sn/object: allow split of a split

CHANGELOG.md

@@ -19,6 +19,7 @@ Changelog for NeoFS Node
 - Shard evacuation replicate for EC parts (#3854)
 - Suboptimal shard selection for EC parts during data evacuation (#3870)
 - No redistribution of objects when adding a new `REP 3` node (#3873)
+- Split of a split is allowed (#3867)
 
 ### Changed
 - SN returns unsigned responses to requests with API >= `v2.22` (#3785)

pkg/core/object/fmt.go

@@ -142,10 +142,12 @@ func NewFormatValidator(fsChain FSChain, netmapContract NetmapContract, containe
 //
 // Returns nil error if the object has valid structure.
 func (v *FormatValidator) Validate(obj *object.Object, unprepared bool) error {
-	return v.validate(obj, unprepared, false)
+	return v.validate(obj, unprepared, 0)
 }
 
-func (v *FormatValidator) validate(obj *object.Object, unprepared, isParent bool) error {
+const maxObjectNestingLevel = 2
+
+func (v *FormatValidator) validate(obj *object.Object, unprepared bool, nestingLevel int) error {
 	if obj == nil {
 		return errNilObject
 	}
@@ -194,7 +196,7 @@ func (v *FormatValidator) validate(obj *object.Object, unprepared, isParent bool
 		return fmt.Errorf("read container by ID=%s: %w", cnrID, err)
 	}
 
-	isEC, err := checkEC(*obj, cnr.PlacementPolicy().ECRules(), unprepared, isParent)
+	isEC, err := checkEC(*obj, cnr.PlacementPolicy().ECRules(), unprepared, nestingLevel > 0)
 	if err != nil {
 		return err
 	}
@@ -208,10 +210,6 @@ func (v *FormatValidator) validate(obj *object.Object, unprepared, isParent bool
 	par := obj.Parent()
 
 	if !isEC && obj.HasParent() {
-		if par != nil && par.HasParent() {
-			return errors.New("parent object has a parent itself")
-		}
-
 		if splitID != nil {
 			// V1 split
 			if firstSet {
@@ -257,9 +255,14 @@ func (v *FormatValidator) validate(obj *object.Object, unprepared, isParent bool
 		}
 	}
 
-	if par != nil && (firstSet || splitID != nil || isEC) {
-		// Parent object already exists.
-		return v.validate(par, false, true)
+	if par != nil {
+		if nestingLevel == maxObjectNestingLevel {
+			return fmt.Errorf("max object nesting level %d overflow", maxObjectNestingLevel)
+		}
+
+		// it is possible to have a split of a split
+		prepared := firstSet || splitID != nil || isEC
+		return v.validate(par, !prepared, nestingLevel+1)
 	}
 
 	return nil

pkg/core/object/fmt_test.go

@@ -18,6 +18,7 @@ import (
 	"github.com/nspcc-dev/neofs-sdk-go/object"
 	oid "github.com/nspcc-dev/neofs-sdk-go/object/id"
 	oidtest "github.com/nspcc-dev/neofs-sdk-go/object/id/test"
+	objecttest "github.com/nspcc-dev/neofs-sdk-go/object/test"
 	"github.com/nspcc-dev/neofs-sdk-go/session"
 	sessiontest "github.com/nspcc-dev/neofs-sdk-go/session/test"
 	"github.com/nspcc-dev/neofs-sdk-go/user"
@@ -406,6 +407,27 @@ func TestFormatValidator_Validate(t *testing.T) {
 			})
 		})
 	})
+
+	t.Run("split", func(t *testing.T) {
+		t.Run("nesting limit exceeded", func(t *testing.T) {
+			chain := getParentChain(t, maxObjectNestingLevel+2) // one exceeds and one is a child
+			child := chain[len(chain)-1]
+
+			registerContainer(child.GetContainerID())
+
+			require.EqualError(t, v.Validate(&child, true), "max object nesting level 2 overflow")
+		})
+
+		t.Run("nesting is ok", func(t *testing.T) {
+			chain := getParentChain(t, maxObjectNestingLevel+1) // one exceeds and one is a child
+			child := chain[len(chain)-1]
+
+			registerContainer(child.GetContainerID())
+
+			require.NoError(t, v.Validate(&child, true))
+		})
+	})
+
 	for _, tc := range []struct {
 		scheme neofscrypto.Scheme
 		object object.Object
@@ -420,6 +442,44 @@ func TestFormatValidator_Validate(t *testing.T) {
 	}
 }
 
+func getParentChain(t *testing.T, nesting int) []object.Object {
+	var (
+		signer   neofscrypto.Signer
+		parChain []object.Object
+		cID      = cidtest.ID()
+	)
+	pk, err := keys.NewPrivateKey()
+	require.NoError(t, err)
+	signer = neofsecdsa.SignerRFC6979(pk.PrivateKey)
+	owner := user.NewFromECDSAPublicKey(pk.PrivateKey.PublicKey)
+
+	for i := range nesting {
+		o := objecttest.Object()
+
+		o.SetOwner(owner)
+		o.SetSessionToken(nil)
+		o.SetContainerID(cID)
+		o.ResetRelations()
+		o.SetType(object.TypeRegular)
+		if i != 0 {
+			o.SetParent(&parChain[i-1])
+		}
+		err = o.SetIDWithSignature(signer)
+		require.NoError(t, err)
+
+		err := o.CalculateAndSetID()
+		require.NoError(t, err)
+
+		parChain = append(parChain, o)
+	}
+
+	child := &parChain[len(parChain)-1]
+	child.SetFirstID(oidtest.ID())
+	child.SetPreviousID(oidtest.ID())
+
+	return parChain
+}
+
 type testSplitVerifier struct {
 }
 

pkg/services/object/split/verify.go

@@ -149,7 +149,6 @@ func (v *Verifier) verifySinglePart(ctx context.Context, cnr cid.ID, firstID *oi
 	var prm getsvc.HeadPrm
 	prm.SetHeaderWriter(&hw)
 	prm.WithAddress(childAddr)
-	prm.WithRawFlag(true)
 
 	err := v.get.Head(ctx, prm)
 	if err != nil {