jsonEscapedStringSize(e.topic);
+            topicSize;
 
         if (e.valueTemplate && e.valueTemplate[0] != '\0') {
             size += strlen_P(HASerializerJsonPropertiesSeparator);
+            const uint16_t valueTemplateSize = jsonEscapedStringSize(e.valueTemplate);
+            if (valueTemplateSize == 0) {
+                return 0;
+            }
             size +=
                 strlen_P(HASerializerJsonPropertyPrefix) +
                 strlen_P(HAValueTemplateProperty) +
                 strlen_P(HASerializerJsonPropertySuffix) +
-                jsonEscapedStringSize(e.valueTemplate);
+                valueTemplateSize;
         }
         if (e.payloadAvailable && e.payloadAvailable[0] != '\0') {
             size += strlen_P(HASerializerJsonPropertiesSeparator);
+            const uint16_t payloadAvailableSize = jsonEscapedStringSize(e.payloadAvailable);
+            if (payloadAvailableSize == 0) {
+                return 0;
+            }
             size +=
                 strlen_P(HASerializerJsonPropertyPrefix) +
                 strlen_P(HAPayloadAvailableProperty) +
                 strlen_P(HASerializerJsonPropertySuffix) +
-                jsonEscapedStringSize(e.payloadAvailable);
+                payloadAvailableSize;
         }
         if (e.payloadNotAvailable && e.payloadNotAvailable[0] != '\0') {
             size += strlen_P(HASerializerJsonPropertiesSeparator);
+            const uint16_t payloadNotAvailableSize = jsonEscapedStringSize(e.payloadNotAvailable);
+            if (payloadNotAvailableSize == 0) {
+                return 0;
+            }
             size +=
                 strlen_P(HASerializerJsonPropertyPrefix) +
                 strlen_P(HAPayloadNotAvailableProperty) +
                 strlen_P(HASerializerJsonPropertySuffix) +
-                jsonEscapedStringSize(e.payloadNotAvailable);
+                payloadNotAvailableSize;
         }
     }
 
-    return size;
+    if (size > UINT16_MAX) {
+        return 0;
+    }
+
+    return static_cast<uint16_t>(size);
 }
 
 bool HAAvailabilityConfig::serialize(char* output) const
@@ -148,6 +165,12 @@ bool HAAvailabilityConfig::serialize(char* output) const
         return false;
     }
 
+    const uint16_t jsonSize = calculateJsonSize();
+    if (jsonSize == 0) {
+        return false;
+    }
+
+    char* const end = output + jsonSize;
     output[0] = 0;
     strcat_P(output, HASerializerJsonArrayPrefix);
 
@@ -161,7 +184,9 @@ bool HAAvailabilityConfig::serialize(char* output) const
         strcat_P(output, HASerializerJsonPropertyPrefix);
         strcat_P(output, HATopic);
         strcat_P(output, HASerializerJsonPropertySuffix);
-        appendEscapedString(output, _entries[i].topic);
+        if (!appendEscapedString(output, end, _entries[i].topic)) {
+            return false;
+        }
 
         const Entry& e = _entries[i];
         if (e.valueTemplate && e.valueTemplate[0] != '\0') {
@@ -169,21 +194,27 @@ bool HAAvailabilityConfig::serialize(char* output) const
             strcat_P(output, HASerializerJsonPropertyPrefix);
             strcat_P(output, HAValueTemplateProperty);
             strcat_P(output, HASerializerJsonPropertySuffix);
-            appendEscapedString(output, e.valueTemplate);
+            if (!appendEscapedString(output, end, e.valueTemplate)) {
+                return false;
+            }
         }
         if (e.payloadAvailable && e.payloadAvailable[0] != '\0') {
             strcat_P(output, HASerializerJsonPropertiesSeparator);
             strcat_P(output, HASerializerJsonPropertyPrefix);
             strcat_P(output, HAPayloadAvailableProperty);
             strcat_P(output, HASerializerJsonPropertySuffix);
-            appendEscapedString(output, e.payloadAvailable);
+            if (!appendEscapedString(output, end, e.payloadAvailable)) {
+                return false;
+            }
         }
         if (e.payloadNotAvailable && e.payloadNotAvailable[0] != '\0') {
             strcat_P(output, HASerializerJsonPropertiesSeparator);
             strcat_P(output, HASerializerJsonPropertyPrefix);
             strcat_P(output, HAPayloadNotAvailableProperty);
             strcat_P(output, HASerializerJsonPropertySuffix);
-            appendEscapedString(output, e.payloadNotAvailable);
+            if (!appendEscapedString(output, end, e.payloadNotAvailable)) {
+                return false;
+            }
         }
 
         strcat_P(output, HASerializerJsonDataSuffix);

src/utils/HAAvailabilityConfig.h

@@ -22,6 +22,11 @@ public:
     HAAvailabilityConfig();
     ~HAAvailabilityConfig();
 
+    HAAvailabilityConfig(const HAAvailabilityConfig&) = delete;
+    HAAvailabilityConfig& operator=(const HAAvailabilityConfig&) = delete;
+    HAAvailabilityConfig(HAAvailabilityConfig&&) = delete;
+    HAAvailabilityConfig& operator=(HAAvailabilityConfig&&) = delete;
+
     /**
      * Adds an availability entry. `topic` must be a full MQTT topic string.
      * @return false when full or topic is null/empty.

src/utils/HAJson.cpp

@@ -0,0 +1,174 @@
+#include "HAJson.h"
+
+#include <Arduino.h>
+#include <limits.h>
+#include <string.h>
+
+namespace {
+uint8_t escapedByteSize(const uint8_t value)
+{
+    switch (value) {
+    case '"':
+    case '\\':
+    case '\b':
+    case '\f':
+    case '\n':
+    case '\r':
+    case '\t':
+        return 2;
+    default:
+        return value < 0x20 ? 6 : 1;
+    }
+}
+
+char hexDigit(const uint8_t value)
+{
+    return value < 10 ? static_cast<char>('0' + value) : static_cast<char>('A' + (value - 10));
+}
+
+void appendEscapedByte(char*& cursor, const uint8_t value)
+{
+    switch (value) {
+    case '"':
+        *cursor++ = '\\';
+        *cursor++ = '"';
+        return;
+    case '\\':
+        *cursor++ = '\\';
+        *cursor++ = '\\';
+        return;
+    case '\b':
+        *cursor++ = '\\';
+        *cursor++ = 'b';
+        return;
+    case '\f':
+        *cursor++ = '\\';
+        *cursor++ = 'f';
+        return;
+    case '\n':
+        *cursor++ = '\\';
+        *cursor++ = 'n';
+        return;
+    case '\r':
+        *cursor++ = '\\';
+        *cursor++ = 'r';
+        return;
+    case '\t':
+        *cursor++ = '\\';
+        *cursor++ = 't';
+        return;
+    default:
+        if (value < 0x20) {
+            *cursor++ = '\\';
+            *cursor++ = 'u';
+            *cursor++ = '0';
+            *cursor++ = '0';
+            *cursor++ = hexDigit(static_cast<uint8_t>(value >> 4));
+            *cursor++ = hexDigit(static_cast<uint8_t>(value & 0x0F));
+        } else {
+            *cursor++ = static_cast<char>(value);
+        }
+    }
+}
+} // namespace
+
+uint16_t HAJson::calculateEscapedStringSize(const char* value)
+{
+    if (!value) {
+        return 0;
+    }
+
+    uint32_t size = 2; // surrounding quotes
+    for (const uint8_t* p = reinterpret_cast<const uint8_t*>(value); *p != 0; p++) {
+        size += escapedByteSize(*p);
+        if (size > UINT16_MAX) {
+            return 0;
+        }
+    }
+
+    return static_cast<uint16_t>(size);
+}
+
+uint16_t HAJson::calculateEscapedProgmemStringSize(const char* value)
+{
+    if (!value) {
+        return 0;
+    }
+
+    uint32_t size = 2; // surrounding quotes
+    for (uint16_t i = 0; ; i++) {
+        const uint8_t byte = pgm_read_byte(value + i);
+        if (byte == 0) {
+            break;
+        }
+
+        size += escapedByteSize(byte);
+        if (size > UINT16_MAX) {
+            return 0;
+        }
+    }
+
+    return static_cast<uint16_t>(size);
+}
+
+bool HAJson::appendEscapedString(char*& cursor, char* end, const char* value)
+{
+    if (!cursor || !end || !value || cursor > end) {
+        return false;
+    }
+
+    const uint16_t size = calculateEscapedStringSize(value);
+    if (size == 0 || static_cast<size_t>(end - cursor) < size) {
+        return false;
+    }
+
+    *cursor++ = '"';
+    for (const uint8_t* p = reinterpret_cast<const uint8_t*>(value); *p != 0; p++) {
+        appendEscapedByte(cursor, *p);
+    }
+    *cursor++ = '"';
+    *cursor = 0;
+    return true;
+}
+
+bool HAJson::appendEscapedProgmemString(char*& cursor, char* end, const char* value)
+{
+    if (!cursor || !end || !value || cursor > end) {
+        return false;
+    }
+
+    const uint16_t size = calculateEscapedProgmemStringSize(value);
+    if (size == 0 || static_cast<size_t>(end - cursor) < size) {
+        return false;
+    }
+
+    *cursor++ = '"';
+    for (uint16_t i = 0; ; i++) {
+        const uint8_t byte = pgm_read_byte(value + i);
+        if (byte == 0) {
+            break;
+        }
+        appendEscapedByte(cursor, byte);
+    }
+    *cursor++ = '"';
+    *cursor = 0;
+    return true;
+}
+
+bool HAJson::isValidDiscoveryTopicToken(const char* value)
+{
+    if (!value || value[0] == '\0') {
+        return false;
+    }
+
+    for (const unsigned char* p = reinterpret_cast<const unsigned char*>(value); *p != 0; p++) {
+        const bool isLower = *p >= 'a' && *p <= 'z';
+        const bool isUpper = *p >= 'A' && *p <= 'Z';
+        const bool isDigit = *p >= '0' && *p <= '9';
+        if (!isLower && !isUpper && !isDigit && *p != '_' && *p != '-') {
+            return false;
+        }
+    }
+
+    return true;
+}

src/utils/HAJson.h

@@ -0,0 +1,46 @@
+#ifndef AHA_JSON_H
+#define AHA_JSON_H
+
+#include <stdint.h>
+
+/**
+ * Small JSON helpers used by discovery serializers.
+ *
+ * The library streams discovery documents directly to PubSubClient, so the
+ * calculated size must exactly match the escaped JSON representation before a
+ * retained payload is started.
+ */
+namespace HAJson
+{
+    /**
+     * Returns the number of bytes needed to encode value as a JSON string,
+     * including its surrounding quotes. Returns zero for a null value or when
+     * the result cannot fit in a uint16_t.
+     */
+    uint16_t calculateEscapedStringSize(const char* value);
+
+    /**
+     * As calculateEscapedStringSize(), but reads value from program memory.
+     */
+    uint16_t calculateEscapedProgmemStringSize(const char* value);
+
+    /**
+     * Appends a program-memory value as a JSON string to [cursor, end).
+     */
+    bool appendEscapedProgmemString(char*& cursor, char* end, const char* value);
+
+    /**
+     * Appends value as a JSON string to [cursor, end). end points at the last
+     * usable byte for the terminating null character. The output is left
+     * unchanged when the complete escaped value cannot fit.
+     */
+    bool appendEscapedString(char*& cursor, char* end, const char* value);
+
+    /**
+     * Home Assistant discovery node/object IDs may only contain these topic
+     * token characters: [A-Za-z0-9_-].
+     */
+    bool isValidDiscoveryTopicToken(const char* value);
+}
+
+#endif

src/utils/HASerializer.cpp

@@ -12,9 +12,112 @@
 #include "../HAMqtt.h"
 #include "../utils/HAUtils.h"
 #include "../utils/HANumeric.h"
+#include "../utils/HAJson.h"
 #include "../utils/HAAvailabilityConfig.h"
 #include "../device-types/HABaseDeviceType.h"
 
+namespace {
+bool writeJsonEscapedByte(HAMqtt* mqtt, const uint8_t value)
+{
+    char output[6];
+    uint8_t length = 0;
+
+    switch (value) {
+    case '"':
+        output[0] = '\\';
+        output[1] = '"';
+        length = 2;
+        break;
+    case '\\':
+        output[0] = '\\';
+        output[1] = '\\';
+        length = 2;
+        break;
+    case '\b':
+        output[0] = '\\';
+        output[1] = 'b';
+        length = 2;
+        break;
+    case '\f':
+        output[0] = '\\';
+        output[1] = 'f';
+        length = 2;
+        break;
+    case '\n':
+        output[0] = '\\';
+        output[1] = 'n';
+        length = 2;
+        break;
+    case '\r':
+        output[0] = '\\';
+        output[1] = 'r';
+        length = 2;
+        break;
+    case '\t':
+        output[0] = '\\';
+        output[1] = 't';
+        length = 2;
+        break;
+    default:
+        if (value < 0x20) {
+            static const char hex[] = "0123456789ABCDEF";
+            output[0] = '\\';
+            output[1] = 'u';
+            output[2] = '0';
+            output[3] = '0';
+            output[4] = hex[value >> 4];
+            output[5] = hex[value & 0x0F];
+            length = 6;
+        } else {
+            output[0] = static_cast<char>(value);
+            length = 1;
+        }
+        break;
+    }
+
+    return mqtt && mqtt->writePayload(output, length);
+}
+
+bool writeJsonString(HAMqtt* mqtt, const char* value, const bool progmem)
+{
+    if (!mqtt || !value) {
+        return false;
+    }
+
+    const char quote = '"';
+    if (!mqtt->writePayload(&quote, 1)) {
+        return false;
+    }
+    for (size_t i = 0; ; i++) {
+        const uint8_t byte = progmem
+            ? pgm_read_byte(value + i)
+            : static_cast<uint8_t>(value[i]);
+        if (byte == 0) {
+            break;
+        }
+        if (!writeJsonEscapedByte(mqtt, byte)) {
+            return false;
+        }
+    }
+    return mqtt->writePayload(&quote, 1);
+}
+
+bool writeJsonStringContents(HAMqtt* mqtt, const char* value)
+{
+    if (!mqtt || !value) {
+        return false;
+    }
+
+    for (size_t i = 0; value[i] != '\0'; i++) {
+        if (!writeJsonEscapedByte(mqtt, static_cast<uint8_t>(value[i]))) {
+            return false;
+        }
+    }
+
+    return true;
+}
+} // namespace
+
 uint16_t HASerializer::calculateConfigTopicLength(
     const __FlashStringHelper* componentName,
     const char* objectId
@@ -26,7 +129,10 @@ uint16_t HASerializer::calculateConfigTopicLength(
         !objectId ||
         !mqtt ||
         !mqtt->getDiscoveryPrefix() ||
-        !mqtt->getDevice()
+        !mqtt->getDevice() ||
+        !mqtt->getDevice()->getUniqueId() ||
+        !HAJson::isValidDiscoveryTopicToken(mqtt->getDevice()->getUniqueId()) ||
+        !HAJson::isValidDiscoveryTopicToken(objectId)
     ) {
         return 0;
     }
@@ -52,7 +158,10 @@ bool HASerializer::generateConfigTopic(
         !objectId ||
         !mqtt ||
         !mqtt->getDiscoveryPrefix() ||
-        !mqtt->getDevice()
+        !mqtt->getDevice() ||
+        !mqtt->getDevice()->getUniqueId() ||
+        !HAJson::isValidDiscoveryTopicToken(mqtt->getDevice()->getUniqueId()) ||
+        !HAJson::isValidDiscoveryTopicToken(objectId)
     ) {
         return false;
     }
@@ -83,7 +192,8 @@ uint16_t HASerializer::calculateDataTopicLength(
         !topic ||
         !mqtt ||
         !mqtt->getDataPrefix() ||
-        !mqtt->getDevice()
+        !mqtt->getDevice() ||
+        !mqtt->getDevice()->getUniqueId()
     ) {
         return 0;
     }
@@ -112,7 +222,8 @@ bool HASerializer::generateDataTopic(
         !topic ||
         !mqtt ||
         !mqtt->getDataPrefix() ||
-        !mqtt->getDevice()
+        !mqtt->getDevice() ||
+        !mqtt->getDevice()->getUniqueId()
     ) {
         return false;
     }
@@ -162,7 +273,7 @@ HASerializer::HASerializer(
     _deviceType(deviceType),
     _entriesNb(0),
     _maxEntriesNb(maxEntriesNb),
-    _entries(new SerializerEntry[maxEntriesNb])
+    _entries(new (std::nothrow) SerializerEntry[maxEntriesNb])
 {
 
