[#399] container: Support homomorphic hash disabling

Container could now have "__NEOFS__DISABLE_HOMOMORPHIC_HASHING" well-known
attribute. Setting that to "true" means disabling homomorphic hashing for
objects that belong to that container, any other cases mean that homomorphic
hashing is enabled.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

container/attributes_test.go

@@ -0,0 +1,59 @@
+package container_test
+
+import (
+	"testing"
+
+	"github.com/nspcc-dev/neofs-api-go/v2/container"
+	containertest "github.com/nspcc-dev/neofs-api-go/v2/container/test"
+	"github.com/stretchr/testify/require"
+)
+
+func TestContainer_HomomorphicHashingDisabled(t *testing.T) {
+	cnr := containertest.GenerateContainer(false)
+
+	t.Run("defaults", func(t *testing.T) {
+		require.True(t, cnr.HomomorphicHashingState())
+	})
+
+	t.Run("disabled", func(t *testing.T) {
+		attr := container.Attribute{}
+		attr.SetKey(container.SysAttributeHomomorphicHashing)
+		attr.SetValue("NOT_true")
+
+		cnr.SetAttributes(append(cnr.GetAttributes(), attr))
+		require.True(t, cnr.HomomorphicHashingState())
+
+		attr.SetValue("true")
+
+		cnr.SetAttributes([]container.Attribute{attr})
+		require.False(t, cnr.HomomorphicHashingState())
+	})
+}
+
+func TestContainer_SetHomomorphicHashingState(t *testing.T) {
+	cnr := containertest.GenerateContainer(false)
+	attrs := cnr.GetAttributes()
+	attrLen := len(attrs)
+
+	cnr.SetHomomorphicHashingState(true)
+
+	// enabling hashing should not add any new attributes
+	require.Equal(t, attrLen, len(cnr.GetAttributes()))
+	require.True(t, cnr.HomomorphicHashingState())
+
+	cnr.SetHomomorphicHashingState(false)
+
+	// disabling hashing should add exactly one attribute
+	require.Equal(t, attrLen+1, len(cnr.GetAttributes()))
+	require.False(t, cnr.HomomorphicHashingState())
+
+	cnr.SetHomomorphicHashingState(true)
+
+	// enabling hashing should remove 1 attribute if
+	// hashing was disabled before
+	require.Equal(t, attrLen, len(cnr.GetAttributes()))
+	require.True(t, cnr.HomomorphicHashingState())
+
+	// hashing operations should not change any other attributes
+	require.ElementsMatch(t, attrs, cnr.GetAttributes())
+}