[#39] service/object: Implement right child searcher on Search service

Signed-off-by: Leonard Lyubich <leonard@nspcc.ru>

pkg/services/object/search/service.go

@@ -3,6 +3,7 @@ package searchsvc
 import (
 	"context"
 	"crypto/ecdsa"
+	"io"
 	"sync"
 
 	"github.com/nspcc-dev/neofs-api-go/pkg/object"
@@ -10,7 +11,9 @@ import (
 	"github.com/nspcc-dev/neofs-node/pkg/core/netmap"
 	"github.com/nspcc-dev/neofs-node/pkg/local_object_storage/localstore"
 	"github.com/nspcc-dev/neofs-node/pkg/network"
+	"github.com/nspcc-dev/neofs-node/pkg/services/object/search/query/v1"
 	"github.com/nspcc-dev/neofs-node/pkg/util"
+	"github.com/pkg/errors"
 )
 
 type Service struct {
@@ -61,6 +64,46 @@ func (p *Service) Search(ctx context.Context, prm *Prm) (*Streamer, error) {
 	}, nil
 }
 
+func (p *Service) SearchRightChild(ctx context.Context, addr *object.Address) (*object.ID, error) {
+	streamer, err := p.Search(ctx, new(Prm).
+		WithContainerID(addr.GetContainerID()).
+		WithSearchQuery(
+			query.NewRightChildQuery(addr.GetObjectID()),
+		),
+	)
+	if err != nil {
+		return nil, errors.Wrapf(err, "(%T) could not create search streamer", p)
+	}
+
+	res, err := readFullStream(streamer, 1)
+	if err != nil {
+		return nil, errors.Wrapf(err, "(%T) could not read full search stream", p)
+	} else if ln := len(res); ln != 1 {
+		return nil, errors.Errorf("(%T) unexpected amount of found objects %d", p, ln)
+	}
+
+	return res[0], nil
+}
+
+func readFullStream(s *Streamer, cap int) ([]*object.ID, error) {
+	res := make([]*object.ID, 0, cap)
+
+	for {
+		r, err := s.Recv()
+		if err != nil {
+			if errors.Is(errors.Cause(err), io.EOF) {
+				break
+			}
+
+			return nil, errors.Wrapf(err, "(%s) could not receive search result", "readFullStream")
+		}
+
+		res = append(res, r.IDList()...)
+	}
+
+	return res, nil
+}
+
 func WithKey(v *ecdsa.PrivateKey) Option {
 	return func(c *cfg) {
 		c.key = v