 }
@@ -229,6 +340,10 @@ void HASerializer::topic(const __FlashStringHelper* topic)
 
 HASerializer::SerializerEntry* HASerializer::addEntry()
 {
+    if (!_entries) {
+        return nullptr;
+    }
+
     if (_entriesNb >= _maxEntriesNb) {
         if (_maxEntriesNb == UINT8_MAX) {
             return nullptr;
@@ -259,14 +374,18 @@ HASerializer::SerializerEntry* HASerializer::addEntry()
 
 uint16_t HASerializer::calculateSize() const
 {
-    uint16_t size =
+    if (!_entries) {
+        return 0;
+    }
+
+    uint32_t size =
         strlen_P(HASerializerJsonDataPrefix) +
         strlen_P(HASerializerJsonDataSuffix);
 
     for (uint8_t i = 0; i < _entriesNb; i++) {
         const uint16_t entrySize = calculateEntrySize(&_entries[i]);
         if (entrySize == 0) {
-            continue;
+            return 0;
         }
 
         size += entrySize;
@@ -275,9 +394,13 @@ uint16_t HASerializer::calculateSize() const
         if (i > 0) {
             size += strlen_P(HASerializerJsonPropertiesSeparator);
         }
+
+        if (size > UINT16_MAX) {
+            return 0;
+        }
     }
 
-    return size;
+    return static_cast<uint16_t>(size);
 }
 
 bool HASerializer::flush() const
@@ -287,11 +410,19 @@ bool HASerializer::flush() const
         return false;
     }
 
-    mqtt->writePayload(AHATOFSTR(HASerializerJsonDataPrefix));
+    if (calculateSize() == 0) {
+        return false;
+    }
+
+    if (!mqtt->writePayload(AHATOFSTR(HASerializerJsonDataPrefix))) {
+        return false;
+    }
 
     for (uint8_t i = 0; i < _entriesNb; i++) {
         if (i > 0) {
-            mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertiesSeparator));
+            if (!mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertiesSeparator))) {
+                return false;
+            }
         }
 
         if (!flushEntry(&_entries[i])) {
@@ -299,21 +430,27 @@ bool HASerializer::flush() const
         }
     }
 
-    mqtt->writePayload(AHATOFSTR(HASerializerJsonDataSuffix));
-    return true;
+    return mqtt->writePayload(AHATOFSTR(HASerializerJsonDataSuffix));
 }
 
 uint16_t HASerializer::calculateEntrySize(const SerializerEntry* entry) const
 {
     switch (entry->type) {
-    case PropertyEntryType:
-        return
-            // property name
+    case PropertyEntryType: {
+        if (!entry->property) {
+            return 0;
+        }
+        const uint16_t valueSize = calculatePropertyValueSize(entry);
+        if (valueSize == 0) {
+            return 0;
+        }
+        const uint32_t size =
             strlen_P(HASerializerJsonPropertyPrefix) +
             strlen_P(AHAFROMFSTR(entry->property)) +
             strlen_P(HASerializerJsonPropertySuffix) +
-            // property value
-            calculatePropertyValueSize(entry);
+            valueSize;
+        return size > UINT16_MAX ? 0 : static_cast<uint16_t>(size);
+    }
 
     case TopicEntryType:
         return calculateTopicEntrySize(entry);
@@ -335,56 +472,74 @@ uint16_t HASerializer::calculateTopicEntrySize(
     const SerializerEntry* entry
 ) const
 {
-    uint16_t size = 0;
-
-    // property name
-    size +=
+    uint32_t size =
         strlen_P(HASerializerJsonPropertyPrefix) +
         strlen_P(AHAFROMFSTR(entry->property)) +
         strlen_P(HASerializerJsonPropertySuffix);
 
-    // topic escape
-    size += 2 * strlen_P(HASerializerJsonEscapeChar);
-
-    // topic
+    uint16_t topicSize = 0;
     if (entry->value) {
-        size += strlen(static_cast<const char*>(entry->value));
+        topicSize = HAJson::calculateEscapedStringSize(
+            static_cast<const char*>(entry->value)
+        );
     } else {
-        if (!_deviceType) {
+        if (!_deviceType || !_deviceType->uniqueId()) {
             return 0;
         }
 
-        size += calculateDataTopicLength(
+        const uint16_t length = calculateDataTopicLength(
             _deviceType->uniqueId(),
             entry->property
-        ) - 1; // exclude null terminator
+        );
+        if (length == 0) {
+            return 0;
+        }
+
+        char topic[length];
+        if (!generateDataTopic(topic, _deviceType->uniqueId(), entry->property)) {
+            return 0;
+        }
+        topicSize = HAJson::calculateEscapedStringSize(topic);
     }
 
-    return size;
+    if (topicSize == 0 || (size + topicSize) > UINT16_MAX) {
+        return 0;
+    }
+
+    return static_cast<uint16_t>(size + topicSize);
 }
 
 uint16_t HASerializer::calculateAvailabilityArrayEntrySize(
     const SerializerEntry* entry
 ) const
 {
-    if (!entry->value) {
+    if (!entry->value || !entry->property) {
         return 0;
     }
 
     const HAAvailabilityConfig* cfg = static_cast<const HAAvailabilityConfig*>(
         entry->value
     );
+    const uint16_t jsonSize = cfg->calculateJsonSize();
+    if (jsonSize == 0) {
+        return 0;
+    }
 
-    return
+    const uint32_t size =
         strlen_P(HASerializerJsonPropertyPrefix) +
         strlen_P(AHAFROMFSTR(entry->property)) +
         strlen_P(HASerializerJsonPropertySuffix) +
-        cfg->calculateJsonSize();
+        jsonSize;
+
+    return size > UINT16_MAX ? 0 : static_cast<uint16_t>(size);
 }
 
 uint16_t HASerializer::calculateFlagSize(const FlagType flag) const
 {
     const HAMqtt* mqtt = HAMqtt::instance();
+    if (!mqtt || !mqtt->getDevice()) {
+        return 0;
+    }
     const HADevice* device = mqtt->getDevice();
 
     if (flag == WithDevice && device->getSerializer()) {
@@ -393,26 +548,44 @@ uint16_t HASerializer::calculateFlagSize(const FlagType flag) const
             return 0;
         }
 
-        return
+        const uint32_t size =
             strlen_P(HASerializerJsonPropertyPrefix) +
             strlen_P(HADeviceProperty) +
             strlen_P(HASerializerJsonPropertySuffix) +
             deviceLength;
-    } else if (flag == WithUniqueId && _deviceType) {
-        uint16_t uniqueIdLength = strlen(_deviceType->uniqueId());
-
-        if (device->isExtendedUniqueIdsEnabled()) {
-            uniqueIdLength += strlen(device->getUniqueId()) + 1; // with separator
+        return size > UINT16_MAX ? 0 : static_cast<uint16_t>(size);
+    } else if (flag == WithUniqueId && _deviceType && _deviceType->uniqueId()) {
+        const uint16_t uniqueIdSize = HAJson::calculateEscapedStringSize(
+            _deviceType->uniqueId()
+        );
+        if (uniqueIdSize == 0) {
+            return 0;
         }
 
-        return
-            // property name
+        uint32_t valueSize = uniqueIdSize;
+
+        if (device->isExtendedUniqueIdsEnabled()) {
+            if (!device->getUniqueId()) {
+                return 0;
+            }
+
+            const uint16_t deviceIdSize = HAJson::calculateEscapedStringSize(
+                device->getUniqueId()
+            );
+            if (deviceIdSize == 0) {
+                return 0;
+            }
+
+            // Both helper sizes include quotes; the combined value has one pair.
+            valueSize = deviceIdSize + uniqueIdSize - 1;
+        }
+
+        const uint32_t size =
             strlen_P(HASerializerJsonPropertyPrefix) +
             strlen_P(HAUniqueIdProperty) +
             strlen_P(HASerializerJsonPropertySuffix) +
-            // property value
-            2 * strlen_P(HASerializerJsonEscapeChar) +
-            uniqueIdLength;
+            valueSize;
+        return size > UINT16_MAX ? 0 : static_cast<uint16_t>(size);
     }
 
     return 0;
@@ -426,9 +599,9 @@ uint16_t HASerializer::calculatePropertyValueSize(
     case ConstCharPropertyValue:
     case ProgmemPropertyValue: {
         const char* value = static_cast<const char*>(entry->value);
-        const uint16_t len =
-            entry->subtype == ConstCharPropertyValue ? strlen(value) : strlen_P(value);
-        return 2 * strlen_P(HASerializerJsonEscapeChar) + len;
+        return entry->subtype == ConstCharPropertyValue
+            ? HAJson::calculateEscapedStringSize(value)
+            : HAJson::calculateEscapedProgmemStringSize(value);
     }
 
     case BoolPropertyType: {
@@ -447,7 +620,7 @@ uint16_t HASerializer::calculatePropertyValueSize(
         const HASerializerArray* array = static_cast<const HASerializerArray*>(
             entry->value
         );
-        return array->calculateSize();
+        return array ? array->calculateSize() : 0;
     }
 
     case JsonLiteralPropertyValue: {
@@ -466,9 +639,11 @@ bool HASerializer::flushEntry(const SerializerEntry* entry) const
 
     switch (entry->type) {
     case PropertyEntryType: {
-        mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertyPrefix));
-        mqtt->writePayload(entry->property);
-        mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertySuffix));
+        if (!mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertyPrefix)) ||
+            !mqtt->writePayload(entry->property) ||
+            !mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertySuffix))) {
+            return false;
+        }
 
         return flushEntryValue(entry);
     }
@@ -495,22 +670,12 @@ bool HASerializer::flushEntryValue(const SerializerEntry* entry) const
     case ConstCharPropertyValue:
     case ProgmemPropertyValue: {
         const char* value = static_cast<const char*>(entry->value);
-        mqtt->writePayload(AHATOFSTR(HASerializerJsonEscapeChar));
-
-        if (entry->subtype == ConstCharPropertyValue) {
-            mqtt->writePayload(value, strlen(value));
-        } else {
-            mqtt->writePayload(AHATOFSTR(value));
-        }
-
-        mqtt->writePayload(AHATOFSTR(HASerializerJsonEscapeChar));
-        return true;
+        return writeJsonString(mqtt, value, entry->subtype == ProgmemPropertyValue);
     }
 
     case BoolPropertyType: {
         const bool value = *static_cast<const bool*>(entry->value);
-        mqtt->writePayload(AHATOFSTR(value ? HATrue : HAFalse));
-        return true;
+        return mqtt->writePayload(AHATOFSTR(value ? HATrue : HAFalse));
     }
 
     case NumberPropertyType: {
@@ -521,21 +686,34 @@ bool HASerializer::flushEntryValue(const SerializerEntry* entry) const
         char tmp[HANumeric::MaxDigitsNb + 1];
         const uint16_t length = value->toStr(tmp);
 
-        mqtt->writePayload(tmp, length);
-        return true;
+        return mqtt->writePayload(tmp, length);
     }
 
     case ArrayPropertyType: {
         const HASerializerArray* array = static_cast<const HASerializerArray*>(
             entry->value
         );
-        const uint16_t size = array->calculateSize();
-        char tmp[size + 1]; // including null terminator
-        tmp[0] = 0;
-        array->serialize(tmp);
-        mqtt->writePayload(tmp, size);
+        if (!array) {
+            return false;
+        }
 
-        return true;
+        const uint16_t size = array->calculateSize();
+        if (size == 0) {
+            return false;
+        }
+
+        char* tmp = new (std::nothrow) char[size + 1];
+        if (!tmp) {
+            return false;
+        }
+        tmp[0] = 0;
+        bool serialized = array->serialize(tmp);
+        if (serialized) {
+            serialized = mqtt->writePayload(tmp, size);
+        }
+        delete[] tmp;
+
+        return serialized;
     }
 
     case JsonLiteralPropertyValue: {
@@ -544,8 +722,7 @@ bool HASerializer::flushEntryValue(const SerializerEntry* entry) const
             return false;
         }
 
-        mqtt->writePayload(value, strlen(value));
-        return true;
+        return mqtt->writePayload(value, strlen(value));
     }
 
     default:
@@ -558,17 +735,20 @@ bool HASerializer::flushTopic(const SerializerEntry* entry) const
     HAMqtt* mqtt = HAMqtt::instance();
 
     // property name
-    mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertyPrefix));
-    mqtt->writePayload(entry->property);
-    mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertySuffix));
-
-    // value (escaped)
-    mqtt->writePayload(AHATOFSTR(HASerializerJsonEscapeChar));
+    if (!mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertyPrefix)) ||
+        !mqtt->writePayload(entry->property) ||
+        !mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertySuffix))) {
+        return false;
+    }
 
     if (entry->value) {
         const char* topic = static_cast<const char*>(entry->value);
-        mqtt->writePayload(topic, strlen(topic));
+        return writeJsonString(mqtt, topic, false);
     } else {
+        if (!_deviceType || !_deviceType->uniqueId()) {
+            return false;
+        }
+
         const uint16_t length = calculateDataTopicLength(
             _deviceType->uniqueId(),
             entry->property
@@ -578,82 +758,103 @@ bool HASerializer::flushTopic(const SerializerEntry* entry) const
         }
 
         char topic[length];
-        generateDataTopic(
+        if (!generateDataTopic(
             topic,
             _deviceType->uniqueId(),
             entry->property
-        );
+        )) {
+            return false;
+        }
 
