From c2ea143d00252fe01c36f7eaf740bf6e753e1f92 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Fri, 17 Feb 2023 12:52:46 +0300
Subject: [PATCH 01/12] [#19] object: Move transformer implementation from node

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 object/transformer/fmt.go         | 116 ++++++++++++
 object/transformer/transformer.go | 294 ++++++++++++++++++++++++++++++
 object/transformer/types.go       | 111 +++++++++++
 3 files changed, 521 insertions(+)
 create mode 100644 object/transformer/fmt.go
 create mode 100644 object/transformer/transformer.go
 create mode 100644 object/transformer/types.go

diff --git a/object/transformer/fmt.go b/object/transformer/fmt.go
new file mode 100644
index 0000000..b0ca5c9
--- /dev/null
+++ b/object/transformer/fmt.go
@@ -0,0 +1,116 @@
+package transformer
+
+import (
+	"crypto/ecdsa"
+	"fmt"
+
+	"github.com/TrueCloudLab/frostfs-sdk-go/object"
+	oid "github.com/TrueCloudLab/frostfs-sdk-go/object/id"
+	"github.com/TrueCloudLab/frostfs-sdk-go/session"
+	"github.com/TrueCloudLab/frostfs-sdk-go/version"
+)
+
+type formatter struct {
+	prm *FormatterParams
+
+	obj *object.Object
+
+	sz uint64
+}
+
+type EpochSource interface {
+	CurrentEpoch() uint64
+}
+
+// FormatterParams groups NewFormatTarget parameters.
+type FormatterParams struct {
+	Key *ecdsa.PrivateKey
+
+	NextTarget ObjectTarget
+
+	SessionToken *session.Object
+
+	NetworkState EpochSource
+}
+
+// NewFormatTarget returns ObjectTarget instance that finalizes object structure
+// and writes it to the next target.
+//
+// Chunks must be written before the WriteHeader call.
+//
+// Object changes:
+// - sets version to current SDK version;
+// - sets payload size to the total length of all written chunks;
+// - sets session token;
+// - sets number of creation epoch;
+// - calculates and sets verification fields (ID, Signature).
+func NewFormatTarget(p *FormatterParams) ObjectTarget {
+	return &formatter{
+		prm: p,
+	}
+}
+
+func (f *formatter) WriteHeader(obj *object.Object) error {
+	f.obj = obj
+
+	return nil
+}
+
+func (f *formatter) Write(p []byte) (n int, err error) {
+	n, err = f.prm.NextTarget.Write(p)
+
+	f.sz += uint64(n)
+
+	return
+}
+
+func (f *formatter) Close() (*AccessIdentifiers, error) {
+	curEpoch := f.prm.NetworkState.CurrentEpoch()
+	ver := version.Current()
+
+	f.obj.SetVersion(&ver)
+	f.obj.SetPayloadSize(f.sz)
+	f.obj.SetSessionToken(f.prm.SessionToken)
+	f.obj.SetCreationEpoch(curEpoch)
+
+	var (
+		parID  *oid.ID
+		parHdr *object.Object
+	)
+
+	if par := f.obj.Parent(); par != nil && par.Signature() == nil {
+		rawPar := object.NewFromV2(par.ToV2())
+
+		rawPar.SetSessionToken(f.prm.SessionToken)
+		rawPar.SetCreationEpoch(curEpoch)
+
+		if err := object.SetIDWithSignature(*f.prm.Key, rawPar); err != nil {
+			return nil, fmt.Errorf("could not finalize parent object: %w", err)
+		}
+
+		id, _ := rawPar.ID()
+		parID = &id
+		parHdr = rawPar
+
+		f.obj.SetParent(parHdr)
+	}
+
+	if err := object.SetIDWithSignature(*f.prm.Key, f.obj); err != nil {
+		return nil, fmt.Errorf("could not finalize object: %w", err)
+	}
+
+	if err := f.prm.NextTarget.WriteHeader(f.obj); err != nil {
+		return nil, fmt.Errorf("could not write header to next target: %w", err)
+	}
+
+	if _, err := f.prm.NextTarget.Close(); err != nil {
+		return nil, fmt.Errorf("could not close next target: %w", err)
+	}
+
+	id, _ := f.obj.ID()
+
+	return new(AccessIdentifiers).
+		WithSelfID(id).
+		WithParentID(parID).
+		WithParent(parHdr), nil
+}
diff --git a/object/transformer/transformer.go b/object/transformer/transformer.go
new file mode 100644
index 0000000..cfd7098
--- /dev/null
+++ b/object/transformer/transformer.go
@@ -0,0 +1,294 @@
+package transformer
+
+import (
+	"crypto/sha256"
+	"fmt"
+	"hash"
+	"io"
+
+	"github.com/TrueCloudLab/frostfs-sdk-go/checksum"
+	"github.com/TrueCloudLab/frostfs-sdk-go/object"
+	oid "github.com/TrueCloudLab/frostfs-sdk-go/object/id"
+	"github.com/TrueCloudLab/tzhash/tz"
+)
+
+type payloadSizeLimiter struct {
+	maxSize, written uint64
+
+	withoutHomomorphicHash bool
+
+	targetInit func() ObjectTarget
+
+	target ObjectTarget
+
+	current, parent *object.Object
+
+	currentHashers, parentHashers []*payloadChecksumHasher
+
+	previous []oid.ID
+
+	chunkWriter io.Writer
+
+	splitID *object.SplitID
+
+	parAttrs []object.Attribute
+}
+
+type payloadChecksumHasher struct {
+	hasher hash.Hash
+
+	checksumWriter func([]byte)
+}
+
+// NewPayloadSizeLimiter returns ObjectTarget instance that restricts payload length
+// of the writing object and writes generated objects to targets from initializer.
+//
+// Calculates and adds homomorphic hash to resulting objects only if withoutHomomorphicHash
+// is false.
+//
+// Objects w/ payload size less or equal than max size remain untouched.
+func NewPayloadSizeLimiter(maxSize uint64, withoutHomomorphicHash bool, targetInit TargetInitializer) ObjectTarget {
+	return &payloadSizeLimiter{
+		maxSize:                maxSize,
+		withoutHomomorphicHash: withoutHomomorphicHash,
+		targetInit:             targetInit,
+		splitID:                object.NewSplitID(),
+	}
+}
+
+func (s *payloadSizeLimiter) WriteHeader(hdr *object.Object) error {
+	s.current = fromObject(hdr)
+
+	s.initialize()
+
+	return nil
+}
+
+func (s *payloadSizeLimiter) Write(p []byte) (int, error) {
+	if err := s.writeChunk(p); err != nil {
+		return 0, err
+	}
+
+	return len(p), nil
+}
+
+func (s *payloadSizeLimiter) Close() (*AccessIdentifiers, error) {
+	return s.release(true)
+}
+
+func (s *payloadSizeLimiter) initialize() {
+	// if it is an object after the 1st
+	if ln := len(s.previous); ln > 0 {
+		// initialize parent object once (after 1st object)
+		if ln == 1 {
+			s.detachParent()
+		}
+
+		// set previous object to the last previous identifier
+		s.current.SetPreviousID(s.previous[ln-1])
+	}
+
+	s.initializeCurrent()
+}
+
+func fromObject(obj *object.Object) *object.Object {
+	cnr, _ := obj.ContainerID()
+
+	res := object.New()
+	res.SetContainerID(cnr)
+	res.SetOwnerID(obj.OwnerID())
+	res.SetAttributes(obj.Attributes()...)
+	res.SetType(obj.Type())
+
+	// obj.SetSplitID creates splitHeader but we don't need to do it in case
+	// of small objects, so we should make nil check.
+	if obj.SplitID() != nil {
+		res.SetSplitID(obj.SplitID())
+	}
+
+	return res
+}
+
+func (s *payloadSizeLimiter) initializeCurrent() {
+	// initialize current object target
+	s.target = s.targetInit()
+
+	// create payload hashers
+	s.currentHashers = payloadHashersForObject(s.current, s.withoutHomomorphicHash)
+
+	// compose multi-writer from target and all payload hashers
+	ws := make([]io.Writer, 0, 1+len(s.currentHashers)+len(s.parentHashers))
+
+	ws = append(ws, s.target)
+
+	for i := range s.currentHashers {
+		ws = append(ws, s.currentHashers[i].hasher)
+	}
+
+	for i := range s.parentHashers {
+		ws = append(ws, s.parentHashers[i].hasher)
+	}
+
+	s.chunkWriter = io.MultiWriter(ws...)
+}
+
+func payloadHashersForObject(obj *object.Object, withoutHomomorphicHash bool) []*payloadChecksumHasher {
