[#205] object: Initial EC implementation

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/antlr4-go/antlr/v4 v4.13.0
 	github.com/google/uuid v1.3.0
 	github.com/hashicorp/golang-lru/v2 v2.0.2
+	github.com/klauspost/reedsolomon v1.12.1
 	github.com/mr-tron/base58 v1.2.0
 	github.com/nspcc-dev/neo-go v0.101.2-0.20230601131642-a0117042e8fc
 	github.com/stretchr/testify v1.8.3
@@ -28,6 +29,7 @@ require (
 	github.com/golang/protobuf v1.5.3 // indirect
 	github.com/gorilla/websocket v1.5.0 // indirect
 	github.com/hashicorp/golang-lru v0.6.0 // indirect
+	github.com/klauspost/cpuid/v2 v2.2.6 // indirect
 	github.com/nspcc-dev/go-ordered-json v0.0.0-20220111165707-25110be27d22 // indirect
 	github.com/nspcc-dev/neo-go/pkg/interop v0.0.0-20230615193820-9185820289ce // indirect
 	github.com/nspcc-dev/rfc6979 v0.2.0 // indirect

object/erasure_code.go

@@ -0,0 +1,121 @@
+package object
+
+import (
+	"errors"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/object"
+	refs "git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/refs"
+	oid "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/id"
+)
+
+// ECHeader represents erasure coding header.
+type ECHeader struct {
+	parent       oid.ID
+	index        uint32
+	total        uint32
+	header       []byte
+	headerLength uint32
+}
+
+// NewECHeader constructs new erasure coding header.
+func NewECHeader(parent oid.ID, index, total uint32, header []byte, headerLength uint32) *ECHeader {
+	return &ECHeader{
+		parent:       parent,
+		index:        index,
+		total:        total,
+		header:       header,
+		headerLength: headerLength,
+	}
+}
+
+// WriteToV2 converts SDK structure to v2-api one.
+func (e *ECHeader) WriteToV2(h *object.ECHeader) {
+	var parent refs.ObjectID
+	e.parent.WriteToV2(&parent)
+	h.Parent = &parent
+	h.Index = e.index
+	h.Total = e.total
+	h.Header = e.header
+	h.HeaderLength = e.headerLength
+}
+
+// ReadFromV2 converts v2-api structure to SDK one.
+func (e *ECHeader) ReadFromV2(h *object.ECHeader) error {
+	if h == nil {
+		return nil
+	}
+	if h.Parent == nil {
+		return errors.New("empty parent")
+	}
+
+	_ = e.parent.ReadFromV2(*h.Parent)
+	e.index = h.Index
+	e.total = h.Total
+	e.header = h.Header
+	e.headerLength = h.HeaderLength
+	return nil
+}
+
+func (o *Object) ECHeader() *ECHeader {
+	ec := (*object.Object)(o).GetHeader().GetEC()
+	if ec == nil {
+		return nil
+	}
+
+	h := new(ECHeader)
+	_ = h.ReadFromV2(ec)
+	return h
+}
+
+func (o *Object) SetECHeader(ec *ECHeader) {
+	o.setHeaderField(func(h *object.Header) {
+		if ec == nil {
+			h.SetEC(nil)
+			return
+		}
+
+		v2 := new(object.ECHeader)
+		ec.WriteToV2(v2)
+		h.SetEC(v2)
+	})
+}
+
+func (e *ECHeader) Parent() oid.ID {
+	return e.parent
+}
+
+func (e *ECHeader) SetParent(id oid.ID) {
+	e.parent = id
+}
+
+func (e *ECHeader) Index() uint32 {
+	return e.index
+}
+
+func (e *ECHeader) SetIndex(i uint32) {
+	e.index = i
+}
+
+func (e *ECHeader) Total() uint32 {
+	return e.total
+}
+
+func (e *ECHeader) SetTotal(i uint32) {
+	e.total = i
+}
+
+func (e *ECHeader) Header() []byte {
+	return e.header
+}
+
+func (e *ECHeader) SetHeader(header []byte) {
+	e.header = header
+}
+
+func (e *ECHeader) HeaderLength() uint32 {
+	return e.headerLength
+}
+
+func (e *ECHeader) SetHeaderLength(l uint32) {
+	e.headerLength = l
+}

