[#990] nodeValidators: Add subnet entrance validator

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

pkg/innerring/processors/netmap/nodevalidation/subnet/validator.go

@@ -0,0 +1,41 @@
+package subnet
+
+import (
+	"errors"
+
+	morphsubnet "github.com/nspcc-dev/neofs-node/pkg/morph/client/subnet"
+)
+
+// Validator is an utility that verifies node subnet
+// allowance.
+//
+// For correct operation, Validator must be created
+// using the constructor (New). After successful creation,
+// the Validator is immediately ready to work through API.
+type Validator struct {
+	subnetClient *morphsubnet.Client
+}
+
+// Prm groups the required parameters of the Validator's constructor.
+//
+// All values must comply with the requirements imposed on them.
+// Passing incorrect parameter values will result in constructor
+// failure (error or panic depending on the implementation).
+type Prm struct {
+	SubnetClient *morphsubnet.Client
+}
+
+// New creates a new instance of the Validator.
+//
+// The created Validator does not require additional
+// initialization and is completely ready for work.
+func New(prm Prm) (*Validator, error) {
+	switch {
+	case prm.SubnetClient == nil:
+		return nil, errors.New("ir/nodeValidator: subnet client is not set")
+	}
+
+	return &Validator{
+		subnetClient: prm.SubnetClient,
+	}, nil
+}