Initial reusable HA kiosk MQTT controls

runtime/availability-watch.sh

@@ -0,0 +1,43 @@
+#!/usr/bin/env bash
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+set -u
+
+KIOSK_CONFIG_FILE="${KIOSK_CONFIG_FILE:-$HOME/.config/ha-kiosk/config}"
+if [[ -r "$KIOSK_CONFIG_FILE" ]]; then
+  # shellcheck source=/dev/null
+  source "$KIOSK_CONFIG_FILE"
+fi
+: "${KIOSK_ID:=kiosk}"
+: "${COMMAND_ROOT:=kiosk/commands}"
+: "${STATUS_ROOT:=kiosk/status}"
+AVAILABILITY_TOPIC="${STATUS_ROOT}/${KIOSK_ID}/availability"
+PING_TOPIC="${COMMAND_ROOT}/${KIOSK_ID}/availability/ping"
+PUBLISH_INTERVAL_SECONDS="${AVAILABILITY_INTERVAL_SECONDS:-30}"
+
+publish_available() {
+  /usr/bin/mosquitto_pub -r -t "$AVAILABILITY_TOPIC" -m "ON"
+}
+
+# Keep the MQTT connection that owns the Last Will open in the background.
+/usr/bin/mosquitto_sub \
+  -t "$PING_TOPIC" \
+  --will-topic "$AVAILABILITY_TOPIC" \
+  --will-payload "OFF" \
+  --will-retain &
+subscriber_pid=$!
+
+cleanup() {
+  kill "$subscriber_pid" 2>/dev/null || true
+  wait "$subscriber_pid" 2>/dev/null || true
+}
+trap cleanup EXIT INT TERM
+
+# Reassert retained availability after Mosquitto reconnects internally. The
+# Last Will has already published OFF when a broker connection was lost.
+while kill -0 "$subscriber_pid" 2>/dev/null; do
+  publish_available || true
+  sleep "$PUBLISH_INTERVAL_SECONDS"
+done
+
+wait "$subscriber_pid"