Add ServerAgentFactory SPI for extension-contributed agents

src/main/java/io/mapsmessaging/ServerAgentFactory.java

@@ -0,0 +1,39 @@
+/*
+ *
+ *  Copyright [ 2020 - 2024 ] Matthew Buckton
+ *  Copyright [ 2024 - 2026 ] MapsMessaging B.V.
+ *
+ *  Licensed under the Apache License, Version 2.0 with the Commons Clause
+ *  (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
+ *      https://commonsclause.com/
+ *
+ *  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 io.mapsmessaging;
+
+import io.mapsmessaging.utilities.Agent;
+
+/**
+ * SPI allowing extension jars to contribute a lifecycle {@link Agent} to the server.
+ * Implementations are discovered via {@link java.util.ServiceLoader} at startup and
+ * started/stopped by {@link SubSystemManager} using the supplied ordering weights.
+ */
+public interface ServerAgentFactory {
+
+  /** Create the agent instance to be managed by the server. */
+  Agent create();
+
+  /** Start ordering weight; lower values start earlier. */
+  int startOrder();
+
+  /** Stop ordering weight; lower values stop earlier. */
+  int stopOrder();
+}

src/main/java/io/mapsmessaging/SubSystemManager.java

@@ -258,6 +258,7 @@ private void createAgentStartStopList() throws IOException {
       addToMap(2200, 70, new DeviceManager(featureManager));
     }
     addOptionalML();
+    loadExtensionAgents();
   }
 
   private void addOptionalML(){
@@ -275,6 +276,38 @@ private void addOptionalML(){
     }
   }
 
+  private void loadExtensionAgents() {
+    Set<String> allowed = new HashSet<>();
+    for (String entry : System.getProperty("extension.agents.allowed", "").split(",")) {
+      String trimmed = entry.trim();
+      if (!trimmed.isEmpty()) {
+        allowed.add(trimmed);
+      }
+    }
+    ServiceLoader<ServerAgentFactory> loader = ServiceLoader.load(ServerAgentFactory.class);
+    for (Iterator<ServerAgentFactory> iterator = loader.iterator(); iterator.hasNext(); ) {
+      try {
+        ServerAgentFactory factory = iterator.next();
+        String factoryClass = factory.getClass().getName();
+        if (!allowed.contains(factoryClass)) {
+          logger.log(ServerLogMessages.MESSAGE_DAEMON_EXTENSION_AGENT_FAILED,
+              factoryClass + " (not listed in -Dextension.agents.allowed; skipped)");
+          continue;
+        }
+        Agent agent = factory.create();
+        if (agentMap.containsKey(agent.getName())) {
+          logger.log(ServerLogMessages.MESSAGE_DAEMON_EXTENSION_AGENT_FAILED,
+              agent.getName() + " (duplicate name, ignored)");
+          continue;
+        }
+        addToMap(factory.startOrder(), factory.stopOrder(), agent);
+        logger.log(ServerLogMessages.MESSAGE_DAEMON_SERVICE_LOADED, agent.getName());
+      } catch (Throwable t) {
+        logger.log(ServerLogMessages.MESSAGE_DAEMON_EXTENSION_AGENT_FAILED, String.valueOf(t.getMessage()));
+      }
+    }
+  }
+
 
 
   /**

src/main/java/io/mapsmessaging/logging/ServerLogMessages.java

@@ -63,6 +63,7 @@ public enum ServerLogMessages implements LogMessage {
   MESSAGE_DAEMON_AGENT_STARTING(LEVEL.AUDIT, SERVER_CATEGORY.DAEMON, "Starting {} "),
   MESSAGE_DAEMON_AGENT_STARTED(LEVEL.WARN, SERVER_CATEGORY.DAEMON, "Started {} took {}ms"),
   MESSAGE_DAEMON_AGENT_FAILED(LEVEL.FATAL, SERVER_CATEGORY.DAEMON, "Failed to start {}, exception {}, system exitting"),
+  MESSAGE_DAEMON_EXTENSION_AGENT_FAILED(LEVEL.WARN, SERVER_CATEGORY.DAEMON, "Failed to load extension agent, {}"),
 
   MESSAGE_DAEMON_AGENT_STOPPING(LEVEL.AUDIT, SERVER_CATEGORY.DAEMON, "Stopping {} "),
   MESSAGE_DAEMON_AGENT_STOPPED(LEVEL.WARN, SERVER_CATEGORY.DAEMON, "Stopped {} took {}ms"),