[#163] object: Implement functions linking Object and Lock instances

Add `WriteLock`/`ReadLock` function which writes/read `Lock` instace
to/from the `Object` instance.

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

object/lock.go

@@ -8,8 +8,28 @@ import (
 
 // Lock represents record with locked objects. It is compatible with
 // NeoFS API V2 protocol.
+//
+// Lock instance can be written to the Object, see WriteLock/ReadLock.
 type Lock v2object.Lock
 
+// WriteLock writes Lock to the Object, and sets its type to TypeLock.
+// The object must not be nil.
+//
+// See also ReadLock.
+func WriteLock(obj *Object, l Lock) {
+	obj.SetType(TypeLock)
+	obj.SetPayload(l.Marshal())
+}
+
+// ReadLock reads Lock from the Object. The lock must not be nil.
+// Returns an error describing incorrect format. Makes sense only
+// if object has TypeLock type.
+//
+// See also WriteLock.
+func ReadLock(l *Lock, obj Object) error {
+	return l.Unmarshal(obj.Payload())
+}
+
 // NumberOfMembers returns number of members in lock list.
 func (x Lock) NumberOfMembers() int {
 	return (*v2object.Lock)(&x).NumberOfMembers()

object/lock_test.go

@@ -0,0 +1,39 @@
+package object_test
+
+import (
+	"testing"
+
+	"github.com/nspcc-dev/neofs-sdk-go/object"
+	objecttest "github.com/nspcc-dev/neofs-sdk-go/object/test"
+	"github.com/stretchr/testify/require"
+)
+
+func TestLockEncoding(t *testing.T) {
+	l := *objecttest.Lock()
+
+	t.Run("binary", func(t *testing.T) {
+		data := l.Marshal()
+
+		var l2 object.Lock
+		require.NoError(t, l2.Unmarshal(data))
+
+		require.Equal(t, l, l2)
+	})
+}
+
+func TestWriteLock(t *testing.T) {
+	l := *objecttest.Lock()
+	var o object.Object
+
+	object.WriteLock(&o, l)
+
+	var l2 object.Lock
+
+	require.NoError(t, object.ReadLock(&l2, o))
+	require.Equal(t, l, l2)
+
+	// corrupt payload
+	o.Payload()[0]++
+
+	require.Error(t, object.ReadLock(&l2, o))
+}

object/test/generate.go

@@ -112,3 +112,11 @@ func SearchFilters() object.SearchFilters {
 
 	return x
 }
+
+// Lock returns random object.Lock.
+func Lock() *object.Lock {
+	var l object.Lock
+	l.WriteMembers([]oid.ID{*oidtest.ID(), *oidtest.ID()})
+
+	return &l
+}