[#130] sdk: Define object identifier type

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

pkg/object/id.go

@@ -0,0 +1,54 @@
+package object
+
+import (
+	"crypto/sha256"
+
+	"github.com/nspcc-dev/neofs-api-go/v2/refs"
+	"github.com/pkg/errors"
+)
+
+// ID represents object identifier that
+// supports different type of values.
+type ID struct {
+	val []byte
+}
+
+// SetSHA256 sets object identifier value to SHA256 checksum.
+func (id *ID) SetSHA256(v [sha256.Size]byte) {
+	if id != nil {
+		id.val = v[:]
+	}
+}
+
+// ToV2 converts ID to v2 ObjectID message.
+func (id *ID) ToV2() *refs.ObjectID {
+	if id != nil {
+		idV2 := new(refs.ObjectID)
+		idV2.SetValue(id.val)
+
+		return idV2
+	}
+
+	return nil
+}
+
+// IDFromV2 converts v2 ObjectID message to ID.
+//
+// Returns an error if the format of the identifier
+// in the message is broken.
+func IDFromV2(idV2 *refs.ObjectID) (*ID, error) {
+	if idV2 == nil {
+		return nil, nil
+	}
+
+	val := idV2.GetValue()
+	if ln := len(val); ln != sha256.Size {
+		return nil, errors.Errorf("could not convert %T to %T: invalid length %d",
+			idV2, (*ID)(nil), ln,
+		)
+	}
+
+	return &ID{
+		val: val,
+	}, nil
+}

pkg/object/id_test.go

@@ -0,0 +1,27 @@
+package object
+
+import (
+	"crypto/rand"
+	"crypto/sha256"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestIDV2(t *testing.T) {
+	id := new(ID)
+
+	checksum := [sha256.Size]byte{}
+
+	_, err := rand.Read(checksum[:])
+	require.NoError(t, err)
+
+	id.SetSHA256(checksum)
+
+	idV2 := id.ToV2()
+
+	id2, err := IDFromV2(idV2)
+	require.NoError(t, err)
+
+	require.Equal(t, id, id2)
+}