object/erasurecode/constructor.go

@@ -0,0 +1,87 @@
+package erasurecode
+
+import (
+	"errors"
+
+	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
+	"github.com/klauspost/reedsolomon"
+)
+
+var (
+	// ErrMalformedSlice is returned when a slice of EC chunks is inconsistent.
+	ErrMalformedSlice = errors.New("inconsistent EC headers")
+	// ErrInvShardNum is returned from NewConstructor when the number of shards is invalid.
+	ErrInvShardNum = reedsolomon.ErrInvShardNum
+	// ErrMaxShardNum is returned from NewConstructor when the number of shards is too big.
+	ErrMaxShardNum = reedsolomon.ErrMaxShardNum
+)
+
+// MaxShardCount is the maximum number of shards.
+const MaxShardCount = 256
+
+// Constructor is a wrapper around encoder allowing to reconstruct objects.
+// It's methods are not thread-safe.
+type Constructor struct {
+	enc           reedsolomon.Encoder
+	headerLength  uint32
+	payloadShards [][]byte
+	headerShards  [][]byte
+}
+
+// NewConstructor returns new constructor instance.
+func NewConstructor(dataCount int, parityCount int) (*Constructor, error) {
+	// The library supports up to 65536 shards with some restrictions.
+	// This can easily result in OOM or panic, thus SDK declares it's own restriction.
+	if dataCount+parityCount > MaxShardCount {
+		return nil, ErrMaxShardNum
+	}
+
+	enc, err := reedsolomon.New(dataCount, parityCount)
+	if err != nil {
+		return nil, err
+	}
+	return &Constructor{enc: enc}, nil
+}
+
+// clear clears internal state of the constructor, so it can be reused.
+func (c *Constructor) clear() {
+	c.headerLength = 0
+	c.payloadShards = nil
+	c.headerShards = nil
+}
+
+func (c *Constructor) fillHeader(parts []*objectSDK.Object) error {
+	shards := make([][]byte, len(parts))
+	headerLength := 0
+	for i := range parts {
+		if parts[i] == nil {
+			continue
+		}
+
+		var err error
+		headerLength, err = validatePart(parts, i, headerLength)
+		if err != nil {
+			return err
+		}
+
+		shards[i] = parts[i].GetECHeader().Header()
+	}
+
+	c.headerLength = uint32(headerLength)
+	c.headerShards = shards
+	return nil
+}
+
+// fillPayload fills the payload shards.
+// Currently there is no case when it can be called without reconstructing header,
+// thus fillHeader() must be called before and this function performs no validation.
+func (c *Constructor) fillPayload(parts []*objectSDK.Object) {
+	shards := make([][]byte, len(parts))
+	for i := range parts {
+		if parts[i] == nil {
+			continue
+		}
+		shards[i] = parts[i].Payload()
+	}
+	c.payloadShards = shards
+}

object/erasurecode/constructor_test.go

@@ -0,0 +1,31 @@
+package erasurecode_test
+
+import (
+	"testing"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/erasurecode"
+	"github.com/stretchr/testify/require"
+)
+
+func TestErasureConstruct(t *testing.T) {
+	t.Run("negative, no panic", func(t *testing.T) {
+		_, err := erasurecode.NewConstructor(-1, 2)
+		require.ErrorIs(t, err, erasurecode.ErrInvShardNum)
+	})
+	t.Run("negative, no panic", func(t *testing.T) {
+		_, err := erasurecode.NewConstructor(2, -1)
+		require.ErrorIs(t, err, erasurecode.ErrInvShardNum)
+	})
+	t.Run("zero parity", func(t *testing.T) {
+		_, err := erasurecode.NewConstructor(1, 0)
+		require.NoError(t, err)
+	})
+	t.Run("max shard num", func(t *testing.T) {
+		_, err := erasurecode.NewConstructor(erasurecode.MaxShardCount, 0)
+		require.NoError(t, err)
+	})
+	t.Run("max+1 shard num", func(t *testing.T) {
+		_, err := erasurecode.NewConstructor(erasurecode.MaxShardCount+1, 0)
+		require.ErrorIs(t, err, erasurecode.ErrMaxShardNum)
+	})
+}

