kvida-os/components/transport/README.md

transport

Wi-Fi connectivity, MQTT client, and Home Assistant MQTT Discovery payloads. Exposes a semantic publish(topic, value)-style API — application code (including Lua) never depends on MQTT directly, per the transport abstraction principle in AGENTS.md. No dependency on other Kvida components.

Also owns Wi-Fi/MQTT configuration storage for now (not broken out into its own component since AGENTS.md doesn't call out a separate config layer — revisit if this grows).

Future transports (Zigbee, Thread, Matter) should implement the same publish API as alternate backends behind this component's interface, without changing callers.

Wi-Fi commissioning

include/commissioning.h / src/commissioning.cpp implement first-time Wi-Fi setup, no companion app required:

• On boot, try_stored_credentials() attempts to connect using credentials saved in NVS from a previous session.
• If none exist (or the caller chooses to), start_commissioning() opens a SoftAP (Kvida-XXXXXX, derived from the MAC) with a captive portal: a DNS server (src/dns_server.c/.h, vendored from ESP-IDF's official captive_portal example, Unlicense/CC0) answers every query with the AP's own IP, and DHCP option 114 plus a 404-redirects-to-/ HTTP handler get most phones/laptops to auto-open the setup page (src/portal.html) in a plain browser.
• Submitting the form (POST /api/wifi, JSON body {"ssid","password"}) saves the credentials to NVS and switches Wi-Fi to STA mode. The AP is open (no password) by design -- see the comment above ap_config.ap.authmode in commissioning.cpp for the reasoning and the tradeoff.
• A 5-minute esp_timer closes the commissioning window automatically if nobody submits credentials.
• IPv6: once STA gets its IPv4 address (IP_EVENT_STA_GOT_IP -- not WIFI_EVENT_STA_CONNECTED, see the comment in commissioning.cpp for why that timing matters), esp_netif_create_ip6_linklocal() requests a link-local address (CONFIG_LWIP_IPV6=y is set explicitly in sdkconfig.defaults); IP_EVENT_GOT_IP6 is logged when it arrives. Verified end-to-end on real ESP32-C6 hardware.
• Not yet wired up: re-entering commissioning on an already-configured device needs a physical trigger (the user button) per AGENTS.md's "configuration mode requires physical user interaction" principle -- blocked on drivers having a real button implementation. Network scanning (SSID dropdown instead of free text) was left out of this first pass to keep scope tight.

MQTT + Home Assistant Discovery

include/mqtt.h / src/mqtt.cpp. Neither esp_mqtt_client (mqtt_client.h) nor mdns.h ship with ESP-IDF core in this version (both were moved to the IDF Component Registry) -- pulled in via idf_component.yml (espressif/mqtt, mdns), the project's first external managed dependencies.

• Once Wi-Fi STA has an IPv4 address, start_mqtt() advertises the device on the LAN as kvida-xxxxxx.local (mDNS hostname, matching the commissioning AP's SSID) and starts a persistent settings HTTP server there -- the ongoing configuration channel for anything beyond the one-time Wi-Fi bootstrap (MQTT broker/credentials now, more later).
• Broker address: the settings page has a required host/port field, used directly and given priority over mDNS auto-discovery. mDNS discovery of _mqtt._tcp (mdns_query_ptr) is attempted as a fallback only if no manual host is saved, retried every 30s -- verified against a real Home Assistant + Mosquitto add-on setup that this mDNS discovery does not reliably find the broker (confirmed with a from-scratch raw mDNS query test from the host machine: no PTR answer for _mqtt._tcp.local was ever received on that network), hence the manual field being the primary path rather than a rarely-needed fallback.
• Credentials: also collected on the same settings page (blank username = anonymous; blank password on a resubmit means "keep the current one", since the password is never echoed back into the page for basic hygiene). Real brokers, including Home Assistant's Mosquitto add-on, require auth -- confirmed on real hardware.
• On MQTT_EVENT_CONNECTED: publishes (retained) an HA MQTT Discovery config for a diagnostic connectivity binary_sensor, grouped under a device block (identifiers/name = the same kvida-xxxxxx id, manufacturer "Xylon", model "Kvida"), then publishes online to the availability topic. MQTT's own LWT (session.last_will, set at client init) publishes offline to the same topic if the connection drops. Verified end-to-end: device appears in Home Assistant with a "Connected" Connectivity sensor.
• publish_value(name, value): the generic semantic publish API, finally built once there was a real caller -- lua_runtime's kvida.publish(), not called directly by other components. Builds kvida/<id>/<name> (state) and homeassistant/sensor/<id>/<name>/config (discovery) topics from the name. No device_class/unit_of_measurement or prettified HA display name, since neither can be inferred from just a name -- the entity shows up in HA labeled with the raw name (e.g. chip_temperature).

JSON API

Both httpd servers (the commissioning AP's and the settings server's) expose a small JSON API, CORS-enabled (src/http_cors.h) so a separately-hosted web app (kvida-sdk, e.g. via npm run dev) can call them from a browser across origins -- not just the on-device pages, which use the same endpoints via fetch():

• POST /api/wifi (commissioning AP only) -- {"ssid","password"}, replaces the old form-urlencoded /connect.
• GET /api/status (settings server) -- {"device_id","wifi_connected","mqtt_connected"}.
• GET /api/mqtt / POST /api/mqtt (settings server) -- {"host","port","username"[,"password"]}; GET never returns the password.

No JSON library ships with ESP-IDF v6.0.2 core (verified: no cJSON, no bundled json component). Given these payloads are tiny, flat, fixed-shape objects, src/json_helpers.h hand-rolls minimal strstr-based extraction rather than adding a 4th external registry dependency (already have mdns, mqtt, led_strip) -- explicitly not a general parser (no nesting, arrays, or escaping beyond what these specific request bodies need).

Important constraint that shaped this: the Wi-Fi captive portal must keep being served by the device itself -- a phone connected to the isolated SoftAP has no route to any externally-run app. Only the MQTT/settings step (once the device has real LAN connectivity) can be driven by a separately-run web app. See kvida-sdk.

TODO: A/B OTA update-checking belongs here, driven by ESP-IDF's native esp_ota_ops against the ota_0/ota_1 partitions in partitions.csv — no extra dependency needed either.