packet-manager: sort incoming request ID queue

Incoming queue is not guaranteed to contain request IDs in ascending
order. Such state may be achieved by using a single sftp.Client
connection from multiple goroutines. Sort incoming queue to avoid
livelock due to different request/response order, like this:

2017/03/27 18:29:07 incoming: [55 56 54 57 58]
2017/03/27 18:29:07 outgoing: [54 55 56 57 58]

For single-threaded clients request/response order will remain intact
and nothing should break.

Signed-off-by: Pavel Borzenkov <pavel.borzenkov@gmail.com>

packet-manager.go

@@ -14,7 +14,7 @@ type packetManager struct {
 	requests  chan requestPacket
 	responses chan responsePacket
 	fini      chan struct{}
-	incoming  []uint32
+	incoming  requestPacketIDs
 	outgoing  responsePackets
 	sender    packetSender // connection object
 }
@@ -55,6 +55,9 @@ func (s *packetManager) worker() {
 		case pkt := <-s.requests:
 			debug("incoming id: %v", pkt.id())
 			s.incoming = append(s.incoming, pkt.id())
+			if len(s.incoming) > 1 {
+				s.incoming.Sort()
+			}
 		case pkt := <-s.responses:
 			debug("outgoing pkt: %v", pkt.id())
 			s.outgoing = append(s.outgoing, pkt)

packet-manager_go1.8.go

@@ -11,3 +11,11 @@ func (r responsePackets) Sort() {
 		return r[i].id() < r[j].id()
 	})
 }
+
+type requestPacketIDs []uint32
+
+func (r requestPacketIDs) Sort() {
+	sort.Slice(r, func(i, j int) bool {
+		return r[i] < r[j]
+	})
+}

packet-manager_legacy.go

@@ -4,10 +4,18 @@ package sftp
 
 import "sort"
 
-// for sorting/ordering incoming/outgoing
+// for sorting/ordering outgoing
 type responsePackets []responsePacket
 
 func (r responsePackets) Len() int           { return len(r) }
 func (r responsePackets) Swap(i, j int)      { r[i], r[j] = r[j], r[i] }
 func (r responsePackets) Less(i, j int) bool { return r[i].id() < r[j].id() }
 func (r responsePackets) Sort()              { sort.Sort(r) }
+
+// for sorting/ordering incoming
+type requestPacketIDs []uint32
+
+func (r requestPacketIDs) Len() int           { return len(r) }
+func (r requestPacketIDs) Swap(i, j int)      { r[i], r[j] = r[j], r[i] }
+func (r requestPacketIDs) Less(i, j int) bool { return r[i] < r[j] }
+func (r requestPacketIDs) Sort()              { sort.Sort(r) }