Improve isolation of embedded JFFI dependency (#7789)

Author: mcculls

dd-java-agent/agent-bootstrap/src/main/java/datadog/trace/bootstrap/DatadogClassLoader.java

@@ -105,11 +105,28 @@ protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundE
         }
       }
       return cl.loadInstrumentationClass(name, agentCodeSource);
+    } else if (name.startsWith("com.kenai.jffi")) {
+      // prefer our embedded JFFI to other versions exposed by the parent class-loader
+      return loadLocalClass(name, resolve);
     } else {
       return super.loadClass(name, resolve);
     }
   }
 
+  /** Same as {@link #loadClass(String, boolean)} but it doesn't delegate to the parent. */
+  private Class<?> loadLocalClass(String name, boolean resolve) throws ClassNotFoundException {
+    synchronized (getClassLoadingLock(name)) {
+      Class<?> c = findLoadedClass(name);
+      if (null == c) {
+        c = findClass(name);
+      }
+      if (resolve) {
+        resolveClass(c);
+      }
+      return c;
+    }
+  }
+
   @Override
   protected Class<?> findClass(String name) throws ClassNotFoundException {
     byte[] buf = loadClassBytes(name);

dd-java-agent/build.gradle

@@ -53,6 +53,9 @@ ext.generalShadowJarConfig = {
   relocate 'net.jpountz', 'datadog.jpountz'
   // rewrite dependencies calling Logger.getLogger
   relocate 'java.util.logging.Logger', 'datadog.trace.bootstrap.PatchLogger'
+  // patch JFFI loading mechanism to maintain isolation
+  exclude '**/com/kenai/jffi/Init.class'
+  relocate('com.kenai.jffi.Init', 'com.kenai.jffi.PatchInit')
 
   final String projectName = "${project.name}"
 

utils/socket-utils/src/main/java/com/kenai/jffi/PatchInit.java

@@ -0,0 +1,27 @@
+package com.kenai.jffi;
+
+import com.kenai.jffi.internal.StubLoader;
+
+/** Replacement Init class that loads StubLoader from the same (isolating) class-loader. */
+final class PatchInit {
+  private static volatile boolean loaded;
+
+  private PatchInit() {}
+
+  static void load() {
+    if (loaded) {
+      return;
+    }
+    try {
+      if (StubLoader.isLoaded()) {
+        loaded = true;
+      } else {
+        throw StubLoader.getFailureCause();
+      }
+    } catch (UnsatisfiedLinkError e) {
+      throw e;
+    } catch (Throwable e) {
+      throw (UnsatisfiedLinkError) new UnsatisfiedLinkError(e.getLocalizedMessage()).initCause(e);
+    }
+  }
+}