[#19] transformer: Do not allocate intermeate slice for hashers

```
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/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
+}

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:
+	}
+}

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")
+	}
+}

object/transformer/transformer.go

@@ -0,0 +1,298 @@
+package transformer
+
+import (
+	"crypto/ecdsa"
+	"crypto/sha256"
+	"fmt"
+
+	"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 {
+	Params
+
+	written, writtenCurrent uint64
+
+	current, parent *object.Object
+
+	currentHashers, parentHashers []payloadChecksumHasher
+
+	previous []oid.ID
+
+	splitID *object.SplitID
+
+	parAttrs []object.Attribute
+}
+
+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.
+//
+// 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(p Params) ObjectTarget {
+	return &payloadSizeLimiter{
+		Params:  p,
+		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() {
+	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.parent = fromObject(s.current)
+			s.parentHashers = append(s.parentHashers[:0], s.currentHashers...)
+
+			// return source attributes
+			s.parent.SetAttributes(s.parAttrs...)
+		}
+
+		// 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() {
+	// create payload hashers
+	s.writtenCurrent = 0
+	s.initPayloadHashers()
+}
+
+func (s *payloadSizeLimiter) initPayloadHashers() {
+	s.currentHashers = append(s.currentHashers[:0], payloadChecksumHasher{
+		hasher: sha256.New(),
+		typ:    checksum.SHA256,
+	})
+
+	if !s.WithoutHomomorphicHash {
+		s.currentHashers = append(s.currentHashers, payloadChecksumHasher{
+			hasher: tz.New(),
+			typ:    checksum.TZ,
+		})
+	}
+}
+
+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 {
+		for i := range s.parentHashers {
+			s.parentHashers[i].writeChecksum(s.parent)
+		}
+		s.parent.SetPayloadSize(s.written)
+		s.current.SetParent(s.parent)
+	}
+
+	// release current object
+	for i := range s.currentHashers {
+		s.currentHashers[i].writeChecksum(s.current)
+	}
+
+	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)
+	}
+
+	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
+	s.previous = append(s.previous, ids.SelfID)
+
+	if withParent {
+		// generate and release linking object
+		s.initializeLinking(ids.ParentHeader)
+		s.initializeCurrent()
+
+		if _, err := s.release(false); err != nil {
+			return nil, fmt.Errorf("could not release linking object: %w", err)
+		}
+	}
+
+	return ids, 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 {
+	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()
+		}
+
+		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.writeHashes(chunk[:cut]); err != nil {
+			return fmt.Errorf("could not write chunk to target: %w", err)
+		}
+
+		// increase written bytes counter
+		s.writtenCurrent += cut
+		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:]
+	}
+}
+
+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()
+	s.current.SetSplitID(s.splitID)
+
+	// cut source attributes
+	s.parAttrs = s.current.Attributes()
+	s.current.SetAttributes()
+
+	// attributes will be added to parent in detachParent
+}

object/transformer/transformer_test.go

@@ -0,0 +1,189 @@
+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"
+)
+
+func TestTransformer(t *testing.T) {
+	const maxSize = 100
+
+	tt := new(testTarget)
+
+	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)
+
+	ids := writeObject(t, target, hdr, expectedPayload)
+	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())
+		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))
+		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)
+
+	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 {
+	ver := version.Current()
+	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)
+	})
+	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(Params{
+		Key:                    &p.PrivateKey,
+		NextTarget:             nextTarget,
+		NetworkState:           dummyEpochSource(123),
+		MaxSize:                maxSize,
+		WithoutHomomorphicHash: true,
+	}), 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)
+	tt.objects = append(tt.objects, tt.current)
+	tt.current = nil
+	tt.payload = nil
+	return nil, nil // AccessIdentifiers should not be used.
+}

object/transformer/types.go

@@ -0,0 +1,55 @@
+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 {
+	ParentID     *oid.ID
+	SelfID       oid.ID
+	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.
+	// 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