fix data race in ownership of RPC when piggybacking control messages.

comm.go

@@ -122,3 +122,19 @@ func rpcWithControl(msgs []*pb.Message,
 		},
 	}
 }
+
+func copyRPC(rpc *RPC) *RPC {
+	return &RPC{
+		RPC: pb.RPC{
+			Subscriptions: rpc.Subscriptions,
+			Publish:       rpc.Publish,
+			Control: &pb.ControlMessage{
+				Ihave: rpc.Control.Ihave,
+				Iwant: rpc.Control.Iwant,
+				Graft: rpc.Control.Graft,
+				Prune: rpc.Control.Prune,
+			},
+		},
+		from: rpc.from,
+	}
+}

gossipsub.go

@@ -308,9 +308,14 @@ func (gs *GossipSubRouter) sendPrune(p peer.ID, topic string) {
 }
 
 func (gs *GossipSubRouter) sendRPC(p peer.ID, out *RPC) {
+	// do we own the RPC?
+	own := false
+
 	// piggyback cotrol message retries
 	ctl, ok := gs.control[p]
 	if ok {
+		out = copyRPC(out)
+		own = true
 		gs.piggybackControl(p, out, ctl)
 		delete(gs.control, p)
 	}
@@ -318,6 +323,10 @@ func (gs *GossipSubRouter) sendRPC(p peer.ID, out *RPC) {
 	// piggyback gossip
 	ihave, ok := gs.gossip[p]
 	if ok {
+		if !own {
+			out = copyRPC(out)
+			own = true
+		}
 		gs.piggybackGossip(p, out, ihave)
 		delete(gs.gossip, p)
 	}