object/erasurecode/reconstruct.go

@@ -0,0 +1,142 @@
+package erasurecode
+
+import (
+	"bytes"
+	"crypto/ecdsa"
+	"fmt"
+
+	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
+	"github.com/klauspost/reedsolomon"
+)
+
+// Reconstruct returns full object reconstructed from parts.
+// All non-nil objects in parts must have EC header with the same `total` field equal to len(parts).
+// The slice must contain at least one non nil object.
+// Index of the objects in parts must be equal to it's index field in the EC header.
+// The parts slice isn't changed and can be used concurrently for reading.
+func (c *Constructor) Reconstruct(parts []*objectSDK.Object) (*objectSDK.Object, error) {
+	res, err := c.ReconstructHeader(parts)
+	if err != nil {
+		return nil, err
+	}
+
+	c.fillPayload(parts)
+
+	payload, err := reconstructExact(c.enc, int(res.PayloadSize()), c.payloadShards)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrMalformedSlice, err)
+	}
+
+	res.SetPayload(payload)
+	return res, nil
+}
+
+// ReconstructHeader returns object header reconstructed from parts.
+// All non-nil objects in parts must have EC header with the same `total` field equal to len(parts).
+// The slice must contain at least one non nil object.
+// Index of the objects in parts must be equal to it's index field in the EC header.
+// The parts slice isn't changed and can be used concurrently for reading.
+func (c *Constructor) ReconstructHeader(parts []*objectSDK.Object) (*objectSDK.Object, error) {
+	c.clear()
+
+	if err := c.fillHeader(parts); err != nil {
+		return nil, err
+	}
+
+	obj, err := c.reconstructHeader()
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", ErrMalformedSlice, err)
+	}
+	return obj, nil
+}
+
+// ReconstructParts reconstructs specific EC parts without reconstructing full object.
+// All non-nil objects in parts must have EC header with the same `total` field equal to len(parts).
+// The slice must contain at least one non nil object.
+// Index of the objects in parts must be equal to it's index field in the EC header.
+// Those parts for which corresponding element in required is true must be nil and will be overwritten.
+// Because partial reconstruction only makes sense for full objects, all parts must have non-empty payload.
+// If key is not nil, all reconstructed parts are signed with this key.
+func (c *Constructor) ReconstructParts(parts []*objectSDK.Object, required []bool, key *ecdsa.PrivateKey) error {
+	if len(required) != len(parts) {
+		return fmt.Errorf("len(parts) != len(required): %d != %d", len(parts), len(required))
+	}
+
+	c.clear()
+
+	if err := c.fillHeader(parts); err != nil {
+		return err
+	}
+	c.fillPayload(parts)
+
+	if err := c.enc.ReconstructSome(c.payloadShards, required); err != nil {
+		return fmt.Errorf("%w: %w", ErrMalformedSlice, err)
+	}
+	if err := c.enc.ReconstructSome(c.headerShards, required); err != nil {
+		return fmt.Errorf("%w: %w", ErrMalformedSlice, err)
+	}
+
+	nonNilPart := 0
+	for i := range parts {
+		if parts[i] != nil {
+			nonNilPart = i
+			break
+		}
+	}
+
+	ec := parts[nonNilPart].GetECHeader()
+	parent := ec.Parent()
+	total := ec.Total()
+
+	for i := range required {
+		if parts[i] != nil || !required[i] {
+			continue
+		}
+
+		part := objectSDK.New()
+		copyRequiredFields(part, parts[nonNilPart])
+		part.SetPayload(c.payloadShards[i])
+		part.SetPayloadSize(uint64(len(c.payloadShards[i])))
+		part.SetECHeader(objectSDK.NewECHeader(parent, uint32(i), total,
+			c.headerShards[i], c.headerLength))
+
+		if err := setIDWithSignature(part, key); err != nil {
+			return err
+		}
+		parts[i] = part
+	}
+	return nil
+}
+
+func (c *Constructor) reconstructHeader() (*objectSDK.Object, error) {
+	data, err := reconstructExact(c.enc, int(c.headerLength), c.headerShards)
+	if err != nil {
+		return nil, err
+	}
+
+	var obj objectSDK.Object
+	return &obj, obj.Unmarshal(data)
+}
+
+func reconstructExact(enc reedsolomon.Encoder, size int, shards [][]byte) ([]byte, error) {
+	if err := enc.ReconstructData(shards); err != nil {
+		return nil, err
+	}
+
+	// Technically, this error will be returned from enc.Join().
+	// However, allocating based on unvalidated user data is an easy attack vector.
+	// Preallocating seems to have enough benefits to justify a slight increase in code complexity.
+	maxSize := 0
+	for i := range shards {
+		maxSize += len(shards[i])
+	}
+	if size > maxSize {
+		return nil, reedsolomon.ErrShortData
+	}
+
+	buf := bytes.NewBuffer(make([]byte, 0, size))
+	if err := enc.Join(buf, shards, size); err != nil {
+		return nil, err
+	}
+	return buf.Bytes(), nil
+}

