Make RestController pluggable (#98187)

This commit changes the ActionModules to allow  the RestController to be
provided by an internal plugin.

It renames  `RestInterceptorActionPlugin` to `RestServerActionPlugin`
and adds a new `getRestController` method to it.

There may be multiple RestServerActionPlugins installed on a node, but
only 1 may provide a Rest Wrapper (getRestHandlerInterceptor) and only 1
may provide a RestController (getRestController).

qa/custom-rest-controller/src/javaRestTest/java/co/elastic/elasticsearch/test/CustomRestPlugin.java

@@ -0,0 +1,92 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package co.elastic.elasticsearch.test;
+
+import org.elasticsearch.client.internal.node.NodeClient;
+import org.elasticsearch.common.util.concurrent.ThreadContext;
+import org.elasticsearch.indices.breaker.CircuitBreakerService;
+import org.elasticsearch.logging.LogManager;
+import org.elasticsearch.logging.Logger;
+import org.elasticsearch.plugins.Plugin;
+import org.elasticsearch.plugins.interceptor.RestServerActionPlugin;
+import org.elasticsearch.rest.RestChannel;
+import org.elasticsearch.rest.RestController;
+import org.elasticsearch.rest.RestHandler;
+import org.elasticsearch.rest.RestRequest;
+import org.elasticsearch.tracing.Tracer;
+import org.elasticsearch.usage.UsageService;
+
+import java.util.function.UnaryOperator;
+
+public class CustomRestPlugin extends Plugin implements RestServerActionPlugin {
+
+    private static final Logger logger = LogManager.getLogger(CustomRestPlugin.class);
+
+    private static void echoHeader(String name, RestRequest request, ThreadContext threadContext) {
+        var value = request.header(name);
+        if (value != null) {
+            threadContext.addResponseHeader(name, value);
+        }
+    }
+
+    public static class CustomInterceptor implements RestHandler {
+
+        private final ThreadContext threadContext;
+        private final RestHandler delegate;
+
+        public CustomInterceptor(ThreadContext threadContext, RestHandler delegate) {
+            this.threadContext = threadContext;
+            this.delegate = delegate;
+        }
+
+        @Override
+        public void handleRequest(RestRequest request, RestChannel channel, NodeClient client) throws Exception {
+            logger.info("intercept request {} {}", request.method(), request.uri());
+            echoHeader("x-test-interceptor", request, threadContext);
+            delegate.handleRequest(request, channel, client);
+        }
+
+    }
+
+    public static class CustomController extends RestController {
+        public CustomController(
+            UnaryOperator<RestHandler> handlerWrapper,
+            NodeClient client,
+            CircuitBreakerService circuitBreakerService,
+            UsageService usageService,
+            Tracer tracer
+        ) {
+            super(handlerWrapper, client, circuitBreakerService, usageService, tracer);
+        }
+
+        @Override
+        public void dispatchRequest(RestRequest request, RestChannel channel, ThreadContext threadContext) {
+            logger.info("dispatch request {} {}", request.method(), request.uri());
+            echoHeader("x-test-controller", request, threadContext);
+            super.dispatchRequest(request, channel, threadContext);
+        }
+    }
+
+    @Override
+    public UnaryOperator<RestHandler> getRestHandlerInterceptor(ThreadContext threadContext) {
+        return handler -> new CustomInterceptor(threadContext, handler);
+    }
+
+    @Override
+    public RestController getRestController(
+        UnaryOperator<RestHandler> handlerWrapper,
+        NodeClient client,
+        CircuitBreakerService circuitBreakerService,
+        UsageService usageService,
+        Tracer tracer
+    ) {
+        return new CustomController(handlerWrapper, client, circuitBreakerService, usageService, tracer);
+    }
+
+}

qa/custom-rest-controller/src/javaRestTest/java/org/elasticsearch/plugins/interceptor/CustomRestPluginIT.java

@@ -0,0 +1,64 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0 and the Server Side Public License, v 1; you may not use this file except
+ * in compliance with, at your election, the Elastic License 2.0 or the Server
+ * Side Public License, v 1.
+ */
+
+package org.elasticsearch.plugins.interceptor;
+
+import co.elastic.elasticsearch.test.CustomRestPlugin;
+
+import org.elasticsearch.client.Request;
+import org.elasticsearch.client.RequestOptions;
+import org.elasticsearch.client.Response;
+import org.elasticsearch.plugins.Plugin;
+import org.elasticsearch.test.ESIntegTestCase;
+
+import java.io.IOException;
+import java.util.Collection;
+
+import static org.elasticsearch.common.util.CollectionUtils.appendToCopyNoNullElements;
+import static org.hamcrest.CoreMatchers.equalTo;
+import static org.hamcrest.CoreMatchers.notNullValue;
+
+public class CustomRestPluginIT extends ESIntegTestCase {
+
+    @Override
+    protected Collection<Class<? extends Plugin>> nodePlugins() {
+        return appendToCopyNoNullElements(super.nodePlugins(), CustomRestPlugin.class);
+    }
+
+    @Override
+    protected boolean addMockHttpTransport() {
+        return false; // enable http
+    }
+
+    public void testInterceptor() throws Exception {
+        var headerValue = randomAlphaOfLengthBetween(4, 12);
+        assertThat(doRequest("x-test-interceptor", headerValue), equalTo(headerValue));
+        assertThat(doRequest("x-test-interceptor", null), equalTo(null));
+    }
+
+    public void testController() throws Exception {
+        var headerValue = randomAlphaOfLengthBetween(4, 12);
+        assertThat(doRequest("x-test-controller", headerValue), equalTo(headerValue));
+        assertThat(doRequest("x-test-controller", null), equalTo(null));
+    }
+
+    private String doRequest(String headerName, String headerValue) throws IOException {
+        assertThat(headerName, notNullValue());
+
+        var client = getRestClient();
+        RequestOptions.Builder options = RequestOptions.DEFAULT.toBuilder();
+        if (headerValue != null) {
+            options.addHeader(headerName, headerValue);
+        }
+        var request = new Request("GET", "/_nodes/_local/plugins");
+        request.setOptions(options);
+
+        final Response response = client.performRequest(request);
+        return response.getHeader(headerName);
+    }
+}