Issue #117: Develop ClassLoader Agent

metricshub-classloader-agent/pom.xml

@@ -0,0 +1,61 @@
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+	xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
+	<modelVersion>4.0.0</modelVersion>
+	<parent>
+		<groupId>org.sentrysoftware</groupId>
+		<artifactId>metricshub-parent</artifactId>
+		<version>0.9.02-SNAPSHOT</version>
+	</parent>
+
+	<artifactId>metricshub-classloader-agent</artifactId>
+	<name>MetricsHub ClassLoader Agent</name>
+	<description>MetricsHub ClassLoader Agent for dynamic class loading</description>
+
+	<properties>
+		<agentClass>org.sentrysoftware.metricshub.classloader.agent.ClassLoaderAgent</agentClass>
+	</properties>
+
+	<dependencies>
+
+	</dependencies>
+
+	<build>
+		<pluginManagement>
+			<plugins>
+				<plugin>
+					<groupId>org.apache.maven.plugins</groupId>
+					<artifactId>maven-compiler-plugin</artifactId>
+					<version>3.8.1</version>
+				</plugin>
+			</plugins>
+		</pluginManagement>
+		<plugins>
+			<plugin>
+				<groupId>org.apache.maven.plugins</groupId>
+				<artifactId>maven-shade-plugin</artifactId>
+				<version>3.5.2</version>
+				<executions>
+					<execution>
+						<phase>package</phase>
+						<goals>
+							<goal>shade</goal>
+						</goals>
+						<configuration>
+							<transformers>
+								<transformer
+									implementation="org.apache.maven.plugins.shade.resource.ManifestResourceTransformer">
+									<manifestEntries>
+										<Premain-Class>${agentClass}</Premain-Class>
+										<Agent-Class>${agentClass}</Agent-Class>
+									</manifestEntries>
+								</transformer>
+							</transformers>
+							<minimizeJar>false</minimizeJar>
+						</configuration>
+					</execution>
+				</executions>
+			</plugin>
+		</plugins>
+	</build>
+</project>

metricshub-classloader-agent/src/main/java/org/sentrysoftware/metricshub/classloader/agent/ClassLoaderAgent.java

@@ -0,0 +1,58 @@
+package org.sentrysoftware.metricshub.classloader.agent;
+
+import java.lang.instrument.Instrumentation;
+import java.util.Optional;
+import java.util.jar.JarFile;
+
+/**
+ * Class Loader Agent for dynamic class loading. (Needed for module-winrm and
+ * java 11)
+ *
+ * @link https://cgjennings.ca/articles/java-9-dynamic-jar-loading/
+ */
+public class ClassLoaderAgent {
+
+	private ClassLoaderAgent() {}
+
+	private static Instrumentation inst;
+
+	/**
+	 * Called by the JRE. <em>Do not call this method from user code.</em>
+	 * <p>
+	 *
+	 * @param unusedArgs      currently ignored
+	 * @param instrumentation provided by the JRE
+	 */
+	public static void premain(final String unusedArgs, final Instrumentation instrumentation) {
+		agentmain(unusedArgs, instrumentation);
+	}
+
+	/**
+	 * Called by the JRE. <em>Do not call this method from user code.</em>
+	 * <p>
+	 *
+	 * @param unusedArgs      currently ignored
+	 * @param instrumentation provided by the JRE
+	 */
+	public static void agentmain(final String unusedArgs, final Instrumentation instrumentation) {
+		inst = instrumentation;
+	}
+
+	/**
+	 * Adds a JAR file to the system class loader's classpath.
+	 *
+	 * @param jarFile the JAR file to add to the classpath
+	 */
+	public static synchronized void addToClassPath(final JarFile jarFile) {
+		getInstrumentation().ifPresent(instrumentation -> instrumentation.appendToSystemClassLoaderSearch(jarFile));
+	}
+
+	/**
+	 * Retrieves the current instrumentation instance, if available.
+	 *
+	 * @return an {@code Optional} containing the current instrumentation instance, or an empty {@code Optional} if not available
+	 */
+	static Optional<Instrumentation> getInstrumentation() {
+		return Optional.ofNullable(inst);
+	}
+}

metricshub-engine/pom.xml

@@ -16,6 +16,10 @@
 	<description>MetricsHub Monitoring Engine</description>
 
 	<dependencies>
+		<dependency>
+			<groupId>org.sentrysoftware</groupId>
+			<artifactId>metricshub-classloader-agent</artifactId>
+		</dependency>
 		<dependency>
 			<groupId>org.projectlombok</groupId>
 			<artifactId>lombok</artifactId>

metricshub-engine/src/main/java/org/sentrysoftware/metricshub/engine/configuration/HostConfiguration.java

@@ -96,7 +96,8 @@ public class HostConfiguration {
 	/**
 	 * Determine the accepted sources that can be executed using the current engine configuration
 	 *
-	 * @param isLocalhost Whether the host should be localhost or not
+	 * @param isLocalhost      Whether the host should be localhost or not.
+	 * @param extensionManager Where all the extensions are managed.
 	 * @return {@link Set} of accepted source types
 	 */
 	public Set<Class<? extends Source>> determineAcceptedSources(

metricshub-engine/src/main/java/org/sentrysoftware/metricshub/engine/extension/ExtensionLoader.java

@@ -29,12 +29,14 @@
 import java.util.List;
 import java.util.ServiceLoader;
 import java.util.ServiceLoader.Provider;
+import java.util.jar.JarFile;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
 import lombok.AllArgsConstructor;
 import lombok.Data;
 import lombok.NonNull;
 import lombok.extern.slf4j.Slf4j;
+import org.sentrysoftware.metricshub.classloader.agent.ClassLoaderAgent;
 
 /**
  * Manages the loading of extensions from a specified directory and produces an {@link ExtensionManager}.
@@ -73,7 +75,7 @@ public ExtensionManager load() throws IOException {
 			final File jarFile = extensionJars[i];
 
 			// Make sure to add the jar to the system class loader search
-
+			ClassLoaderAgent.addToClassPath(new JarFile(jarFile));
 			urls[i] = jarFile.toURI().toURL();
 		}
 

metricshub-engine/src/test/java/org/sentrysoftware/metricshub/engine/strategy/collect/ProtocolHealthCheckStrategyTest.java

@@ -348,7 +348,6 @@ void testCheckHealth() throws Exception {
 			clientsExecutorMock,
 			extensionManager
 		);
-
 		assertDoesNotThrow(() -> healthCheckStrategy.run());
 	}
 

pom.xml

@@ -123,6 +123,7 @@
 	</properties>
 
 	<modules>
+		<module>metricshub-classloader-agent</module>
 		<module>metricshub-engine</module>
 		<module>metricshub-it-common</module>
 		<module>metricshub-snmp-extension</module>
@@ -221,6 +222,11 @@
 				<artifactId>metricshub-engine</artifactId>
 				<version>${project.version}</version>
 			</dependency>
+			<dependency>
+				<groupId>org.sentrysoftware</groupId>
+				<artifactId>metricshub-classloader-agent</artifactId>
+				<version>${project.version}</version>
+			</dependency>
 			<dependency>
 				<groupId>org.sentrysoftware</groupId>
 				<artifactId>metricshub-it-common</artifactId>