[#1318] service: Add tombstone checker service

The service fetches tombstones from the network via object service, every
request is handled in the following order:
1. checks local LRU cache;
2. checks local storage engine;
3. tries to find object in the placement nodes.

Signed-off-by: Pavel Karpy <carpawell@nspcc.ru>

pkg/services/object_manager/tombstone/source/source.go

@@ -0,0 +1,84 @@
+package tsourse
+
+import (
+	"context"
+	"errors"
+	"fmt"
+
+	getsvc "github.com/nspcc-dev/neofs-node/pkg/services/object/get"
+	"github.com/nspcc-dev/neofs-node/pkg/services/object/util"
+	apistatus "github.com/nspcc-dev/neofs-sdk-go/client/status"
+	"github.com/nspcc-dev/neofs-sdk-go/object"
+	objectSDK "github.com/nspcc-dev/neofs-sdk-go/object"
+	addressSDK "github.com/nspcc-dev/neofs-sdk-go/object/address"
+)
+
+// Source represents wrapper over the object service that
+// allows checking if a tombstone is available in NeoFS
+// network.
+//
+// Must be created via NewSource function. `var` and `Source{}`
+// declarations leads to undefined behaviour and may lead
+// to panics.
+type Source struct {
+	s *getsvc.Service
+}
+
+// TombstoneSourcePrm groups required parameters for Source creation.
+type TombstoneSourcePrm struct {
+	s *getsvc.Service
+}
+
+// SetGetService sets object service.
+func (s *TombstoneSourcePrm) SetGetService(v *getsvc.Service) {
+	s.s = v
+}
+
+// NewSource creates, initialize and returns local tombstone Source.
+// The returned structure is ready to use.
+//
+// Panics if any of the provided options does not allow
+// constructing a valid tombstone local Source.
+func NewSource(p TombstoneSourcePrm) Source {
+	if p.s == nil {
+		panic("Tombstone source: nil object service")
+	}
+
+	return Source{s: p.s}
+}
+
+type headerWriter struct {
+	o *objectSDK.Object
+}
+
+func (h *headerWriter) WriteHeader(o *objectSDK.Object) error {
+	h.o = o
+	return nil
+}
+
+// Tombstone checks if the engine stores tombstone.
+// Returns nil, nil if the tombstone has been removed
+// or marked for removal.
+func (s Source) Tombstone(ctx context.Context, a *addressSDK.Address, _ uint64) (*object.Object, error) {
+	var hr headerWriter
+
+	var headPrm getsvc.HeadPrm
+	headPrm.WithAddress(a)
+	headPrm.SetHeaderWriter(&hr)
+	headPrm.SetCommonParameters(&util.CommonPrm{}) //default values are ok for that operation
+
+	err := s.s.Head(ctx, headPrm)
+	switch {
+	case errors.As(err, new(apistatus.ObjectNotFound)) || errors.As(err, new(apistatus.ObjectAlreadyRemoved)):
+		return nil, nil
+	case err != nil:
+		return nil, fmt.Errorf("could not get tombstone from the source: %w", err)
+	default:
+	}
+
+	if hr.o.Type() != objectSDK.TypeTombstone {
+		return nil, fmt.Errorf("returned %s object is not a tombstone", a)
+	}
+
+	return hr.o, nil
+}