[#216] blobovnicza: Implement main methods and logic

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

pkg/local_object_storage/blobovnicza/get.go

@@ -0,0 +1,78 @@
+package blobovnicza
+
+import (
+	objectSDK "github.com/nspcc-dev/neofs-api-go/pkg/object"
+	"github.com/nspcc-dev/neofs-node/pkg/core/object"
+	"github.com/pkg/errors"
+	"go.etcd.io/bbolt"
+	"go.uber.org/zap"
+)
+
+// GetPrm groups the parameters of Get operation.
+type GetPrm struct {
+	addr *objectSDK.Address
+}
+
+// GetRes groups resulting values of Get operation.
+type GetRes struct {
+	obj *object.Object
+}
+
+// ErrObjectNotFound is returns on read operations requested on a missing object.
+var ErrObjectNotFound = errors.New("object not found")
+
+// SetAddress sets address of the requested object.
+func (p *GetPrm) SetAddress(addr *objectSDK.Address) {
+	p.addr = addr
+}
+
+// Object returns the requested object.
+func (p *GetRes) Object() *object.Object {
+	return p.obj
+}
+
+// Get reads the object from Blobovnicza by address.
+//
+// Returns any error encountered that
+// did not allow to completely read the object.
+func (b *Blobovnicza) Get(prm *GetPrm) (*GetRes, error) {
+	var (
+		data    []byte
+		addrKey = addressKey(prm.addr)
+	)
+
+	if err := b.boltDB.View(func(tx *bbolt.Tx) error {
+		return b.iterateBuckets(tx, func(lower, upper uint64, buck *bbolt.Bucket) (bool, error) {
+			data = buck.Get(addrKey)
+
+			stop := data != nil
+
+			if stop {
+				b.log.Debug("object is found in bucket",
+					zap.String("binary size", stringifyByteSize(uint64(len(data)))),
+					zap.String("range", stringifyBounds(lower, upper)),
+				)
+			}
+
+			return stop, nil
+		})
+	}); err != nil {
+		return nil, err
+	}
+
+	if data == nil {
+		return nil, ErrObjectNotFound
+	}
+
+	// TODO: add decompression step
+
+	// unmarshal the object
+	obj := object.New()
+	if err := obj.Unmarshal(data); err != nil {
+		return nil, errors.Wrap(err, "could not unmarshal the object")
+	}
+
+	return &GetRes{
+		obj: obj,
+	}, nil
+}