[#170] checksum: Do not use pointers

Do not return pointers from getters. Do not pass pointers to the methods
that does not modify the checksum. Add `Empty` method.

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

checksum/test/generate.go

@@ -8,7 +8,7 @@ import (
 )
 
 // Checksum returns random checksum.Checksum.
-func Checksum() *checksum.Checksum {
+func Checksum() checksum.Checksum {
 	var cs [sha256.Size]byte
 
 	rand.Read(cs[:])
@@ -17,5 +17,5 @@ func Checksum() *checksum.Checksum {
 
 	x.SetSHA256(cs)
 
-	return &x
+	return x
 }

eacl/record.go

@@ -137,7 +137,7 @@ func (r *Record) AddObjectPayloadLengthFilter(m Match, size uint64) {
 }
 
 // AddObjectPayloadHashFilter adds filter by object payload hash value.
-func (r *Record) AddObjectPayloadHashFilter(m Match, h *checksum.Checksum) {
+func (r *Record) AddObjectPayloadHashFilter(m Match, h checksum.Checksum) {
 	r.addObjectReservedFilter(m, fKeyObjPayloadHash, h)
 }
 
@@ -147,7 +147,7 @@ func (r *Record) AddObjectTypeFilter(m Match, t object.Type) {
 }
 
 // AddObjectHomomorphicHashFilter adds filter by object payload homomorphic hash value.
-func (r *Record) AddObjectHomomorphicHashFilter(m Match, h *checksum.Checksum) {
+func (r *Record) AddObjectHomomorphicHashFilter(m Match, h checksum.Checksum) {
 	r.addObjectReservedFilter(m, fKeyObjHomomorphicHash, h)
 }
 

object/fmt.go

@@ -20,11 +20,11 @@ var errIncorrectID = errors.New("incorrect object identifier")
 
 // CalculatePayloadChecksum calculates and returns checksum of
 // object payload bytes.
-func CalculatePayloadChecksum(payload []byte) *checksum.Checksum {
+func CalculatePayloadChecksum(payload []byte) checksum.Checksum {
 	var res checksum.Checksum
 	checksum.Calculate(&res, checksum.SHA256, payload)
 
-	return &res
+	return res
 }
 
 // CalculateAndSetPayloadChecksum calculates checksum of current

object/object.go

@@ -200,19 +200,26 @@ func (o *Object) SetCreationEpoch(v uint64) {
 }
 
 // PayloadChecksum returns checksum of the object payload.
-func (o *Object) PayloadChecksum() *checksum.Checksum {
+//
+// Zero Object has zero checksum.
+//
+// See also SetPayloadChecksum.
+func (o *Object) PayloadChecksum() checksum.Checksum {
 	var v checksum.Checksum
-	v.ReadFromV2(
-		*(*object.Object)(o).
-			GetHeader().
-			GetPayloadHash(),
-	)
+	v2 := (*object.Object)(o)
 
-	return &v
+	if hash := v2.GetHeader().GetPayloadHash(); hash != nil {
+		v.ReadFromV2(*hash)
+	}
+
+	return v
 }
 
 // SetPayloadChecksum sets checksum of the object payload.
-func (o *Object) SetPayloadChecksum(v *checksum.Checksum) {
+// Checksum must not be nil.
+//
+// See also PayloadChecksum.
+func (o *Object) SetPayloadChecksum(v checksum.Checksum) {
 	var v2 refs.Checksum
 	v.WriteToV2(&v2)
 
@@ -222,19 +229,26 @@ func (o *Object) SetPayloadChecksum(v *checksum.Checksum) {
 }
 
 // PayloadHomomorphicHash returns homomorphic hash of the object payload.
-func (o *Object) PayloadHomomorphicHash() *checksum.Checksum {
+//
+// Zero Object has zero checksum.
+//
+// See also SetPayloadHomomorphicHash.
+func (o *Object) PayloadHomomorphicHash() checksum.Checksum {
 	var v checksum.Checksum
-	v.ReadFromV2(
-		*(*object.Object)(o).
-			GetHeader().
-			GetHomomorphicHash(),
-	)
+	v2 := (*object.Object)(o)
 
-	return &v
+	if hash := v2.GetHeader().GetHomomorphicHash(); hash != nil {
+		v.ReadFromV2(*hash)
+	}
+
+	return v
 }
 
 // SetPayloadHomomorphicHash sets homomorphic hash of the object payload.
-func (o *Object) SetPayloadHomomorphicHash(v *checksum.Checksum) {
+// Checksum must not be nil.
+//
+// See also PayloadHomomorphicHash.
+func (o *Object) SetPayloadHomomorphicHash(v checksum.Checksum) {
 	var v2 refs.Checksum
 	v.WriteToV2(&v2)
 

object/raw_test.go

@@ -125,9 +125,9 @@ func TestObject_SetPayloadChecksum(t *testing.T) {
 	var cs checksum.Checksum
 	cs.SetSHA256(randSHA256Checksum(t))
 
-	obj.SetPayloadChecksum(&cs)
+	obj.SetPayloadChecksum(cs)
 
-	require.Equal(t, &cs, obj.PayloadChecksum())
+	require.Equal(t, cs, obj.PayloadChecksum())
 }
 
 func TestObject_SetPayloadHomomorphicHash(t *testing.T) {
@@ -136,9 +136,9 @@ func TestObject_SetPayloadHomomorphicHash(t *testing.T) {
 	var cs checksum.Checksum
 	cs.SetTillichZemor(randTZChecksum(t))
 
-	obj.SetPayloadHomomorphicHash(&cs)
+	obj.SetPayloadHomomorphicHash(cs)
 
-	require.Equal(t, &cs, obj.PayloadHomomorphicHash())
+	require.Equal(t, cs, obj.PayloadHomomorphicHash())
 }
 
 func TestObject_SetAttributes(t *testing.T) {

storagegroup/storagegroup.go

@@ -42,20 +42,24 @@ func (sg *StorageGroup) SetValidationDataSize(epoch uint64) {
 
 // ValidationDataHash returns homomorphic hash from the
 // concatenation of the payloads of the storage group members.
-func (sg *StorageGroup) ValidationDataHash() *checksum.Checksum {
-	if v2 := (*storagegroup.StorageGroup)(sg).GetValidationHash(); v2 != nil {
-		var v checksum.Checksum
-		v.ReadFromV2(*v2)
-
-		return &v
+//
+// Zero StorageGroup has zero checksum.
+//
+// See also SetValidationDataHash.
+func (sg StorageGroup) ValidationDataHash() (v checksum.Checksum) {
+	v2 := (storagegroup.StorageGroup)(sg)
+	if checksumV2 := v2.GetValidationHash(); checksumV2 != nil {
+		v.ReadFromV2(*checksumV2)
 	}
 
-	return nil
+	return
 }
 
 // SetValidationDataHash sets homomorphic hash from the
 // concatenation of the payloads of the storage group members.
-func (sg *StorageGroup) SetValidationDataHash(hash *checksum.Checksum) {
+//
+// See also ValidationDataHash.
+func (sg *StorageGroup) SetValidationDataHash(hash checksum.Checksum) {
 	var v2 refs.Checksum
 	hash.WriteToV2(&v2)
 

storagegroup/storagegroup_test.go

@@ -78,7 +78,7 @@ func TestNew(t *testing.T) {
 
 		// check initial values
 		require.Nil(t, sg.Members())
-		require.Nil(t, sg.ValidationDataHash())
+		require.True(t, sg.ValidationDataHash().Empty())
 		require.Zero(t, sg.ExpirationEpoch())
 		require.Zero(t, sg.ValidationDataSize())