Add Serial Number to Avahi Service for Board Deduplication (#48)

* set serial number for network discovery at post install time

* adds space in a comment

* set script running before Avahi service

* code review fix

* code review fix

* code review fix

Author: mirkoCrobu

debian/arduino-app-cli/DEBIAN/postinst

@@ -4,3 +4,4 @@ chown -R arduino:arduino /home/arduino/.local/share/arduino-app-cli
 
 systemctl enable arduino-app-cli
 systemctl enable arduino-burn-bootloader
+systemctl enable arduino-avahi-serial.service

debian/arduino-app-cli/DEBIAN/prerm

@@ -2,3 +2,4 @@
 
 systemctl disable arduino-app-cli
 systemctl disable arduino-burn-bootloader
+systemctl disable arduino-avahi-serial.service

debian/arduino-app-cli/etc/systemd/system/arduino-avahi-serial.service

@@ -0,0 +1,17 @@
+[Unit]
+Description=Configure Avahi with board serial number
+Before=avahi-daemon.service
+ConditionPathExists=!/var/lib/arduino-app-cli/avahi_serial_configured.flag
+
+[Service]
+Type=oneshot
+RemainAfterExit=true
+ExecStart=/var/lib/arduino-app-cli/arduino-avahi-serial.sh
+ExecStartPost=/bin/mkdir -p /var/lib/arduino-app-cli
+ExecStartPost=/bin/touch /var/lib/arduino-app-cli/avahi_serial_configured.flag
+
+StandardOutput=journal
+StandardError=journal
+
+[Install]
+WantedBy=multi-user.target

debian/arduino-app-cli/var/lib/arduino-app-cli/arduino-avahi-serial.sh

@@ -0,0 +1,37 @@
+#!/bin/sh
+# Configure Avahi with the serial number.
+
+
+TARGET_FILE="/etc/avahi/services/arduino.service"
+SERIAL_NUMBER_PATH="/sys/devices/soc0/serial_number"
+
+echo "Configuring Avahi with serial number for network discovery..."
+
+if [ ! -f "$SERIAL_NUMBER_PATH" ]; then
+    echo "Error: Serial number path not found at $SERIAL_NUMBER_PATH." >&2
+    exit 1 
+fi
+
+
+if [ ! -w "$TARGET_FILE" ]; then
+    echo "Error: Target file $TARGET_FILE not found or not writable." >&2
+    exit 1
+fi
+
+SERIAL_NUMBER=$(cat "$SERIAL_NUMBER_PATH")
+
+if [ -z "$SERIAL_NUMBER" ]; then
+    echo "Error: Serial number file is empty." >&2
+    exit 1 
+fi
+
+if grep -q "serial_number=" "$TARGET_FILE"; then
+    echo "Serial number ($SERIAL_NUMBER) already configured."
+    exit 0
+fi
+
+echo "Adding serial number to $TARGET_FILE..."
+sed -i "/<\/service>/i <txt-record>serial_number=${SERIAL_NUMBER}<\/txt-record>" "$TARGET_FILE"
+
+echo "Avahi configuration attempt finished."
+exit 0