+	hashers := make([]*payloadChecksumHasher, 0, 2)
+
+	hashers = append(hashers, &payloadChecksumHasher{
+		hasher: sha256.New(),
+		checksumWriter: func(binChecksum []byte) {
+			if ln := len(binChecksum); ln != sha256.Size {
+				panic(fmt.Sprintf("wrong checksum length: expected %d, has %d", sha256.Size, ln))
+			}
+
+			csSHA := [sha256.Size]byte{}
+			copy(csSHA[:], binChecksum)
+
+			var cs checksum.Checksum
+			cs.SetSHA256(csSHA)
+
+			obj.SetPayloadChecksum(cs)
+		},
+	})
+
+	if !withoutHomomorphicHash {
+		hashers = append(hashers, &payloadChecksumHasher{
+			hasher: tz.New(),
+			checksumWriter: func(binChecksum []byte) {
+				if ln := len(binChecksum); ln != tz.Size {
+					panic(fmt.Sprintf("wrong checksum length: expected %d, has %d", tz.Size, ln))
+				}
+
+				csTZ := [tz.Size]byte{}
+				copy(csTZ[:], binChecksum)
+
+				var cs checksum.Checksum
+				cs.SetTillichZemor(csTZ)
+
+				obj.SetPayloadHomomorphicHash(cs)
+			},
+		})
+	}
+
+	return hashers
+}
+
+func (s *payloadSizeLimiter) release(finalize bool) (*AccessIdentifiers, error) {
+	// Arg finalize is true only when called from Close method.
+	// We finalize parent and generate linking objects only if it is more
+	// than 1 object in split-chain.
+	withParent := finalize && len(s.previous) > 0
+
+	if withParent {
+		writeHashes(s.parentHashers)
+		s.parent.SetPayloadSize(s.written)
+		s.current.SetParent(s.parent)
+	}
+
+	// release current object
+	writeHashes(s.currentHashers)
+
+	// release current, get its id
+	if err := s.target.WriteHeader(s.current); err != nil {
+		return nil, fmt.Errorf("could not write header: %w", err)
+	}
+
+	ids, err := s.target.Close()
+	if err != nil {
+		return nil, fmt.Errorf("could not close target: %w", err)
+	}
+
+	// save identifier of the released object
+	s.previous = append(s.previous, ids.SelfID())
+
+	if withParent {
+		// generate and release linking object
+		s.initializeLinking(ids.Parent())
+		s.initializeCurrent()
+
+		if _, err := s.release(false); err != nil {
+			return nil, fmt.Errorf("could not release linking object: %w", err)
+		}
+	}
+
+	return ids, nil
+}
+
+func writeHashes(hashers []*payloadChecksumHasher) {
+	for i := range hashers {
+		hashers[i].checksumWriter(hashers[i].hasher.Sum(nil))
+	}
+}
+
+func (s *payloadSizeLimiter) initializeLinking(parHdr *object.Object) {
+	s.current = fromObject(s.current)
+	s.current.SetParent(parHdr)
+	s.current.SetChildren(s.previous...)
+	s.current.SetSplitID(s.splitID)
+}
+
+func (s *payloadSizeLimiter) writeChunk(chunk []byte) error {
+	// statement is true if the previous write of bytes reached exactly the boundary.
+	if s.written > 0 && s.written%s.maxSize == 0 {
+		if s.written == s.maxSize {
+			s.prepareFirstChild()
+		}
+
+		// we need to release current object
+		if _, err := s.release(false); err != nil {
+			return fmt.Errorf("could not release object: %w", err)
+		}
+
+		// initialize another object
+		s.initialize()
+	}
+
+	var (
+		ln         = uint64(len(chunk))
+		cut        = ln
+		leftToEdge = s.maxSize - s.written%s.maxSize
+	)
+
+	// write bytes no further than the boundary of the current object
+	if ln > leftToEdge {
+		cut = leftToEdge
+	}
+
+	if _, err := s.chunkWriter.Write(chunk[:cut]); err != nil {
+		return fmt.Errorf("could not write chunk to target: %w", err)
+	}
+
+	// increase written bytes counter
+	s.written += cut
+
+	// if there are more bytes in buffer we call method again to start filling another object
+	if ln > leftToEdge {
+		return s.writeChunk(chunk[cut:])
+	}
+
+	return nil
+}
+
+func (s *payloadSizeLimiter) prepareFirstChild() {
+	// initialize split header with split ID on first object in chain
+	s.current.InitRelations()
+	s.current.SetSplitID(s.splitID)
+
+	// cut source attributes
+	s.parAttrs = s.current.Attributes()
+	s.current.SetAttributes()
+
+	// attributes will be added to parent in detachParent
+}
+
+func (s *payloadSizeLimiter) detachParent() {
+	s.parent = s.current
+	s.current = fromObject(s.parent)
+	s.parent.ResetRelations()
+	s.parent.SetSignature(nil)
+	s.parentHashers = s.currentHashers
+
+	// return source attributes
+	s.parent.SetAttributes(s.parAttrs...)
+}
diff --git a/object/transformer/types.go b/object/transformer/types.go
new file mode 100644
index 0000000..72e6a74
--- /dev/null
+++ b/object/transformer/types.go
@@ -0,0 +1,111 @@
+package transformer
+
+import (
+	"io"
+
+	"github.com/TrueCloudLab/frostfs-sdk-go/object"
+	oid "github.com/TrueCloudLab/frostfs-sdk-go/object/id"
+)
+
+// AccessIdentifiers represents group of the object identifiers
+// that are returned after writing the object.
+// Consists of the ID of the stored object and the ID of the parent object.
+type AccessIdentifiers struct {
+	par *oid.ID
+
+	self oid.ID
+
+	parHdr *object.Object
+}
+
+// ObjectTarget is an interface of the object writer.
+type ObjectTarget interface {
+	// WriteHeader writes object header w/ payload part.
+	// The payload of the object may be incomplete.
+	//
+	// Must be called exactly once. Control remains with the caller.
+	// Missing a call or re-calling can lead to undefined behavior
+	// that depends on the implementation.
+	//
+	// Must not be called after Close call.
+	WriteHeader(*object.Object) error
+
+	// Write writes object payload chunk.
+	//
+	// Can be called multiple times.
+	//
+	// Must not be called after Close call.
+	io.Writer
+
+	// Close is used to finish object writing.
+	//
+	// Close must return access identifiers of the object
+	// that has been written.
+	//
+	// Must be called no more than once. Control remains with the caller.
+	// Re-calling can lead to undefined behavior
+	// that depends on the implementation.
+	Close() (*AccessIdentifiers, error)
+}
+
+// TargetInitializer represents ObjectTarget constructor.
+type TargetInitializer func() ObjectTarget
+
+// SelfID returns identifier of the written object.
+func (a AccessIdentifiers) SelfID() oid.ID {
+	return a.self
+}
+
+// WithSelfID returns AccessIdentifiers with passed self identifier.
+func (a *AccessIdentifiers) WithSelfID(v oid.ID) *AccessIdentifiers {
+	res := a
+	if res == nil {
+		res = new(AccessIdentifiers)
+	}
+
+	res.self = v
+
+	return res
+}
+
+// ParentID return identifier of the parent of the written object.
+func (a *AccessIdentifiers) ParentID() *oid.ID {
+	if a != nil {
+		return a.par
+	}
+
+	return nil
+}
+
+// WithParentID returns AccessIdentifiers with passed parent identifier.
+func (a *AccessIdentifiers) WithParentID(v *oid.ID) *AccessIdentifiers {
+	res := a
+	if res == nil {
+		res = new(AccessIdentifiers)
+	}
+
+	res.par = v
+
+	return res
+}
+
+// Parent return identifier of the parent of the written object.
+func (a *AccessIdentifiers) Parent() *object.Object {
+	if a != nil {
+		return a.parHdr
+	}
+
+	return nil
+}
+
+// WithParent returns AccessIdentifiers with passed parent identifier.
+func (a *AccessIdentifiers) WithParent(v *object.Object) *AccessIdentifiers {
+	res := a
+	if res == nil {
+		res = new(AccessIdentifiers)
+	}
+
+	res.parHdr = v
+
+	return res
+}
-- 
2.45.2


