Support for multiple extension jars by scanning the given folder

examples/extension/build.gradle

@@ -30,6 +30,7 @@ ext {
 }
 
 repositories {
+  mavenLocal()
   mavenCentral()
   maven {
     url = uri("https://oss.sonatype.org/content/repositories/snapshots")

examples/extension/src/main/java/com/example/javaagent/instrumentation/DemoServlet3Instrumentation.java

@@ -1,9 +1,10 @@
 package com.example.javaagent.instrumentation;
 
+import static net.bytebuddy.matcher.ElementMatchers.namedOneOf;
+
 import io.opentelemetry.javaagent.extension.instrumentation.TypeInstrumentation;
 import io.opentelemetry.javaagent.extension.instrumentation.TypeTransformer;
 import io.opentelemetry.javaagent.extension.matcher.AgentElementMatchers;
-import io.opentelemetry.javaagent.extension.matcher.NameMatchers;
 import io.opentelemetry.javaagent.instrumentation.api.Java8BytecodeBridge;
 import net.bytebuddy.asm.Advice;
 import net.bytebuddy.description.type.TypeDescription;
@@ -17,13 +18,13 @@ public class DemoServlet3Instrumentation implements TypeInstrumentation {
   @Override
   public ElementMatcher<TypeDescription> typeMatcher() {
     return AgentElementMatchers.safeHasSuperType(
-        NameMatchers.namedOneOf("javax.servlet.Filter", "javax.servlet.http.HttpServlet"));
+        namedOneOf("javax.servlet.Filter", "javax.servlet.http.HttpServlet"));
   }
 
   @Override
   public void transform(TypeTransformer typeTransformer) {
     typeTransformer.applyAdviceToMethod(
-        NameMatchers.namedOneOf("doFilter", "service")
+        namedOneOf("doFilter", "service")
             .and(
                 ElementMatchers.takesArgument(
                     0, ElementMatchers.named("javax.servlet.ServletRequest")))

examples/extension/src/test/java/com/example/javaagent/smoketest/IntegrationTest.java

@@ -79,9 +79,9 @@ static void setupSpec() {
 
   protected GenericContainer<?> target;
 
-  void startTarget(int jdk) {
+  void startTarget(String extensionLocation) {
     target =
-        new GenericContainer<>(getTargetImage(jdk))
+        new GenericContainer<>(getTargetImage(11))
             .withExposedPorts(8080)
             .withNetwork(network)
             .withLogConsumer(new Slf4jLogConsumer(logger))
@@ -93,7 +93,7 @@ void startTarget(int jdk) {
             .withEnv("JAVA_TOOL_OPTIONS",
                 "-javaagent:/opentelemetry-javaagent.jar -Dotel.javaagent.debug=true")
             //Asks instrumentation agent to include this extension archive into its runtime
-            .withEnv("OTEL_JAVAAGENT_EXPERIMENTAL_EXTENSIONS", "/opentelemetry-extensions.jar")
+            .withEnv("OTEL_JAVAAGENT_EXPERIMENTAL_EXTENSIONS", extensionLocation)
             .withEnv("OTEL_BSP_MAX_EXPORT_BATCH", "1")
             .withEnv("OTEL_BSP_SCHEDULE_DELAY", "10")
             .withEnv("OTEL_PROPAGATORS", "tracecontext,baggage,demo")

examples/extension/src/test/java/com/example/javaagent/smoketest/SpringBootIntegrationTest.java

@@ -19,8 +19,25 @@ protected String getTargetImage(int jdk) {
   }
 
   @Test
-  public void springBootSmokeTestOnJDK() throws IOException, InterruptedException {
-    startTarget(11);
+  public void extensionsAreLoadedFromJar() throws IOException, InterruptedException {
+    startTarget("/opentelemetry-extensions.jar");
+
+    testAndVerify();
+
+    stopTarget();
+  }
+
+  @Test
+  public void extensionsAreLoadedFromFolder() throws IOException, InterruptedException {
+    startTarget("/");
+
+    testAndVerify();
+
+    stopTarget();
+  }
+
+
+  private void testAndVerify() throws IOException, InterruptedException {
     String url = String.format("http://localhost:%d/greeting", target.getMappedPort(8080));
     Request request = new Request.Builder().url(url).get().build();
 
@@ -45,7 +62,5 @@ public void springBootSmokeTestOnJDK() throws IOException, InterruptedException
     Assertions.assertNotEquals(0,
         countResourcesByValue(traces, "telemetry.auto.version", currentAgentVersion));
     Assertions.assertNotEquals(0, countResourcesByValue(traces, "custom.resource", "demo"));
-
-    stopTarget();
   }
 }

javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/ExtensionClassLoader.java

@@ -9,69 +9,84 @@
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLClassLoader;
+import java.util.ArrayList;
+import java.util.List;
+import net.bytebuddy.dynamic.loading.MultipleParentClassLoader;
 