-        mqtt->writePayload(topic, length - 1);
+        return writeJsonString(mqtt, topic, false);
     }
-
-    mqtt->writePayload(AHATOFSTR(HASerializerJsonEscapeChar));
-    return true;
 }
 
 bool HASerializer::flushAvailabilityArray(const SerializerEntry* entry) const
 {
     HAMqtt* mqtt = HAMqtt::instance();
-    if (!entry->value) {
+    if (!mqtt || !entry->value || !entry->property) {
         return false;
     }
 
     const HAAvailabilityConfig* cfg = static_cast<const HAAvailabilityConfig*>(
         entry->value
     );
-
-    mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertyPrefix));
-    mqtt->writePayload(entry->property);
-    mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertySuffix));
-
     const uint16_t jsonSize = cfg->calculateJsonSize();
-    if (jsonSize >= 512) {
+    if (jsonSize == 0) {
         return false;
     }
 
-    char buf[512];
-    if (!cfg->serialize(buf)) {
+    char* buf = new (std::nothrow) char[jsonSize + 1];
+    if (!buf) {
         return false;
     }
 
-    mqtt->writePayload(buf, jsonSize);
-    return true;
+    const bool serialized = cfg->serialize(buf);
+    if (!serialized) {
+        delete[] buf;
+        return false;
+    }
+
+    const bool written = mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertyPrefix)) &&
+        mqtt->writePayload(entry->property) &&
+        mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertySuffix)) &&
+        mqtt->writePayload(buf, jsonSize);
+    delete[] buf;
+    return written;
 }
 
 bool HASerializer::flushFlag(const SerializerEntry* entry) const
 {
     HAMqtt* mqtt = HAMqtt::instance();
+    if (!mqtt || !mqtt->getDevice()) {
+        return false;
+    }
     const HADevice* device = mqtt->getDevice();
     const FlagType flag = static_cast<FlagType>(entry->subtype);
 
-    if (flag == WithDevice && device) {
+    if (flag == WithDevice && device->getSerializer()) {
         // property name
-        mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertyPrefix));
-        mqtt->writePayload(AHATOFSTR(HADeviceProperty));
-        mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertySuffix));
+        if (!mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertyPrefix)) ||
+            !mqtt->writePayload(AHATOFSTR(HADeviceProperty)) ||
+            !mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertySuffix))) {
+            return false;
+        }
 
         // property value
         return device->getSerializer()->flush();
-    } else if (flag == WithUniqueId && _deviceType) {
+    } else if (flag == WithUniqueId && _deviceType && _deviceType->uniqueId()) {
+        if (device->isExtendedUniqueIdsEnabled() && !device->getUniqueId()) {
+            return false;
+        }
+
         // property name
-        mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertyPrefix));
-        mqtt->writePayload(AHATOFSTR(HAUniqueIdProperty));
-        mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertySuffix));
+        if (!mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertyPrefix)) ||
+            !mqtt->writePayload(AHATOFSTR(HAUniqueIdProperty)) ||
+            !mqtt->writePayload(AHATOFSTR(HASerializerJsonPropertySuffix))) {
+            return false;
+        }
 
         // value
         const char* uniqueId = _deviceType->uniqueId();
-        mqtt->writePayload(AHATOFSTR(HASerializerJsonEscapeChar));
+        const char quote = '"';
+        if (!mqtt->writePayload(&quote, 1)) {
+            return false;
+        }
 
         if (device->isExtendedUniqueIdsEnabled()) {
             const char* deviceUniqueId = device->getUniqueId();
-            mqtt->writePayload(deviceUniqueId, strlen(deviceUniqueId));
-            mqtt->writePayload(AHATOFSTR(HASerializerUnderscore));
+            if (!writeJsonStringContents(mqtt, deviceUniqueId)) {
+                return false;
+            }
+            const char separator = '_';
+            if (!mqtt->writePayload(&separator, 1)) {
+                return false;
+            }
         }
 
-        mqtt->writePayload(uniqueId, strlen(uniqueId));
-        mqtt->writePayload(AHATOFSTR(HASerializerJsonEscapeChar));
-
-        return true;
+        return writeJsonStringContents(mqtt, uniqueId) &&
+            mqtt->writePayload(&quote, 1);
     }
 
     return false;

src/utils/HASerializerArray.cpp

@@ -3,6 +3,7 @@
 
 #include "HASerializerArray.h"
 #include "HADictionary.h"
+#include "HAJson.h"
 
 HASerializerArray::HASerializerArray(const uint8_t size, const bool progmemItems) :
     _progmemItems(progmemItems),
@@ -39,24 +40,36 @@ const char* HASerializerArray::getItem(const uint8_t index) const
 
 uint16_t HASerializerArray::calculateSize() const
 {
-    uint16_t size =
+    uint32_t size =
         strlen_P(HASerializerJsonArrayPrefix) +
         strlen_P(HASerializerJsonArraySuffix);
 
     if (_itemsNb == 0) {
-        return size;
+        return static_cast<uint16_t>(size);
     }
 
     // separators between elements
     size += (_itemsNb - 1) * strlen_P(HASerializerJsonPropertiesSeparator);
 
     for (uint8_t i = 0; i < _itemsNb; i++) {
-        size +=
-            2 * strlen_P(HASerializerJsonEscapeChar)
-            + (_progmemItems ? strlen_P(_items[i]) : strlen(_items[i]));
+        if (!_items[i]) {
+            return 0;
+        }
+
+        const uint16_t itemSize = _progmemItems
+            ? HAJson::calculateEscapedProgmemStringSize(_items[i])
+            : HAJson::calculateEscapedStringSize(_items[i]);
+        if (itemSize == 0) {
+            return 0;
+        }
+
+        size += itemSize;
+        if (size > UINT16_MAX) {
+            return 0;
+        }
     }
 
-    return size;
+    return static_cast<uint16_t>(size);
 }
 
 bool HASerializerArray::serialize(char* output) const
@@ -65,26 +78,33 @@ bool HASerializerArray::serialize(char* output) const
         return false;
     }
 
-    strcat_P(output, HASerializerJsonArrayPrefix);
+    const uint16_t size = calculateSize();
+    if (size == 0) {
+        return false;
+    }
+
+    char* cursor = output;
+    char* const end = output + size;
+    *cursor++ = '[';
+    *cursor = 0;
 
     for (uint8_t i = 0; i < _itemsNb; i++) {
         if (i > 0) {
-            strcat_P(output, HASerializerJsonPropertiesSeparator);
+            *cursor++ = ',';
+            *cursor = 0;
         }
 
-        strcat_P(output, HASerializerJsonEscapeChar);
-
-        if (_progmemItems) {
-            strcat_P(output, _items[i]);
-        } else {
-            strcat(output, _items[i]);
+        const bool serialized = _progmemItems
+            ? HAJson::appendEscapedProgmemString(cursor, end, _items[i])
+            : HAJson::appendEscapedString(cursor, end, _items[i]);
+        if (!serialized) {
+            return false;
         }
-
-        strcat_P(output, HASerializerJsonEscapeChar);
     }
 
-    strcat_P(output, HASerializerJsonArraySuffix);
-    return true;
+    *cursor++ = ']';
+    *cursor = 0;
+    return static_cast<uint16_t>(cursor - output) == size;
 }
 
 void HASerializerArray::clear()

test-support/ha-mqtt-test-harness/README.md

@@ -0,0 +1,18 @@
+# HA/MQTT test harness testkit
+
+This small Python package supplies generic test transport primitives for a
+disposable Home Assistant + MQTT test harness environment:
+
+- Home Assistant onboarding, MQTT config-entry setup, WebSocket registry access,
+  REST state/service helpers, and readiness waiting;
+- retained MQTT publishing and discovery observation; and
+- JSON/JSONL artifact output plus bounded retry helpers.
+
+It deliberately contains no ArduinoHA discovery fixture, DeviceFramework
+import, entity expectation, or release policy. ArduinoHA owns its migration
+fixture in `tests/ha-test-harness`; DeviceFramework owns its hardware fixture and
+Docker adapter in its own repository. Other projects can reuse this package by
+providing their own retained MQTT messages and assertions.
+
+The package is copied into a test container as a local build context and is not
+part of the Arduino firmware library export.

test-support/ha-mqtt-test-harness/pyproject.toml

@@ -0,0 +1,17 @@
+[build-system]
+requires = ["setuptools>=68"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "ha-mqtt-test-harness-testkit"
+version = "0.1.0"
+description = "Generic Home Assistant MQTT test-harness support"
+requires-python = ">=3.11"
+dependencies = [
+    "paho-mqtt==2.1.0",
+    "requests==2.34.2",
+    "websocket-client==1.9.2",
+]
+
+[tool.setuptools.packages.find]
+where = ["src"]

test-support/ha-mqtt-test-harness/src/ha_mqtt_test_harness/__init__.py

@@ -0,0 +1,21 @@
+"""Generic Home Assistant MQTT test harness-test support.
+
+This package deliberately knows nothing about ArduinoHA, DeviceFramework, or
+any particular discovery schema.  Consumers own their fixtures and assertions;
+the package owns only HA/MQTT transport, readiness, and artifact primitives.
+"""
+
+from .artifacts import write_json_artifact, write_json_lines
+from .home_assistant import HomeAssistantClient
+from .mqtt import MqttObserver, RetainedPublisher
+from .wait import TestHarnessError, wait_until
+
+__all__ = [
+    "TestHarnessError",
+    "HomeAssistantClient",
+    "MqttObserver",
+    "RetainedPublisher",
+    "wait_until",
+    "write_json_artifact",
+    "write_json_lines",
+]

test-support/ha-mqtt-test-harness/src/ha_mqtt_test_harness/artifacts.py

@@ -0,0 +1,30 @@
+"""Small artifact writers which keep container tests independent of host tools."""
+
+from __future__ import annotations
+
+import json
+import pathlib
+from collections.abc import Iterable
+from typing import Any
+
+
+def _path(root: str | pathlib.Path, name: str) -> pathlib.Path:
+    path = pathlib.Path(root) / name
+    path.parent.mkdir(parents=True, exist_ok=True)
+    return path
+
+
+def write_json_artifact(root: str | pathlib.Path, name: str, value: Any) -> pathlib.Path:
+    """Write a deterministic UTF-8 JSON artifact and return its path."""
+    path = _path(root, name)
+    path.write_text(json.dumps(value, indent=2, sort_keys=True) + "\n", encoding="utf-8")
+    return path
+
+
+def write_json_lines(root: str | pathlib.Path, name: str, values: Iterable[Any]) -> pathlib.Path:
+    """Write a deterministic JSONL artifact and return its path."""
+    path = _path(root, name)
+    with path.open("w", encoding="utf-8") as output:
+        for value in values:
+            output.write(json.dumps(value, sort_keys=True) + "\n")
+    return path