From 1e1c836310705f69ddd78fc0002d3aa4307d1f35 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Sat, 18 Feb 2023 10:13:14 +0300
Subject: [PATCH 02/12] [#19] transformer: Cover with unit-tests

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 object/transformer/transformer_test.go | 164 +++++++++++++++++++++++++
 1 file changed, 164 insertions(+)
 create mode 100644 object/transformer/transformer_test.go

diff --git a/object/transformer/transformer_test.go b/object/transformer/transformer_test.go
new file mode 100644
index 0000000..fe35fe3
--- /dev/null
+++ b/object/transformer/transformer_test.go
@@ -0,0 +1,164 @@
+package transformer
+
+import (
+	"crypto/rand"
+	"testing"
+
+	cidtest "github.com/TrueCloudLab/frostfs-sdk-go/container/id/test"
+	objectSDK "github.com/TrueCloudLab/frostfs-sdk-go/object"
+	"github.com/TrueCloudLab/frostfs-sdk-go/version"
+	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTransformer(t *testing.T) {
+	const maxSize = 100
+
+	tt := new(testTarget)
+
+	target, _ := newPayloadSizeLimiter(maxSize, tt)
+
+	ver := version.Current()
+	cnr := cidtest.ID()
+	hdr := objectSDK.New()
+	hdr.SetContainerID(cnr)
+	hdr.SetType(objectSDK.TypeRegular)
+	hdr.SetVersion(&ver)
+	require.NoError(t, target.WriteHeader(hdr))
+
+	expectedPayload := make([]byte, maxSize*2+maxSize/2)
+	_, _ = rand.Read(expectedPayload)
+
+	_, err := target.Write(expectedPayload)
+	require.NoError(t, err)
+
+	ids, err := target.Close()
+	require.NoError(t, err)
+
+	require.Equal(t, 4, len(tt.objects)) // 3 parts + linking object
+
+	var actualPayload []byte
+	for i := range tt.objects {
+		childCnr, ok := tt.objects[i].ContainerID()
+		require.True(t, ok)
+		require.Equal(t, cnr, childCnr)
+		require.Equal(t, objectSDK.TypeRegular, tt.objects[i].Type())
+
+		payload := tt.objects[i].Payload()
+		require.EqualValues(t, tt.objects[i].PayloadSize(), len(payload))
+		actualPayload = append(actualPayload, payload...)
+
+		switch i {
+		case 0, 1:
+			require.EqualValues(t, maxSize, len(payload))
+		case 2:
+			require.EqualValues(t, maxSize/2, len(payload))
+		case 3:
+			parID, ok := tt.objects[i].ParentID()
+			require.True(t, ok)
+			require.Equal(t, ids.ParentID(), &parID)
+		}
+	}
+	require.Equal(t, expectedPayload, actualPayload)
+}
+
+func BenchmarkTransformer(b *testing.B) {
+	ver := version.Current()
+	cnr := cidtest.ID()
+	hdr := objectSDK.New()
+	hdr.SetContainerID(cnr)
+	hdr.SetType(objectSDK.TypeRegular)
+	hdr.SetVersion(&ver)
+
+	b.Run("small", func(b *testing.B) {
+		benchmarkTransformer(b, hdr, 8*1024)
+	})
+	b.Run("big", func(b *testing.B) {
+		benchmarkTransformer(b, hdr, 64*1024*1024*9/2)
+	})
+}
+
+func benchmarkTransformer(b *testing.B, header *objectSDK.Object, payloadSize int) {
+	const maxSize = 64 * 1024 * 1024
+
+	payload := make([]byte, payloadSize)
+
+	b.ReportAllocs()
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		f, _ := newPayloadSizeLimiter(maxSize, benchTarget{})
+		if err := f.WriteHeader(header); err != nil {
+			b.Fatalf("write header: %v", err)
+		}
+		if _, err := f.Write(payload); err != nil {
+			b.Fatalf("write: %v", err)
+		}
+		if _, err := f.Close(); err != nil {
+			b.Fatalf("close: %v", err)
+		}
+	}
+}
+
+func newPayloadSizeLimiter(maxSize uint64, nextTarget ObjectTarget) (ObjectTarget, *keys.PrivateKey) {
+	p, err := keys.NewPrivateKey()
+	if err != nil {
+		panic(err)
+	}
+
+	return NewPayloadSizeLimiter(maxSize, true, func() ObjectTarget {
+		return NewFormatTarget(&FormatterParams{
+			Key:          &p.PrivateKey,
+			NextTarget:   nextTarget,
+			NetworkState: dummyEpochSource(123),
+		})
+	}), p
+}
+
+type dummyEpochSource uint64
+
+func (s dummyEpochSource) CurrentEpoch() uint64 {
+	return uint64(s)
+}
+
+type benchTarget struct{}
+
+func (benchTarget) WriteHeader(object *objectSDK.Object) error {
+	return nil
+}
+
+func (benchTarget) Write(p []byte) (n int, err error) {
+	return len(p), nil
+}
+
+func (benchTarget) Close() (*AccessIdentifiers, error) {
+	return nil, nil
+}
+
+type testTarget struct {
+	current *objectSDK.Object
+	payload []byte
+	objects []*objectSDK.Object
+}
+
+func (tt *testTarget) WriteHeader(object *objectSDK.Object) error {
+	tt.current = object
+	return nil
+}
+
+func (tt *testTarget) Write(p []byte) (n int, err error) {
+	tt.payload = append(tt.payload, p...)
+	return len(p), nil
+}
+
+func (tt *testTarget) Close() (*AccessIdentifiers, error) {
+	tt.current.SetPayload(tt.payload)
+	// We need to marshal, because current implementation reuses written object.
+	data, _ := tt.current.Marshal()
+	obj := objectSDK.New()
+	_ = obj.Unmarshal(data)
+
+	tt.objects = append(tt.objects, obj)
+	tt.current = nil
+	tt.payload = nil
+	return nil, nil // AccessIdentifiers should not be used.
+}
-- 
2.45.2


From 2af5889a053ffdaafed8517ceab86cfb6458ac95 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Fri, 17 Feb 2023 13:00:27 +0300
Subject: [PATCH 03/12] [#19] transformer: Simplify `AccessIdentifiers`

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 object/transformer/fmt.go              |  9 ++--
 object/transformer/transformer.go      |  4 +-
 object/transformer/transformer_test.go |  2 +-
 object/transformer/types.go            | 67 ++------------------------
 4 files changed, 11 insertions(+), 71 deletions(-)

diff --git a/object/transformer/fmt.go b/object/transformer/fmt.go
index b0ca5c9..31357d7 100644
--- a/object/transformer/fmt.go
+++ b/object/transformer/fmt.go
@@ -109,8 +109,9 @@ func (f *formatter) Close() (*AccessIdentifiers, error) {
 
 	id, _ := f.obj.ID()
 
-	return new(AccessIdentifiers).
-		WithSelfID(id).
-		WithParentID(parID).
-		WithParent(parHdr), nil
+	return &AccessIdentifiers{
+		ParentID:     parID,
+		SelfID:       id,
+		ParentHeader: parHdr,
+	}, nil
 }
diff --git a/object/transformer/transformer.go b/object/transformer/transformer.go
index cfd7098..d3b5b8d 100644
--- a/object/transformer/transformer.go
+++ b/object/transformer/transformer.go
@@ -200,11 +200,11 @@ func (s *payloadSizeLimiter) release(finalize bool) (*AccessIdentifiers, error)
 	}
 
 	// save identifier of the released object
-	s.previous = append(s.previous, ids.SelfID())
+	s.previous = append(s.previous, ids.SelfID)
 
 	if withParent {
 		// generate and release linking object
-		s.initializeLinking(ids.Parent())
+		s.initializeLinking(ids.ParentHeader)
 		s.initializeCurrent()
 
 		if _, err := s.release(false); err != nil {
diff --git a/object/transformer/transformer_test.go b/object/transformer/transformer_test.go
index fe35fe3..8fcd680 100644
--- a/object/transformer/transformer_test.go
+++ b/object/transformer/transformer_test.go
@@ -56,7 +56,7 @@ func TestTransformer(t *testing.T) {
 		case 3:
 			parID, ok := tt.objects[i].ParentID()
 			require.True(t, ok)
-			require.Equal(t, ids.ParentID(), &parID)
+			require.Equal(t, ids.ParentID, &parID)
 		}
 	}
 	require.Equal(t, expectedPayload, actualPayload)
diff --git a/object/transformer/types.go b/object/transformer/types.go
index 72e6a74..0525eb0 100644
--- a/object/transformer/types.go
+++ b/object/transformer/types.go
@@ -11,11 +11,9 @@ import (
 // that are returned after writing the object.
 // Consists of the ID of the stored object and the ID of the parent object.
 type AccessIdentifiers struct {
-	par *oid.ID
-
-	self oid.ID
-
-	parHdr *object.Object
+	ParentID     *oid.ID
+	SelfID       oid.ID
+	ParentHeader *object.Object
 }
 
 // ObjectTarget is an interface of the object writer.
@@ -50,62 +48,3 @@ type ObjectTarget interface {
 
