Improve btcd connection management.

This change slightly improves the goroutines managing sends and
receives for a btcd connection by improving the logging (logging the
exact errors that caused the connection to be lost) as well as
cleaning up the shutdown handling by closing the websocket connection
for any fail and closing the response channel when no more responses
can be read.

rpcclient.go

@@ -158,13 +158,20 @@ func (btcd *BtcdRPCConn) Start() {
 
 				if err := btcd.send(rpcrequest); err != nil {
 					// Connection lost.
+					log.Infof("Cannot complete btcd websocket send: %v",
+						err)
 					btcd.ws.Close()
 					close(done)
 				}
 
 				addrequest.ResponseChan <- rpcrequest.response
 
-			case recvResponse := <-responses:
+			case recvResponse, ok := <-responses:
+				if !ok {
+					responses = nil
+					close(done)
+					break
+				}
 				rpcrequest, ok := m[recvResponse.id]
 				if !ok {
 					log.Warnf("Received unexpected btcd response")
@@ -197,10 +204,10 @@ func (btcd *BtcdRPCConn) Start() {
 				rpcrequest.response <- response
 
 			case <-done:
+				response := &ServerResponse{
+					err: &ErrBtcdDisconnected,
+				}
 				for _, request := range m {
-					response := &ServerResponse{
-						err: &ErrBtcdDisconnected,
-					}
 					request.response <- response
 				}
 				return
@@ -218,8 +225,10 @@ func (btcd *BtcdRPCConn) Start() {
 		for {
 			var m string
 			if err := websocket.Message.Receive(btcd.ws, &m); err != nil {
-				log.Debugf("Cannot receive btcd message: %v", err)
+				log.Infof("Cannot receive btcd websocket message: %v",
-				close(done)
+					err)
+				btcd.ws.Close()
+				close(responses)
 				return
 			}