[#493] node/config: Implement sections of local object storage

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

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

@@ -0,0 +1,34 @@
+package engineconfig
+
+import (
+	"strconv"
+
+	"github.com/nspcc-dev/neofs-node/cmd/neofs-node/config"
+	shardconfig "github.com/nspcc-dev/neofs-node/cmd/neofs-node/config/engine/shard"
+)
+
+// IterateShards iterates over subsections ["0":"N") (N - "shard_num" value)
+// of "shard" subsection of "storage" section of c, wrap them into
+// shardconfig.Config and passes to f.
+//
+// Panics if N is not a positive number.
+func IterateShards(c *config.Config, f func(*shardconfig.Config)) {
+	c = c.Sub("storage")
+
+	num := config.Uint(c, "shard_num")
+	if num == 0 {
+		panic("no shard configured")
+	}
+
+	c = c.Sub("shard")
+
+	for i := uint64(0); i < num; i++ {
+		si := strconv.FormatUint(i, 10)
+
+		sc := shardconfig.From(
+			c.Sub(si),
+		)
+
+		f(sc)
+	}
+}