 // TargetInitializer represents ObjectTarget constructor.
 type TargetInitializer func() ObjectTarget
-
-// SelfID returns identifier of the written object.
-func (a AccessIdentifiers) SelfID() oid.ID {
-	return a.self
-}
-
-// WithSelfID returns AccessIdentifiers with passed self identifier.
-func (a *AccessIdentifiers) WithSelfID(v oid.ID) *AccessIdentifiers {
-	res := a
-	if res == nil {
-		res = new(AccessIdentifiers)
-	}
-
-	res.self = v
-
-	return res
-}
-
-// ParentID return identifier of the parent of the written object.
-func (a *AccessIdentifiers) ParentID() *oid.ID {
-	if a != nil {
-		return a.par
-	}
-
-	return nil
-}
-
-// WithParentID returns AccessIdentifiers with passed parent identifier.
-func (a *AccessIdentifiers) WithParentID(v *oid.ID) *AccessIdentifiers {
-	res := a
-	if res == nil {
-		res = new(AccessIdentifiers)
-	}
-
-	res.par = v
-
-	return res
-}
-
-// Parent return identifier of the parent of the written object.
-func (a *AccessIdentifiers) Parent() *object.Object {
-	if a != nil {
-		return a.parHdr
-	}
-
-	return nil
-}
-
-// WithParent returns AccessIdentifiers with passed parent identifier.
-func (a *AccessIdentifiers) WithParent(v *object.Object) *AccessIdentifiers {
-	res := a
-	if res == nil {
-		res = new(AccessIdentifiers)
-	}
-
-	res.parHdr = v
-
-	return res
-}
-- 
2.45.2


From fb807e80ce0e7652cca85f42835cbcd246714378 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Sat, 18 Feb 2023 10:36:20 +0300
Subject: [PATCH 04/12] [#19] transformer: Make `writeChunk` non-recursive

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 object/transformer/transformer.go | 69 ++++++++++++++++---------------
 1 file changed, 35 insertions(+), 34 deletions(-)

diff --git a/object/transformer/transformer.go b/object/transformer/transformer.go
index d3b5b8d..8c819fa 100644
--- a/object/transformer/transformer.go
+++ b/object/transformer/transformer.go
@@ -229,45 +229,46 @@ func (s *payloadSizeLimiter) initializeLinking(parHdr *object.Object) {
 }
 
 func (s *payloadSizeLimiter) writeChunk(chunk []byte) error {
-	// statement is true if the previous write of bytes reached exactly the boundary.
-	if s.written > 0 && s.written%s.maxSize == 0 {
-		if s.written == s.maxSize {
-			s.prepareFirstChild()
+	for {
+		// statement is true if the previous write of bytes reached exactly the boundary.
+		if s.written > 0 && s.written%s.maxSize == 0 {
+			if s.written == s.maxSize {
+				s.prepareFirstChild()
+			}
+
+			// we need to release current object
+			if _, err := s.release(false); err != nil {
+				return fmt.Errorf("could not release object: %w", err)
+			}
+
+			// initialize another object
+			s.initialize()
 		}
 
-		// we need to release current object
-		if _, err := s.release(false); err != nil {
-			return fmt.Errorf("could not release object: %w", err)
+		var (
+			ln         = uint64(len(chunk))
+			cut        = ln
+			leftToEdge = s.maxSize - s.written%s.maxSize
+		)
+
+		// write bytes no further than the boundary of the current object
+		if ln > leftToEdge {
+			cut = leftToEdge
 		}
 
-		// initialize another object
-		s.initialize()
+		if _, err := s.chunkWriter.Write(chunk[:cut]); err != nil {
+			return fmt.Errorf("could not write chunk to target: %w", err)
+		}
+
+		// increase written bytes counter
+		s.written += cut
+
+		if cut == ln {
+			return nil
+		}
+		// if there are more bytes in buffer we call method again to start filling another object
+		chunk = chunk[cut:]
 	}
-
-	var (
-		ln         = uint64(len(chunk))
-		cut        = ln
-		leftToEdge = s.maxSize - s.written%s.maxSize
-	)
-
-	// write bytes no further than the boundary of the current object
-	if ln > leftToEdge {
-		cut = leftToEdge
-	}
-
-	if _, err := s.chunkWriter.Write(chunk[:cut]); err != nil {
-		return fmt.Errorf("could not write chunk to target: %w", err)
-	}
-
-	// increase written bytes counter
-	s.written += cut
-
-	// if there are more bytes in buffer we call method again to start filling another object
-	if ln > leftToEdge {
-		return s.writeChunk(chunk[cut:])
-	}
-
-	return nil
 }
 
 func (s *payloadSizeLimiter) prepareFirstChild() {
-- 
2.45.2


From 51bad6dfdbfde150cdb857c975c537a59582e4fe Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Sat, 18 Feb 2023 10:43:34 +0300
Subject: [PATCH 05/12] [#19] transformer: Merge formatter and payload splitter

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 object/transformer/fmt.go              | 112 -------------------------
 object/transformer/transformer.go      |  95 +++++++++++++++------
 object/transformer/transformer_test.go |  12 +--
 3 files changed, 76 insertions(+), 143 deletions(-)

diff --git a/object/transformer/fmt.go b/object/transformer/fmt.go
index 31357d7..193b8f4 100644
--- a/object/transformer/fmt.go
+++ b/object/transformer/fmt.go
@@ -1,117 +1,5 @@
 package transformer
 
-import (
-	"crypto/ecdsa"
-	"fmt"
-
-	"github.com/TrueCloudLab/frostfs-sdk-go/object"
-	oid "github.com/TrueCloudLab/frostfs-sdk-go/object/id"
-	"github.com/TrueCloudLab/frostfs-sdk-go/session"
-	"github.com/TrueCloudLab/frostfs-sdk-go/version"
-)
-
-type formatter struct {
-	prm *FormatterParams
-
-	obj *object.Object
-
-	sz uint64
-}
-
 type EpochSource interface {
 	CurrentEpoch() uint64
 }
-
-// FormatterParams groups NewFormatTarget parameters.
-type FormatterParams struct {
-	Key *ecdsa.PrivateKey
-
-	NextTarget ObjectTarget
-
-	SessionToken *session.Object
-
-	NetworkState EpochSource
-}
-
-// NewFormatTarget returns ObjectTarget instance that finalizes object structure
-// and writes it to the next target.
-//
-// Chunks must be written before the WriteHeader call.
-//
-// Object changes:
-// - sets version to current SDK version;
-// - sets payload size to the total length of all written chunks;
-// - sets session token;
-// - sets number of creation epoch;
-// - calculates and sets verification fields (ID, Signature).
-func NewFormatTarget(p *FormatterParams) ObjectTarget {
-	return &formatter{
-		prm: p,
-	}
-}
-
-func (f *formatter) WriteHeader(obj *object.Object) error {
-	f.obj = obj
-
-	return nil
-}
-
-func (f *formatter) Write(p []byte) (n int, err error) {
-	n, err = f.prm.NextTarget.Write(p)
-
-	f.sz += uint64(n)
-
-	return
-}
-
-func (f *formatter) Close() (*AccessIdentifiers, error) {
-	curEpoch := f.prm.NetworkState.CurrentEpoch()
-	ver := version.Current()
-
-	f.obj.SetVersion(&ver)
-	f.obj.SetPayloadSize(f.sz)
-	f.obj.SetSessionToken(f.prm.SessionToken)
-	f.obj.SetCreationEpoch(curEpoch)
-
-	var (
-		parID  *oid.ID
-		parHdr *object.Object
-	)
-
-	if par := f.obj.Parent(); par != nil && par.Signature() == nil {
-		rawPar := object.NewFromV2(par.ToV2())
-
-		rawPar.SetSessionToken(f.prm.SessionToken)
-		rawPar.SetCreationEpoch(curEpoch)
-
-		if err := object.SetIDWithSignature(*f.prm.Key, rawPar); err != nil {
-			return nil, fmt.Errorf("could not finalize parent object: %w", err)
-		}
-
-		id, _ := rawPar.ID()
-		parID = &id
-		parHdr = rawPar
-
-		f.obj.SetParent(parHdr)
-	}
-
-	if err := object.SetIDWithSignature(*f.prm.Key, f.obj); err != nil {
-		return nil, fmt.Errorf("could not finalize object: %w", err)
-	}
-
-	if err := f.prm.NextTarget.WriteHeader(f.obj); err != nil {
-		return nil, fmt.Errorf("could not write header to next target: %w", err)
-	}
-
-	if _, err := f.prm.NextTarget.Close(); err != nil {
-		return nil, fmt.Errorf("could not close next target: %w", err)
-	}
-
-	id, _ := f.obj.ID()
-
-	return &AccessIdentifiers{
-		ParentID:     parID,
-		SelfID:       id,
-		ParentHeader: parHdr,
-	}, nil
-}
diff --git a/object/transformer/transformer.go b/object/transformer/transformer.go
index 8c819fa..55ad9ff 100644
--- a/object/transformer/transformer.go
+++ b/object/transformer/transformer.go
@@ -1,6 +1,7 @@
 package transformer
 
 import (
+	"crypto/ecdsa"
 	"crypto/sha256"
 	"fmt"
 	"hash"
@@ -9,17 +10,15 @@ import (
 	"github.com/TrueCloudLab/frostfs-sdk-go/checksum"
 	"github.com/TrueCloudLab/frostfs-sdk-go/object"
 	oid "github.com/TrueCloudLab/frostfs-sdk-go/object/id"
+	"github.com/TrueCloudLab/frostfs-sdk-go/session"
+	"github.com/TrueCloudLab/frostfs-sdk-go/version"
 	"github.com/TrueCloudLab/tzhash/tz"
 )
 
 type payloadSizeLimiter struct {
-	maxSize, written uint64
+	Params
 
-	withoutHomomorphicHash bool
-
-	targetInit func() ObjectTarget
-
-	target ObjectTarget
+	written, writtenCurrent uint64
 
 	current, parent *object.Object
 
@@ -40,6 +39,15 @@ type payloadChecksumHasher struct {
 	checksumWriter func([]byte)
 }
 
