[CHECKER] Implement ConfigGuard

app/src/main/java/org/astraea/app/checker/Config.java

@@ -16,11 +16,14 @@
  */
 package org.astraea.app.checker;
 
+import java.util.Locale;
 import java.util.Optional;
+import org.apache.kafka.common.config.ConfigResource;
 
 public class Config {
   private String name;
   private Optional<String> value;
+  private String type;
   private String commit;
   private String kip;
 
@@ -32,6 +35,14 @@ public Optional<String> value() {
     return value;
   }
 
+  public ConfigResource.Type type() {
+    return switch (type.toLowerCase(Locale.ENGLISH)) {
+      case "broker" -> ConfigResource.Type.BROKER;
+      case "topic" -> ConfigResource.Type.TOPIC;
+      default -> throw new IllegalArgumentException();
+    };
+  }
+
   public String commit() {
     return commit;
   }

app/src/main/java/org/astraea/app/checker/ConfigGuard.java

@@ -0,0 +1,91 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ *    http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.astraea.app.checker;
+
+import java.util.Collection;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+import org.apache.kafka.clients.admin.Admin;
+import org.apache.kafka.common.Node;
+import org.apache.kafka.common.config.ConfigResource;
+import org.astraea.common.metrics.MBeanClient;
+
+public class ConfigGuard implements Guard {
+  @Override
+  public Collection<Report> run(
+      Admin admin, Function<Node, MBeanClient> clients, Changelog changelog) throws Exception {
+    var nameToCheckerConfig = changelog.configs();
+    var nodes = admin.describeCluster().nodes().get();
+    var idToNode =
+        nodes.stream()
+            .collect(Collectors.toMap(node -> String.valueOf(node.id()), Function.identity()));
+
+    var brokerReports =
+        processConfigs(
+            nodes.stream()
+                .map(
+                    node ->
+                        new ConfigResource(ConfigResource.Type.BROKER, String.valueOf(node.id())))
+                .toList(),
+            admin,
+            nameToCheckerConfig,
+            resource -> idToNode.get(resource.name()));
+
+    var topicReports =
+        processConfigs(
+            admin.listTopics().listings().get().stream()
+                .map(topic -> new ConfigResource(ConfigResource.Type.TOPIC, topic.name()))
+                .toList(),
+            admin,
+            nameToCheckerConfig,
+            resource -> null);
+
+    return Stream.concat(brokerReports.stream(), topicReports.stream())
+        .filter(report -> !report.why().isEmpty())
+        .toList();
+  }
+
+  private List<Report> processConfigs(
+      List<ConfigResource> resources,
+      Admin admin,
+      Map<String, org.astraea.app.checker.Config> nameToCheckerConfig,
+      Function<ConfigResource, Node> nodeResolver)
+      throws Exception {
+    return admin.describeConfigs(resources).all().get().entrySet().stream()
+        .flatMap(
+            entry ->
+                entry.getValue().entries().stream()
+                    .filter(config -> nameToCheckerConfig.containsKey(config.name()))
+                    .map(
+                        config ->
+                            nameToCheckerConfig
+                                .get(config.name())
+                                .value()
+                                .filter(defaultValue -> !config.value().equals(defaultValue))
+                                .map(
+                                    __ ->
+                                        Report.of(
+                                            nodeResolver.apply(entry.getKey()),
+                                            String.format(
+                                                "%s has been removed from AK 4.0", config.name())))
+                                .orElseGet(Report::empty)))
+        .toList();
+  }
+}