object/erasurecode/reconstruct_test.go

@@ -0,0 +1,284 @@
+package erasurecode_test
+
+import (
+	"context"
+	"crypto/rand"
+	"math"
+	"testing"
+
+	cidtest "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/container/id/test"
+	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
+	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/erasurecode"
+	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/transformer"
+	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/user"
+	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/version"
+	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
+	"github.com/stretchr/testify/require"
+)
+
+func TestErasureCodeReconstruct(t *testing.T) {
+	const payloadSize = 99
+	const dataCount = 3
+	const parityCount = 2
+
+	// We would also like to test padding behaviour,
+	// so ensure padding is done.
+	require.NotZero(t, payloadSize%(dataCount+parityCount))
+
+	pk, err := keys.NewPrivateKey()
+	require.NoError(t, err)
+
+	original := newObject(t, payloadSize, pk)
+
+	c, err := erasurecode.NewConstructor(dataCount, parityCount)
+	require.NoError(t, err)
+
+	parts, err := c.Split(original, &pk.PrivateKey)
+	require.NoError(t, err)
+
+	t.Run("reconstruct header", func(t *testing.T) {
+		original := original.CutPayload()
+		parts := cloneSlice(parts)
+		for i := range parts {
+			parts[i] = parts[i].CutPayload()
+		}
+		t.Run("from data", func(t *testing.T) {
+			parts := cloneSlice(parts)
+			for i := dataCount; i < dataCount+parityCount; i++ {
+				parts[i] = nil
+			}
+			reconstructed, err := c.ReconstructHeader(parts)
+			require.NoError(t, err)
+			verifyReconstruction(t, original, reconstructed)
+		})
+		t.Run("from parity", func(t *testing.T) {
+			parts := cloneSlice(parts)
+			for i := 0; i < parityCount; i++ {
+				parts[i] = nil
+			}
+			reconstructed, err := c.ReconstructHeader(parts)
+			require.NoError(t, err)
+			verifyReconstruction(t, original, reconstructed)
+
+			t.Run("not enough shards", func(t *testing.T) {
+				parts[parityCount] = nil
+				_, err := c.ReconstructHeader(parts)
+				require.ErrorIs(t, err, erasurecode.ErrMalformedSlice)
+			})
+		})
+		t.Run("only nil parts", func(t *testing.T) {
+			parts := make([]*objectSDK.Object, len(parts))
+			_, err := c.ReconstructHeader(parts)
+			require.ErrorIs(t, err, erasurecode.ErrMalformedSlice)
+		})
+		t.Run("missing EC header", func(t *testing.T) {
+			parts := cloneSlice(parts)
+			parts[0] = deepCopy(t, parts[0])
+			parts[0].SetECHeader(nil)
+
+			_, err := c.ReconstructHeader(parts)
+			require.ErrorIs(t, err, erasurecode.ErrMalformedSlice)
+		})
+		t.Run("invalid index", func(t *testing.T) {
+			parts := cloneSlice(parts)
+			parts[0] = deepCopy(t, parts[0])
+
+			ec := parts[0].GetECHeader()
+			ec.SetIndex(1)
+			parts[0].SetECHeader(ec)
