Add snapctl wrapper to check connected interfaces (#82)

* Add snapctl is-connected wrapper

* Update makefile and readme to use LXD by default

Makefile

@@ -1,6 +1,6 @@
 
 try:
-	snapcraft try
+	snapcraft try --use-lxd
 	snap try prime
 
 sync:
@@ -12,4 +12,4 @@ test:
 		./log \
 		./snapctl \
 		./env \
-		./options
+		./options

README.md

@@ -88,7 +88,7 @@ sudo edgex-snap-hooks.test ./snapctl -run TestGet
 
 #### Development
 ```
-SNAPCRAFT_BUILD_ENVIRONMENT=lxd make try
+make try
 ```
 
 You can now edit the files locally, copy them to prime directory, and re-run the

snap/snapcraft.yaml

@@ -7,6 +7,11 @@ description: This snap is used to run tests on this package
 grade: devel
 confinement: strict
 
+plugs:
+  # Plug for testing snapctl commands
+  test-plug:
+    interface: content
+    target: $SNAP_DATA
 
 apps:
   # App for running the tests
@@ -21,13 +26,12 @@ apps:
     install-mode: disable
   mock-service-2: *ms
 
-
 parts:
   go:
-    ## Using stage go snap doesn't work, 
+    ## Using stage go snap doesn't work,
     ## resulting in core dump when running go:
     # plugin: nil
-    # stage-snaps: 
+    # stage-snaps:
     #   - go/1.17
     # organize:
     #   '*': go/

snapctl/README.md

@@ -1,12 +1,12 @@
 # snapctl
 Go wrapper library for the [snapctl](https://snapcraft.io/docs/using-snapctl) tool.
 
-Wrappers for following subcommands are implemented:
+Wrappers for following subcommands are partially implemented for EdgeX use cases:
 
 - [ ] `fde-setup-request`: Obtain full disk encryption setup request
 - [ ] `fde-setup-result`: Set result for full disk encryption
 - [x] `get`: The get command prints configuration and interface connection settings.                
-- [ ] `is-connected`: Return success if the given plug or slot is connected, and failure otherwise   
+- [x] `is-connected`: Return success if the given plug or slot is connected, and failure otherwise
 - [ ] `reboot`: Control the reboot behavior of the system          
 - [x] `restart`: Restart services    
 - [x] `services`: Query the status of services      
@@ -96,4 +96,4 @@ func main() {
 		panic(err)
 	}
 }
-```
+```

snapctl/is-connected.go

@@ -0,0 +1,85 @@
+/*
+Usage:
+snapctl [OPTIONS] is-connected [is-connected-OPTIONS] <plug|slot>
+
+	The is-connected command returns success if the given plug or slot of the
+	calling snap is connected, and failure otherwise.
+
+	$ snapctl is-connected plug
+	$ echo $?
+	1
+
+	Snaps can only query their own plugs and slots - snap name is implicit and
+	implied by the snapctl execution context.
+
+	The --pid and --aparmor-label options can be used to determine whether
+	a plug or slot is connected to the snap identified by the given
+	process ID or AppArmor label.  In this mode, additional failure exit
+	codes may be returned: 10 if the other snap is not connected but uses
+	classic confinement, or 11 if the other process is not snap confined.
+
+	The --pid and --apparmor-label options may only be used with slots of
+	interface type "pulseaudio", "audio-record", or "cups-control".
+
+
+	Help Options:
+	-h, --help                Show this help message
+
+	[is-connected command options]
+			--pid=            Process ID for a plausibly connected process
+			--apparmor-label= AppArmor label for a plausibly connected process
+
+*/
+
+package snapctl
+
+import (
+	"fmt"
+	"strings"
+)
+
+type isConnected struct {
+	plug       string
+	validators []func() error
+}
+
+// IsConnected checks the connection status of a plug or slot
+// It returns an object for setting the CLI arguments before running the command
+func IsConnected(plug string) (cmd isConnected) {
+	cmd.plug = plug
+
+	cmd.validators = append(cmd.validators, func() error {
+		if strings.Contains(plug, " ") {
+			return fmt.Errorf("plug must not contain spaces. Got: '%s'", plug)
+		}
+
+		return nil
+	})
+
+	return cmd
+}
+
+// Run executes the get command
+func (cmd isConnected) Run() (bool, error) {
+	// validate all input
+	for _, validate := range cmd.validators {
+		if err := validate(); err != nil {
+			return false, err
+		}
+	}
+
+	// construct the command args
+	// snapctl [OPTIONS] is-connected [is-connected-OPTIONS] <plug|slot>
+	var args []string
+
+	// plug
+	args = append(args, cmd.plug)
+
+	out, err := run("is-connected", args...)
+	if err != nil && out == "" {
+		return false, nil
+	} else if err != nil {
+		return false, err
+	}
+	return true, nil
+}

snapctl/is-connected_test.go

@@ -0,0 +1,19 @@
+package snapctl_test
+
+import (
+	"testing"
+
+	"github.com/canonical/edgex-snap-hooks/v3/snapctl"
+	"github.com/stretchr/testify/require"
+)
+
+func TestIsConnected(t *testing.T) {
+	t.Run("snapctl is-connected", func(t *testing.T) {
+
+		connected, err := snapctl.IsConnected("test-plug").Run()
+		require.NoError(t, err, "Error checking plug status.")
+		require.False(t, connected)
+
+	})
+
+}