correct handling of pings and pongs

server:
- always has read & write timeouts
- ping handler never blocks the reader (see A)
- sends regular pings to check up on a client

A:
at some point server write buffer can become full, so in order not to
block reads from a client (see
https://github.com/gorilla/websocket/issues/97), server may skip some
pongs. As a result, client may disconnect. But you either have to do
that or block the reader. There is no third way.

client:
- optional read & write timeouts
- optional ping/pong to measure latency

node/node.go

@@ -330,9 +330,9 @@ func (n *Node) startRPC() ([]net.Listener, error) {
 	listeners := make([]net.Listener, len(listenAddrs))
 	for i, listenAddr := range listenAddrs {
 		mux := http.NewServeMux()
-		wm := rpcserver.NewWebsocketManager(rpccore.Routes, n.evsw)
 		rpcLogger := n.Logger.With("module", "rpc-server")
-		wm.SetLogger(rpcLogger)
+		wm := rpcserver.NewWebsocketManager(rpccore.Routes, n.evsw)
+		wm.SetLogger(rpcLogger.With("protocol", "websocket"))
 		mux.HandleFunc("/websocket", wm.WebsocketHandler)
 		rpcserver.RegisterRPCFuncs(mux, rpccore.Routes, rpcLogger)
 		listener, err := rpcserver.StartHTTPServer(listenAddr, mux, rpcLogger)