test-support/ha-mqtt-test-harness/src/ha_mqtt_test_harness/home_assistant.py

@@ -0,0 +1,245 @@
+"""Home Assistant onboarding, MQTT setup, registry, and service helpers."""
+
+from __future__ import annotations
+
+import json
+import pathlib
+import time
+from typing import Any
+
+import requests
+import websocket
+
+from .wait import TestHarnessError, wait_until
+
+
+class HomeAssistantClient:
+    """Authenticated HA API client with a deliberately small test harness surface."""
+
+    def __init__(self, base_url: str, token: str):
+        self.base_url = base_url.rstrip("/")
+        self.token = token
+        self._socket: websocket.WebSocket | None = None
+        self._next_id = 1
+
+    @property
+    def _headers(self) -> dict[str, str]:
+        return {"Authorization": f"Bearer {self.token}"}
+
+    @classmethod
+    def bootstrap(
+        cls,
+        base_url: str,
+        state_dir: str | pathlib.Path,
+        *,
+        owner_name: str = "HA MQTT Test Harness Owner",
+        username: str = "ha-mqtt-test-harness",
+        password: str = "ha-mqtt-test-harness-password",
+    ) -> "HomeAssistantClient":
+        """Create or load an isolated owner token for a disposable HA volume."""
+        base_url = base_url.rstrip("/")
+        state = pathlib.Path(state_dir)
+        token_file = state / "ha-token"
+        cls.wait_until_ready(base_url)
+        if token_file.exists():
+            return cls(base_url, token_file.read_text(encoding="utf-8").strip())
+
+        client_id = "http://ha-mqtt-test-harness.local/"
+        user = {
+            "client_id": client_id,
+            "name": owner_name,
+            "username": username,
+            "password": password,
+            "language": "en",
+        }
+        created = cls._response_json(
+            requests.post(f"{base_url}/api/onboarding/users", json=user, timeout=10),
+            "Home Assistant onboarding user creation",
+        )
+        auth_code = created.get("auth_code")
+        if not auth_code:
+            raise TestHarnessError("Home Assistant onboarding did not return an auth_code")
+        token_response = cls._response_json(
+            requests.post(
+                f"{base_url}/auth/token",
+                data={"client_id": client_id, "grant_type": "authorization_code", "code": auth_code},
+                timeout=10,
+            ),
+            "Home Assistant token exchange",
+        )
+        token = token_response.get("access_token")
+        if not token:
+            raise TestHarnessError("Home Assistant token exchange did not return an access_token")
+
+        client = cls(base_url, token)
+        for path, payload in (
+            ("/api/onboarding/core_config", {}),
+            ("/api/onboarding/analytics", {"preferences": {}}),
+        ):
+            response = requests.post(f"{base_url}{path}", headers=client._headers, json=payload, timeout=10)
+            if response.status_code not in (200, 201, 400, 404):
+                raise TestHarnessError(
+                    f"Home Assistant onboarding step {path} failed: {response.status_code} {response.text}"
+                )
+        state.mkdir(parents=True, exist_ok=True)
+        token_file.write_text(token, encoding="utf-8")
+        return client
+
+    @classmethod
+    def from_state(cls, base_url: str, state_dir: str | pathlib.Path) -> "HomeAssistantClient":
+        token_file = pathlib.Path(state_dir) / "ha-token"
+        if not token_file.exists():
+            raise TestHarnessError("Home Assistant token has not been bootstrapped")
+        return cls(base_url, token_file.read_text(encoding="utf-8").strip())
+
+    @staticmethod
+    def _response_json(response: requests.Response, context: str) -> dict[str, Any]:
+        if not response.ok:
+            raise TestHarnessError(f"{context} failed ({response.status_code}): {response.text}")
+        try:
+            value = response.json()
+        except ValueError as error:
+            raise TestHarnessError(f"{context} returned invalid JSON: {error}") from error
+        if not isinstance(value, dict):
+            raise TestHarnessError(f"{context} returned unexpected JSON: {value}")
+        return value
+
+    @classmethod
+    def wait_until_ready(cls, base_url: str, *, timeout: float = 180) -> None:
+        def ready() -> bool:
+            response = requests.get(f"{base_url.rstrip('/')}/api/", timeout=5)
+            return response.status_code in (200, 401)
+
+        wait_until("Home Assistant HTTP API", ready, timeout=timeout)
+
+    def configure_mqtt(self, host: str, port: int) -> None:
+        """Create HA's MQTT config entry, negotiating current/older form schemas."""
+        flow = self._response_json(
+            requests.post(
+                f"{self.base_url}/api/config/config_entries/flow",
+                headers=self._headers,
+                json={"handler": "mqtt"},
+                timeout=15,
+            ),
+            "MQTT config-entry flow creation",
+        )
+        if flow.get("type") == "create_entry":
+            return
+        if flow.get("type") != "form" or not flow.get("flow_id"):
+            raise TestHarnessError(f"unexpected MQTT config-entry flow result: {flow}")
+        user_input: dict[str, Any] = {"broker": host, "port": port}
+        schema_names = {
+            field.get("name") for field in flow.get("data_schema", []) if isinstance(field, dict)
+        }
+        if "other_settings" in schema_names:
+            user_input["other_settings"] = {
+                "set_client_cert": False,
+                "set_ca_cert": "off",
+                "transport": "tcp",
+            }
+        configured = self._response_json(
+            requests.post(
+                f"{self.base_url}/api/config/config_entries/flow/{flow['flow_id']}",
+                headers=self._headers,
+                json=user_input,
+                timeout=15,
+            ),
+            "MQTT config-entry flow configuration",
+        )
+        if configured.get("type") != "create_entry":
+            raise TestHarnessError(f"MQTT config-entry flow did not create an entry: {configured}")
+        time.sleep(3)
+
+    def _ensure_socket(self) -> websocket.WebSocket:
+        if self._socket is not None:
+            return self._socket
+        scheme = "wss" if self.base_url.startswith("https://") else "ws"
+        address = self.base_url.split("://", 1)[1]
+        socket = websocket.create_connection(f"{scheme}://{address}/api/websocket", timeout=15)
+        required = json.loads(socket.recv())
+        if required.get("type") != "auth_required":
+            socket.close()
+            raise TestHarnessError(f"unexpected Home Assistant WebSocket greeting: {required}")
+        socket.send(json.dumps({"type": "auth", "access_token": self.token}))
+        authenticated = json.loads(socket.recv())
+        if authenticated.get("type") != "auth_ok":
+            socket.close()
+            raise TestHarnessError(f"Home Assistant WebSocket authentication failed: {authenticated}")
+        self._socket = socket
+        return socket
+
+    def close(self) -> None:
+        if self._socket is not None:
+            self._socket.close()
+            self._socket = None
+
+    def call(self, message_type: str, **kwargs: Any) -> Any:
+        socket = self._ensure_socket()
+        message_id = self._next_id
+        self._next_id += 1
+        socket.send(json.dumps({"id": message_id, "type": message_type, **kwargs}))
+        while True:
+            result = json.loads(socket.recv())
+            if result.get("id") != message_id:
+                continue
+            if not result.get("success"):
+                raise TestHarnessError(f"WebSocket {message_type} failed: {result}")
+            return result.get("result")
+
+    def entity_registry(self) -> list[dict[str, Any]]:
+        result = self.call("config/entity_registry/list")
+        if not isinstance(result, list):
+            raise TestHarnessError(f"entity registry returned unexpected value: {result}")
+        return result
+
+    # A concise compatibility spelling for test harness suites; this remains schema-neutral.
+    def registry_entries(self) -> list[dict[str, Any]]:
+        return self.entity_registry()
+
+    def device_registry(self) -> list[dict[str, Any]]:
+        result = self.call("config/device_registry/list")
+        if not isinstance(result, list):
+            raise TestHarnessError(f"device registry returned unexpected value: {result}")
+        return result
+
+    def entities_for_device(self, device_id: str) -> list[dict[str, Any]]:
+        return [entry for entry in self.entity_registry() if entry.get("device_id") == device_id]
+
+    def wait_for_entity(self, unique_id: str, *, timeout: float = 60) -> dict[str, Any]:
+        def find() -> dict[str, Any] | None:
+            matches = [entry for entry in self.entity_registry() if entry.get("unique_id") == unique_id]
+            if len(matches) > 1:
+                raise TestHarnessError(f"duplicate entity-registry entries for {unique_id}: {matches}")
+            return matches[0] if matches else None
+
+        return wait_until(f"entity registry entry {unique_id}", find, timeout=timeout)
+
+    def state(self, entity_id: str) -> dict[str, Any] | None:
+        response = requests.get(f"{self.base_url}/api/states/{entity_id}", headers=self._headers, timeout=10)
+        if response.status_code == 404:
+            return None
+        return self._response_json(response, f"state lookup for {entity_id}")
+
+    def wait_for_state(self, entity_id: str, state: str, *, timeout: float = 60) -> dict[str, Any]:
+        return wait_until(
+            f"Home Assistant state {entity_id}={state}",
+            lambda: value if (value := self.state(entity_id)) and value.get("state") == state else None,
+            timeout=timeout,
+        )
+
+    def call_service(self, domain: str, service: str, data: dict[str, Any]) -> list[dict[str, Any]]:
+        response = requests.post(
+            f"{self.base_url}/api/services/{domain}/{service}",
+            headers=self._headers,
+            json=data,
+            timeout=15,
+        )
+        if not response.ok:
+            raise TestHarnessError(f"service {domain}.{service} failed ({response.status_code}): {response.text}")
+        try:
+            result = response.json()
+        except ValueError as error:
+            raise TestHarnessError(f"service {domain}.{service} returned invalid JSON: {error}") from error
+        if not isinstance(result, list):
+            raise TestHarnessError(f"service {domain}.{service} returned unexpected JSON: {result}")
+        return result

test-support/ha-mqtt-test-harness/src/ha_mqtt_test_harness/mqtt.py

@@ -0,0 +1,122 @@
+"""MQTT publishing and observation helpers for retained-discovery test harnesses."""
+
+from __future__ import annotations
+
+import threading
+import time
+import uuid
+from collections.abc import Iterable
+from typing import Any
+
+import paho.mqtt.client as mqtt
+
+from .wait import TestHarnessError, wait_until
+
+
+class _MqttClient:
+    def __init__(self, host: str, port: int, *, client_prefix: str):
+        self._connected = threading.Event()
+        self._client = mqtt.Client(
+            mqtt.CallbackAPIVersion.VERSION2,
+            client_id=f"{client_prefix}-{uuid.uuid4()}",
+        )
+        self._client.on_connect = self._on_connect
+        self._client.connect(host, port, keepalive=15)
+        self._client.loop_start()
+        if not self._connected.wait(timeout=15):
+            self.close()
+            raise TestHarnessError(f"MQTT client {client_prefix} did not connect within 15 seconds")
+
+    def _on_connect(self, _client: mqtt.Client, _userdata: Any, _flags: Any, reason_code: Any, _properties: Any) -> None:
+        if reason_code == 0:
+            self._connected.set()
+
+    def close(self) -> None:
+        self._client.loop_stop()
+        self._client.disconnect()
+
+
+class RetainedPublisher(_MqttClient):
+    """A QoS-1 retained publisher used by schema/migration fixtures."""
+
+    def __init__(self, host: str, port: int):
+        super().__init__(host, port, client_prefix="test-harness-publisher")
+
+    def publish(self, topic: str, payload: str, *, retain: bool = True) -> None:
+        info = self._client.publish(topic, payload, qos=1, retain=retain)
+        info.wait_for_publish(timeout=10)
+        if not info.is_published():
+            raise TestHarnessError(f"MQTT publish timed out for {topic}")
+
+    def retained_payload(self, topic: str, *, timeout: float = 30) -> str:
+        received: list[str] = []
+
+        def on_message(_client: mqtt.Client, _userdata: Any, message: mqtt.MQTTMessage) -> None:
+            if message.topic == topic:
+                received.append(message.payload.decode("utf-8"))
+
+        self._client.on_message = on_message
+        self._client.subscribe(topic, qos=1)
+        try:
+            return wait_until(
+                f"retained MQTT message {topic}",
+                lambda: received[0] if received else None,
+                timeout=timeout,
+            )
+        finally:
+            self._client.unsubscribe(topic)
+            self._client.on_message = None
+
+
+class MqttObserver(_MqttClient):
+    """Observe MQTT traffic without imposing a discovery-schema interpretation."""
+
+    def __init__(self, host: str, port: int, topics: Iterable[str] = ("homeassistant/#",)):
+        self._messages: list[dict[str, Any]] = []
+        self._lock = threading.Lock()
+        self._subscription_ack = threading.Event()
+        super().__init__(host, port, client_prefix="test-harness-observer")
+        self._client.on_message = self._on_message
+        self._client.on_subscribe = self._on_subscribe
+        for topic in topics:
+            result, _mid = self._client.subscribe(topic, qos=1)
+            if result != mqtt.MQTT_ERR_SUCCESS:
+                self.close()
+                raise TestHarnessError(f"unable to subscribe to MQTT topic {topic}")
+            if not self._subscription_ack.wait(timeout=15):
+                self.close()
+                raise TestHarnessError(f"MQTT subscription to {topic} was not acknowledged within 15 seconds")
+            self._subscription_ack.clear()
+
+    def _on_subscribe(
+        self,
+        _client: mqtt.Client,
+        _userdata: Any,
+        _mid: int,
+        _reason_codes: Any,
+        _properties: Any,
+    ) -> None:
+        self._subscription_ack.set()
+
+    def _on_message(self, _client: mqtt.Client, _userdata: Any, message: mqtt.MQTTMessage) -> None:
+        with self._lock:
+            self._messages.append(
+                {
+                    "topic": message.topic,
+                    "payload": message.payload.decode("utf-8", errors="replace"),
+                    "qos": message.qos,
+                    "retain": message.retain,
+                    "received_at": time.time(),
+                }
+            )
+
+    def messages(self) -> list[dict[str, Any]]:
+        with self._lock:
+            return list(self._messages)
+
+    def wait_for_topic(self, topic: str, *, timeout: float = 60) -> dict[str, Any]:
+        return wait_until(
+            f"MQTT topic {topic}",
+            lambda: next((entry for entry in reversed(self.messages()) if entry["topic"] == topic), None),
+            timeout=timeout,
+        )

test-support/ha-mqtt-test-harness/src/ha_mqtt_test_harness/wait.py

@@ -0,0 +1,36 @@
+"""Bounded wait helpers shared by integration test harnesses."""
+
+from __future__ import annotations
+
+import time
+from collections.abc import Callable
+from typing import TypeVar
+
+
+class TestHarnessError(RuntimeError):
+    """An external Home Assistant or MQTT test harness could not be satisfied."""
+
+
+T = TypeVar("T")
+
+
+def wait_until(
+    description: str,
+    predicate: Callable[[], T | None | bool],
+    *,
+    timeout: float = 90,
+    interval: float = 1,
+) -> T:
+    """Return the first truthy predicate result or raise a useful timeout."""
+    deadline = time.monotonic() + timeout
+    last_error: Exception | None = None
+    while time.monotonic() < deadline:
+        try:
+            result = predicate()
+            if result:
+                return result  # type: ignore[return-value]
+        except Exception as error:  # Services are expected to be starting.
+            last_error = error
+        time.sleep(interval)
+    suffix = f" (last error: {last_error})" if last_error else ""
+    raise TestHarnessError(f"timed out waiting for {description}{suffix}")

test/native/include/Arduino.h

@@ -0,0 +1,235 @@
+#ifndef AHA_NATIVE_ARDUINO_H
+#define AHA_NATIVE_ARDUINO_H
+
+// Minimal Arduino API shim for the host-only PlatformIO native test target.
+// It is deliberately test-only: production builds continue to use each
+// platform's Arduino core and PROGMEM implementation.
+
+#include <stdint.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <string.h>
+
+#include <iostream>
+#include <string>
+
+typedef uint8_t byte;
+
+class __FlashStringHelper;
+
+#ifndef PROGMEM
+#define PROGMEM
+#endif
+
+#ifndef PGM_P
+typedef const char* PGM_P;
+#endif
+
+#define F(value) reinterpret_cast<const __FlashStringHelper*>(value)
+#ifndef pgm_read_byte
+#define pgm_read_byte(address) (*reinterpret_cast<const uint8_t*>(address))
+#endif
+
+#ifndef strlen_P
+inline size_t strlen_P(PGM_P value)
+{
+    return value ? strlen(value) : 0;
+}
+#endif
+
+#ifndef strcpy_P
+inline char* strcpy_P(char* destination, PGM_P source)
+{
+    return strcpy(destination, source);
+}
+#endif
+
+#ifndef strncpy_P
+inline char* strncpy_P(char* destination, PGM_P source, size_t count)
+{
+    return strncpy(destination, source, count);
+}
+#endif
+
+#ifndef strcat_P
+inline char* strcat_P(char* destination, PGM_P source)
+{
+    return strcat(destination, source);
+}
+#endif
+
+#ifndef strcmp_P
+inline int strcmp_P(const char* left, PGM_P right)
+{
+    return strcmp(left, right);
+}
+#endif
+
+#ifndef memcpy_P
+inline void* memcpy_P(void* destination, PGM_P source, size_t count)
+{
+    return memcpy(destination, source, count);
+}
+#endif
+
+class String
+{
+public:
+    String() = default;
+
+    String(const char* value) :
+        _value(value ? value : "")
+    {
+
+    }
+
+    String(const __FlashStringHelper* value) :
+        _value(value ? reinterpret_cast<const char*>(value) : "")
+    {
+
+    }
+
+    String(const std::string& value) :
+        _value(value)
+    {
+
+    }
+
+    String(char value) :
+        _value(1, value)
+    {
+
+    }
+
+    String(bool value) :
+        _value(value ? "1" : "0")
+    {
+
+    }
+
+    String(int value) : _value(std::to_string(value)) { }
+    String(unsigned int value) : _value(std::to_string(value)) { }
+    String(long value) : _value(std::to_string(value)) { }
+    String(unsigned long value) : _value(std::to_string(value)) { }
+    String(long long value) : _value(std::to_string(value)) { }
+    String(unsigned long long value) : _value(std::to_string(value)) { }
+    String(float value) : _value(std::to_string(value)) { }
+    String(double value) : _value(std::to_string(value)) { }
+
+    const char* c_str() const
+    {
+        return _value.c_str();
+    }
+
+    size_t length() const
+    {
+        return _value.length();
+    }
+
+    String& operator+=(const String& value)
+    {
+        _value += value._value;
+        return *this;
+    }
+
+    String& operator+=(const char* value)
+    {
+        _value += value ? value : "";
+        return *this;
+    }
+
+    String& operator+=(const __FlashStringHelper* value)
+    {
+        _value += value ? reinterpret_cast<const char*>(value) : "";
+        return *this;
+    }
+
+    String operator+(const String& value) const
+    {
+        return String(_value + value._value);
+    }
+
+    String operator+(const char* value) const
+    {
+        return String(_value + (value ? value : ""));
+    }
+
+    String operator+(const __FlashStringHelper* value) const
+    {
+        return String(_value + (value ? reinterpret_cast<const char*>(value) : ""));
+    }
+
+private:
+    std::string _value;
+};
+
+inline String operator+(const char* left, const String& right)
+{
+    return String(left) + right;
+}
+
+inline String operator+(const __FlashStringHelper* left, const String& right)
+{
+    return String(left) + right;
+}
+
+class NativeSerial
+{
+public:
+    void begin(unsigned long) { }
+
+    template<typename T>
+    size_t print(const T& value)
+    {
+        std::cout << value;
+        return 1;
+    }
+
+    size_t print(const __FlashStringHelper* value)
+    {
+        std::cout << reinterpret_cast<const char*>(value);
+        return 1;
+    }
+
+    size_t print(const String& value)
+    {
+        std::cout << value.c_str();
+        return value.length();
+    }
+
+    template<typename T>
+    size_t println(const T& value)
+    {
+        print(value);
+        std::cout << '\n';
+        return 1;
+    }
+
+    size_t println()
+    {
+        std::cout << '\n';
+        return 1;
+    }
+};
+
+static NativeSerial Serial;
+
+inline uint32_t& nativeArduinoMillisStorage()
+{
+    static uint32_t value = 0;
+    return value;
+}
+
+inline unsigned long millis()
+{
+    return nativeArduinoMillisStorage();
+}
+
+inline void delay(unsigned long duration)
+{
+    nativeArduinoMillisStorage() += static_cast<uint32_t>(duration);
+}
+
+inline void yield() { }
+
+#endif

