[#222] Add Head method in shard

Signed-off-by: Alex Vanin <alexey@nspcc.ru>

pkg/local_object_storage/shard/head.go

@@ -0,0 +1,43 @@
+package shard
+
+import (
+	objectSDK "github.com/nspcc-dev/neofs-api-go/pkg/object"
+	"github.com/nspcc-dev/neofs-node/pkg/core/object"
+)
+
+// HeadPrm groups the parameters of Head operation.
+type HeadPrm struct {
+	addr *objectSDK.Address
+}
+
+// HeadRes groups resulting values of Head operation.
+type HeadRes struct {
+	obj *object.Object
+}
+
+// WithAddress is a Head option to set the address of the requested object.
+//
+// Option is required.
+func (p *HeadPrm) WithAddress(addr *objectSDK.Address) *HeadPrm {
+	if p != nil {
+		p.addr = addr
+	}
+
+	return p
+}
+
+// Object returns the requested object header.
+func (r *HeadRes) Object() *object.Object {
+	return r.obj
+}
+
+// Head reads header of the object from the shard.
+//
+// Returns any error encountered.
+func (s *Shard) Head(prm *HeadPrm) (*HeadRes, error) {
+	head, err := s.metaBase.Get(prm.addr)
+
+	return &HeadRes{
+		obj: head,
+	}, err
+}