[#493] node/config: Change Sub implementation

In some cases viper doesn't interpret `section.value` as a subsection with
`section` name, but value is value still can be accessed through full
pathname.

Fix `Config.Sub` method implementation in order to always interpret
configuration like described above as a subsection. From now method never
returns nil, therefore an additional check has been removed from the `Value`
method.

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

cmd/neofs-node/config/calls.go

@@ -1,14 +1,17 @@
 package config
 
 import (
-	"github.com/spf13/viper"
+	"strings"
 )
 
-// Sub returns sub-section of the Config by name.
+// Sub returns subsection of the Config by name.
+//
+// Returns nil if subsection if missing.
 func (x *Config) Sub(name string) *Config {
-	return (*Config)(
-		(*viper.Viper)(x).Sub(name),
-	)
+	return &Config{
+		v:    x.v,
+		path: append(x.path, name),
+	}
 }
 
 // Value returns configuration value by name.
@@ -20,9 +23,5 @@ func (x *Config) Sub(name string) *Config {
 //
 // Returns nil if config is nil.
 func (x *Config) Value(name string) interface{} {
-	if x != nil {
-		return (*viper.Viper)(x).Get(name)
-	}
-
-	return nil
+	return x.v.Get(strings.Join(append(x.path, name), separator))
 }

cmd/neofs-node/config/calls_test.go

@@ -21,9 +21,6 @@ func TestConfigCommon(t *testing.T) {
 
 		const nonExistentSub = "non-existent sub-section"
 
-		sub = c.Sub(nonExistentSub)
-		require.Nil(t, sub)
-
 		val = c.Sub(nonExistentSub).Value("value")
 		require.Nil(t, val)
 	})

cmd/neofs-node/config/config.go

@@ -13,7 +13,11 @@ import (
 // Sub-trees are named configuration sub-sections,
 // leaves are named configuration values.
 // Names are of string type.
-type Config viper.Viper
+type Config struct {
+	v *viper.Viper
+
+	path []string
+}
 
 const (
 	separator    = "."
@@ -49,5 +53,7 @@ func New(_ Prm, opts ...Option) *Config {
 		}
 	}
 
-	return (*Config)(v)
+	return &Config{
+		v: v,
+	}
 }