test/native/include/Client.h

@@ -0,0 +1,10 @@
+#ifndef AHA_NATIVE_CLIENT_H
+#define AHA_NATIVE_CLIENT_H
+
+class Client
+{
+public:
+    virtual ~Client() = default;
+};
+
+#endif

test/native/include/IPAddress.h

@@ -0,0 +1,33 @@
+#ifndef AHA_NATIVE_IPADDRESS_H
+#define AHA_NATIVE_IPADDRESS_H
+
+#include <Arduino.h>
+
+class IPAddress
+{
+public:
+    IPAddress() :
+        _octets{0, 0, 0, 0}
+    {
+
+    }
+
+    IPAddress(uint8_t a, uint8_t b, uint8_t c, uint8_t d) :
+        _octets{a, b, c, d}
+    {
+
+    }
+
+    String toString() const
+    {
+        return String(static_cast<unsigned int>(_octets[0])) + "." +
+            String(static_cast<unsigned int>(_octets[1])) + "." +
+            String(static_cast<unsigned int>(_octets[2])) + "." +
+            String(static_cast<unsigned int>(_octets[3]));
+    }
+
+private:
+    uint8_t _octets[4];
+};
+
+#endif

test/test_device_metadata/test_main.cpp

@@ -0,0 +1,109 @@
+#include <Arduino.h>
+#include <unity.h>
+
+#include <ArduinoHA.h>
+#include "mocks/PubSubClientMock.h"
+
+using TestFn = void (*)(void);
+
+struct TestCase {
+    const char* name;
+    TestFn fn;
+    uint16_t line;
+};
+
+#define TEST_ENTRY(fn) { #fn, fn, __LINE__ }
+
+static void flushDeviceSerializer(
+    PubSubClientMock* mock,
+    const HADevice& device
+)
+{
+    mock->connectDummy();
+    const HASerializer* serializer = device.getSerializer();
+    TEST_ASSERT_NOT_NULL(serializer);
+    TEST_ASSERT_TRUE(mock->beginPublish("test/device/config", serializer->calculateSize(), true));
+    TEST_ASSERT_TRUE(serializer->flush());
+    TEST_ASSERT_TRUE(mock->endPublish());
+}
+
+void test_DeviceMetadata_add_connection_escapes_json()
+{
+    PubSubClientMock* mock = new PubSubClientMock();
+    HADevice device("testDevice");
+    HAMqtt mqtt(mock, device);
+
+    TEST_ASSERT_TRUE(device.addConnection("mac", "aa\"\\bb\n"));
+    flushDeviceSerializer(mock, device);
+
+    TEST_ASSERT_EQUAL_UINT8(1, mock->getFlushedMessagesNb());
+    TEST_ASSERT_EQUAL_STRING(
+        "{\"ids\":\"testDevice\",\"cns\":[[\"mac\",\"aa\\\"\\\\bb\\n\"]]}",
+        mock->getFlushedMessages()[0]->buffer
+    );
+}
+
+void test_DeviceMetadata_raw_connections_reject_malformed_input()
+{
+    PubSubClientMock* mock = new PubSubClientMock();
+    HADevice device("testDevice");
+    HAMqtt mqtt(mock, device);
+
+    TEST_ASSERT_FALSE(device.setConnectionsJson("[[\"mac\",invalid]]"));
+    flushDeviceSerializer(mock, device);
+
+    TEST_ASSERT_EQUAL_STRING(
+        "{\"ids\":\"testDevice\"}",
+        mock->getFlushedMessages()[0]->buffer
+    );
+}
+
+void test_DeviceMetadata_raw_connections_accept_complete_tuple_array()
+{
+    PubSubClientMock* mock = new PubSubClientMock();
+    HADevice device("testDevice");
+    HAMqtt mqtt(mock, device);
+
+    TEST_ASSERT_TRUE(device.setConnectionsJson("[[\"mac\",\"aa:bb\"],[\"serial\",\"42\"]]"));
+    flushDeviceSerializer(mock, device);
+
+    TEST_ASSERT_EQUAL_STRING(
+        "{\"ids\":\"testDevice\",\"cns\":[[\"mac\",\"aa:bb\"],[\"serial\",\"42\"]]}",
+        mock->getFlushedMessages()[0]->buffer
+    );
+}
+
+static TestCase tests[] = {
+    TEST_ENTRY(test_DeviceMetadata_add_connection_escapes_json),
+    TEST_ENTRY(test_DeviceMetadata_raw_connections_reject_malformed_input),
+    TEST_ENTRY(test_DeviceMetadata_raw_connections_accept_complete_tuple_array),
+};
+
+static const size_t testCount = sizeof(tests) / sizeof(tests[0]);
+static size_t nextTest = 0;
+static bool begun = false;
+
+void setUp(void) { }
+void tearDown(void) { }
+
+void setup()
+{
+    Serial.begin(115200);
+    delay(500);
+    UNITY_BEGIN();
+    begun = true;
+}
+
+void loop()
+{
+    if (begun && nextTest < testCount) {
+        TestCase& test = tests[nextTest++];
+        UnityDefaultTestRun(test.fn, test.name, test.line);
+        return;
+    }
+
+    if (begun) {
+        UNITY_END();
+        begun = false;
+    }
+}

test/test_entities_basic/test_main.cpp

@@ -125,6 +125,10 @@ static TestCase tests[] = {
     TEST_ENTRY(test_TextTest_publish_state_debounce),
     TEST_ENTRY(test_TextTest_callback_publish_is_deferred_until_after_dispatch),
     TEST_ENTRY(test_TextTest_retain_setter),
+    TEST_ENTRY(test_TextTest_current_state_is_owned),
+    TEST_ENTRY(test_TextTest_oversized_state_is_rejected),
+    TEST_ENTRY(test_TextTest_callback_state_is_owned_after_dispatch),
+    TEST_ENTRY(test_TextTest_oversized_command_is_ignored),
 };
 
 static const size_t TEST_COUNT = sizeof(tests) / sizeof(tests[0]);

test/test_entities_basic/test_main.h

@@ -135,5 +135,9 @@ extern void test_TextTest_publish_state(void);
 extern void test_TextTest_publish_state_debounce(void);
 extern void test_TextTest_retain_setter(void);
 extern void test_TextTest_callback_publish_is_deferred_until_after_dispatch(void);
+extern void test_TextTest_current_state_is_owned(void);
+extern void test_TextTest_oversized_state_is_rejected(void);
+extern void test_TextTest_callback_state_is_owned_after_dispatch(void);
+extern void test_TextTest_oversized_command_is_ignored(void);
 
 #endif

test/test_entities_basic/tests/test_binary_sensor.cpp

@@ -110,7 +110,6 @@ void test_BinarySensorTest_object_id_setter(void) {
         sensor,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueSensor\","
             "\"dev\":{\"ids\":\"testDevice\"},"
             "\"stat_t\":\"testData/testDevice/uniqueSensor/stat_t\""

test/test_entities_basic/tests/test_button.cpp

@@ -139,7 +139,6 @@ void test_ButtonTest_object_id_setter(void) {
         button,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueButton\","
             "\"dev\":{\"ids\":\"testDevice\"},"
             "\"cmd_t\":\"testData/testDevice/uniqueButton/cmd_t\""

test/test_entities_basic/tests/test_sensor.cpp

@@ -100,7 +100,6 @@ void test_SensorTest_object_id_setter(void) {
         sensor,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueSensor\","
             "\"dev\":{\"ids\":\"testDevice\"},"
             "\"stat_t\":\"testData/testDevice/uniqueSensor/stat_t\""

test/test_entities_basic/tests/test_switch.cpp

@@ -110,7 +110,7 @@ void test_SwitchTest_device_discovery_payload(void) {
         (
             "{"
             "\"dev\":{\"ids\":\"testDevice\"},"
-            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"2.1.0\"},"
+            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"3.0.2\"},"
             "\"cmps\":{"
                 "\"uniqueSwitch\":{"
                     "\"p\":\"switch\","
@@ -206,7 +206,6 @@ void test_SwitchTest_object_id_setter(void) {
         testSwitch,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueSwitch\","
             "\"dev\":{\"ids\":\"testDevice\"},"
             "\"stat_t\":\"testData/testDevice/uniqueSwitch/stat_t\","

test/test_entities_basic/tests/test_text.cpp

@@ -51,6 +51,14 @@ void onCommandDeferredPublish(const char* value, HAText* caller)
     TEST_ASSERT_TRUE(caller->setState(value));
 }
 
+void onCommandSetStateAndOverwrite(const char* value, HAText* caller)
+{
+    TEST_ASSERT_TRUE(caller->setState(value));
+    char* mutableValue = const_cast<char*>(value);
+    mutableValue[0] = 'x';
+    TEST_ASSERT_EQUAL_STRING("hello", caller->getCurrentState());
+}
+
 void test_TextTest_invalid_unique_id(void) {
     prepareTest
 
@@ -178,7 +186,6 @@ void test_TextTest_object_id_setter(void) {
         text,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueText\","
             "\"dev\":{\"ids\":\"testDevice\"},"
             "\"stat_t\":\"testData/testDevice/uniqueText/stat_t\","
@@ -318,6 +325,32 @@ void test_TextTest_publish_state_debounce(void) {
     TEST_ASSERT_EQUAL(0, mock->getFlushedMessagesNb());
 }
 
+void test_TextTest_current_state_is_owned(void) {
+    prepareTest
+
+    HAText text(testUniqueId);
+    char state[] = "initial";
+    text.setCurrentState(state);
+    state[0] = 'x';
+
+    TEST_ASSERT_EQUAL_STRING("initial", text.getCurrentState());
+}
+
+void test_TextTest_oversized_state_is_rejected(void) {
+    prepareTest
+
+    HAText text(testUniqueId);
+    text.setCurrentState("initial");
+    char state[HAText::MaxCommandLength + 2];
+    memset(state, 'x', sizeof(state) - 1);
+    state[sizeof(state) - 1] = 0;
+
+    text.setCurrentState(state);
+    TEST_ASSERT_EQUAL_STRING("initial", text.getCurrentState());
+    TEST_ASSERT_FALSE(text.setState(state));
+    TEST_ASSERT_EQUAL_STRING("initial", text.getCurrentState());
+}
+
 void test_TextTest_command_callback(void) {
     prepareTest
 
@@ -343,6 +376,32 @@ void test_TextTest_callback_publish_is_deferred_until_after_dispatch(void) {
     AHA_ASSERT_MQTT_MESSAGE(mock, 0, AHATOFSTR(StateTopic), "hello", true);
 }
 
+void test_TextTest_callback_state_is_owned_after_dispatch(void) {
+    prepareTest
+
+    mock->connectDummy();
+    HAText text(testUniqueId);
+    text.onCommand(onCommandSetStateAndOverwrite);
+
+    mock->fakeMessage(AHATOFSTR(CommandTopic), F("hello"));
+
+    TEST_ASSERT_EQUAL_STRING("hello", text.getCurrentState());
+}
+
+void test_TextTest_oversized_command_is_ignored(void) {
+    prepareTest
+
+    HAText text(testUniqueId);
+    text.onCommand(onCommandReceived);
+    char command[HAText::MaxCommandLength + 2];
+    memset(command, 'x', sizeof(command) - 1);
+    command[sizeof(command) - 1] = 0;
+
+    mock->fakeMessage(AHATOFSTR(CommandTopic), command);
+
+    assertCommandCallbackNotCalled()
+}
+
 void test_TextTest_different_text_command(void) {
     prepareTest
 

test/test_entities_extended/tests/test_camera.cpp

@@ -66,7 +66,7 @@ void test_CameraTest_device_discovery_payload(void) {
         (
             "{"
             "\"dev\":{\"ids\":\"testDevice\"},"
-            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"2.1.0\"},"
+            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"3.0.2\"},"
             "\"cmps\":{"
                 "\"uniqueCamera\":{"
                     "\"p\":\"camera\","
@@ -127,7 +127,6 @@ void test_CameraTest_object_id_setter(void) {
         camera,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueCamera\","
             "\"dev\":{\"ids\":\"testDevice\"},"
             "\"t\":\"testData/testDevice/uniqueCamera/t\""

test/test_entities_extended/tests/test_cover.cpp

@@ -104,7 +104,7 @@ void test_CoverTest_device_discovery_payload(void) {
         (
             "{"
             "\"dev\":{\"ids\":\"testDevice\"},"
-            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"2.1.0\"},"
+            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"3.0.2\"},"
             "\"cmps\":{"
                 "\"uniqueCover\":{"
                     "\"p\":\"cover\","
@@ -234,7 +234,6 @@ void test_CoverTest_object_id_setter(void) {
         cover,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueCover\","
             "\"dev\":{\"ids\":\"testDevice\"},"
             "\"stat_t\":\"testData/testDevice/uniqueCover/stat_t\","

test/test_entities_extended/tests/test_fan.cpp

@@ -136,7 +136,7 @@ void test_FanTest_device_discovery_payload(void) {
         (
             "{"
             "\"dev\":{\"ids\":\"testDevice\"},"
-            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"2.1.0\"},"
+            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"3.0.2\"},"
             "\"cmps\":{"
                 "\"uniqueFan\":{"
                     "\"p\":\"fan\","
@@ -279,7 +279,6 @@ void test_FanTest_object_id_setter(void) {
         fan,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueFan\","
             "\"dev\":{\"ids\":\"testDevice\"},"
             "\"stat_t\":\"testData/testDevice/uniqueFan/stat_t\","