+type Params struct {
+	Key                    *ecdsa.PrivateKey
+	NextTarget             ObjectTarget
+	SessionToken           *session.Object
+	NetworkState           EpochSource
+	MaxSize                uint64
+	WithoutHomomorphicHash bool
+}
+
 // NewPayloadSizeLimiter returns ObjectTarget instance that restricts payload length
 // of the writing object and writes generated objects to targets from initializer.
 //
@@ -47,12 +55,10 @@ type payloadChecksumHasher struct {
 // is false.
 //
 // Objects w/ payload size less or equal than max size remain untouched.
-func NewPayloadSizeLimiter(maxSize uint64, withoutHomomorphicHash bool, targetInit TargetInitializer) ObjectTarget {
+func NewPayloadSizeLimiter(p Params) ObjectTarget {
 	return &payloadSizeLimiter{
-		maxSize:                maxSize,
-		withoutHomomorphicHash: withoutHomomorphicHash,
-		targetInit:             targetInit,
-		splitID:                object.NewSplitID(),
+		Params:  p,
+		splitID: object.NewSplitID(),
 	}
 }
 
@@ -110,16 +116,14 @@ func fromObject(obj *object.Object) *object.Object {
 }
 
 func (s *payloadSizeLimiter) initializeCurrent() {
-	// initialize current object target
-	s.target = s.targetInit()
-
 	// create payload hashers
-	s.currentHashers = payloadHashersForObject(s.current, s.withoutHomomorphicHash)
+	s.writtenCurrent = 0
+	s.currentHashers = payloadHashersForObject(s.current, s.WithoutHomomorphicHash)
 
 	// compose multi-writer from target and all payload hashers
 	ws := make([]io.Writer, 0, 1+len(s.currentHashers)+len(s.parentHashers))
 
-	ws = append(ws, s.target)
+	ws = append(ws, s.NextTarget)
 
 	for i := range s.currentHashers {
 		ws = append(ws, s.currentHashers[i].hasher)
@@ -189,14 +193,54 @@ func (s *payloadSizeLimiter) release(finalize bool) (*AccessIdentifiers, error)
 	// release current object
 	writeHashes(s.currentHashers)
 
-	// release current, get its id
-	if err := s.target.WriteHeader(s.current); err != nil {
-		return nil, fmt.Errorf("could not write header: %w", err)
+	curEpoch := s.NetworkState.CurrentEpoch()
+	ver := version.Current()
+
+	s.current.SetVersion(&ver)
+	s.current.SetPayloadSize(s.writtenCurrent)
+	s.current.SetSessionToken(s.SessionToken)
+	s.current.SetCreationEpoch(curEpoch)
+
+	var (
+		parID  *oid.ID
+		parHdr *object.Object
+	)
+
+	if par := s.current.Parent(); par != nil && par.Signature() == nil {
+		rawPar := object.NewFromV2(par.ToV2())
+
+		rawPar.SetSessionToken(s.SessionToken)
+		rawPar.SetCreationEpoch(curEpoch)
+
+		if err := object.SetIDWithSignature(*s.Key, rawPar); err != nil {
+			return nil, fmt.Errorf("could not finalize parent object: %w", err)
+		}
+
+		id, _ := rawPar.ID()
+		parID = &id
+		parHdr = rawPar
+
+		s.current.SetParent(parHdr)
 	}
 
-	ids, err := s.target.Close()
-	if err != nil {
-		return nil, fmt.Errorf("could not close target: %w", err)
+	if err := object.SetIDWithSignature(*s.Key, s.current); err != nil {
+		return nil, fmt.Errorf("could not finalize object: %w", err)
+	}
+
+	if err := s.NextTarget.WriteHeader(s.current); err != nil {
+		return nil, fmt.Errorf("could not write header to next target: %w", err)
+	}
+
+	if _, err := s.NextTarget.Close(); err != nil {
+		return nil, fmt.Errorf("could not close next target: %w", err)
+	}
+
+	id, _ := s.current.ID()
+
+	ids := &AccessIdentifiers{
+		ParentID:     parID,
+		SelfID:       id,
+		ParentHeader: parHdr,
 	}
 
 	// save identifier of the released object
@@ -231,8 +275,8 @@ func (s *payloadSizeLimiter) initializeLinking(parHdr *object.Object) {
 func (s *payloadSizeLimiter) writeChunk(chunk []byte) error {
 	for {
 		// statement is true if the previous write of bytes reached exactly the boundary.
-		if s.written > 0 && s.written%s.maxSize == 0 {
-			if s.written == s.maxSize {
+		if s.written > 0 && s.written%s.MaxSize == 0 {
+			if s.written == s.MaxSize {
 				s.prepareFirstChild()
 			}
 
@@ -248,7 +292,7 @@ func (s *payloadSizeLimiter) writeChunk(chunk []byte) error {
 		var (
 			ln         = uint64(len(chunk))
 			cut        = ln
-			leftToEdge = s.maxSize - s.written%s.maxSize
+			leftToEdge = s.MaxSize - s.written%s.MaxSize
 		)
 
 		// write bytes no further than the boundary of the current object
@@ -261,6 +305,7 @@ func (s *payloadSizeLimiter) writeChunk(chunk []byte) error {
 		}
 
 		// increase written bytes counter
+		s.writtenCurrent += cut
 		s.written += cut
 
 		if cut == ln {
diff --git a/object/transformer/transformer_test.go b/object/transformer/transformer_test.go
index 8fcd680..545945d 100644
--- a/object/transformer/transformer_test.go
+++ b/object/transformer/transformer_test.go
@@ -105,12 +105,12 @@ func newPayloadSizeLimiter(maxSize uint64, nextTarget ObjectTarget) (ObjectTarge
 		panic(err)
 	}
 
-	return NewPayloadSizeLimiter(maxSize, true, func() ObjectTarget {
-		return NewFormatTarget(&FormatterParams{
-			Key:          &p.PrivateKey,
-			NextTarget:   nextTarget,
-			NetworkState: dummyEpochSource(123),
-		})
+	return NewPayloadSizeLimiter(Params{
+		Key:                    &p.PrivateKey,
+		NextTarget:             nextTarget,
+		NetworkState:           dummyEpochSource(123),
+		MaxSize:                maxSize,
+		WithoutHomomorphicHash: true,
 	}), p
 }
 
-- 
2.45.2


From 4917a718555dec1850bed2724f23bc593437c6d3 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Thu, 23 Feb 2023 16:56:38 +0300
Subject: [PATCH 06/12] [#19] transformer: Move `EpochSource` to other types

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 object/transformer/fmt.go   | 5 -----
 object/transformer/types.go | 5 +++++
 2 files changed, 5 insertions(+), 5 deletions(-)
 delete mode 100644 object/transformer/fmt.go

diff --git a/object/transformer/fmt.go b/object/transformer/fmt.go
deleted file mode 100644
index 193b8f4..0000000
--- a/object/transformer/fmt.go
+++ /dev/null
@@ -1,5 +0,0 @@
-package transformer
-
-type EpochSource interface {
-	CurrentEpoch() uint64
-}
diff --git a/object/transformer/types.go b/object/transformer/types.go
index 0525eb0..f030e26 100644
--- a/object/transformer/types.go
+++ b/object/transformer/types.go
@@ -16,6 +16,11 @@ type AccessIdentifiers struct {
 	ParentHeader *object.Object
 }
 
+// EpochSource is a source for the current epoch.
+type EpochSource interface {
+	CurrentEpoch() uint64
+}
+
 // ObjectTarget is an interface of the object writer.
 type ObjectTarget interface {
 	// WriteHeader writes object header w/ payload part.
-- 
2.45.2


From 43987aae7ac399b1181ae2fbbd791c099ecfa6b2 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Thu, 23 Feb 2023 17:13:13 +0300
Subject: [PATCH 07/12] [#19] transformer/test: Add helper functions

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 object/transformer/transformer_test.go | 35 +++++++++++++++-----------
 1 file changed, 21 insertions(+), 14 deletions(-)

diff --git a/object/transformer/transformer_test.go b/object/transformer/transformer_test.go
index 545945d..f1f6722 100644
--- a/object/transformer/transformer_test.go
+++ b/object/transformer/transformer_test.go
@@ -4,6 +4,7 @@ import (
 	"crypto/rand"
 	"testing"
 