+
+			_, err := c.ReconstructHeader(parts)
+			require.ErrorIs(t, err, erasurecode.ErrMalformedSlice)
+		})
+		t.Run("invalid total", func(t *testing.T) {
+			parts := cloneSlice(parts)
+			parts[0] = deepCopy(t, parts[0])
+
+			ec := parts[0].GetECHeader()
+			ec.SetTotal(uint32(len(parts) + 1))
+			parts[0].SetECHeader(ec)
+
+			_, err := c.ReconstructHeader(parts)
+			require.ErrorIs(t, err, erasurecode.ErrMalformedSlice)
+		})
+		t.Run("inconsistent header length", func(t *testing.T) {
+			parts := cloneSlice(parts)
+			parts[0] = deepCopy(t, parts[0])
+
+			ec := parts[0].GetECHeader()
+			ec.SetHeaderLength(ec.HeaderLength() - 1)
+			parts[0].SetECHeader(ec)
+
+			_, err := c.ReconstructHeader(parts)
+			require.ErrorIs(t, err, erasurecode.ErrMalformedSlice)
+		})
+		t.Run("invalid header length", func(t *testing.T) {
+			parts := cloneSlice(parts)
+			for i := range parts {
+				parts[i] = deepCopy(t, parts[i])
+
+				ec := parts[0].GetECHeader()
+				ec.SetHeaderLength(math.MaxUint32)
+				parts[0].SetECHeader(ec)
+			}
+
+			_, err := c.ReconstructHeader(parts)
+			require.ErrorIs(t, err, erasurecode.ErrMalformedSlice)
+		})
+	})
+	t.Run("reconstruct data", func(t *testing.T) {
+		t.Run("from data", func(t *testing.T) {
+			parts := cloneSlice(parts)
+			for i := dataCount; i < dataCount+parityCount; i++ {
+				parts[i] = nil
+			}
+			reconstructed, err := c.Reconstruct(parts)
+			require.NoError(t, err)
+			verifyReconstruction(t, original, reconstructed)
+		})
+		t.Run("from parity", func(t *testing.T) {
+			parts := cloneSlice(parts)
+			for i := 0; i < parityCount; i++ {
+				parts[i] = nil
+			}
+			reconstructed, err := c.Reconstruct(parts)
+			require.NoError(t, err)
+			verifyReconstruction(t, original, reconstructed)
+
+			t.Run("not enough shards", func(t *testing.T) {
+				parts[parityCount] = nil
+				_, err := c.Reconstruct(parts)
+				require.ErrorIs(t, err, erasurecode.ErrMalformedSlice)
+			})
+		})
+	})
+	t.Run("reconstruct parts", func(t *testing.T) {
+		// We would like to also test that ReconstructParts doesn't perform
+		// excessive work, so ensure this test makes sense.
+		require.GreaterOrEqual(t, parityCount, 2)
+
+		t.Run("from data", func(t *testing.T) {
+			oldParts := parts
+			parts := cloneSlice(parts)
+			for i := dataCount; i < dataCount+parityCount; i++ {
+				parts[i] = nil
+			}
+
+			required := make([]bool, len(parts))
+			required[dataCount] = true
+
+			require.NoError(t, c.ReconstructParts(parts, required, nil))
+
+			old := deepCopy(t, oldParts[dataCount])
+			old.SetSignature(nil)
+			require.Equal(t, old, parts[dataCount])
+
+			for i := dataCount + 1; i < dataCount+parityCount; i++ {
+				require.Nil(t, parts[i])
+			}
+		})
+		t.Run("from parity", func(t *testing.T) {
+			oldParts := parts