test/test_entities_extended/tests/test_hvac.cpp

@@ -257,7 +257,7 @@ void test_HVACTest_device_discovery_payload(void) {
         (
             "{"
             "\"dev\":{\"ids\":\"testDevice\"},"
-            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"2.1.0\"},"
+            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"3.0.2\"},"
             "\"cmps\":{"
                 "\"uniqueHVAC\":{"
                     "\"p\":\"climate\","
@@ -579,7 +579,6 @@ void test_HVACTest_object_id_setter(void) {
         hvac,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueHVAC\","
             "\"curr_temp_t\":\"testData/testDevice/uniqueHVAC/curr_temp_t\","
             "\"dev\":{\"ids\":\"testDevice\"}"

test/test_entities_extended/tests/test_light.cpp

@@ -429,7 +429,6 @@ void test_LightTest_object_id_setter(void) {
         light,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueLight\","
             "\"dev\":{\"ids\":\"testDevice\"},"
             "\"stat_t\":\"testData/testDevice/uniqueLight/stat_t\","

test/test_entities_extended/tests/test_lock.cpp

@@ -103,7 +103,7 @@ void test_LockTest_device_discovery_payload(void) {
         (
             "{"
             "\"dev\":{\"ids\":\"testDevice\"},"
-            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"2.1.0\"},"
+            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"3.0.2\"},"
             "\"cmps\":{"
                 "\"uniqueLock\":{"
                     "\"p\":\"lock\","
@@ -198,7 +198,6 @@ void test_LockTest_object_id_setter(void) {
         lock,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueLock\","
             "\"dev\":{\"ids\":\"testDevice\"},"
             "\"stat_t\":\"testData/testDevice/uniqueLock/stat_t\","

test/test_entities_misc/tests/test_device_tracker.cpp

@@ -68,7 +68,7 @@ void test_DeviceTrackerTest_device_discovery_payload(void) {
         (
             "{"
             "\"dev\":{\"ids\":\"testDevice\"},"
-            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"2.1.0\"},"
+            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"3.0.2\"},"
             "\"cmps\":{"
                 "\"uniqueTracker\":{"
                     "\"p\":\"device_tracker\","
@@ -215,7 +215,6 @@ void test_DeviceTrackerTest_object_id_setter(void) {
         tracker,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueTracker\","
             "\"dev\":{\"ids\":\"testDevice\"},"
             "\"stat_t\":\"testData/testDevice/uniqueTracker/stat_t\""

test/test_entities_misc/tests/test_device_trigger.cpp

@@ -99,7 +99,7 @@ void test_DeviceTriggerTest_device_discovery_payload(void) {
         (
             "{"
             "\"dev\":{\"ids\":\"testDevice\"},"
-            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"2.1.0\"},"
+            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"3.0.2\"},"
             "\"cmps\":{"
                 "\"myType_mySubtype\":{"
                     "\"p\":\"device_automation\","

test/test_entities_misc/tests/test_scene.cpp

@@ -95,7 +95,7 @@ void test_SceneTest_device_discovery_payload(void) {
         (
             "{"
             "\"dev\":{\"ids\":\"testDevice\"},"
-            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"2.1.0\"},"
+            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"3.0.2\"},"
             "\"cmps\":{"
                 "\"uniqueScene\":{"
                     "\"p\":\"scene\","
@@ -167,7 +167,6 @@ void test_SceneTest_object_id_setter(void) {
         scene,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueScene\","
             "\"pl_on\":\"ON\","
             "\"cmd_t\":\"testData/testDevice/uniqueScene/cmd_t\""

test/test_entities_misc/tests/test_tag_scanner.cpp

@@ -46,7 +46,7 @@ void test_TagScannerTest_device_discovery_payload(void) {
         (
             "{"
             "\"dev\":{\"ids\":\"testDevice\"},"
-            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"2.1.0\"},"
+            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"3.0.2\"},"
             "\"cmps\":{"
                 "\"uniqueScanner\":{"
                     "\"p\":\"tag\","

test/test_entities_numeric/tests/test_number.cpp

@@ -351,7 +351,6 @@ void test_NumberTest_object_id_setter(void) {
         number,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueNumber\","
             "\"dev\":{\"ids\":\"testDevice\"},"
             "\"stat_t\":\"testData/testDevice/uniqueNumber/stat_t\","
@@ -926,7 +925,7 @@ void test_NumberTest_update_min_max_step_republishes_device_discovery_when_enabl
         (
             "{"
             "\"dev\":{\"ids\":\"testDevice\"},"
-            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"2.1.0\"},"
+            "\"o\":{\"name\":\"ArduinoHA\",\"sw\":\"3.0.2\"},"
             "\"cmps\":{"
                 "\"uniqueNumber\":{"
                     "\"p\":\"number\","

test/test_entities_numeric/tests/test_select.cpp

@@ -280,7 +280,6 @@ void test_SelectTest_object_id_setter(void) {
         select,
         (
             "{"
-            "\"obj_id\":\"testId\","
             "\"uniq_id\":\"uniqueSelect\","
             "\"options\":[\"Option A\",\"B\",\"C\"],"
             "\"dev\":{\"ids\":\"testDevice\"},"

test/test_native_core/test_main.cpp

@@ -0,0 +1,355 @@
+#include <Arduino.h>
+#include <string.h>
+#include <unity.h>
+
+#include "HADevice.h"
+#include "HAMqtt.h"
+#include "device-types/HABaseDeviceType.h"
+#include "device-types/HAText.h"
+#include "mocks/PubSubClientMock.h"
+#include "utils/HAAvailabilityConfig.h"
+#include "utils/HAJson.h"
+#include "utils/HASerializer.h"
+#include "utils/HASerializerArray.h"
+
+namespace {
+class NativeSerializerEntity : public HABaseDeviceType
+{
+public:
+    explicit NativeSerializerEntity(const char* uniqueId) :
+        HABaseDeviceType(F("sensor"), uniqueId)
+    {
+
+    }
+
+protected:
+    void onMqttConnected() override { }
+};
+class NativeDiscoveryEntity : public HABaseDeviceType
+{
+public:
+    explicit NativeDiscoveryEntity(const char* uniqueId) :
+        HABaseDeviceType(F("sensor"), uniqueId)
+    {
+
+    }
+
+protected:
+    void buildSerializer() override
+    {
+        if (_serializer) {
+            return;
+        }
+
+        _serializer = new HASerializer(this, 2);
+        _serializer->set(F("name"), uniqueId());
+        _serializer->set(HASerializer::WithUniqueId);
+    }
+
+    HASerializer* buildDeviceDiscoverySerializer() override
+    {
+        HASerializer* serializer = new HASerializer(this, 3);
+        serializer->set(
+            F("p"),
+            componentName(),
+            HASerializer::ProgmemPropertyValue
+        );
+        serializer->set(F("name"), uniqueId());
+        serializer->set(HASerializer::WithUniqueId);
+        return serializer;
+    }
+
+    bool supportsDeviceDiscovery() const override
+    {
+        return true;
+    }
+
+    void onMqttConnected() override { }
+};
+
+uint8_t disconnectedCallbackCalls = 0;
+uint8_t stateCallbackCalls = 0;
+
+void onNativeDisconnected()
+{
+    disconnectedCallbackCalls++;
+}
+
+void onNativeStateChanged(HAMqtt::ConnectionState)
+{
+    stateCallbackCalls++;
+}
+
+
+void test_json_helpers_escape_control_bytes_and_preserve_cursor_contract()
+{
+    const char value[] = "quote\" slash\\ newline\n tab\t control\x01";
+    char output[96] = {};
+    char* cursor = output;
+
+    TEST_ASSERT_EQUAL_UINT16(
+        strlen("\"quote\\\" slash\\\\ newline\\n tab\\t control\\u0001\""),
+        HAJson::calculateEscapedStringSize(value)
+    );
+    TEST_ASSERT_TRUE(HAJson::appendEscapedString(cursor, output + sizeof(output) - 1, value));
+    TEST_ASSERT_EQUAL_STRING(
+        "\"quote\\\" slash\\\\ newline\\n tab\\t control\\u0001\"",
+        output
+    );
+    TEST_ASSERT_EQUAL_PTR(output + strlen(output), cursor);
+}
+
+void test_availability_and_serializer_array_escape_json_values()
+{
+    HAAvailabilityConfig availability;
+    TEST_ASSERT_TRUE(availability.add("availability/\"main\"", "{{ value_json.\\n }}", "on\nline", "off\\line"));
+
+    const uint16_t availabilitySize = availability.calculateJsonSize();
+    char availabilityJson[availabilitySize + 1];
+    TEST_ASSERT_TRUE(availability.serialize(availabilityJson));
+    TEST_ASSERT_EQUAL_STRING(
+        "[{\"t\":\"availability/\\\"main\\\"\",\"val_tpl\":\"{{ value_json.\\\\n }}\",\"pl_avail\":\"on\\nline\",\"pl_not_avail\":\"off\\\\line\"}]",
+        availabilityJson
+    );
+    TEST_ASSERT_EQUAL_UINT16(strlen(availabilityJson), availabilitySize);
+
+    HASerializerArray values(2, false);
+    TEST_ASSERT_TRUE(values.add("first\"item"));
+    TEST_ASSERT_TRUE(values.add("second\nitem"));
+    const uint16_t valuesSize = values.calculateSize();
+    char valuesJson[valuesSize + 1];
+    TEST_ASSERT_TRUE(values.serialize(valuesJson));
+    TEST_ASSERT_EQUAL_STRING("[\"first\\\"item\",\"second\\nitem\"]", valuesJson);
+    TEST_ASSERT_EQUAL_UINT16(strlen(valuesJson), valuesSize);
+}
+
+void test_discovery_topic_tokens_are_rejected_before_topic_generation()
+{
+    HADevice device("native_device");
+    PubSubClientMock* mock = new PubSubClientMock();
+    HAMqtt mqtt(mock, device);
+
+    const __FlashStringHelper* component = F("sensor");
+    const uint16_t topicSize = HASerializer::calculateConfigTopicLength(component, "valid_entity-1");
+    char topic[topicSize];
+    TEST_ASSERT_TRUE(HASerializer::generateConfigTopic(topic, component, "valid_entity-1"));
+    TEST_ASSERT_EQUAL_STRING("homeassistant/sensor/native_device/valid_entity-1/config", topic);
+
+    TEST_ASSERT_EQUAL_UINT16(0, HASerializer::calculateConfigTopicLength(component, "invalid/entity"));
+    TEST_ASSERT_FALSE(HASerializer::generateConfigTopic(topic, component, "invalid entity"));
+}
+
+void test_streaming_serializer_writes_exact_escaped_payload_to_mqtt_mock()
+{
+    HADevice device("native_device");
+    PubSubClientMock* mock = new PubSubClientMock();
+    HAMqtt mqtt(mock, device);
+    NativeSerializerEntity entity("native_entity");
+
+    TEST_ASSERT_TRUE(mqtt.begin("native-host"));
+    TEST_ASSERT_TRUE(mock->connectDummy());
+
+    HASerializer serializer(&entity, 2);
+    serializer.set(F("name"), "Name \"quoted\"\\line\nnext");
+    serializer.set(F("unit_of_meas"), "C\tunit");
+
+    const uint16_t payloadSize = serializer.calculateSize();
+    TEST_ASSERT_NOT_EQUAL(0, payloadSize);
+    TEST_ASSERT_TRUE(mqtt.beginPublish("native/serializer", payloadSize, true));
+    TEST_ASSERT_TRUE(serializer.flush());
+    TEST_ASSERT_TRUE(mqtt.endPublish());
+
+    TEST_ASSERT_EQUAL_UINT8(1, mock->getFlushedMessagesNb());
+    MqttMessage* message = mock->getFlushedMessages()[0];
+    TEST_ASSERT_EQUAL_STRING("native/serializer", message->topic);
+    TEST_ASSERT_EQUAL_STRING(
+        "{\"name\":\"Name \\\"quoted\\\"\\\\line\\nnext\",\"unit_of_meas\":\"C\\tunit\"}",
+        message->buffer
+    );
+    TEST_ASSERT_EQUAL_UINT16(strlen(message->buffer), message->writtenSize);
+    TEST_ASSERT_EQUAL_UINT16(payloadSize, message->writtenSize);
+}
+void test_staged_migration_orders_markers_device_payload_and_legacy_cleanup()
+{
+    HADevice device("native_device");
+    PubSubClientMock* mock = new PubSubClientMock();
+    HAMqtt mqtt(mock, device);
+    NativeDiscoveryEntity first("first");
+    NativeDiscoveryEntity second("second");
+    TEST_ASSERT_TRUE(mock->connectDummy());
+
+    TEST_ASSERT_TRUE(mqtt.beginDeviceDiscoveryMigration());
+    TEST_ASSERT_EQUAL_INT(HAMqtt::DeviceDiscoveryMigrationMarkersPending,
+        mqtt.getDeviceDiscoveryMigrationState());
+    TEST_ASSERT_FALSE(mqtt.publishDeviceDiscovery());
+    TEST_ASSERT_EQUAL_UINT8(0, mock->getFlushedMessagesNb());
+
+    TEST_ASSERT_TRUE(mqtt.publishDeviceDiscoveryMigrationMarkers());
+    TEST_ASSERT_EQUAL_UINT8(2, mock->getFlushedMessagesNb());
+    TEST_ASSERT_EQUAL_STRING("homeassistant/sensor/native_device/first/config",
+        mock->getFlushedMessages()[0]->topic);
+    TEST_ASSERT_EQUAL_STRING("{\"migrate_discovery\":true}",
+        mock->getFlushedMessages()[0]->buffer);
+    TEST_ASSERT_EQUAL_STRING("homeassistant/sensor/native_device/second/config",
+        mock->getFlushedMessages()[1]->topic);
+
+    TEST_ASSERT_TRUE(mqtt.publishDeviceDiscoveryMigrationConfig());
+    TEST_ASSERT_EQUAL_UINT8(3, mock->getFlushedMessagesNb());
+    TEST_ASSERT_EQUAL_STRING("homeassistant/device/native_device/config",
+        mock->getFlushedMessages()[2]->topic);
+    TEST_ASSERT_NOT_NULL(strstr(mock->getFlushedMessages()[2]->buffer, "\"cmps\""));
+    TEST_ASSERT_NOT_NULL(strstr(mock->getFlushedMessages()[2]->buffer, "\"first\""));
+    TEST_ASSERT_NOT_NULL(strstr(mock->getFlushedMessages()[2]->buffer, "\"second\""));
+
+    TEST_ASSERT_TRUE(mqtt.completeDeviceDiscoveryMigration());
+    TEST_ASSERT_EQUAL_UINT8(5, mock->getFlushedMessagesNb());
+    TEST_ASSERT_EQUAL_STRING("homeassistant/sensor/native_device/first/config",
+        mock->getFlushedMessages()[3]->topic);
+    TEST_ASSERT_EQUAL_STRING("", mock->getFlushedMessages()[3]->buffer);
+    TEST_ASSERT_EQUAL_STRING("homeassistant/sensor/native_device/second/config",
+        mock->getFlushedMessages()[4]->topic);
+    TEST_ASSERT_EQUAL_STRING("", mock->getFlushedMessages()[4]->buffer);
+    TEST_ASSERT_EQUAL_INT(HAMqtt::DeviceDiscoveryMigrationCompleted,
+        mqtt.getDeviceDiscoveryMigrationState());
+
+    TEST_ASSERT_TRUE(mqtt.rollbackDeviceDiscoveryMigration());
+    TEST_ASSERT_EQUAL_UINT8(9, mock->getFlushedMessagesNb());
+    TEST_ASSERT_EQUAL_STRING("homeassistant/device/native_device/config",
+        mock->getFlushedMessages()[5]->topic);
+    TEST_ASSERT_EQUAL_STRING("{\"migrate_discovery\":true}",
+        mock->getFlushedMessages()[5]->buffer);
+    TEST_ASSERT_EQUAL_STRING("homeassistant/sensor/native_device/first/config",
+        mock->getFlushedMessages()[6]->topic);
+    TEST_ASSERT_EQUAL_STRING("homeassistant/sensor/native_device/second/config",
+        mock->getFlushedMessages()[7]->topic);
+    TEST_ASSERT_EQUAL_STRING("homeassistant/device/native_device/config",
+        mock->getFlushedMessages()[8]->topic);
+    TEST_ASSERT_EQUAL_STRING("", mock->getFlushedMessages()[8]->buffer);
+    TEST_ASSERT_EQUAL_INT(HAMqtt::DeviceDiscoveryMigrationIdle,
+        mqtt.getDeviceDiscoveryMigrationState());
+    TEST_ASSERT_FALSE(mqtt.isDeviceDiscoveryEnabled());
+}
+
+void test_failed_rollback_stays_staged_until_it_can_complete()
+{
+    HADevice device("native_device");
+    PubSubClientMock* mock = new PubSubClientMock();
+    HAMqtt mqtt(mock, device);
+    NativeDiscoveryEntity entity("entity");
+    TEST_ASSERT_TRUE(mock->connectDummy());
+
+    TEST_ASSERT_TRUE(mqtt.beginDeviceDiscoveryMigration());
+    TEST_ASSERT_TRUE(mqtt.publishDeviceDiscoveryMigrationMarkers());
+    TEST_ASSERT_TRUE(mqtt.publishDeviceDiscoveryMigrationConfig());
+
+    mock->failNextBeginPublish();
+    TEST_ASSERT_FALSE(mqtt.rollbackDeviceDiscoveryMigration());
+    TEST_ASSERT_EQUAL_INT(HAMqtt::DeviceDiscoveryMigrationRollbackPending,
+        mqtt.getDeviceDiscoveryMigrationState());
+    TEST_ASSERT_TRUE(mqtt.isDeviceDiscoveryMigrationInProgress());
+    TEST_ASSERT_FALSE(mqtt.publishDeviceDiscovery());
+
+    TEST_ASSERT_TRUE(mqtt.rollbackDeviceDiscoveryMigration());
+    TEST_ASSERT_EQUAL_INT(HAMqtt::DeviceDiscoveryMigrationIdle,
+        mqtt.getDeviceDiscoveryMigrationState());
+    TEST_ASSERT_FALSE(mqtt.isDeviceDiscoveryEnabled());
+}
+
+void test_device_component_removal_uses_marker_then_omission_and_readd()
+{
+    HADevice device("native_device");
+    PubSubClientMock* mock = new PubSubClientMock();
+    HAMqtt mqtt(mock, device);
+    NativeDiscoveryEntity first("first");
+    NativeDiscoveryEntity second("second");
+    TEST_ASSERT_TRUE(mock->connectDummy());
+    mqtt.enableDeviceDiscovery();
+
+    TEST_ASSERT_TRUE(first.removeFromDiscovery());
+    TEST_ASSERT_TRUE(first.isRemovedFromDeviceDiscovery());
+    TEST_ASSERT_EQUAL_UINT8(2, mock->getFlushedMessagesNb());
+    TEST_ASSERT_NOT_NULL(strstr(mock->getFlushedMessages()[0]->buffer,
+        "\"first\":{\"p\":\"sensor\"}"));
+    TEST_ASSERT_NULL(strstr(mock->getFlushedMessages()[1]->buffer, "\"first\""));
+    TEST_ASSERT_NOT_NULL(strstr(mock->getFlushedMessages()[1]->buffer, "\"second\""));
+
+    TEST_ASSERT_TRUE(first.republishDiscovery());
+    TEST_ASSERT_FALSE(first.isRemovedFromDeviceDiscovery());
+    TEST_ASSERT_EQUAL_UINT8(3, mock->getFlushedMessagesNb());
+    TEST_ASSERT_NOT_NULL(strstr(mock->getFlushedMessages()[2]->buffer, "\"first\""));
+}
+
+void test_entities_before_or_after_mqtt_have_safe_registration_lifetimes()
+{
+    NativeDiscoveryEntity before("before");
+    HADevice device("native_device");
+    PubSubClientMock* mock = new PubSubClientMock();
+    HAMqtt mqtt(mock, device, 2);
+    TEST_ASSERT_EQUAL_UINT8(1, mqtt.getRegisteredDeviceTypeCount());
+
+    NativeDiscoveryEntity* after = new NativeDiscoveryEntity("after");
+    TEST_ASSERT_EQUAL_UINT8(2, mqtt.getRegisteredDeviceTypeCount());
+    delete after;
+    TEST_ASSERT_EQUAL_UINT8(1, mqtt.getRegisteredDeviceTypeCount());
+}
+
+void test_text_state_is_bounded_and_retains_the_last_valid_value()
+{
+    HADevice device("native_device");
+    PubSubClientMock* mock = new PubSubClientMock();
+    HAMqtt mqtt(mock, device);
+    HAText text("text");
+    char oversizedState[HAText::MaxCommandLength + 2];
+    memset(oversizedState, 'x', sizeof(oversizedState) - 1);
+    oversizedState[sizeof(oversizedState) - 1] = 0;
+
+    text.setCurrentState("initial");
+    text.setCurrentState(oversizedState);
+    TEST_ASSERT_EQUAL_STRING("initial", text.getCurrentState());
+    TEST_ASSERT_FALSE(text.setState(oversizedState));
+    TEST_ASSERT_EQUAL_STRING("initial", text.getCurrentState());
+}
+
+void test_registration_cap_and_explicit_disconnect_are_reported()
+{
+    HADevice device("native_device");
+    PubSubClientMock* mock = new PubSubClientMock();
+    HAMqtt mqtt(mock, device, 1);
+    NativeDiscoveryEntity first("first");
+    NativeDiscoveryEntity second("second");
+    TEST_ASSERT_EQUAL_UINT8(1, mqtt.getRegisteredDeviceTypeCount());
+    TEST_ASSERT_EQUAL_UINT16(1, mqtt.getDeviceTypeRegistrationFailures());
+
+    disconnectedCallbackCalls = 0;
+    stateCallbackCalls = 0;
+    mqtt.onDisconnected(onNativeDisconnected);
+    mqtt.onStateChanged(onNativeStateChanged);
+    TEST_ASSERT_TRUE(mqtt.begin("native-host"));
+    TEST_ASSERT_TRUE(mock->connectDummy());
+    mock->setState(HAMqtt::StateConnected);
+    mqtt.loop();
+    TEST_ASSERT_TRUE(mqtt.disconnect());
+    TEST_ASSERT_EQUAL_UINT8(1, disconnectedCallbackCalls);
+    TEST_ASSERT_TRUE(stateCallbackCalls >= 2);
+}
+
+} // namespace
+
+void setUp(void) { }
+void tearDown(void) { }
+
+int main(int, char**)
+{
+    UNITY_BEGIN();
+    RUN_TEST(test_json_helpers_escape_control_bytes_and_preserve_cursor_contract);
+    RUN_TEST(test_availability_and_serializer_array_escape_json_values);
+    RUN_TEST(test_discovery_topic_tokens_are_rejected_before_topic_generation);
+    RUN_TEST(test_streaming_serializer_writes_exact_escaped_payload_to_mqtt_mock);
+    RUN_TEST(test_staged_migration_orders_markers_device_payload_and_legacy_cleanup);
+    RUN_TEST(test_failed_rollback_stays_staged_until_it_can_complete);
+    RUN_TEST(test_device_component_removal_uses_marker_then_omission_and_readd);
+    RUN_TEST(test_entities_before_or_after_mqtt_have_safe_registration_lifetimes);
+    RUN_TEST(test_text_state_is_bounded_and_retains_the_last_valid_value);
+    RUN_TEST(test_registration_cap_and_explicit_disconnect_are_reported);
+    return UNITY_END();
+}

