slicer: Allow to toggle homomorphic hashing

Homomorphic hashing of object payload is not always necessary. There is
a need to provide ability to skip calculation. It's also worth to not
calculate it by default since current implementation of Tillich-Zemor
algorithm has large resource cost.

Do not calculate homomorphic checksum in `Slicer` methods by default.
Provide option to enable the calculation. Make tests to randomize
calculation flag and assert results according to it.

Refs #342.

Signed-off-by: Leonard Lyubich <leonard@morphbits.io>

client/object_put.go

@@ -342,6 +342,9 @@ func CreateObject(ctx context.Context, cli *Client, signer neofscrypto.Signer, c
 	var opts slicer.Options
 	opts.SetObjectPayloadLimit(netInfo.MaxObjectSize())
 	opts.SetCurrentNeoFSEpoch(netInfo.CurrentEpoch())
+	if !netInfo.HomomorphicHashingDisabled() {
+		opts.CalculateHomomorphicChecksum()
+	}
 
 	s := slicer.New(signer, cnr, owner, &objectWriter{
 		context: ctx,

object/slicer/options.go

@@ -5,6 +5,8 @@ type Options struct {
 	objectPayloadLimit uint64
 
 	currentNeoFSEpoch uint64
+
+	withHomoChecksum bool
 }
 
 // SetObjectPayloadLimit specifies data size limit for produced physically
@@ -17,3 +19,9 @@ func (x *Options) SetObjectPayloadLimit(l uint64) {
 func (x *Options) SetCurrentNeoFSEpoch(e uint64) {
 	x.currentNeoFSEpoch = e
 }
+
+// CalculateHomomorphicChecksum makes Slicer to calculate and set homomorphic
+// checksum of the processed objects.
+func (x *Options) CalculateHomomorphicChecksum() {
+	x.withHomoChecksum = true
+}

object/slicer/slicer.go

@@ -143,16 +143,15 @@ func (x *Slicer) Slice(data io.Reader, attributes ...string) (oid.ID, error) {
 
 	var rootID oid.ID
 	var rootHeader object.Object
-	var rootMeta dynamicObjectMetadata
 	var offset uint64
 	var isSplit bool
 	var childMeta dynamicObjectMetadata
 	var writtenChildren []oid.ID
 	var childHeader object.Object
+	rootMeta := newDynamicObjectMetadata(x.opts.withHomoChecksum)
 	bChunk := make([]byte, x.opts.objectPayloadLimit+1)
 
 	x.fillCommonMetadata(&rootHeader)
-	rootMeta.reset()
 
 	for {
 		n, err := data.Read(bChunk[offset:])
@@ -264,7 +263,7 @@ func (x *Slicer) Slice(data io.Reader, attributes ...string) (oid.ID, error) {
 
 			// shift overflow bytes to the beginning
 			if !isSplitCp {
-				childMeta = dynamicObjectMetadata{} // to avoid rootMeta corruption
+				childMeta = newDynamicObjectMetadata(x.opts.withHomoChecksum) // to avoid rootMeta corruption
 			}
 			childMeta.reset()
 			childMeta.accumulateNextPayloadChunk(bChunk[toSend:])
@@ -297,6 +296,8 @@ func (x *Slicer) InitPayloadStream(attributes ...string) (*PayloadWriter, error)
 		currentEpoch: x.opts.currentNeoFSEpoch,
 		sessionToken: x.sessionToken,
 		attributes:   attributes,
+		rootMeta:     newDynamicObjectMetadata(x.opts.withHomoChecksum),
+		childMeta:    newDynamicObjectMetadata(x.opts.withHomoChecksum),
 	}
 
 	res.buf.Grow(int(x.childPayloadSizeLimit()))
@@ -486,11 +487,13 @@ func flushObjectMetadata(signer neofscrypto.Signer, meta dynamicObjectMetadata,
 	cs.SetSHA256(csBytes)
 	header.SetPayloadChecksum(cs)
 
