[#83] services/util: Implement response service

Create response package. Implement response Service that sets values of
response meta header.

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

pkg/services/util/response/server_stream.go

@@ -0,0 +1,42 @@
+package response
+
+import (
+	"context"
+
+	"github.com/nspcc-dev/neofs-node/pkg/services/util"
+	"github.com/pkg/errors"
+)
+
+// ServerMessageStreamer represents server-side message streamer
+// that sets meta values to all response messages.
+type ServerMessageStreamer struct {
+	cfg *cfg
+
+	recv util.ResponseMessageReader
+}
+
+// Recv calls Recv method of internal streamer, sets response meta
+// values and returns the response.
+func (s *ServerMessageStreamer) Recv() (util.ResponseMessage, error) {
+	m, err := s.recv()
+	if err != nil {
+		return nil, errors.Wrap(err, "could not receive response message for signing")
+	}
+
+	setMeta(m, s.cfg)
+
+	return m, nil
+}
+
+// HandleServerStreamRequest builds internal streamer via handlers, wraps it to ServerMessageStreamer and returns the result.
+func (s *Service) HandleServerStreamRequest(ctx context.Context, req interface{}, handler util.ServerStreamHandler) (*ServerMessageStreamer, error) {
+	msgRdr, err := handler(ctx, req)
+	if err != nil {
+		return nil, errors.Wrap(err, "could not create message reader")
+	}
+
+	return &ServerMessageStreamer{
+		cfg:  s.cfg,
+		recv: msgRdr,
+	}, nil
+}