+	cid "github.com/TrueCloudLab/frostfs-sdk-go/container/id"
 	cidtest "github.com/TrueCloudLab/frostfs-sdk-go/container/id/test"
 	objectSDK "github.com/TrueCloudLab/frostfs-sdk-go/object"
 	"github.com/TrueCloudLab/frostfs-sdk-go/version"
@@ -18,23 +19,13 @@ func TestTransformer(t *testing.T) {
 
 	target, _ := newPayloadSizeLimiter(maxSize, tt)
 
-	ver := version.Current()
 	cnr := cidtest.ID()
-	hdr := objectSDK.New()
-	hdr.SetContainerID(cnr)
-	hdr.SetType(objectSDK.TypeRegular)
-	hdr.SetVersion(&ver)
-	require.NoError(t, target.WriteHeader(hdr))
+	hdr := newObject(cnr)
 
 	expectedPayload := make([]byte, maxSize*2+maxSize/2)
 	_, _ = rand.Read(expectedPayload)
 
-	_, err := target.Write(expectedPayload)
-	require.NoError(t, err)
-
-	ids, err := target.Close()
-	require.NoError(t, err)
-
+	ids := writeObject(t, target, hdr, expectedPayload)
 	require.Equal(t, 4, len(tt.objects)) // 3 parts + linking object
 
 	var actualPayload []byte
@@ -62,13 +53,29 @@ func TestTransformer(t *testing.T) {
 	require.Equal(t, expectedPayload, actualPayload)
 }
 
-func BenchmarkTransformer(b *testing.B) {
+func newObject(cnr cid.ID) *objectSDK.Object {
 	ver := version.Current()
-	cnr := cidtest.ID()
 	hdr := objectSDK.New()
 	hdr.SetContainerID(cnr)
 	hdr.SetType(objectSDK.TypeRegular)
 	hdr.SetVersion(&ver)
+	return hdr
+}
+
+func writeObject(t *testing.T, target ObjectTarget, header *objectSDK.Object, payload []byte) *AccessIdentifiers {
+	require.NoError(t, target.WriteHeader(header))
+
+	_, err := target.Write(payload)
+	require.NoError(t, err)
+
+	ids, err := target.Close()
+	require.NoError(t, err)
+
+	return ids
+}
+
+func BenchmarkTransformer(b *testing.B) {
+	hdr := newObject(cidtest.ID())
 
 	b.Run("small", func(b *testing.B) {
 		benchmarkTransformer(b, hdr, 8*1024)
-- 
2.45.2


From f102456c746b9af6e25a2fbad79017229fe51566 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Fri, 24 Feb 2023 16:21:56 +0300
Subject: [PATCH 08/12] [#19] transformer/test: Check owner ID and payload hash
 for parts

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 object/transformer/transformer_test.go | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/object/transformer/transformer_test.go b/object/transformer/transformer_test.go
index f1f6722..2b4ee31 100644
--- a/object/transformer/transformer_test.go
+++ b/object/transformer/transformer_test.go
@@ -2,11 +2,13 @@ package transformer
 
 import (
 	"crypto/rand"
+	"crypto/sha256"
 	"testing"
 
 	cid "github.com/TrueCloudLab/frostfs-sdk-go/container/id"
 	cidtest "github.com/TrueCloudLab/frostfs-sdk-go/container/id/test"
 	objectSDK "github.com/TrueCloudLab/frostfs-sdk-go/object"
+	"github.com/TrueCloudLab/frostfs-sdk-go/user"
 	"github.com/TrueCloudLab/frostfs-sdk-go/version"
 	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
 	"github.com/stretchr/testify/require"
@@ -17,11 +19,15 @@ func TestTransformer(t *testing.T) {
 
 	tt := new(testTarget)
 
-	target, _ := newPayloadSizeLimiter(maxSize, tt)
+	target, pk := newPayloadSizeLimiter(maxSize, tt)
 
 	cnr := cidtest.ID()
 	hdr := newObject(cnr)
 
+	var owner user.ID
+	user.IDFromKey(&owner, pk.PrivateKey.PublicKey)
+	hdr.SetOwnerID(&owner)
+
 	expectedPayload := make([]byte, maxSize*2+maxSize/2)
 	_, _ = rand.Read(expectedPayload)
 
@@ -34,11 +40,20 @@ func TestTransformer(t *testing.T) {
 		require.True(t, ok)
 		require.Equal(t, cnr, childCnr)
 		require.Equal(t, objectSDK.TypeRegular, tt.objects[i].Type())
+		require.Equal(t, &owner, tt.objects[i].OwnerID())
 
 		payload := tt.objects[i].Payload()
 		require.EqualValues(t, tt.objects[i].PayloadSize(), len(payload))
 		actualPayload = append(actualPayload, payload...)
 
+		if len(payload) != 0 {
+			cs, ok := tt.objects[i].PayloadChecksum()
+			require.True(t, ok)
+
+			h := sha256.Sum256(payload)
+			require.Equal(t, h[:], cs.Value())
+		}
+
 		switch i {
 		case 0, 1:
 			require.EqualValues(t, maxSize, len(payload))
@@ -51,6 +66,14 @@ func TestTransformer(t *testing.T) {
 		}
 	}
 	require.Equal(t, expectedPayload, actualPayload)
+
+	t.Run("parent checksum", func(t *testing.T) {
+		cs, ok := ids.ParentHeader.PayloadChecksum()
+		require.True(t, ok)
+
+		h := sha256.Sum256(expectedPayload)
+		require.Equal(t, h[:], cs.Value())
+	})
 }
 
 func newObject(cnr cid.ID) *objectSDK.Object {
-- 
2.45.2


From bf7e56c64d96072f420a6204236869d6269bffe5 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Fri, 24 Feb 2023 16:31:12 +0300
Subject: [PATCH 09/12] [#19] transformer: Do not reuse memory of sent objects
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Slower, but more correct.
```
name                 old time/op    new time/op    delta
Transformer/small-8    72.4µs ± 8%    74.8µs ±11%     ~     (p=0.278 n=9+10)
Transformer/big-8       1.31s ± 8%     1.38s ±11%   +5.50%  (p=0.035 n=10+10)

name                 old alloc/op   new alloc/op   delta
Transformer/small-8    7.39kB ± 0%    7.69kB ± 0%   +4.04%  (p=0.000 n=10+10)
Transformer/big-8      46.9kB ± 0%    49.2kB ± 0%   +4.87%  (p=0.000 n=10+10)

name                 old allocs/op  new allocs/op  delta
Transformer/small-8      94.6 ± 1%     102.0 ± 0%   +7.82%  (p=0.000 n=10+9)
Transformer/big-8         560 ± 0%       620 ± 1%  +10.66%  (p=0.000 n=10+10)
```

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 object/transformer/hasher.go           | 38 ++++++++++++++
 object/transformer/transformer.go      | 72 ++++++--------------------
 object/transformer/transformer_test.go |  7 +--
 3 files changed, 56 insertions(+), 61 deletions(-)
 create mode 100644 object/transformer/hasher.go

diff --git a/object/transformer/hasher.go b/object/transformer/hasher.go
new file mode 100644
index 0000000..4482a79
--- /dev/null
+++ b/object/transformer/hasher.go
@@ -0,0 +1,38 @@
+package transformer
+
+import (
+	"crypto/sha256"
+	"hash"
+
+	"github.com/TrueCloudLab/frostfs-sdk-go/checksum"
+	objectSDK "github.com/TrueCloudLab/frostfs-sdk-go/object"
+	"github.com/TrueCloudLab/tzhash/tz"
+)
+
+type payloadChecksumHasher struct {
+	hasher hash.Hash
+	typ    checksum.Type
+}
+
+func (h payloadChecksumHasher) writeChecksum(obj *objectSDK.Object) {
+	switch h.typ {
+	case checksum.SHA256:
+		csSHA := [sha256.Size]byte{}
+		h.hasher.Sum(csSHA[:0])
+
+		var cs checksum.Checksum
+		cs.SetSHA256(csSHA)
+
+		obj.SetPayloadChecksum(cs)
+	case checksum.TZ:
+		csTZ := [tz.Size]byte{}
+		h.hasher.Sum(csTZ[:0])
+
+		var cs checksum.Checksum
+		cs.SetTillichZemor(csTZ)
+
+		obj.SetPayloadHomomorphicHash(cs)
+	default:
+		panic("unreachable")
+	}
+}
diff --git a/object/transformer/transformer.go b/object/transformer/transformer.go
index 55ad9ff..86b0a39 100644
--- a/object/transformer/transformer.go
+++ b/object/transformer/transformer.go
@@ -4,7 +4,6 @@ import (
 	"crypto/ecdsa"
 	"crypto/sha256"
 	"fmt"
-	"hash"
 	"io"
 
 	"github.com/TrueCloudLab/frostfs-sdk-go/checksum"
@@ -33,12 +32,6 @@ type payloadSizeLimiter struct {
 	parAttrs []object.Attribute
 }
 