test/test_utils_json/test_main.cpp

@@ -0,0 +1,86 @@
+#include <Arduino.h>
+#include <string.h>
+#include <unity.h>
+
+#include "utils/HAJson.h"
+
+using TestFn = void (*)(void);
+
+struct TestCase {
+    const char* name;
+    TestFn fn;
+    uint16_t line;
+};
+
+#define TEST_ENTRY(fn) { #fn, fn, __LINE__ }
+
+void test_HAJson_escapes_all_required_json_characters()
+{
+    const char value[] = "quote\" slash\\ newline\n tab\t control\x01";
+    char output[96] = {};
+    char* cursor = output;
+
+    TEST_ASSERT_EQUAL_UINT16(
+        strlen("\"quote\\\" slash\\\\ newline\\n tab\\t control\\u0001\""),
+        HAJson::calculateEscapedStringSize(value)
+    );
+    TEST_ASSERT_TRUE(HAJson::appendEscapedString(cursor, output + sizeof(output) - 1, value));
+    TEST_ASSERT_EQUAL_STRING(
+        "\"quote\\\" slash\\\\ newline\\n tab\\t control\\u0001\"",
+        output
+    );
+}
+
+void test_HAJson_rejects_too_small_output_buffer_without_partial_output()
+{
+    char output[5] = "ok";
+    char* cursor = output;
+
+    TEST_ASSERT_FALSE(HAJson::appendEscapedString(cursor, output + sizeof(output) - 1, "toolong"));
+    TEST_ASSERT_EQUAL_STRING("ok", output);
+    TEST_ASSERT_EQUAL_PTR(output, cursor);
+}
+
+void test_HAJson_validates_home_assistant_discovery_topic_tokens()
+{
+    TEST_ASSERT_TRUE(HAJson::isValidDiscoveryTopicToken("device_01-A"));
+    TEST_ASSERT_FALSE(HAJson::isValidDiscoveryTopicToken(""));
+    TEST_ASSERT_FALSE(HAJson::isValidDiscoveryTopicToken("device/id"));
+    TEST_ASSERT_FALSE(HAJson::isValidDiscoveryTopicToken("device id"));
+    TEST_ASSERT_FALSE(HAJson::isValidDiscoveryTopicToken("device\n"));
+}
+
+static TestCase tests[] = {
+    TEST_ENTRY(test_HAJson_escapes_all_required_json_characters),
+    TEST_ENTRY(test_HAJson_rejects_too_small_output_buffer_without_partial_output),
+    TEST_ENTRY(test_HAJson_validates_home_assistant_discovery_topic_tokens),
+};
+
+static const size_t testCount = sizeof(tests) / sizeof(tests[0]);
+static size_t nextTest = 0;
+static bool begun = false;
+
+void setUp(void) { }
+void tearDown(void) { }
+
+void setup()
+{
+    Serial.begin(115200);
+    delay(500);
+    UNITY_BEGIN();
+    begun = true;
+}
+
+void loop()
+{
+    if (begun && nextTest < testCount) {
+        TestCase& test = tests[nextTest++];
+        UnityDefaultTestRun(test.fn, test.name, test.line);
+        return;
+    }
+
+    if (begun) {
+        UNITY_END();
+        begun = false;
+    }
+}

tests/ha-test-harness/Dockerfile

@@ -0,0 +1,10 @@
+FROM python:3.12-slim
+
+WORKDIR /tests
+COPY test-support/ha-mqtt-test-harness /opt/ha-mqtt-test-harness
+COPY tests/ha-test-harness/requirements.txt .
+RUN pip install --no-cache-dir -r requirements.txt
+RUN pip install --no-cache-dir /opt/ha-mqtt-test-harness
+COPY tests/ha-test-harness/test_harness.py .
+
+CMD ["python", "test_harness.py"]

tests/ha-test-harness/README.md

@@ -0,0 +1,57 @@
+# Home Assistant MQTT test harness tests
+
+This harness runs retained MQTT discovery messages through Mosquitto and a real
+Home Assistant container. It verifies the behavior that firmware unit tests
+cannot: Home Assistant's entity-registry identity, user-owned registry changes,
+and retained discovery after a Home Assistant restart.
+
+It has two ordered modes:
+
+1. `migration` publishes single-component discovery, applies a user rename and
+   disable, then sends `migrate_discovery` markers, a device bundle, and legacy
+   retained-topic cleanup.
+2. `retained-restart` runs after Home Assistant restarts and verifies the
+   retained device bundle plus preserved registry customization.
+
+The migration case also rejects malformed retained JSON, checks that a direct
+single-to-device publication does not duplicate registry identity, exercises the
+device-component tombstone/omission sequence, and makes the current
+`def_ent_id`/no-`obj_id` schema expectation explicit.
+
+## Run locally
+
+From the repository root:
+
+```bash
+HA_VERSION=2024.11.3 docker compose -f tests/ha-test-harness/compose.yaml up -d mqtt homeassistant
+HA_VERSION=2024.11.3 docker compose -f tests/ha-test-harness/compose.yaml run --rm tests
+HA_VERSION=2024.11.3 docker compose -f tests/ha-test-harness/compose.yaml restart homeassistant
+TEST_HARNESS_MODE=retained-restart HA_VERSION=2024.11.3 docker compose -f tests/ha-test-harness/compose.yaml run --rm tests
+HA_VERSION=2024.11.3 docker compose -f tests/ha-test-harness/compose.yaml down -v
+```
+
+Use `HA_VERSION=stable` and `HA_VERSION=dev` for the current supported and
+development Home Assistant images.
+
+The checked-in GitHub workflow runs the baseline, stable, and development images
+as a compatibility audit. When it is on the repository's default branch, GitHub
+exposes it for manual dispatch and the weekly schedule. It is not a tag-release
+gate.
+
+For a local development-image test, add `TEST_HARNESS_EXPECT_DISABLED_CLEANUP=1` to
+both `docker compose run ... tests` commands. That lane checks that initially
+disabled device components are cleaned. The test uses only ephemeral named volumes;
+`down -v` removes its broker data, Home Assistant config, owner token, and
+registry state.
+
+## Shared support
+
+The schema-neutral [HA/MQTT test harness testkit](../../test-support/ha-mqtt-test-harness/README.md) owns only Docker-side Home Assistant onboarding, MQTT transport, registry/service access, retries, and artifact helpers. It has no ArduinoHA discovery assertions. This suite owns ArduinoHA migration fixtures; DeviceFramework carries its own fixtures and hardware adapter while reusing the testkit.
+
+## Scope
+
+The firmware's native Unity suite covers JSON escaping, invalid topic tokens,
+serializer preflight, migration ordering, component removal, and lifecycle
+behavior. This container suite covers Home Assistant's persistence test harness. It
+does not need a physical board: fixture discovery documents mirror retained
+payloads emitted by ArduinoHA and isolate Home Assistant/MQTT compatibility.

