[#53] services/object: Implement GetRangeHash service

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

pkg/services/object/rangehash/util.go

@@ -0,0 +1,71 @@
+package rangehashsvc
+
+import (
+	"context"
+	"hash"
+	"sync"
+
+	"github.com/nspcc-dev/neofs-node/pkg/services/object_manager/placement"
+	"github.com/nspcc-dev/tzhash/tz"
+)
+
+type onceHashWriter struct {
+	once *sync.Once
+
+	traverser *placement.Traverser
+
+	resp *Response
+
+	cancel context.CancelFunc
+}
+
+type hasher interface {
+	add([]byte)
+	sum() ([]byte, error)
+}
+
+type tzHasher struct {
+	hashes [][]byte
+}
+
+type commonHasher struct {
+	h hash.Hash
+}
+
+type singleHasher struct {
+	hash []byte
+}
+
+func (h *singleHasher) add(p []byte) {
+	h.hash = p
+}
+
+func (h *singleHasher) sum() ([]byte, error) {
+	return h.hash, nil
+}
+
+func (w *onceHashWriter) write(hs [][]byte) {
+	w.once.Do(func() {
+		w.resp.hashes = hs
+		w.traverser.SubmitSuccess()
+		w.cancel()
+	})
+}
+
+func (h *tzHasher) add(p []byte) {
+	h.hashes = append(h.hashes, p)
+
+	return
+}
+
+func (h *tzHasher) sum() ([]byte, error) {
+	return tz.Concat(h.hashes)
+}
+
+func (h *commonHasher) add(p []byte) {
+	h.h.Write(p)
+}
+
+func (h *commonHasher) sum() ([]byte, error) {
+	return h.h.Sum(nil), nil
+}