[#52] services/object: Implement Get service

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

pkg/services/object/get/streamer.go

@@ -0,0 +1,26 @@
+package getsvc
+
+import (
+	rangesvc "github.com/nspcc-dev/neofs-node/pkg/services/object/range"
+	"github.com/pkg/errors"
+)
+
+type Streamer struct {
+	headSent bool
+
+	rngRes *rangesvc.Result
+}
+
+func (p *Streamer) Recv() (interface{}, error) {
+	if !p.headSent {
+		p.headSent = true
+		return p.rngRes.Head(), nil
+	}
+
+	rngResp, err := p.rngRes.Stream().Recv()
+	if err != nil {
+		return nil, errors.Wrapf(err, "(%T) could not receive range response", p)
+	}
+
+	return rngResp.PayloadChunk(), nil
+}