[#176] localstore: Draft storage engine structure and ops

Implement the primary structure and operation of the local object
storage engine.

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

pkg/local_object_storage/engine/select.go

@@ -0,0 +1,64 @@
+package engine
+
+import (
+	"github.com/nspcc-dev/neofs-api-go/pkg/object"
+	objectSDK "github.com/nspcc-dev/neofs-api-go/pkg/object"
+	"github.com/nspcc-dev/neofs-node/pkg/local_object_storage/shard"
+	"go.uber.org/zap"
+)
+
+// SelectPrm groups the parameters of Select operation.
+type SelectPrm struct {
+	filters object.SearchFilters
+}
+
+// SelectRes groups resulting values of Select operation.
+type SelectRes struct {
+	addrList []*object.Address
+}
+
+// WithFilters is a Select option to set the object filters.
+func (p *SelectPrm) WithFilters(fs objectSDK.SearchFilters) *SelectPrm {
+	if p != nil {
+		p.filters = fs
+	}
+
+	return p
+}
+
+// AddressList returns list of addresses of the selected objects.
+func (r *SelectRes) AddressList() []*objectSDK.Address {
+	return r.addrList
+}
+
+// Select selects the objects from local storage that match select parameters.
+//
+// Returns any error encountered that did not allow to completely select the objects.
+func (e *StorageEngine) Select(prm *SelectPrm) (*SelectRes, error) {
+	e.mtx.RLock()
+	defer e.mtx.RUnlock()
+
+	addrList := make([]*object.Address, 0)
+
+	shPrm := new(shard.SelectPrm).
+		WithFilters(prm.filters)
+
+	e.iterateOverSortedShards(nil, func(sh *shard.Shard) (stop bool) {
+		res, err := sh.Select(shPrm)
+		if err != nil {
+			// TODO: smth wrong with shard, need to be processed
+			e.log.Warn("could not select objects from shard",
+				zap.Stringer("shard", sh.ID()),
+				zap.String("error", err.Error()),
+			)
+		} else {
+			addrList = append(addrList, res.AddressList()...)
+		}
+
+		return false
+	})
+
+	return &SelectRes{
+		addrList: addrList,
+	}, nil
+}