+	if meta.homomorphicChecksum != nil {
 		var csHomoBytes [tz.Size]byte
 		copy(csHomoBytes[:], meta.homomorphicChecksum.Sum(nil))
 
 		cs.SetTillichZemor(csHomoBytes)
 		header.SetPayloadHomomorphicHash(cs)
+	}
 
 	header.SetPayloadSize(meta.length)
 
@@ -552,6 +555,18 @@ type dynamicObjectMetadata struct {
 	homomorphicChecksum hash.Hash
 }
 
+func newDynamicObjectMetadata(withHomoChecksum bool) dynamicObjectMetadata {
+	m := dynamicObjectMetadata{
+		checksum: sha256.New(),
+	}
+
+	if withHomoChecksum {
+		m.homomorphicChecksum = tz.New()
+	}
+
+	return m
+}
+
 func (x *dynamicObjectMetadata) Write(chunk []byte) (int, error) {
 	x.accumulateNextPayloadChunk(chunk)
 	return len(chunk), nil
@@ -562,23 +577,17 @@ func (x *dynamicObjectMetadata) Write(chunk []byte) (int, error) {
 func (x *dynamicObjectMetadata) accumulateNextPayloadChunk(chunk []byte) {
 	x.length += uint64(len(chunk))
 	x.checksum.Write(chunk)
+	if x.homomorphicChecksum != nil {
 		x.homomorphicChecksum.Write(chunk)
 	}
+}
 
 // reset resets all accumulated metadata.
 func (x *dynamicObjectMetadata) reset() {
 	x.length = 0
-
-	if x.checksum != nil {
 	x.checksum.Reset()
-	} else {
-		x.checksum = sha256.New()
-	}
-
 	if x.homomorphicChecksum != nil {
 		x.homomorphicChecksum.Reset()
-	} else {
-		x.homomorphicChecksum = tz.New()
 	}
 }
 

object/slicer/slicer_test.go

@@ -141,6 +141,7 @@ type input struct {
 	sessionToken *session.Object
 	payload      []byte
 	attributes   []string
+	withHomo     bool
 }
 
 func randomData(size uint64) []byte {
@@ -181,9 +182,14 @@ func randomInput(tb testing.TB, size, sizeLimit uint64) (input, slicer.Options)
 		in.owner = *usertest.ID(tb)
 	}
 
+	in.withHomo = rand.Int()%2 == 0
+
 	var opts slicer.Options
 	opts.SetObjectPayloadLimit(in.payloadLimit)
 	opts.SetCurrentNeoFSEpoch(in.currentEpoch)
+	if in.withHomo {
+		opts.CalculateHomomorphicChecksum()
+	}
 
 	return in, opts
 }
@@ -340,6 +346,9 @@ func checkStaticMetadata(tb testing.TB, header object.Object, in input) {
 	require.Equal(tb, in.sessionToken, header.SessionToken(), "configured session token must be written into objects")
 
 	require.NoError(tb, object.CheckHeaderVerificationFields(&header), "verification fields must be correctly set in header")
+
+	_, ok = header.PayloadHomomorphicHash()
+	require.Equal(tb, in.withHomo, ok)
 }
 
 func (x *chainCollector) handleOutgoingObject(header object.Object, payload io.Reader) {
@@ -404,14 +413,19 @@ func (x *chainCollector) handleOutgoingObject(header object.Object, payload io.R
 	cs, ok := header.PayloadChecksum()
 	require.True(x.tb, ok)
 
-	csHomo, ok := header.PayloadHomomorphicHash()
-	require.True(x.tb, ok)
-
-	x.mPayloads[id] = payloadWithChecksum{
+	pcs := payloadWithChecksum{
 		r:  payload,
-		cs: []checksum.Checksum{cs, csHomo},
-		hs: []hash.Hash{sha256.New(), tz.New()},
+		cs: []checksum.Checksum{cs},
+		hs: []hash.Hash{sha256.New()},
 	}
+
+	csHomo, ok := header.PayloadHomomorphicHash()
+	if ok {
+		pcs.cs = append(pcs.cs, csHomo)
+		pcs.hs = append(pcs.hs, tz.New())
+	}
+
+	x.mPayloads[id] = pcs
 }
 
 func (x *chainCollector) verify(in input, rootID oid.ID) {