Delete unneeded nio client (elastic#27408)

This is a follow up to elastic#27132. As that PR greatly simplified the
connection logic inside a low level transport implementation, much of
the functionality provided by the NioClient class is no longer
necessary. This commit removes that class.

test/framework/src/main/java/org/elasticsearch/transport/nio/NioShutdown.java

@@ -34,13 +34,7 @@ public NioShutdown(Logger logger) {
         this.logger = logger;
     }
 
-    void orderlyShutdown(OpenChannels openChannels, NioClient client, ArrayList<AcceptingSelector> acceptors,
-                         ArrayList<SocketSelector> socketSelectors) {
-        // Close the client. This ensures that no new send connections will be opened. Client could be null if exception was
-        // throw on start up
-        if (client != null) {
-            client.close();
-        }
+    void orderlyShutdown(OpenChannels openChannels, ArrayList<AcceptingSelector> acceptors, ArrayList<SocketSelector> socketSelectors) {
 
         // Start by closing the server channels. Once these are closed, we are guaranteed to no accept new connections
         openChannels.closeServerChannels();

test/framework/src/main/java/org/elasticsearch/transport/nio/NioTransport.java

@@ -72,7 +72,8 @@ public class NioTransport extends TcpTransport<NioChannel> {
     private final ConcurrentMap<String, ChannelFactory> profileToChannelFactory = newConcurrentMap();
     private final ArrayList<AcceptingSelector> acceptors = new ArrayList<>();
     private final ArrayList<SocketSelector> socketSelectors = new ArrayList<>();
-    private NioClient client;
+    private RoundRobinSelectorSupplier clientSelectorSupplier;
+    private ChannelFactory clientChannelFactory;
     private int acceptorNumber;
 
     public NioTransport(Settings settings, ThreadPool threadPool, NetworkService networkService, BigArrays bigArrays,
@@ -111,10 +112,8 @@ protected void sendMessage(NioChannel channel, BytesReference reference, ActionL
     @Override
     protected NioChannel initiateChannel(DiscoveryNode node, TimeValue connectTimeout, ActionListener<NioChannel> connectListener)
         throws IOException {
-        NioSocketChannel channel = client.initiateConnection(node.getAddress().address());
-        if (channel == null) {
-            throw new ElasticsearchException("client is shutdown");
-        }
+        NioSocketChannel channel = clientChannelFactory.openNioChannel(node.getAddress().address(), clientSelectorSupplier.get());
+        openChannels.clientChannelOpened(channel);
         channel.addConnectListener(connectListener);
         return channel;
     }
@@ -137,7 +136,8 @@ protected void doStart() {
                 }
             }
 
-            client = createClient();
+            clientSelectorSupplier = new RoundRobinSelectorSupplier(socketSelectors);
+            clientChannelFactory = new ChannelFactory(new ProfileSettings(settings, "default"), contextSetter);
 
             if (NetworkService.NETWORK_SERVER.get(settings)) {
                 int acceptorCount = NioTransport.NIO_ACCEPTOR_COUNT.get(settings);
@@ -178,7 +178,7 @@ protected void doStart() {
     @Override
     protected void stopInternal() {
         NioShutdown nioShutdown = new NioShutdown(logger);
-        nioShutdown.orderlyShutdown(openChannels, client, acceptors, socketSelectors);
+        nioShutdown.orderlyShutdown(openChannels, acceptors, socketSelectors);
 
         profileToChannelFactory.clear();
         socketSelectors.clear();
@@ -193,10 +193,4 @@ final void exceptionCaught(NioSocketChannel channel, Throwable cause) {
         final Throwable t = unwrapped != null ? unwrapped : cause;
         onException(channel, t instanceof Exception ? (Exception) t : new ElasticsearchException(t));
     }
-
-    private NioClient createClient() {
-        Supplier<SocketSelector> selectorSupplier = new RoundRobinSelectorSupplier(socketSelectors);
-        ChannelFactory channelFactory = new ChannelFactory(new ProfileSettings(settings, "default"), contextSetter);
-        return new NioClient(openChannels, selectorSupplier, channelFactory);
-    }
 }