Added checking for closed connections in websocket handler helpers

Since the websocket handlers run in their own separate goroutines, it's
possible that they execute after the websocket connection has been
closed and cleaned up.  This commit add the necessary checks to ensure
stale data isn't added to notification lists and that requests to closed
connections are ignored.

This closes #92.

rpcwebsocket.go

@@ -80,7 +80,10 @@ func (r *wsContext) AddBlockUpdateRequest(n ntfnChan) {
 	r.Lock()
 	defer r.Unlock()
 
-	rc := r.connections[n]
+	rc, ok := r.connections[n]
+	if !ok {
+		return
+	}
 	rc.blockUpdates = true
 }
 
@@ -90,7 +93,10 @@ func (r *wsContext) AddAllNewTxRequest(n ntfnChan, verbose bool) {
 	r.Lock()
 	defer r.Unlock()
 
-	rc := r.connections[n]
+	rc, ok := r.connections[n]
+	if !ok {
+		return
+	}
 	rc.allTxUpdates = true
 	rc.verboseTxUpdates = verbose
 }
@@ -100,6 +106,12 @@ func (r *wsContext) AddTxRequest(n ntfnChan, addr string) {
 	r.Lock()
 	defer r.Unlock()
 
+	rc, ok := r.connections[n]
+	if !ok {
+		return
+	}
+	rc.txRequests[addr] = struct{}{}
+
 	clist, ok := r.txNotifications[addr]
 	if !ok {
 		clist = list.New()
@@ -107,9 +119,6 @@ func (r *wsContext) AddTxRequest(n ntfnChan, addr string) {
 	}
 
 	clist.PushBack(n)
-
-	rc := r.connections[n]
-	rc.txRequests[addr] = struct{}{}
 }
 
 func (r *wsContext) removeGlobalTxRequest(n ntfnChan, addr string) {
@@ -135,15 +144,18 @@ func (r *wsContext) AddSpentRequest(n ntfnChan, op *btcwire.OutPoint) {
 	r.Lock()
 	defer r.Unlock()
 
+	rc, ok := r.connections[n]
+	if !ok {
+		return
+	}
+	rc.spentRequests[*op] = struct{}{}
+
 	clist, ok := r.spentNotifications[*op]
 	if !ok {
 		clist = list.New()
 		r.spentNotifications[*op] = clist
 	}
 	clist.PushBack(n)
-
-	rc := r.connections[n]
-	rc.spentRequests[*op] = struct{}{}
 }
 
 func (r *wsContext) removeGlobalSpentRequest(n ntfnChan, op *btcwire.OutPoint) {
@@ -170,7 +182,10 @@ func (r *wsContext) RemoveSpentRequest(n ntfnChan, op *btcwire.OutPoint) {
 	defer r.Unlock()
 
 	r.removeGlobalSpentRequest(n, op)
-	rc := r.connections[n]
+	rc, ok := r.connections[n]
+	if !ok {
+		return
+	}
 	delete(rc.spentRequests, *op)
 }
 
@@ -180,15 +195,18 @@ func (r *wsContext) AddMinedTxRequest(n ntfnChan, txID *btcwire.ShaHash) {
 	r.Lock()
 	defer r.Unlock()
 
+	rc, ok := r.connections[n]
+	if !ok {
+		return
+	}
+	rc.minedTxRequests[*txID] = struct{}{}
+
 	clist, ok := r.minedTxNotifications[*txID]
 	if !ok {
 		clist = list.New()
 		r.minedTxNotifications[*txID] = clist
 	}
 	clist.PushBack(n)
-
-	rc := r.connections[n]
-	rc.minedTxRequests[*txID] = struct{}{}
 }
 
 func (r *wsContext) removeGlobalMinedTxRequest(n ntfnChan, txID *btcwire.ShaHash) {
@@ -221,7 +239,10 @@ func (r *wsContext) RemoveMinedTxRequest(n ntfnChan, txID *btcwire.ShaHash) {
 // mined transaction without grabbing any locks.
 func (r *wsContext) removeMinedTxRequest(n ntfnChan, txID *btcwire.ShaHash) {
 	r.removeGlobalMinedTxRequest(n, txID)
-	rc := r.connections[n]
+	rc, ok := r.connections[n]
+	if !ok {
+		return
+	}
 	delete(rc.minedTxRequests, *txID)
 }
 
@@ -780,6 +801,10 @@ func (s *rpcServer) websocketJSONHandler(r chan *btcjson.Reply, c handlerChans,
 		// connection is not already authenticated.
 		s.ws.Lock()
 		rc := s.ws.connections[c.n]
+		// Note: c.n is guaranteed to be in the s.ws.connections map since it is
+		// called from the main walletReqNotifications for loop.  Any calls
+		// from that goroutine will always have valid connections since they
+		// are not removed till after that exits.
 		if _, ok := cmd.(*btcws.AuthenticateCmd); ok {
 			// Validate the provided credentials.
 			err := websocketAuthenticate(cmd, rc, s.authsha[:])