 /**
- * This classloader is used to load arbitrary extensions for Otel Java instrumentation agent. Such
- * extensions may include SDK components (exporters or propagators) and additional instrumentations.
- * They have to be isolated and shaded to reduce interference with the user application and to make
- * it compatible with shaded SDK used by the agent.
+ * This class creates a classloader which encapsulates arbitrary extensions for Otel Java
+ * instrumentation agent. Such extensions may include SDK components (exporters or propagators) and
+ * additional instrumentations. They have to be isolated and shaded to reduce interference with the
+ * user application and to make it compatible with shaded SDK used by the agent. Thus each extension
+ * jar gets a separate classloader and all of them are aggregated with the help of {@link
+ * MultipleParentClassLoader}.
  */
 // TODO find a way to initialize logging before using this class
-// TODO support scanning a folder for several extension jars and keep them isolated from each other
 // Used by AgentInitializer
 @SuppressWarnings({"unused", "SystemOut"})
 public class ExtensionClassLoader extends URLClassLoader {
   // NOTE it's important not to use slf4j in this class, because this class is used before slf4j is
   // configured, and so using slf4j here would initialize slf4j-simple before we have a chance to
   // configure the logging levels
 
-  static {
-    ClassLoader.registerAsParallelCapable();
-  }
-
   public static ClassLoader getInstance(ClassLoader parent) {
     // TODO add support for old deprecated property otel.javaagent.experimental.exporter.jar
-    URL extension =
+    List<URL> extension =
         parseLocation(
             System.getProperty(
                 "otel.javaagent.experimental.extensions",
                 System.getenv("OTEL_JAVAAGENT_EXPERIMENTAL_EXTENSIONS")));
 
-    if (extension == null) {
-      extension =
-          parseLocation(
-              System.getProperty(
-                  "otel.javaagent.experimental.initializer.jar",
-                  System.getenv("OTEL_JAVAAGENT_EXPERIMENTAL_INITIALIZER_JAR")));
-      // TODO when logging is configured add warning about deprecated property
+    extension.addAll(
+        parseLocation(
+            System.getProperty(
+                "otel.javaagent.experimental.initializer.jar",
+                System.getenv("OTEL_JAVAAGENT_EXPERIMENTAL_INITIALIZER_JAR"))));
+    // TODO when logging is configured add warning about deprecated property
+
+    List<ClassLoader> delegates = new ArrayList<>(extension.size());
+    for (URL url : extension) {
+      delegates.add(getDelegate(parent, url));
+    }
+    return new MultipleParentClassLoader(parent, delegates);
+  }
+
+  private static List<URL> parseLocation(String locationName) {
+    List<URL> result = new ArrayList<>();
+
+    if (locationName == null) {
+      return result;
     }
 
-    if (extension != null) {
-      try {
-        URL wrappedUrl = new URL("otel", null, -1, "/", new RemappingUrlStreamHandler(extension));
-        return new ExtensionClassLoader(wrappedUrl, parent);
-      } catch (MalformedURLException e) {
-        // This can't happen with current URL constructor
-        throw new IllegalStateException("URL malformed.  Unsupported JDK?", e);
+    File location = new File(locationName);
+    if (location.isFile()) {
+      addFileUrl(result, location);
+    } else if (location.isDirectory()) {
+      File[] files = location.listFiles(f -> f.isFile() && f.getName().endsWith(".jar"));
+      if (files != null) {
+        // TODO filter out agent file itself
+        for (File file : files) {
+          addFileUrl(result, file);
+        }
       }
     }
-    return parent;
+    return result;
   }
 
-  private static URL parseLocation(String name) {
-    if (name == null) {
-      return null;
-    }
+  private static void addFileUrl(List<URL> result, File file) {
     try {
-      return new File(name).toURI().toURL();
-    } catch (MalformedURLException e) {
-      System.err.printf(
-          "Filename could not be parsed: %s. Extension location is ignored%n", e.getMessage());
+      URL wrappedUrl = new URL("otel", null, -1, "/", new RemappingUrlStreamHandler(file));
+      result.add(wrappedUrl);
+    } catch (MalformedURLException ignored) {
+      System.err.println("Ignoring " + file);
     }
-    return null;
   }
 
-  private ExtensionClassLoader(URL url, ClassLoader parent) {
-    super(new URL[] {url}, parent);
+  private static URLClassLoader getDelegate(ClassLoader parent, URL extensionUrl) {
+    return new ExtensionClassLoader(new URL[] {extensionUrl}, parent);
+  }
+
+  private ExtensionClassLoader(URL[] urls, ClassLoader parent) {
+    super(urls, parent);
   }
 }

javaagent-tooling/src/main/java/io/opentelemetry/javaagent/tooling/RemappingUrlStreamHandler.java

@@ -10,7 +10,6 @@
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
-import java.net.URISyntaxException;
 import java.net.URL;
 import java.net.URLConnection;
 import java.net.URLStreamHandler;
@@ -20,10 +19,10 @@
 class RemappingUrlStreamHandler extends URLStreamHandler {
   private final JarFile delegateJarFile;
 
-  public RemappingUrlStreamHandler(URL delegateJarFileLocation) {
+  public RemappingUrlStreamHandler(File delegateFile) {
     try {
-      delegateJarFile = new JarFile(new File(delegateJarFileLocation.toURI()), false);
-    } catch (URISyntaxException | IOException e) {
+      delegateJarFile = new JarFile(delegateFile, false);
+    } catch (IOException e) {
       throw new IllegalStateException("Unable to read internal jar", e);
     }
   }