swarm/network/stream: generalise setting of next batch (#17818)

* swarm/network/stream: generalize SetNextBatch and add Server SessionIndex

* swarm/network/stream: fix a typo in comment

* swarm/network/stream: remove live argument from NewSwarmSyncerServer

swarm/network/stream/stream.go

@@ -375,7 +375,7 @@ func (r *Registry) Run(p *network.BzzPeer) error {
 	defer sp.close()
 
 	if r.doRetrieve {
-		err := r.Subscribe(p.ID(), NewStream(swarmChunkServerStreamName, "", false), nil, Top)
+		err := r.Subscribe(p.ID(), NewStream(swarmChunkServerStreamName, "", true), nil, Top)
 		if err != nil {
 			return err
 		}
@@ -500,10 +500,38 @@ type server struct {
 	stream       Stream
 	priority     uint8
 	currentBatch []byte
+	sessionIndex uint64
+}
+
+// setNextBatch adjusts passed interval based on session index and whether
+// stream is live or history. It calls Server SetNextBatch with adjusted
+// interval and returns batch hashes and their interval.
+func (s *server) setNextBatch(from, to uint64) ([]byte, uint64, uint64, *HandoverProof, error) {
+	if s.stream.Live {
+		if from == 0 {
+			from = s.sessionIndex
+		}
+		if to <= from || from >= s.sessionIndex {
+			to = math.MaxUint64
+		}
+	} else {
+		if (to < from && to != 0) || from > s.sessionIndex {
+			return nil, 0, 0, nil, nil
+		}
+		if to == 0 || to > s.sessionIndex {
+			to = s.sessionIndex
+		}
+	}
+	return s.SetNextBatch(from, to)
 }
 
 // Server interface for outgoing peer Streamer
 type Server interface {
+	// SessionIndex is called when a server is initialized
+	// to get the current cursor state of the stream data.
+	// Based on this index, live and history stream intervals
+	// will be adjusted before calling SetNextBatch.
+	SessionIndex() (uint64, error)
 	SetNextBatch(uint64, uint64) (hashes []byte, from uint64, to uint64, proof *HandoverProof, err error)
 	GetData(context.Context, []byte) ([]byte, error)
 	Close()