Add NeoFS helper to fetch object by refs.Address

Signed-off-by: Evgeniy Kulikov <kim@nspcc.ru>

neofs/layer/layer.go

@@ -5,10 +5,12 @@ import (
 	"crypto/ecdsa"
 	"io"
 	"strings"
+	"time"
 
 	"github.com/minio/minio/neofs/pool"
 	"github.com/nspcc-dev/neofs-api-go/object"
 	"github.com/nspcc-dev/neofs-api-go/refs"
+	"github.com/nspcc-dev/neofs-api-go/service"
 	"github.com/pkg/errors"
 	"go.uber.org/zap"
 )
@@ -44,7 +46,13 @@ type (
 		DstObject string
 	}
 
+	NeoFS interface {
+		Get(ctx context.Context, address refs.Address) (*object.Object, error)
+	}
+
 	Client interface {
+		NeoFS
+
 		ListBuckets(ctx context.Context) ([]BucketInfo, error)
 		GetBucketInfo(ctx context.Context, name string) (*BucketInfo, error)
 
@@ -80,6 +88,80 @@ func NewLayer(log *zap.Logger, cli pool.Client, key *ecdsa.PrivateKey) (Client,
 	}, nil
 }
 
+// Get NeoFS Object by refs.Address (should be used by auth.Center)
+func (n *layer) Get(ctx context.Context, address refs.Address) (*object.Object, error) {
+	conn, err := n.cli.GetConnection(ctx)
+	if err != nil {
+		return nil, err
+	}
+
+	token, err := n.cli.SessionToken(ctx, &pool.SessionParams{
+		Conn: conn,
+		Addr: address,
+		Verb: service.Token_Info_Get,
+	})
+
+	if err != nil {
+		return nil, err
+	}
+
+	req := new(object.GetRequest)
+	req.Address = address
+	req.SetTTL(service.SingleForwardingTTL)
+	req.SetToken(token)
+
+	err = service.SignRequestData(n.key, req)
+	if err != nil {
+		return nil, err
+	}
+
+	// todo: think about timeout
+	ctx, cancel := context.WithTimeout(ctx, 30*time.Second)
+	defer cancel()
+
+	cli, err := object.NewServiceClient(conn).Get(ctx, req)
+	if err != nil {
+		return nil, err
+	}
+
+	var (
+		off int
+		obj *object.Object
+	)
+
+	for {
+		resp, err := cli.Recv()
+		if err != nil {
+			if err == io.EOF {
+				break
+			}
+
+			return nil, err
+		}
+
+		switch o := resp.R.(type) {
+		case *object.GetResponse_Object:
+			obj = o.Object
+
+			_, hdr := obj.LastHeader(object.HeaderType(object.TombstoneHdr))
+			if hdr != nil {
+				return nil, errors.New("object already removed")
+			}
+
+			obj.Payload = make([]byte, obj.SystemHeader.PayloadLength)
+		case *object.GetResponse_Chunk:
+			if obj == nil {
+				return nil, errors.New("object headers not received")
+			}
+			off += copy(obj.Payload[off:], o.Chunk)
+		default:
+			return nil, errors.Errorf("unknown response %T", o)
+		}
+	}
+
+	return obj, nil
+}
+
 // GetBucketInfo returns bucket name.
 func (n *layer) GetBucketInfo(ctx context.Context, name string) (*BucketInfo, error) {
 	list, err := n.containerList(ctx)