Provide a way to configure server for a plugin (#883)

Motivation:
Currently, there's no way to configure the Armeria server outside of the server module. We can perhaps do this by providing DI, SPI, or adding a method to `Plugin`.

Modification:
- Add `AllReplicasPlugin` class for configuring Central Dogma server

Result:
- You can now add configurations to the Central Dogma server for your plugin using `AllReplicasPlugin.init()` method.

it/server/src/test/java/com/linecorp/centraldogma/it/AllReplicasPluginTest.java

@@ -0,0 +1,39 @@
+/*
+ * Copyright 2023 LINE Corporation
+ *
+ * LINE Corporation 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:
+ *
+ *   https://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 com.linecorp.centraldogma.it;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.RegisterExtension;
+
+import com.linecorp.armeria.common.AggregatedHttpResponse;
+import com.linecorp.armeria.common.HttpStatus;
+import com.linecorp.centraldogma.testing.junit.CentralDogmaExtension;
+
+final class AllReplicasPluginTest {
+
+    @RegisterExtension
+    static final CentralDogmaExtension dogma = new CentralDogmaExtension();
+
+    @Test
+    void hello() {
+        // hello service is registered by TestAllReplicasPlugin.
+        final AggregatedHttpResponse res = dogma.httpClient().get("/hello").aggregate().join();
+        assertThat(res.status()).isSameAs(HttpStatus.OK);
+    }
+}

it/server/src/test/java/com/linecorp/centraldogma/it/TestAllReplicasPlugin.java

@@ -0,0 +1,44 @@
+/*
+ * Copyright 2023 LINE Corporation
+ *
+ * LINE Corporation 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:
+ *
+ *   https://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 com.linecorp.centraldogma.it;
+
+import java.util.concurrent.CompletionStage;
+
+import com.linecorp.armeria.common.HttpResponse;
+import com.linecorp.armeria.common.util.UnmodifiableFuture;
+import com.linecorp.centraldogma.server.plugin.AllReplicasPlugin;
+import com.linecorp.centraldogma.server.plugin.PluginContext;
+import com.linecorp.centraldogma.server.plugin.PluginInitContext;
+
+public final class TestAllReplicasPlugin extends AllReplicasPlugin {
+
+    @Override
+    public void init(PluginInitContext pluginInitContext) {
+        pluginInitContext.serverBuilder()
+                         .service("/hello", (ctx, req) -> HttpResponse.of("Hello, world!"));
+    }
+
+    @Override
+    public CompletionStage<Void> start(PluginContext context) {
+        return UnmodifiableFuture.completedFuture(null);
+    }
+
+    @Override
+    public CompletionStage<Void> stop(PluginContext context) {
+        return UnmodifiableFuture.completedFuture(null);
+    }
+}

it/server/src/test/resources/META-INF/services/com.linecorp.centraldogma.server.plugin.Plugin

@@ -0,0 +1 @@
+com.linecorp.centraldogma.it.TestAllReplicasPlugin

server/src/main/java/com/linecorp/centraldogma/server/CentralDogma.java

@@ -145,7 +145,9 @@
 import com.linecorp.centraldogma.server.internal.thrift.TokenlessClientLogger;
 import com.linecorp.centraldogma.server.metadata.MetadataService;
 import com.linecorp.centraldogma.server.metadata.MetadataServiceInjector;
+import com.linecorp.centraldogma.server.plugin.AllReplicasPlugin;
 import com.linecorp.centraldogma.server.plugin.Plugin;
+import com.linecorp.centraldogma.server.plugin.PluginInitContext;
 import com.linecorp.centraldogma.server.plugin.PluginTarget;
 import com.linecorp.centraldogma.server.storage.project.ProjectManager;
 
@@ -364,7 +366,7 @@ private void doStart() throws Exception {
             }
 
             logger.info("Starting the RPC server.");
-            server = startServer(pm, executor, meterRegistry, sessionManager);
+            server = startServer(pm, executor, purgeWorker, meterRegistry, sessionManager);
             logger.info("Started the RPC server at: {}", server.activePorts());
             logger.info("Started the Central Dogma successfully.");
             success = true;
@@ -489,7 +491,8 @@ private SessionManager initializeSessionManager() throws Exception {
     }
 
     private Server startServer(ProjectManager pm, CommandExecutor executor,
-                               MeterRegistry meterRegistry, @Nullable SessionManager sessionManager) {
+                               ScheduledExecutorService purgeWorker, MeterRegistry meterRegistry,
+                               @Nullable SessionManager sessionManager) {
         final ServerBuilder sb = Server.builder();
         sb.verboseResponses(true);
         cfg.ports().forEach(sb::port);
@@ -558,6 +561,18 @@ private Server startServer(ProjectManager pm, CommandExecutor executor,
             sb.accessLogFormat(accessLogFormat);
         }
 