+			parts := cloneSlice(parts)
+			for i := 0; i < parityCount; i++ {
+				parts[i] = nil
+			}
+
+			required := make([]bool, len(parts))
+			required[0] = true
+
+			require.NoError(t, c.ReconstructParts(parts, required, nil))
+
+			old := deepCopy(t, oldParts[0])
+			old.SetSignature(nil)
+			require.Equal(t, old, parts[0])
+
+			for i := 1; i < parityCount; i++ {
+				require.Nil(t, parts[i])
+			}
+		})
+	})
+}
+
+func newObject(t *testing.T, size uint64, pk *keys.PrivateKey) *objectSDK.Object {
+	// Use transformer to form object to avoid potential bugs with yet another helper object creation in tests.
+	tt := &testTarget{}
+	p := transformer.NewPayloadSizeLimiter(transformer.Params{
+		Key:                    &pk.PrivateKey,
+		NextTargetInit:         func() transformer.ObjectWriter { return tt },
+		NetworkState:           dummyEpochSource(123),
+		MaxSize:                size + 1,
+		WithoutHomomorphicHash: true,
+	})
+	cnr := cidtest.ID()
+	ver := version.Current()
+	hdr := objectSDK.New()
+	hdr.SetContainerID(cnr)
+	hdr.SetType(objectSDK.TypeRegular)
+	hdr.SetVersion(&ver)
+
+	var owner user.ID
+	user.IDFromKey(&owner, pk.PrivateKey.PublicKey)
+	hdr.SetOwnerID(owner)
+
+	var attr objectSDK.Attribute
+	attr.SetKey("somekey")
+	attr.SetValue("somevalue")
+	hdr.SetAttributes(attr)
+
+	expectedPayload := make([]byte, size)
+	_, _ = rand.Read(expectedPayload)
+	writeObject(t, context.Background(), p, hdr, expectedPayload)
+	require.Len(t, tt.objects, 1)
+	return tt.objects[0]
+}
+
+func writeObject(t *testing.T, ctx context.Context, target transformer.ChunkedObjectWriter, header *objectSDK.Object, payload []byte) *transformer.AccessIdentifiers {
+	require.NoError(t, target.WriteHeader(ctx, header))
+
+	_, err := target.Write(ctx, payload)
+	require.NoError(t, err)
+
+	ids, err := target.Close(ctx)
+	require.NoError(t, err)
+
+	return ids
+}
+
+func verifyReconstruction(t *testing.T, original, reconstructed *objectSDK.Object) {
+	require.True(t, reconstructed.VerifyIDSignature())
+	reconstructed.ToV2().SetMarshalData(nil)
+	original.ToV2().SetMarshalData(nil)
+
+	require.Equal(t, original, reconstructed)
+}
+
+func deepCopy(t *testing.T, obj *objectSDK.Object) *objectSDK.Object {
+	data, err := obj.Marshal()
+	require.NoError(t, err)
+
+	res := objectSDK.New()
+	require.NoError(t, res.Unmarshal(data))
+	return res
+}
+
+func cloneSlice[T any](src []T) []T {
+	dst := make([]T, len(src))
+	copy(dst, src)
+	return dst
+}
+
+type dummyEpochSource uint64
+
+func (s dummyEpochSource) CurrentEpoch() uint64 {
+	return uint64(s)
+}
+
+type testTarget struct {
+	objects []*objectSDK.Object
+}
+
+func (tt *testTarget) WriteObject(_ context.Context, o *objectSDK.Object) error {
+	tt.objects = append(tt.objects, o)
+	return nil // AccessIdentifiers should not be used.
+}

