Snap Config overrider

overrider/snapconfig/snapconfig.go

@@ -0,0 +1,82 @@
+package snapconfig
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"os"
+
+	"github.com/snapcore/snapd/client"
+	"github.com/snapcore/snapd/dirs"
+)
+
+var (
+	ErrSnapctl       = errors.New("snapctl system call failed")
+	ErrJSONUnmarshal = errors.New("couldn't unmarhsal json")
+)
+
+// This variable copied from
+// Vogt, Michael, et al. “Snapd.” Github.com, 2.54.4, Snapcore, 25 Nov. 2020,
+// https://github.com/snapcore/snapd/blob/67901c9dd5c22f4ece95b53f43fb0acc73e81a23/cmd/snapctl/main.go.
+// Accessed 8 Mar. 2022
+var clientConfig = client.Config{
+	// snapctl should not try to read $HOME/.snap/auth.json, this will
+	// result in apparmor denials and configure task failures
+	// (LP: #1660941)
+	DisableAuth: true,
+
+	// we need the less privileged snap socket in snapctl
+	Socket: dirs.SnapSocket,
+}
+
+// This function modified from
+// Vogt, Michael, et al. “Snapd.” Github.com, 2.54.4, Snapcore, 25 Nov. 2020,
+// https://github.com/snapcore/snapd/blob/67901c9dd5c22f4ece95b53f43fb0acc73e81a23/cmd/snapctl/main.go.
+// Accessed 8 Mar. 2022.
+func runSnapCtl(args []string) (stdout []byte, stderr []byte, err error) {
+	cli := client.New(&clientConfig)
+	cookie := os.Getenv("SNAP_COOKIE")
+	// for compatibility, if re-exec is not enabled and facing older snapd.
+	if cookie == "" {
+		cookie = os.Getenv("SNAP_CONTEXT")
+	}
+
+	return cli.RunSnapctl(&client.SnapCtlOptions{
+		ContextID: cookie,
+		Args:      args,
+	}, nil)
+}
+
+func get(key string) (string, error) {
+	stdout, _, err := runSnapCtl([]string{"get", "-d", key})
+	if err != nil {
+		return "", fmt.Errorf("%w for %s: %v", ErrSnapctl, key, err)
+	}
+	var result map[string]string
+	if err = json.Unmarshal(stdout, &result); err != nil {
+		return "", fmt.Errorf("%w for %s: %v", ErrJSONUnmarshal, key, err)
+	}
+	if len(result) == 0 {
+		return "", nil
+	}
+	return result[key], nil
+}
+
+type snapConfigOverrider struct {
+	ErrHandler func(error)
+}
+
+func (o *snapConfigOverrider) Get(lowerCaseKey string) (string, bool) {
+	result, err := get(lowerCaseKey)
+	if err != nil {
+		o.ErrHandler(err)
+	}
+	return result, err == nil && len(result) > 0
+}
+
+//nolint:revive // we dont want to give access to snapConfigOverrider type without constructor
+func Overrider(errHandler func(error)) *snapConfigOverrider {
+	return &snapConfigOverrider{
+		ErrHandler: errHandler,
+	}
+}