+        if (pluginsForAllReplicas != null) {
+            final PluginInitContext pluginInitContext =
+                    new PluginInitContext(config(), pm, executor, meterRegistry, purgeWorker, sb);
+            pluginsForAllReplicas.plugins()
+                                 .forEach(p -> {
+                                     if (!(p instanceof AllReplicasPlugin)) {
+                                         return;
+                                     }
+                                     final AllReplicasPlugin plugin = (AllReplicasPlugin) p;
+                                     plugin.init(pluginInitContext);
+                                 });
+        }
         // Configure the uncaught exception handler just before starting the server so that override the
         // default exception handler set by third-party libraries such as NIOServerCnxnFactory.
         Thread.setDefaultUncaughtExceptionHandler((t, e) -> logger.warn("Uncaught exception: {}", t, e));

server/src/main/java/com/linecorp/centraldogma/server/plugin/AllReplicasPlugin.java

@@ -0,0 +1,32 @@
+/*
+ * Copyright 2023 LINE Corporation
+ *
+ * LINE Corporation 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:
+ *
+ *   https://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 com.linecorp.centraldogma.server.plugin;
+
+/**
+ * A Base class for {@link Plugin} whose {@link #target()} is {@link PluginTarget#ALL_REPLICAS}.
+ */
+public abstract class AllReplicasPlugin implements Plugin {
+
+    /**
+     * Overrides this method to initialize the plugin using the {@link PluginInitContext}.
+     */
+    public void init(PluginInitContext pluginInitContext) {}
+
+    @Override
+    public final PluginTarget target() {
+        return PluginTarget.ALL_REPLICAS;
+    }
+}

server/src/main/java/com/linecorp/centraldogma/server/plugin/Plugin.java

@@ -20,7 +20,8 @@
 import com.linecorp.centraldogma.server.CentralDogmaConfig;
 
 /**
- * An interface which defines callbacks for a plug-in.
+ * An interface which defines callbacks for a plug-in. If you want to initialize a {@link Plugin} by configuring
+ * the Central Dogma server (e.g. adding a service for your plugin), use {@link AllReplicasPlugin}.
  */
 public interface Plugin {
     /**

server/src/main/java/com/linecorp/centraldogma/server/plugin/PluginContext.java

@@ -30,7 +30,7 @@
 /**
  * A class which is used to pass internally-created instances into the {@link Plugin}.
  */
-public final class PluginContext {
+public class PluginContext {
 
     private final CentralDogmaConfig config;
     private final ProjectManager projectManager;

server/src/main/java/com/linecorp/centraldogma/server/plugin/PluginInitContext.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2023 LINE Corporation
+ *
+ * LINE Corporation 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:
+ *
+ *   https://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 com.linecorp.centraldogma.server.plugin;
+
+import static java.util.Objects.requireNonNull;
+
+import java.util.concurrent.ScheduledExecutorService;
+
+import com.linecorp.armeria.server.ServerBuilder;
+import com.linecorp.centraldogma.server.CentralDogmaConfig;
+import com.linecorp.centraldogma.server.command.CommandExecutor;
+import com.linecorp.centraldogma.server.storage.project.ProjectManager;
+
+import io.micrometer.core.instrument.MeterRegistry;
+
+/**
+ * A context that is used to pass when calling {@link AllReplicasPlugin#init(PluginInitContext)}.
+ */
+public final class PluginInitContext extends PluginContext {
+
+    private final ServerBuilder serverBuilder;
+
+    /**
+     * Creates a new instance.
+     */
+    public PluginInitContext(CentralDogmaConfig config,
+                             ProjectManager projectManager,
+                             CommandExecutor commandExecutor,
+                             MeterRegistry meterRegistry,
+                             ScheduledExecutorService purgeWorker,
+                             ServerBuilder serverBuilder) {
+        super(config, projectManager, commandExecutor, meterRegistry, purgeWorker);
+        this.serverBuilder = requireNonNull(serverBuilder, "serverBuilder");
+    }
+
+    /**
+     * Returns the {@link ServerBuilder} of the Central Dogma server.
+     */
+    public ServerBuilder serverBuilder() {
+        return serverBuilder;
+    }
+}