Merge pull request #741 from DataDog/mar-kolya/tomcat-classloadin-instrumentation

Add instrumentation for Tomcat webapp classloading

dd-java-agent/instrumentation/tomcat-classloading/src/main/java/datadog/trace/instrumentation/tomcat/TomcatClassloadingInstrumentation.java

@@ -0,0 +1,68 @@
+package datadog.trace.instrumentation.tomcat;
+
+import static datadog.trace.agent.tooling.ByteBuddyElementMatchers.safeHasSuperType;
+import static java.util.Collections.singletonMap;
+import static net.bytebuddy.matcher.ElementMatchers.isMethod;
+import static net.bytebuddy.matcher.ElementMatchers.named;
+import static net.bytebuddy.matcher.ElementMatchers.takesArgument;
+import static net.bytebuddy.matcher.ElementMatchers.takesArguments;
+
+import com.google.auto.service.AutoService;
+import datadog.trace.agent.tooling.Constants;
+import datadog.trace.agent.tooling.Instrumenter;
+import datadog.trace.api.GlobalTracer;
+import java.util.Map;
+import net.bytebuddy.asm.Advice;
+import net.bytebuddy.description.method.MethodDescription;
+import net.bytebuddy.description.type.TypeDescription;
+import net.bytebuddy.matcher.ElementMatcher;
+
+/**
+ * Instrument Tomcat's web app classloader so it loads Datadog's bootstrap classes from parent
+ * classloader. Without this change web apps get their oen versions of Datadog's classes leading to
+ * there being multiple {@link GlobalTracer}s in existance, some of them not configured properly.
+ * This is really the same idea we have for OSGi and JBoss.
+ */
+@AutoService(Instrumenter.class)
+public final class TomcatClassloadingInstrumentation extends Instrumenter.Default {
+  public TomcatClassloadingInstrumentation() {
+    super("tomcat-classloading");
+  }
+
+  @Override
+  public ElementMatcher<TypeDescription> typeMatcher() {
+    return safeHasSuperType(named("org.apache.catalina.loader.WebappClassLoaderBase"));
+  }
+
+  @Override
+  public String[] helperClassNames() {
+    return new String[] {Constants.class.getName()};
+  }
+
+  @Override
+  public Map<? extends ElementMatcher<? super MethodDescription>, String> transformers() {
+    return singletonMap(
+        isMethod()
+            .and(named("filter"))
+            .and(takesArgument(0, String.class))
+            // Older versions have 1 argument method, newer versions have two arguments
+            .and(takesArguments(2).or(takesArguments(1))),
+        WebappClassLoaderAdvice.class.getName());
+  }
+
+  public static class WebappClassLoaderAdvice {
+    @Advice.OnMethodExit(suppress = Throwable.class)
+    public static void methodExit(
+        @Advice.Argument(0) final String name, @Advice.Return(readOnly = false) boolean result) {
+      if (result) {
+        return;
+      }
+      for (final String prefix : Constants.BOOTSTRAP_PACKAGE_PREFIXES) {
+        if (name.startsWith(prefix)) {
+          result = true;
+          break;
+        }
+      }
+    }
+  }
+}

dd-java-agent/instrumentation/tomcat-classloading/src/test/groovy/TomcatClassloadingTest.groovy

@@ -0,0 +1,30 @@
+import datadog.trace.agent.test.AgentTestRunner
+import datadog.trace.api.GlobalTracer
+import org.apache.catalina.WebResource
+import org.apache.catalina.WebResourceRoot
+import org.apache.catalina.loader.ParallelWebappClassLoader
+
+class TomcatClassloadingTest extends AgentTestRunner {
+
+  WebResourceRoot resources = Mock(WebResourceRoot) {
+    getResource(_) >> Mock(WebResource)
+    listResources(_) >> []
+    // Looks like 9.x.x needs this one:
+    getResources(_) >> []
+  }
+  ParallelWebappClassLoader classloader = new ParallelWebappClassLoader(null)
+
+  def "tomcat class loading delegates to parent for Datadog classes"() {
+    setup:
+    classloader.setResources(resources)
+    classloader.init()
+    classloader.start()
+
+    when:
+    // If instrumentation didn't work this would blow up with NPE due to incomplete resources mocking
+    def clazz = classloader.loadClass("datadog.trace.api.GlobalTracer")
+
+    then:
+    clazz == GlobalTracer
+  }
+}

dd-java-agent/instrumentation/tomcat-classloading/tomcat-classloading.gradle

@@ -0,0 +1,34 @@
+
+muzzle {
+  pass {
+    group = "org.apache.tomcat"
+    module = 'tomcat-catalina'
+    versions = "[3.0.14,)"
+    assertInverse = true
+  }
+}
+
+apply from: "${rootDir}/gradle/java.gradle"
+
+apply plugin: 'org.unbroken-dome.test-sets'
+
+testSets {
+  latestDepTest {
+    dirName = 'test'
+  }
+}
+
+dependencies {
+  compile project(':dd-java-agent:agent-tooling')
+  compile deps.bytebuddy
+  annotationProcessor deps.autoservice
+  implementation deps.autoservice
+
+  testCompile project(':dd-java-agent:testing')
+
+  //This seems to be the earliest version that has org.apache.catalina.loader.WebappClassLoaderBase
+  //Older versions would require slightly different instrumentation.
+  testCompile group: 'org.apache.tomcat', name: 'tomcat-catalina', version: '8.0.14'
+
+  latestDepTestCompile group: 'org.apache.tomcat', name: 'tomcat-catalina', version: '+'
+}

settings.gradle

@@ -77,6 +77,7 @@ include ':dd-java-agent:instrumentation:sparkjava-2.3'
 include ':dd-java-agent:instrumentation:spring-web'
 include ':dd-java-agent:instrumentation:spring-webflux'
 include ':dd-java-agent:instrumentation:spymemcached-2.12'
+include ':dd-java-agent:instrumentation:tomcat-classloading'
 include ':dd-java-agent:instrumentation:trace-annotation'
 include ':dd-java-agent:instrumentation:vertx'