-type payloadChecksumHasher struct {
-	hasher hash.Hash
-
-	checksumWriter func([]byte)
-}
-
 type Params struct {
 	Key                    *ecdsa.PrivateKey
 	NextTarget             ObjectTarget
@@ -83,11 +76,17 @@ func (s *payloadSizeLimiter) Close() (*AccessIdentifiers, error) {
 }
 
 func (s *payloadSizeLimiter) initialize() {
+	s.current = fromObject(s.current)
+
 	// if it is an object after the 1st
 	if ln := len(s.previous); ln > 0 {
 		// initialize parent object once (after 1st object)
 		if ln == 1 {
-			s.detachParent()
+			s.parent = fromObject(s.current)
+			s.parentHashers = s.currentHashers
+
+			// return source attributes
+			s.parent.SetAttributes(s.parAttrs...)
 		}
 
 		// set previous object to the last previous identifier
@@ -118,7 +117,7 @@ func fromObject(obj *object.Object) *object.Object {
 func (s *payloadSizeLimiter) initializeCurrent() {
 	// create payload hashers
 	s.writtenCurrent = 0
-	s.currentHashers = payloadHashersForObject(s.current, s.WithoutHomomorphicHash)
+	s.currentHashers = payloadHashersForObject(s.WithoutHomomorphicHash)
 
 	// compose multi-writer from target and all payload hashers
 	ws := make([]io.Writer, 0, 1+len(s.currentHashers)+len(s.parentHashers))
@@ -136,42 +135,18 @@ func (s *payloadSizeLimiter) initializeCurrent() {
 	s.chunkWriter = io.MultiWriter(ws...)
 }
 
-func payloadHashersForObject(obj *object.Object, withoutHomomorphicHash bool) []*payloadChecksumHasher {
+func payloadHashersForObject(withoutHomomorphicHash bool) []*payloadChecksumHasher {
 	hashers := make([]*payloadChecksumHasher, 0, 2)
 
 	hashers = append(hashers, &payloadChecksumHasher{
 		hasher: sha256.New(),
-		checksumWriter: func(binChecksum []byte) {
-			if ln := len(binChecksum); ln != sha256.Size {
-				panic(fmt.Sprintf("wrong checksum length: expected %d, has %d", sha256.Size, ln))
-			}
-
-			csSHA := [sha256.Size]byte{}
-			copy(csSHA[:], binChecksum)
-
-			var cs checksum.Checksum
-			cs.SetSHA256(csSHA)
-
-			obj.SetPayloadChecksum(cs)
-		},
+		typ:    checksum.SHA256,
 	})
 
 	if !withoutHomomorphicHash {
 		hashers = append(hashers, &payloadChecksumHasher{
 			hasher: tz.New(),
-			checksumWriter: func(binChecksum []byte) {
-				if ln := len(binChecksum); ln != tz.Size {
-					panic(fmt.Sprintf("wrong checksum length: expected %d, has %d", tz.Size, ln))
-				}
-
-				csTZ := [tz.Size]byte{}
-				copy(csTZ[:], binChecksum)
-
-				var cs checksum.Checksum
-				cs.SetTillichZemor(csTZ)
-
-				obj.SetPayloadHomomorphicHash(cs)
-			},
+			typ:    checksum.TZ,
 		})
 	}
 
@@ -185,13 +160,17 @@ func (s *payloadSizeLimiter) release(finalize bool) (*AccessIdentifiers, error)
 	withParent := finalize && len(s.previous) > 0
 
 	if withParent {
-		writeHashes(s.parentHashers)
+		for i := range s.parentHashers {
+			s.parentHashers[i].writeChecksum(s.parent)
+		}
 		s.parent.SetPayloadSize(s.written)
 		s.current.SetParent(s.parent)
 	}
 
 	// release current object
-	writeHashes(s.currentHashers)
+	for i := range s.currentHashers {
+		s.currentHashers[i].writeChecksum(s.current)
+	}
 
 	curEpoch := s.NetworkState.CurrentEpoch()
 	ver := version.Current()
@@ -259,12 +238,6 @@ func (s *payloadSizeLimiter) release(finalize bool) (*AccessIdentifiers, error)
 	return ids, nil
 }
 
-func writeHashes(hashers []*payloadChecksumHasher) {
-	for i := range hashers {
-		hashers[i].checksumWriter(hashers[i].hasher.Sum(nil))
-	}
-}
-
 func (s *payloadSizeLimiter) initializeLinking(parHdr *object.Object) {
 	s.current = fromObject(s.current)
 	s.current.SetParent(parHdr)
@@ -327,14 +300,3 @@ func (s *payloadSizeLimiter) prepareFirstChild() {
 
 	// attributes will be added to parent in detachParent
 }
-
-func (s *payloadSizeLimiter) detachParent() {
-	s.parent = s.current
-	s.current = fromObject(s.parent)
-	s.parent.ResetRelations()
-	s.parent.SetSignature(nil)
-	s.parentHashers = s.currentHashers
-
-	// return source attributes
-	s.parent.SetAttributes(s.parAttrs...)
-}
diff --git a/object/transformer/transformer_test.go b/object/transformer/transformer_test.go
index 2b4ee31..fbc8e45 100644
--- a/object/transformer/transformer_test.go
+++ b/object/transformer/transformer_test.go
@@ -182,12 +182,7 @@ func (tt *testTarget) Write(p []byte) (n int, err error) {
 
 func (tt *testTarget) Close() (*AccessIdentifiers, error) {
 	tt.current.SetPayload(tt.payload)
-	// We need to marshal, because current implementation reuses written object.
-	data, _ := tt.current.Marshal()
-	obj := objectSDK.New()
-	_ = obj.Unmarshal(data)
-
-	tt.objects = append(tt.objects, obj)
+	tt.objects = append(tt.objects, tt.current)
 	tt.current = nil
 	tt.payload = nil
 	return nil, nil // AccessIdentifiers should not be used.
-- 
2.45.2


From 51fedb5d3b5c886f944cbab8d29b9aee3a23e0c0 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Thu, 23 Feb 2023 17:13:27 +0300
Subject: [PATCH 10/12] [#19] transformer: Add a target which sends parts to a
 channel

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 object/transformer/channel.go      | 44 ++++++++++++++++++++++++
 object/transformer/channel_test.go | 55 ++++++++++++++++++++++++++++++
 2 files changed, 99 insertions(+)
 create mode 100644 object/transformer/channel.go
 create mode 100644 object/transformer/channel_test.go

diff --git a/object/transformer/channel.go b/object/transformer/channel.go
new file mode 100644
index 0000000..707de09
--- /dev/null
+++ b/object/transformer/channel.go
@@ -0,0 +1,44 @@
+package transformer
+
+import (
+	objectSDK "github.com/TrueCloudLab/frostfs-sdk-go/object"
+	"github.com/nspcc-dev/neo-go/pkg/util/slice"
+)
+
+type chanTarget struct {
+	header  *objectSDK.Object
+	payload []byte
+	ch      chan<- *objectSDK.Object
+}
+
+// NewChannelTarget returns ObjectTarget which writes
+// object parts to a provided channel.
+func NewChannelTarget(ch chan<- *objectSDK.Object) ObjectTarget {
+	return &chanTarget{
+		ch: ch,
+	}
+}
+
+// WriteHeader implements the ObjectTarget interface.
+func (c *chanTarget) WriteHeader(object *objectSDK.Object) error {
+	c.header = object
+	return nil
+}
+
+// Write implements the ObjectTarget interface.
+func (c *chanTarget) Write(p []byte) (n int, err error) {
+	c.payload = append(c.payload, p...)
+	return len(p), nil
+}
+
+// Close implements the ObjectTarget interface.
+func (c *chanTarget) Close() (*AccessIdentifiers, error) {
+	if len(c.payload) != 0 {
+		c.header.SetPayload(slice.Copy(c.payload))
+	}
+	c.ch <- c.header
+
+	c.header = nil
+	c.payload = nil
+	return new(AccessIdentifiers), nil
+}
diff --git a/object/transformer/channel_test.go b/object/transformer/channel_test.go
new file mode 100644
index 0000000..99aef23
--- /dev/null
+++ b/object/transformer/channel_test.go
@@ -0,0 +1,55 @@
+package transformer
+
+import (
+	"crypto/rand"
+	"testing"
+
+	cidtest "github.com/TrueCloudLab/frostfs-sdk-go/container/id/test"
+	objectSDK "github.com/TrueCloudLab/frostfs-sdk-go/object"
+	"github.com/TrueCloudLab/frostfs-sdk-go/version"
+	"github.com/stretchr/testify/require"
+)
+
+func TestChannelTarget(t *testing.T) {
+	const maxSize = 100
+
+	ch := make(chan *objectSDK.Object, 10)
+	tt := new(testTarget)
+
+	chTarget, _ := newPayloadSizeLimiter(maxSize, NewChannelTarget(ch))
+	testTarget, _ := newPayloadSizeLimiter(maxSize, tt)
+
+	ver := version.Current()
+	cnr := cidtest.ID()
+	hdr := objectSDK.New()
+	hdr.SetContainerID(cnr)
+	hdr.SetType(objectSDK.TypeRegular)
+	hdr.SetVersion(&ver)
+
+	payload := make([]byte, maxSize*2+maxSize/2)
+	_, _ = rand.Read(payload)
+
+	expectedIDs := writeObject(t, testTarget, hdr, payload)
+	actualIDs := writeObject(t, chTarget, hdr, payload)
+	_ = expectedIDs
+	_ = actualIDs
+	//require.Equal(t, expectedIDs, actualIDs)
+
+	for i := range tt.objects {
+		select {
+		case obj := <-ch:
+			// Because of the split ID objects can be different.
+			// However, payload and attributes must be the same.
+			require.Equal(t, tt.objects[i].Payload(), obj.Payload())
+			require.Equal(t, tt.objects[i].Attributes(), obj.Attributes())
+		default:
+			require.FailNow(t, "received less parts than expected")
+		}
+	}
+
+	select {
+	case <-ch:
+		require.FailNow(t, "received more parts than expected")
+	default:
+	}
+}
-- 
2.45.2


