[#220] blobovnicza: Implement GetRange operation

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

pkg/local_object_storage/blobovnicza/get_range.go

@@ -0,0 +1,62 @@
+package blobovnicza
+
+import (
+	objectSDK "github.com/nspcc-dev/neofs-api-go/pkg/object"
+	"github.com/pkg/errors"
+)
+
+// GetRangePrm groups the parameters of GetRange operation.
+type GetRangePrm struct {
+	addr *objectSDK.Address
+
+	rng *objectSDK.Range
+}
+
+// GetRangeRes groups resulting values of GetRange operation.
+type GetRangeRes struct {
+	rngData []byte
+}
+
+var ErrRangeOutOfBounds = errors.New("payload range is out of bounds")
+
+// SetAddress sets address of the requested object.
+func (p *GetRangePrm) SetAddress(addr *objectSDK.Address) {
+	p.addr = addr
+}
+
+// SetAddress sets range of the requested payload data .
+func (p *GetRangePrm) SetRange(rng *objectSDK.Range) {
+	p.rng = rng
+}
+
+// RangeData returns the requested payload data range.
+func (p *GetRangeRes) RangeData() []byte {
+	return p.rngData
+}
+
+// Get reads the object from Blobovnicza by address.
+//
+// Returns any error encountered that
+// did not allow to completely read the object.
+func (b *Blobovnicza) GetRange(prm *GetRangePrm) (*GetRangeRes, error) {
+	res, err := b.Get(&GetPrm{
+		addr: prm.addr,
+	})
+	if err != nil {
+		return nil, err
+	}
+
+	from := prm.rng.GetOffset()
+	to := from + prm.rng.GetLength()
+	payload := res.obj.Payload()
+
+	if from > to {
+		return nil, errors.Errorf("invalid range [%d:%d]", from, to)
+	} else if uint64(len(payload)) < to {
+		return nil, ErrRangeOutOfBounds
+	}
+
+	return &GetRangeRes{
+		rngData: payload[from:to],
+	}, nil
+}