Fix service restart after adding plug (#740)

snap/hooks/connect-plug-firewall-control

@@ -1,4 +1,10 @@
 #!/bin/sh
-if [ "$(cat ${SNAP_COMMON}/connections/firewall-control 2> /dev/null)" -ne "1" ]; then
-	snapctl restart nordvpn.nordvpnd
+
+INTERFACE_NAME="firewall-control"
+
+if snapctl is-connected ${INTERFACE_NAME}; then
+  echo "The ${INTERFACE_NAME} interface is connected. Restarting the Snap container..."
+  snapctl restart nordvpn.nordvpnd
+else
+  echo "The ${INTERFACE_NAME} interface is not connected."
 fi

snap/hooks/connect-plug-hardware-observe

@@ -0,0 +1,10 @@
+#!/bin/sh
+
+INTERFACE_NAME="hardware-observe"
+
+if snapctl is-connected ${INTERFACE_NAME}; then
+  echo "The ${INTERFACE_NAME} interface is connected. Restarting the Snap container..."
+  snapctl restart nordvpn.nordvpnd
+else
+  echo "The ${INTERFACE_NAME} interface is not connected."
+fi

snap/hooks/connect-plug-network-control

@@ -1,4 +1,10 @@
 #!/bin/sh
-if [ "$(cat ${SNAP_COMMON}/connections/network-control 2> /dev/null)" -ne "1" ]; then
-	snapctl restart nordvpn.nordvpnd
+
+INTERFACE_NAME="network-control"
+
+if snapctl is-connected ${INTERFACE_NAME}; then
+  echo "The ${INTERFACE_NAME} interface is connected. Restarting the Snap container..."
+  snapctl restart nordvpn.nordvpnd
+else
+  echo "The ${INTERFACE_NAME} interface is not connected."
 fi

snapconf/snapconf.go

@@ -30,6 +30,9 @@ const (
 // https://snapcraft.io/docs/supported-interfaces
 type Interface string
 
+// NOTE: Some of the interfaces require restart of the service. This is achieved
+// by using snap hooks see snap/hooks directory.
+// For more information see the docs: https://snapcraft.io/docs/interface-hooks.
 const (
 	InterfaceNetwork             Interface = "network"
 	InterfaceNetworkBind         Interface = "network-bind"
@@ -60,8 +63,6 @@ type ConnChecker struct {
 
 // NewSnapChecker snap permission checker with specific setup
 func NewSnapChecker(publisherErr events.Publisher[error]) *ConnChecker {
-	// currently the order is important for machine ID generation:
-	// At the moment InterfaceHardwareObserve needs to be first because snap restarts the daemon only for some of the interfaces.
 	return NewConnChecker(
 		[]Interface{
 			InterfaceHardwareObserve,