tests/ha-test-harness/compose.yaml

@@ -0,0 +1,44 @@
+services:
+  mqtt:
+    image: eclipse-mosquitto:2
+    command: ["mosquitto", "-c", "/mosquitto/config/mosquitto.conf"]
+    volumes:
+      - ./mosquitto.conf:/mosquitto/config/mosquitto.conf:ro
+    healthcheck:
+      test: ["CMD-SHELL", "mosquitto_sub -h localhost -t '$$SYS/broker/version' -C 1 -W 5 >/dev/null 2>&1"]
+      interval: 3s
+      timeout: 5s
+      retries: 20
+
+  homeassistant:
+    image: ghcr.io/home-assistant/home-assistant:${HA_VERSION:-stable}
+    environment:
+      TZ: UTC
+    volumes:
+      - ha_config:/config
+      - ./configuration.yaml:/config/configuration.yaml:ro
+    depends_on:
+      mqtt:
+        condition: service_healthy
+
+  tests:
+    build:
+      context: ../..
+      dockerfile: tests/ha-test-harness/Dockerfile
+    environment:
+      HA_URL: http://homeassistant:8123
+      MQTT_HOST: mqtt
+      MQTT_PORT: "1883"
+      TEST_HARNESS_MODE: ${TEST_HARNESS_MODE:-migration}
+      TEST_HARNESS_EXPECT_DISABLED_CLEANUP: ${TEST_HARNESS_EXPECT_DISABLED_CLEANUP:-0}
+    volumes:
+      - test_harness_state:/state
+    depends_on:
+      mqtt:
+        condition: service_healthy
+      homeassistant:
+        condition: service_started
+
+volumes:
+  ha_config:
+  test_harness_state:

tests/ha-test-harness/configuration.yaml

@@ -0,0 +1,2 @@
+default_config:
+

tests/ha-test-harness/mosquitto.conf

@@ -0,0 +1,5 @@
+persistence true
+persistence_location /mosquitto/data/
+allow_anonymous true
+listener 1883
+log_type all

tests/ha-test-harness/requirements.txt

@@ -0,0 +1,3 @@
+paho-mqtt==2.1.0
+requests==2.32.3
+websocket-client==1.8.0

tests/ha-test-harness/test_harness.py

@@ -0,0 +1,280 @@
+"""Home Assistant MQTT discovery test harness checks.
+
+The test intentionally uses retained MQTT messages, like a deployed firmware
+node. It inspects HA's entity registry over the authenticated WebSocket API so
+the migration assertion is about HA's persistent identity, not just payload
+shape.
+"""
+
+import json
+import os
+import pathlib
+import time
+
+from ha_mqtt_test_harness import (
+    TestHarnessError,
+    HomeAssistantClient,
+    RetainedPublisher as SharedRetainedPublisher,
+    wait_until,
+)
+
+
+HA_URL = os.environ.get("HA_URL", "http://homeassistant:8123").rstrip("/")
+MQTT_HOST = os.environ.get("MQTT_HOST", "mqtt")
+MQTT_PORT = int(os.environ.get("MQTT_PORT", "1883"))
+MODE = os.environ.get("TEST_HARNESS_MODE", "migration")
+STATE = pathlib.Path("/state")
+TOKEN_FILE = STATE / "ha-token"
+DEVICE_ID = "test_harness_device"
+EDGE_DEVICE_ID = "test_harness_edge_device"
+EXPECT_DISABLED_CLEANUP = os.environ.get("TEST_HARNESS_EXPECT_DISABLED_CLEANUP") == "1"
+
+
+def fail(message):
+    raise TestHarnessError(message)
+
+
+def legacy_topic(object_id, device_id=DEVICE_ID):
+    return f"homeassistant/sensor/{device_id}/{object_id}/config"
+
+
+def device_topic(device_id=DEVICE_ID):
+    return f"homeassistant/device/{device_id}/config"
+
+
+def component(object_id, unique_id=None, device_id=DEVICE_ID, **extra):
+    payload = {
+        "p": "sensor",
+        "name": object_id.replace("_", " ").title(),
+        "uniq_id": unique_id or f"{device_id}_{object_id}",
+        "stat_t": f"test-harness/{object_id}/state",
+    }
+    payload.update(extra)
+    return payload
+
+
+def device_payload(components, device_id=DEVICE_ID):
+    return {
+        "dev": {"ids": [device_id], "name": "ArduinoHA test harness device"},
+        "o": {"name": "ArduinoHA", "sw": "test harness"},
+        "cmps": components,
+    }
+
+
+def legacy_payload(object_id, unique_id=None, device_id=DEVICE_ID, **extra):
+    payload = component(object_id, unique_id, **extra)
+    payload["dev"] = {"ids": [device_id], "name": "ArduinoHA test harness device"}
+    payload.pop("p")
+    return payload
+
+
+def find_unique(entries, unique_id):
+    matches = [entry for entry in entries if entry.get("unique_id") == unique_id]
+    if len(matches) > 1:
+        fail(f"duplicate entity-registry entries for {unique_id}: {matches}")
+    return matches[0] if matches else None
+
+
+def wait_for_entry(ws, unique_id):
+    return wait_until(
+        f"entity registry entry {unique_id}",
+        lambda: find_unique(ws.registry_entries(), unique_id),
+        timeout=60,
+    )
+
+
+def migration_test_harness():
+    publisher = SharedRetainedPublisher(MQTT_HOST, MQTT_PORT)
+    ws = HomeAssistantClient.bootstrap(
+        HA_URL,
+        STATE,
+        owner_name="ArduinoHA Test Harness Owner",
+        username="arduinoha-test-harness",
+        password="arduinoha-test-harness-password",
+    )
+    ws.configure_mqtt(MQTT_HOST, MQTT_PORT)
+    try:
+        # Existing single-component entity and a user-owned registry customization.
+        unique = f"{DEVICE_ID}_temperature"
+        publisher.publish(legacy_topic("temperature"), json.dumps(legacy_payload("temperature", unique)))
+        publisher.publish("test-harness/temperature/state", "21.5")
+        original = wait_for_entry(ws, unique)
+        original_id = original["id"]
+        renamed_entity_id = "sensor.test_harness_temperature_user_name"
+        ws.call(
+            "config/entity_registry/update",
+            entity_id=original["entity_id"],
+            new_entity_id=renamed_entity_id,
+            disabled_by="user",
+        )
+
+        # HA's required sequence: marker, device payload, then retained cleanup.
+        publisher.publish(legacy_topic("temperature"), '{"migrate_discovery":true}')
+        publisher.publish(device_topic(), json.dumps(device_payload({"temperature": component("temperature", unique)})))
+        publisher.publish(legacy_topic("temperature"), "")
+
+        migrated = wait_for_entry(ws, unique)
+        if migrated["id"] != original_id:
+            fail("single-to-device migration changed the entity registry ID")
+        if migrated["entity_id"] != renamed_entity_id or migrated.get("disabled_by") != "user":
+            fail(f"migration did not preserve user registry settings: {migrated}")
+        if find_unique(ws.registry_entries(), unique) is None:
+            fail("migrated entity disappeared from the entity registry")
+
+        # Reverse migration is also ordered: marker the device topic, restore
+        # legacy discovery, then clear the device topic. This is the protocol
+        # HA documents for preserving the existing registry entry.
+        publisher.publish(device_topic(), '{"migrate_discovery":true}')
+        publisher.publish(legacy_topic("temperature"), json.dumps(legacy_payload("temperature", unique)))
+        publisher.publish(device_topic(), "")
+        rolled_back = wait_for_entry(ws, unique)
+        if rolled_back["id"] != original_id:
+            fail("device-to-single rollback changed the entity registry ID")
+        if rolled_back["entity_id"] != renamed_entity_id or rolled_back.get("disabled_by") != "user":
+            fail(f"rollback did not preserve user registry settings: {rolled_back}")
+
+        # Restore device discovery so the retained-restart check continues to
+        # exercise the forward migration form used by deployed firmware.
+        publisher.publish(legacy_topic("temperature"), '{"migrate_discovery":true}')
+        publisher.publish(device_topic(), json.dumps(device_payload({"temperature": component("temperature", unique)})))
+        publisher.publish(legacy_topic("temperature"), "")
+        remigrated = wait_for_entry(ws, unique)
+        if remigrated["id"] != original_id:
+            fail("repeat single-to-device migration changed the entity registry ID")
+
+        retained = json.loads(publisher.retained_payload(device_topic()))
+        if "temperature" not in retained.get("cmps", {}):
+            fail("migration did not retain the primary device discovery payload")
+
+        # Direct publication is deliberately not a migration protocol. It must not
+        # create a second registry entry for the same stable unique ID. Keep it
+        # on a separate device topic so it cannot invalidate the primary
+        # retained-payload/restart test harness.
+        direct_unique = f"{EDGE_DEVICE_ID}_direct"
+        publisher.publish(
+            legacy_topic("direct", EDGE_DEVICE_ID),
+            json.dumps(legacy_payload("direct", direct_unique, device_id=EDGE_DEVICE_ID)),
+        )
+        direct_entry = wait_for_entry(ws, direct_unique)
+        publisher.publish(
+            device_topic(EDGE_DEVICE_ID),
+            json.dumps(device_payload(
+                {"direct": component("direct", direct_unique)}, device_id=EDGE_DEVICE_ID
+            )),
+        )
+        time.sleep(2)
+        entries = [entry for entry in ws.registry_entries() if entry.get("unique_id") == direct_unique]
+        if len(entries) != 1 or entries[0]["id"] != direct_entry["id"]:
+            fail("direct device discovery publish created a duplicate registry entity")
+
+        # Device-mode removal is two root updates: platform tombstone then
+        # omission. This uses the edge fixture so retained-restart behavior is
+        # independently asserted on the migrated primary fixture.
+        removable_unique = f"{EDGE_DEVICE_ID}_removable"
+        publisher.publish(
+            device_topic(EDGE_DEVICE_ID),
+            json.dumps(device_payload({
+                "anchor": component("anchor", device_id=EDGE_DEVICE_ID),
+                "removable": component("removable", removable_unique),
+            }, device_id=EDGE_DEVICE_ID)),
+        )
+        wait_for_entry(ws, removable_unique)
+        publisher.publish(
+            device_topic(EDGE_DEVICE_ID),
+            json.dumps(device_payload({
+                "anchor": component("anchor", device_id=EDGE_DEVICE_ID),
+                "removable": {"p": "sensor"},
+            }, device_id=EDGE_DEVICE_ID)),
+        )
+        publisher.publish(
+            device_topic(EDGE_DEVICE_ID),
+            json.dumps(device_payload({"anchor": component("anchor", device_id=EDGE_DEVICE_ID)}, device_id=EDGE_DEVICE_ID)),
+        )
+
+        # Older Home Assistant versions do not clean initially disabled device
+        # components. Keep that capability assertion in the development lane,
+        # where it detects regressions without making the supported baseline
+        # falsely fail.
+        if EXPECT_DISABLED_CLEANUP:
+            disabled_unique = f"{EDGE_DEVICE_ID}_disabled"
+            publisher.publish(
+                device_topic(EDGE_DEVICE_ID),
+                json.dumps(device_payload({
+                    "anchor": component("anchor", device_id=EDGE_DEVICE_ID),
+                    "disabled": component(
+                        "disabled", disabled_unique, enabled_by_default=False
+                    ),
+                }, device_id=EDGE_DEVICE_ID)),
+            )
+            disabled_entry = wait_for_entry(ws, disabled_unique)
+            if disabled_entry.get("disabled_by") != "integration":
+                fail(f"expected initially disabled entity to be integration-disabled: {disabled_entry}")
+            publisher.publish(
+                device_topic(EDGE_DEVICE_ID),
+                json.dumps(device_payload({
+                    "anchor": component("anchor", device_id=EDGE_DEVICE_ID),
+                    "disabled": {"p": "sensor"},
+                }, device_id=EDGE_DEVICE_ID)),
+            )
+            publisher.publish(
+                device_topic(EDGE_DEVICE_ID),
+                json.dumps(device_payload({"anchor": component("anchor", device_id=EDGE_DEVICE_ID)}, device_id=EDGE_DEVICE_ID)),
+            )
+            wait_until(
+                "disabled device component cleanup",
+                lambda: find_unique(ws.registry_entries(), disabled_unique) is None,
+                timeout=60,
+            )
+
+        # Invalid retained discovery JSON never creates a registry entry. Escaped
+        # strings are covered by the firmware-native serializer tests.
+        publisher.publish(legacy_topic("malformed"), "{not-json")
+        time.sleep(2)
+        if find_unique(ws.registry_entries(), f"{DEVICE_ID}_malformed"):
+            fail("malformed discovery payload created an entity")
+
+        # This fixture documents the current HA field behaviour: def_ent_id is
+        # allowed on first creation; obsolete obj_id is intentionally absent.
+        default_payload = legacy_payload("default_name", def_ent_id="test_harness_default_name")
+        if "obj_id" in default_payload:
+            fail("test harness fixture accidentally contains obsolete obj_id")
+        publisher.publish(legacy_topic("default_name"), json.dumps(default_payload))
+        wait_for_entry(ws, f"{DEVICE_ID}_default_name")
+
+        STATE.mkdir(parents=True, exist_ok=True)
+        (STATE / "migration-complete").write_text("ok", encoding="utf-8")
+    finally:
+        ws.close()
+        publisher.close()
+
+
+def retained_restart_test_harness():
+    if not (STATE / "migration-complete").exists():
+        fail("retained-restart mode requires the migration test harness to run first")
+    publisher = SharedRetainedPublisher(MQTT_HOST, MQTT_PORT)
+    ws = HomeAssistantClient.from_state(HA_URL, STATE)
+    try:
+        migrated = wait_for_entry(ws, f"{DEVICE_ID}_temperature")
+        if migrated["entity_id"] != "sensor.test_harness_temperature_user_name":
+            fail("HA restart lost the user-owned entity rename")
+        retained = json.loads(publisher.retained_payload(device_topic()))
+        if "cmps" not in retained:
+            fail("broker restart check did not receive retained device discovery")
+    finally:
+        ws.close()
+        publisher.close()
+
+
+def main():
+    HomeAssistantClient.wait_until_ready(HA_URL)
+    if MODE == "migration":
+        migration_test_harness()
+    elif MODE == "retained-restart":
+        retained_restart_test_harness()
+    else:
+        fail(f"unknown TEST_HARNESS_MODE: {MODE}")
+    print(f"Home Assistant MQTT test harness mode {MODE} passed")
+
+
+if __name__ == "__main__":
+    main()