From fe394bc0f694f1958995a524bed3b76a90da3dd7 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Fri, 24 Feb 2023 17:01:38 +0300
Subject: [PATCH 11/12] [#19] transformer: Optimize payload hashers a bit
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

```
name                 old time/op    new time/op    delta
Transformer/small-8    74.8µs ±11%    73.7µs ±15%    ~     (p=0.529 n=10+10)
Transformer/big-8       1.38s ±11%     1.36s ± 4%    ~     (p=0.796 n=10+10)

name                 old alloc/op   new alloc/op   delta
Transformer/small-8    7.69kB ± 0%    7.67kB ± 0%  -0.21%  (p=0.000 n=10+10)
Transformer/big-8      49.2kB ± 0%    49.0kB ± 0%  -0.48%  (p=0.004 n=10+10)

name                 old allocs/op  new allocs/op  delta
Transformer/small-8       102 ± 0%       101 ± 0%  -0.98%  (p=0.000 n=9+10)
Transformer/big-8         620 ± 1%       609 ± 0%  -1.66%  (p=0.000 n=10+10)
```

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 object/transformer/transformer.go | 18 +++++++-----------
 1 file changed, 7 insertions(+), 11 deletions(-)

diff --git a/object/transformer/transformer.go b/object/transformer/transformer.go
index 86b0a39..613bc5e 100644
--- a/object/transformer/transformer.go
+++ b/object/transformer/transformer.go
@@ -21,7 +21,7 @@ type payloadSizeLimiter struct {
 
 	current, parent *object.Object
 
-	currentHashers, parentHashers []*payloadChecksumHasher
+	currentHashers, parentHashers []payloadChecksumHasher
 
 	previous []oid.ID
 
@@ -83,7 +83,7 @@ func (s *payloadSizeLimiter) initialize() {
 		// initialize parent object once (after 1st object)
 		if ln == 1 {
 			s.parent = fromObject(s.current)
-			s.parentHashers = s.currentHashers
+			s.parentHashers = append(s.parentHashers[:0], s.currentHashers...)
 
 			// return source attributes
 			s.parent.SetAttributes(s.parAttrs...)
@@ -117,7 +117,7 @@ func fromObject(obj *object.Object) *object.Object {
 func (s *payloadSizeLimiter) initializeCurrent() {
 	// create payload hashers
 	s.writtenCurrent = 0
-	s.currentHashers = payloadHashersForObject(s.WithoutHomomorphicHash)
+	s.initPayloadHashers()
 
 	// compose multi-writer from target and all payload hashers
 	ws := make([]io.Writer, 0, 1+len(s.currentHashers)+len(s.parentHashers))
@@ -135,22 +135,18 @@ func (s *payloadSizeLimiter) initializeCurrent() {
 	s.chunkWriter = io.MultiWriter(ws...)
 }
 
-func payloadHashersForObject(withoutHomomorphicHash bool) []*payloadChecksumHasher {
-	hashers := make([]*payloadChecksumHasher, 0, 2)
-
-	hashers = append(hashers, &payloadChecksumHasher{
+func (s *payloadSizeLimiter) initPayloadHashers() {
+	s.currentHashers = append(s.currentHashers[:0], payloadChecksumHasher{
 		hasher: sha256.New(),
 		typ:    checksum.SHA256,
 	})
 
-	if !withoutHomomorphicHash {
-		hashers = append(hashers, &payloadChecksumHasher{
+	if !s.WithoutHomomorphicHash {
+		s.currentHashers = append(s.currentHashers, payloadChecksumHasher{
 			hasher: tz.New(),
 			typ:    checksum.TZ,
 		})
 	}
-
-	return hashers
 }
 
 func (s *payloadSizeLimiter) release(finalize bool) (*AccessIdentifiers, error) {
-- 
2.45.2


From e7ee4e1f24b5c6d6bd8f9fcd89de18ce1764b924 Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <e.stratonikov@yadro.com>
Date: Fri, 24 Feb 2023 17:09:34 +0300
Subject: [PATCH 12/12] [#19] transformer: Do not allocate intermeate slice for
 hashers
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

```
name                 old time/op    new time/op    delta
Transformer/small-8    73.7µs ±15%    72.4µs ±16%    ~     (p=0.604 n=10+9)
Transformer/big-8       1.36s ± 4%     1.36s ± 8%    ~     (p=0.579 n=10+10)

name                 old alloc/op   new alloc/op   delta
Transformer/small-8    7.67kB ± 0%    7.57kB ± 0%  -1.36%  (p=0.000 n=10+10)
Transformer/big-8      49.0kB ± 0%    48.3kB ± 0%  -1.48%  (p=0.000 n=10+10)

name                 old allocs/op  new allocs/op  delta
Transformer/small-8       101 ± 0%        98 ± 0%  -2.97%  (p=0.000 n=10+10)
Transformer/big-8         609 ± 0%       591 ± 1%  -3.00%  (p=0.000 n=10+9)
```

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>
---
 object/transformer/transformer.go | 38 +++++++++++++++----------------
 1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/object/transformer/transformer.go b/object/transformer/transformer.go
index 613bc5e..1c323a7 100644
--- a/object/transformer/transformer.go
+++ b/object/transformer/transformer.go
@@ -4,7 +4,6 @@ import (
 	"crypto/ecdsa"
 	"crypto/sha256"
 	"fmt"
-	"io"
 
 	"github.com/TrueCloudLab/frostfs-sdk-go/checksum"
 	"github.com/TrueCloudLab/frostfs-sdk-go/object"
@@ -25,8 +24,6 @@ type payloadSizeLimiter struct {
 
 	previous []oid.ID
 
-	chunkWriter io.Writer
-
 	splitID *object.SplitID
 
 	parAttrs []object.Attribute
@@ -118,21 +115,6 @@ func (s *payloadSizeLimiter) initializeCurrent() {
 	// create payload hashers
 	s.writtenCurrent = 0
 	s.initPayloadHashers()
-
-	// compose multi-writer from target and all payload hashers
-	ws := make([]io.Writer, 0, 1+len(s.currentHashers)+len(s.parentHashers))
-
-	ws = append(ws, s.NextTarget)
-
-	for i := range s.currentHashers {
-		ws = append(ws, s.currentHashers[i].hasher)
-	}
-
-	for i := range s.parentHashers {
-		ws = append(ws, s.parentHashers[i].hasher)
-	}
-
-	s.chunkWriter = io.MultiWriter(ws...)
 }
 
 func (s *payloadSizeLimiter) initPayloadHashers() {
@@ -269,7 +251,7 @@ func (s *payloadSizeLimiter) writeChunk(chunk []byte) error {
 			cut = leftToEdge
 		}
 
-		if _, err := s.chunkWriter.Write(chunk[:cut]); err != nil {
+		if err := s.writeHashes(chunk[:cut]); err != nil {
 			return fmt.Errorf("could not write chunk to target: %w", err)
 		}
 
@@ -285,6 +267,24 @@ func (s *payloadSizeLimiter) writeChunk(chunk []byte) error {
 	}
 }
 
+func (s *payloadSizeLimiter) writeHashes(chunk []byte) error {
+	_, err := s.NextTarget.Write(chunk)
+	if err != nil {
+		return err
+	}
+
+	// The `Write` method of `hash.Hash` never returns an error.
+	for i := range s.currentHashers {
+		_, _ = s.currentHashers[i].hasher.Write(chunk)
+	}
+
+	for i := range s.parentHashers {
+		_, _ = s.parentHashers[i].hasher.Write(chunk)
+	}
+
+	return nil
+}
+
 func (s *payloadSizeLimiter) prepareFirstChild() {
 	// initialize split header with split ID on first object in chain
 	s.current.InitRelations()
-- 
2.45.2