Allow extension of CapturingTransport by subclasses (#33012)

Today, CapturingTransport#createCapturingTransportService creates a transport
service with a connection manager with reasonable default behaviours, but
overriding this behaviour in a consumer is a litle tricky. Additionally, the
default behaviour for opening a connection duplicates the content of the
CapturingTransport#openConnection() method.

This change removes this duplication by delegating to openConnection() and
introduces overridable nodeConnected() and onSendRequest() methods so that
consumers can alter this behaviour more easily.

Relates #32246 in which we test the mechanisms for opening connections to
unknown (and possibly unreachable) nodes.

test/framework/src/main/java/org/elasticsearch/test/transport/CapturingTransport.java

@@ -51,7 +51,6 @@ import org.elasticsearch.transport.TransportService;
 import org.elasticsearch.transport.TransportStats;
 
 import java.io.IOException;
-import java.net.UnknownHostException;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -66,11 +65,13 @@ import java.util.function.Function;
 
 import static org.apache.lucene.util.LuceneTestCase.rarely;
 
-/** A transport class that doesn't send anything but rather captures all requests for inspection from tests */
+/**
+ * A transport class that doesn't send anything but rather captures all requests for inspection from tests
+ */
 public class CapturingTransport implements Transport {
 
     private volatile Map<String, RequestHandlerRegistry> requestHandlers = Collections.emptyMap();
-    final Object requestHandlerMutex = new Object();
+    private final Object requestHandlerMutex = new Object();
     private final ResponseHandlers responseHandlers = new ResponseHandlers();
     private TransportMessageListener listener;
 
@@ -80,7 +81,7 @@ public class CapturingTransport implements Transport {
         public final String action;
         public final TransportRequest request;
 
-        public CapturedRequest(DiscoveryNode node, long requestId, String action, TransportRequest request) {
+        CapturedRequest(DiscoveryNode node, long requestId, String action, TransportRequest request) {
             this.node = node;
             this.requestId = requestId;
             this.action = action;
@@ -96,41 +97,15 @@ public class CapturingTransport implements Transport {
                                                             @Nullable ClusterSettings clusterSettings, Set<String> taskHeaders) {
         StubbableConnectionManager connectionManager = new StubbableConnectionManager(new ConnectionManager(settings, this, threadPool),
             settings, this, threadPool);
-        connectionManager.setDefaultNodeConnectedBehavior((cm, discoveryNode) -> true);
-        connectionManager.setDefaultConnectBehavior((cm, discoveryNode) -> new Connection() {
-            @Override
-            public DiscoveryNode getNode() {
-                return discoveryNode;
-            }
-
-            @Override
-            public void sendRequest(long requestId, String action, TransportRequest request, TransportRequestOptions options)
-                throws TransportException {
-                requests.put(requestId, Tuple.tuple(discoveryNode, action));
-                capturedRequests.add(new CapturedRequest(discoveryNode, requestId, action, request));
-            }
-
-            @Override
-            public void addCloseListener(ActionListener<Void> listener) {
-
-            }
-
-            @Override
-            public boolean isClosed() {
-                return false;
-            }
-
-            @Override
-            public void close() {
-
-            }
-        });
+        connectionManager.setDefaultNodeConnectedBehavior((cm, discoveryNode) -> nodeConnected(discoveryNode));
+        connectionManager.setDefaultConnectBehavior((cm, discoveryNode) -> openConnection(discoveryNode, null));
         return new TransportService(settings, this, threadPool, interceptor, localNodeFactory, clusterSettings, taskHeaders,
             connectionManager);
-
     }
 
-    /** returns all requests captured so far. Doesn't clear the captured request list. See {@link #clear()} */
+    /**
+     * returns all requests captured so far. Doesn't clear the captured request list. See {@link #clear()}
+     */
     public CapturedRequest[] capturedRequests() {
         return capturedRequests.toArray(new CapturedRequest[0]);
     }
@@ -178,12 +153,16 @@ public class CapturingTransport implements Transport {
         return groupRequestsByTargetNode(requests);
     }
 