object/erasurecode/split.go

@@ -0,0 +1,69 @@
+package erasurecode
+
+import (
+	"crypto/ecdsa"
+
+	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
+)
+
+// Split splits fully formed object into multiple chunks.
+func (c *Constructor) Split(obj *objectSDK.Object, key *ecdsa.PrivateKey) ([]*objectSDK.Object, error) {
+	c.clear()
+
+	header, err := obj.CutPayload().Marshal()
+	if err != nil {
+		return nil, err
+	}
+
+	headerShards, err := c.encodeRaw(header)
+	if err != nil {
+		return nil, err
+	}
+	payloadShards, err := c.encodeRaw(obj.Payload())
+	if err != nil {
+		return nil, err
+	}
+
+	parts := make([]*objectSDK.Object, len(payloadShards))
+	parent, _ := obj.ID()
+	for i := range parts {
+		chunk := objectSDK.New()
+		copyRequiredFields(chunk, obj)
+		chunk.SetPayload(payloadShards[i])
+		chunk.SetPayloadSize(uint64(len(payloadShards[i])))
+
+		ec := objectSDK.NewECHeader(parent, uint32(i), uint32(len(payloadShards)), headerShards[i], uint32(len(header)))
+		chunk.SetECHeader(ec)
+		if err := setIDWithSignature(chunk, key); err != nil {
+			return nil, err
+		}
+
+		parts[i] = chunk
+	}
+	return parts, nil
+}
+
+func setIDWithSignature(obj *objectSDK.Object, key *ecdsa.PrivateKey) error {
+	if err := objectSDK.CalculateAndSetID(obj); err != nil {
+		return err
+	}
+
+	objectSDK.CalculateAndSetPayloadChecksum(obj)
+
+	if key == nil {
+		return nil
+	}
+
+	return objectSDK.CalculateAndSetSignature(*key, obj)
+}
+
+func (c *Constructor) encodeRaw(data []byte) ([][]byte, error) {
+	shards, err := c.enc.Split(data)
+	if err != nil {
+		return nil, err
+	}
+	if err := c.enc.Encode(shards); err != nil {
+		return nil, err
+	}
+	return shards, nil
+}

object/erasurecode/split_test.go

@@ -0,0 +1,36 @@
+package erasurecode_test
+
+import (
+	"testing"
+
+	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/erasurecode"
+	"github.com/nspcc-dev/neo-go/pkg/crypto/keys"
+	"github.com/stretchr/testify/require"
+)
+
+// The library can behave differently for big shard counts.
+// This test checks we support the maximum number of chunks we promise.
+func TestSplitMaxShardCount(t *testing.T) {
+	pk, err := keys.NewPrivateKey()
+	require.NoError(t, err)
+
+	original := newObject(t, 1024, pk)
+
+	t.Run("only data", func(t *testing.T) {
+		c, err := erasurecode.NewConstructor(erasurecode.MaxShardCount, 0)
+		require.NoError(t, err)
+
+		parts, err := c.Split(original, &pk.PrivateKey)
+		require.NoError(t, err)
+		require.Len(t, parts, erasurecode.MaxShardCount)
+	})
+	t.Run("data + parity", func(t *testing.T) {
+		c, err := erasurecode.NewConstructor(1, erasurecode.MaxShardCount-1)
+		require.NoError(t, err)
+
+		parts, err := c.Split(original, &pk.PrivateKey)
+		require.NoError(t, err)
+		require.Len(t, parts, erasurecode.MaxShardCount)
+	})
+
+}

object/erasurecode/target.go

@@ -0,0 +1,44 @@
+package erasurecode
+
+import (
+	"context"
+	"crypto/ecdsa"
+
+	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
+	"git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object/transformer"
+)
+
+// Target accepts regular objects and splits them into erasure-coded chunks.
+type Target struct {
+	c    *Constructor
+	key  *ecdsa.PrivateKey
+	next transformer.ObjectWriter
+}
+
+// ObjectWriter is an interface of the object writer that writes prepared object.
+type ObjectWriter interface {
+	WriteObject(context.Context, *objectSDK.Object) error
+}
+
+// NewTarget returns new target instance.
+func NewTarget(c *Constructor, key *ecdsa.PrivateKey, next ObjectWriter) *Target {
+	return &Target{
+		c:    c,
+		key:  key,
+		next: next,
+	}
+}
+
+// WriteObject implements the transformer.ObjectWriter interface.
+func (t *Target) WriteObject(ctx context.Context, obj *objectSDK.Object) error {
+	parts, err := t.c.Split(obj, t.key)
+	if err != nil {
+		return err
+	}
+	for i := range parts {
+		if err := t.next.WriteObject(ctx, parts[i]); err != nil {
+			return err
+		}
+	}
+	return nil
+}

