sn: return first found EC part when part index is missing

pkg/local_object_storage/metabase/ec.go

@@ -167,6 +167,10 @@ func (db *DB) resolveECPartInMetaBucket(crs *bbolt.Cursor, parent oid.ID, pi iec
 				return oid.ID{}, object.NewSplitInfoError(sizeSplitInfo)
 			}
 
+			if pi.Index == -1 {
+				return id, nil
+			}
+
 			if (sizeSplitInfo == nil || sizeSplitInfo.GetLastPart().IsZero()) && getObjAttribute(partCrs, id, object.FilterFirstSplitObject) != nil {
 				if sizeSplitInfo == nil {
 					sizeSplitInfo = new(object.SplitInfo)

pkg/services/object/get/ec.go

@@ -21,6 +21,7 @@ import (
 	"github.com/nspcc-dev/neofs-node/pkg/services/object/internal"
 	apistatus "github.com/nspcc-dev/neofs-sdk-go/client/status"
 	"github.com/nspcc-dev/neofs-sdk-go/container"
+	"github.com/nspcc-dev/neofs-sdk-go/container/acl"
 	cid "github.com/nspcc-dev/neofs-sdk-go/container/id"
 	"github.com/nspcc-dev/neofs-sdk-go/netmap"
 	"github.com/nspcc-dev/neofs-sdk-go/object"
@@ -1653,46 +1654,72 @@ func checkECPartInfoRequest(xHdrs []string, cnr container.Container) (iec.PartIn
 		}
 	}
 
-	if ruleIdxStr == "" && partIdxStr == "" {
+	if ruleIdxStr == "" {
+		if partIdxStr != "" {
+			return res, fmt.Errorf("%s X-header must be set in a correct EC part GET request (%s X-header found: %s)",
+				iec.AttributeRuleIdx, iec.AttributePartIdx, partIdxStr)
+		}
+
 		res.RuleIndex = -1
 		return res, nil
 	}
 
-	if (ruleIdxStr == "") != (partIdxStr == "") {
-		return res, fmt.Errorf("%s and %s X-headers must be set together", iec.AttributeRuleIdx, iec.AttributePartIdx)
-	}
+	var (
+		bACL    = cnr.BasicACL()
+		ecRules = cnr.PlacementPolicy().ECRules()
+	)
 
 	// TODO: state limits in https://github.com/nspcc-dev/neofs-api. Share consts for them.
 	ruleIdx, err := strconv.ParseUint(ruleIdxStr, 10, 8)
 	if err != nil {
 		return res, fmt.Errorf("invalid %s X-header: %w", iec.AttributeRuleIdx, err)
 	}
+	res.RuleIndex = int(ruleIdx)
+	err = checkECRuleIdx(bACL, ecRules, res.RuleIndex)
+	if err != nil {
+		return res, err
+	}
+
+	if partIdxStr == "" {
+		res.Index = -1
+		return res, nil
+	}
 
 	partIdx, err := strconv.ParseUint(partIdxStr, 10, 8)
 	if err != nil {
 		return res, fmt.Errorf("invalid %s X-header: %w", iec.AttributePartIdx, err)
 	}
+	res.Index = int(partIdx)
 
-	if cnr.BasicACL() != 0 { // Uninitialized in tests, safe to do anyway, invalid requests will fail.
-		var ecRules = cnr.PlacementPolicy().ECRules()
+	err = checkECPartIdx(bACL, ecRules, res.RuleIndex, res.Index)
+	if err != nil {
+		return res, err
+	}
 
+	return res, nil
+}
+
+func checkECRuleIdx(bACL acl.Basic, ecRules []netmap.ECRule, ruleIdx int) error {
+	if bACL != 0 { // Uninitialized in tests, safe to do anyway, invalid requests will fail.
 		if len(ecRules) == 0 {
-			return res, errors.New("EC part requested in container without EC policy")
+			return errors.New("EC part requested in container without EC policy")
 		}
-
-		if int(ruleIdx) >= len(ecRules) {
-			return res, fmt.Errorf("EC rule index overflows container policy: idx=%d,rules=%d", ruleIdx, len(ecRules))
+		if ruleIdx >= len(ecRules) {
+			return fmt.Errorf("EC rule index overflows container policy: idx=%d,rules=%d", ruleIdx, len(ecRules))
 		}
+	}
+
+	return nil
+}
 
-		if total := ecRules[ruleIdx].DataPartNum() + ecRules[ruleIdx].ParityPartNum(); int(partIdx) >= int(total) {
-			return res, fmt.Errorf("EC part index overflows container policy: idx=%d,parts=%d", partIdx, total)
+func checkECPartIdx(bACL acl.Basic, ecRules []netmap.ECRule, ruleIdx, partIdx int) error {
+	if bACL != 0 { // Uninitialized in tests, safe to do anyway, invalid requests will fail.
+		if total := ecRules[ruleIdx].DataPartNum() + ecRules[ruleIdx].ParityPartNum(); partIdx >= int(total) {
+			return fmt.Errorf("EC part index overflows container policy: idx=%d,parts=%d", partIdx, total)
 		}
 	}
 
-	res.RuleIndex = int(ruleIdx)
-	res.Index = int(partIdx)
-
-	return res, nil
+	return nil
 }
 
 func checkECAttributesInReceivedObject(hdr object.Object, ruleIdx, partIdx string) error {