Do not require CLIENT LIST in cluster topology refresh #973

Topology refresh now no longer requires a successful completion of CLIENT LIST during the refresh. Errors can happen if the command is disabled.

Previously, an entire cluster node was disabled if the client list could not be retrieved and so the node was not considered in the routing table. Ignoring failed CLIENT LIST commands disables default connection load balancing that helped previously to use the cluster node with the least number of connections.

src/main/java/io/lettuce/core/cluster/topology/NodeTopologyView.java

@@ -56,7 +56,7 @@ class NodeTopologyView {
         this.redisURI = redisURI;
 
         this.partitions = ClusterPartitionParser.parse(clusterNodes);
-        this.connectedClients = getClients(clientList);
+        this.connectedClients = clientList != null ? getClients(clientList) : 0;
         this.clusterNodes = clusterNodes;
         this.clientList = clientList;
         this.latency = latency;
@@ -69,11 +69,19 @@ static NodeTopologyView from(RedisURI redisURI, Requests clusterNodesRequests, R
         TimedAsyncCommand<String, String, String> clients = clientListRequests.getRequest(redisURI);
 
         if (resultAvailable(nodes) && resultAvailable(clients)) {
-            return new NodeTopologyView(redisURI, nodes.get(), clients.get(), nodes.duration());
+            return new NodeTopologyView(redisURI, nodes.get(), optionallyGet(clients), nodes.duration());
         }
         return new NodeTopologyView(redisURI);
     }
 
+    private static <T> T optionallyGet(TimedAsyncCommand<?, ?, T> command) throws ExecutionException, InterruptedException {
+
+        if (command.isCompletedExceptionally()) {
+            return null;
+        }
+        return command.get();
+    }
+
     static boolean resultAvailable(RedisFuture<?> redisFuture) {
 
         if (redisFuture != null && redisFuture.isDone() && !redisFuture.isCancelled()) {