object/erasurecode/verify.go

@@ -0,0 +1,104 @@
+package erasurecode
+
+import (
+	"fmt"
+
+	objectSDK "git.frostfs.info/TrueCloudLab/frostfs-sdk-go/object"
+)
+
+// Verify verifies that parts are well formed.
+// All parts are expected to be non-nil.
+// The number of parts must be equal to `total` field of the EC header
+// and parts must be sorted by index.
+func (c *Constructor) Verify(parts []*objectSDK.Object) error {
+	c.clear()
+
+	var headerLength int
+	for i := range parts {
+		if parts[i] == nil {
+			return ErrMalformedSlice
+		}
+
+		var err error
+		headerLength, err = validatePart(parts, i, headerLength)
+		if err != nil {
+			return err
+		}
+	}
+
+	p0 := parts[0]
+	for i := 1; i < len(parts); i++ {
+		// This part must be kept in sync with copyRequiredFields().
+		pi := parts[i]
+		if p0.OwnerID().Equals(pi.OwnerID()) {
+			return fmt.Errorf("%w: owner id mismatch: %s != %s", ErrMalformedSlice, p0.OwnerID(), pi.OwnerID())
+		}
+		if p0.Version() == nil && pi.Version() != nil || !p0.Version().Equal(*pi.Version()) {
+			return fmt.Errorf("%w: version mismatch: %s != %s", ErrMalformedSlice, p0.Version(), pi.Version())
+		}
+
+		cnr0, _ := p0.ContainerID()
+		cnri, _ := pi.ContainerID()
+		if !cnr0.Equals(cnri) {
+			return fmt.Errorf("%w: container id mismatch: %s != %s", ErrMalformedSlice, cnr0, cnri)
+		}
+	}
+
+	if err := c.fillHeader(parts); err != nil {
+		return err
+	}
+	c.fillPayload(parts)
+
+	ok, err := c.enc.Verify(c.headerShards)
+	if err != nil {
+		return err
+	}
+	if !ok {
+		return ErrMalformedSlice
+	}
+
+	ok, err = c.enc.Verify(c.payloadShards)
+	if err != nil {
+		return err
+	}
+	if !ok {
+		return ErrMalformedSlice
+	}
+	return nil
+}
+
+// copyRequiredFields sets all fields in dst which are copied from src and shared among all chunks.
+// src can be either another chunk of full object.
+// dst must be a chunk.
+func copyRequiredFields(dst *objectSDK.Object, src *objectSDK.Object) {
+	dst.SetVersion(src.Version())
+	dst.SetOwnerID(src.OwnerID())
+	dst.SetCreationEpoch(src.CreationEpoch())
+	dst.SetSessionToken(src.SessionToken())
+
+	cnr, _ := src.ContainerID()
+	dst.SetContainerID(cnr)
+}
+
+// validatePart makes i-th part is consistent with the rest.
+// If headerLength is not zero it is asserted to be equal in the ec header.
+// Otherwise, new headerLength is returned.
+func validatePart(parts []*objectSDK.Object, i int, headerLength int) (int, error) {
+	ec := parts[i].GetECHeader()
+	if ec == nil {
+		return headerLength, fmt.Errorf("%w: missing EC header", ErrMalformedSlice)
+	}
+	if ec.Index() != uint32(i) {
+		return headerLength, fmt.Errorf("%w: index=%d, ec.index=%d", ErrMalformedSlice, i, ec.Index())
+	}
+	if ec.Total() != uint32(len(parts)) {
+		return headerLength, fmt.Errorf("%w: len(parts)=%d, total=%d", ErrMalformedSlice, len(parts), ec.Total())
+	}
+	if headerLength == 0 {
+		return int(ec.HeaderLength()), nil
+	}
+	if ec.HeaderLength() != uint32(headerLength) {
+		return headerLength, fmt.Errorf("%w: header length mismatch %d != %d", ErrMalformedSlice, headerLength, ec.HeaderLength())
+	}
+	return headerLength, nil
+}

object/object.go

@@ -366,6 +366,14 @@ func (o *Object) Children() []oid.ID {
 	return res
 }
 
+func (o *Object) GetECHeader() *ECHeader {
+	v2 := (*object.Object)(o).GetHeader().GetEC()
+
+	var ec ECHeader
+	_ = ec.ReadFromV2(v2) // Errors is checked on unmarshal.
+	return &ec
+}
+
 // SetChildren sets list of the identifiers of the child objects.
 func (o *Object) SetChildren(v ...oid.ID) {
 	var (