[#1324] services/tree: Implement Object Tree Service

Object Tree Service allows changing trees assotiated with
the container in runtime.

Signed-off-by: Evgenii Stratonikov <evgeniy@nspcc.ru>

cmd/neofs-node/config/tree/config.go

@@ -0,0 +1,39 @@
+package treeconfig
+
+import (
+	"github.com/nspcc-dev/neofs-node/cmd/neofs-node/config"
+)
+
+// GRPCConfig is a wrapper over "grpc" config section which provides access
+// to gRPC configuration of control service.
+type GRPCConfig struct {
+	cfg *config.Config
+}
+
+const (
+	subsection     = "tree"
+	grpcSubsection = "grpc"
+
+	// GRPCEndpointDefault is a default endpoint of gRPC Control service.
+	GRPCEndpointDefault = ""
+)
+
+// GRPC returns structure that provides access to "grpc" subsection of
+// "tree" section.
+func GRPC(c *config.Config) GRPCConfig {
+	return GRPCConfig{
+		c.Sub(subsection).Sub(grpcSubsection),
+	}
+}
+
+// Endpoint returns value of "endpoint" config parameter.
+//
+// Returns GRPCEndpointDefault if value is not a non-empty string.
+func (g GRPCConfig) Endpoint() string {
+	v := config.String(g.cfg, "endpoint")
+	if v != "" {
+		return v
+	}
+
+	return GRPCEndpointDefault
+}

cmd/neofs-node/config/tree/config_test.go

@@ -0,0 +1,30 @@
+package treeconfig_test
+
+import (
+	"testing"
+
+	"github.com/nspcc-dev/neofs-node/cmd/neofs-node/config"
+	configtest "github.com/nspcc-dev/neofs-node/cmd/neofs-node/config/test"
+	treeconfig "github.com/nspcc-dev/neofs-node/cmd/neofs-node/config/tree"
+	"github.com/stretchr/testify/require"
+)
+
+func TestControlSection(t *testing.T) {
+	t.Run("defaults", func(t *testing.T) {
+		empty := configtest.EmptyConfig()
+
+		require.Equal(t, treeconfig.GRPCEndpointDefault, treeconfig.GRPC(empty).Endpoint())
+	})
+
+	const path = "../../../../config/example/node"
+
+	var fileConfigTest = func(c *config.Config) {
+		require.Equal(t, "127.0.0.1:8091", treeconfig.GRPC(c).Endpoint())
+	}
+
+	configtest.ForEachFileType(path, fileConfigTest)
+
+	t.Run("ENV", func(t *testing.T) {
+		configtest.ForEnvFileType(path, fileConfigTest)
+	})
+}