-    /** clears captured requests */
+    /**
+     * clears captured requests
+     */
     public void clear() {
         capturedRequests.clear();
     }
 
-    /** simulate a response for the given requestId */
+    /**
+     * simulate a response for the given requestId
+     */
     public void handleResponse(final long requestId, final TransportResponse response) {
         responseHandlers.onResponseReceived(requestId, listener).handleResponse(response);
     }
@@ -194,7 +173,7 @@ public class CapturingTransport implements Transport {
      *
      * @param requestId the id corresponding to the captured send
      *                  request
-     * @param t the failure to wrap
+     * @param t         the failure to wrap
      */
     public void handleLocalError(final long requestId, final Throwable t) {
         Tuple<DiscoveryNode, String> request = requests.get(requestId);
@@ -208,7 +187,7 @@ public class CapturingTransport implements Transport {
      *
      * @param requestId the id corresponding to the captured send
      *                  request
-     * @param t the failure to wrap
+     * @param t         the failure to wrap
      */
     public void handleRemoteError(final long requestId, final Throwable t) {
         final RemoteTransportException remoteException;
@@ -234,7 +213,7 @@ public class CapturingTransport implements Transport {
      *
      * @param requestId the id corresponding to the captured send
      *                  request
-     * @param e the failure
+     * @param e         the failure
      */
     public void handleError(final long requestId, final TransportException e) {
         responseHandlers.onResponseReceived(requestId, listener).handleException(e);
@@ -251,13 +230,11 @@ public class CapturingTransport implements Transport {
             @Override
             public void sendRequest(long requestId, String action, TransportRequest request, TransportRequestOptions options)
                 throws TransportException {
-                requests.put(requestId, Tuple.tuple(node, action));
-                capturedRequests.add(new CapturedRequest(node, requestId, action, request));
+                onSendRequest(requestId, action, request, node);
             }
 
             @Override
             public void addCloseListener(ActionListener<Void> listener) {
-
             }
 
             @Override
@@ -267,11 +244,19 @@ public class CapturingTransport implements Transport {
 
             @Override
             public void close() {
-
             }
         };
     }
 
+    protected void onSendRequest(long requestId, String action, TransportRequest request, DiscoveryNode node) {
+        requests.put(requestId, Tuple.tuple(node, action));
+        capturedRequests.add(new CapturedRequest(node, requestId, action, request));
+    }
+
+    protected boolean nodeConnected(DiscoveryNode discoveryNode) {
+        return true;
+    }
+
     @Override
     public TransportStats getStats() {
         throw new UnsupportedOperationException();
@@ -288,7 +273,7 @@ public class CapturingTransport implements Transport {
     }
 
     @Override
-    public TransportAddress[] addressesFromString(String address, int perAddressLimit) throws UnknownHostException {
+    public TransportAddress[] addressesFromString(String address, int perAddressLimit) {
         return new TransportAddress[0];
     }
 
@@ -299,22 +284,23 @@ public class CapturingTransport implements Transport {
 
     @Override
     public void addLifecycleListener(LifecycleListener listener) {
-
     }
 
     @Override
     public void removeLifecycleListener(LifecycleListener listener) {
-
     }
 
     @Override
-    public void start() {}
+    public void start() {
+    }
 
     @Override
-    public void stop() {}
+    public void stop() {
+    }
 
     @Override
-    public void close() {}
+    public void close() {
+    }
 
     @Override
     public List<String> getLocalAddresses() {
@@ -330,6 +316,7 @@ public class CapturingTransport implements Transport {
             requestHandlers = MapBuilder.newMapBuilder(requestHandlers).put(reg.getAction(), reg).immutableMap();
         }
     }
+
     @Override
     public ResponseHandlers getResponseHandlers() {
         return responseHandlers;