Fix rxjava2 NoSuchFieldError (#2836)

instrumentation/rxjava/rxjava-2.0/library/src/main/java/io/opentelemetry/instrumentation/rxjava2/TracingAssembly.java

@@ -178,6 +178,7 @@ public final class TracingAssembly {
 
   @SuppressWarnings({"rawtypes", "unchecked"})
   private static void enableObservable() {
+    if (TracingObserver.canEnable()) {
       oldOnObservableSubscribe = RxJavaPlugins.getOnObservableSubscribe();
       RxJavaPlugins.setOnObservableSubscribe(
           biCompose(
@@ -189,6 +190,7 @@ public final class TracingAssembly {
                 }
               }));
     }
+  }
 
   @SuppressWarnings({"rawtypes", "unchecked"})
   private static void enableSingle() {

instrumentation/rxjava/rxjava-2.0/library/src/main/java/io/opentelemetry/instrumentation/rxjava2/TracingObserver.java

@@ -27,8 +27,11 @@ import io.opentelemetry.context.Scope;
 import io.reactivex.Observer;
 import io.reactivex.internal.fuseable.QueueDisposable;
 import io.reactivex.internal.observers.BasicFuseableObserver;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
 
 class TracingObserver<T> extends BasicFuseableObserver<T, T> {
+  private static final MethodHandle queueDisposableGetter = getQueueDisposableGetter();
 
   // BasicFuseableObserver#actual has been renamed to downstream in newer versions, we can't use it
   // in this class
@@ -64,7 +67,7 @@ class TracingObserver<T> extends BasicFuseableObserver<T, T> {
 
   @Override
   public int requestFusion(int mode) {
-    final QueueDisposable<T> qd = this.qs;
+    final QueueDisposable<T> qd = getQueueDisposable();
     if (qd != null) {
       final int m = qd.requestFusion(mode);
       sourceMode = m;
@@ -75,6 +78,36 @@ class TracingObserver<T> extends BasicFuseableObserver<T, T> {
 
   @Override
   public T poll() throws Exception {
-    return qs.poll();
+    return getQueueDisposable().poll();
+  }
+
+  private QueueDisposable<T> getQueueDisposable() {
+    try {
+      return (QueueDisposable<T>) queueDisposableGetter.invoke(this);
+    } catch (Throwable throwable) {
+      throw new IllegalStateException(throwable);
+    }
+  }
+
+  private static MethodHandle getGetterHandle(String fieldName) {
+    try {
+      return MethodHandles.lookup()
+          .findGetter(BasicFuseableObserver.class, fieldName, QueueDisposable.class);
+    } catch (NoSuchFieldException | IllegalAccessException ignored) {
+    }
+    return null;
+  }
+
+  private static MethodHandle getQueueDisposableGetter() {
+    MethodHandle getter = getGetterHandle("qd");
+    if (getter == null) {
+      // in versions before 2.2.1 field was named "qs"
+      getter = getGetterHandle("qs");
+    }
+    return getter;
+  }
+
+  public static boolean canEnable() {
+    return queueDisposableGetter != null;
   }
 }

instrumentation/rxjava/rxjava-2.0/testing/src/main/groovy/io/opentelemetry/instrumentation/rxjava2/AbstractRxJava2SubscriptionTest.groovy

@@ -6,10 +6,12 @@
 package io.opentelemetry.instrumentation.rxjava2
 
 import static io.opentelemetry.instrumentation.test.utils.TraceUtils.basicSpan
+import static io.opentelemetry.instrumentation.test.utils.TraceUtils.runInternalSpan
 import static io.opentelemetry.instrumentation.test.utils.TraceUtils.runUnderTrace
 
 import io.opentelemetry.api.GlobalOpenTelemetry
 import io.opentelemetry.instrumentation.test.InstrumentationSpecification
+import io.reactivex.Observable
 import io.reactivex.Single
 import io.reactivex.functions.Consumer
 
@@ -17,7 +19,7 @@ import java.util.concurrent.CountDownLatch
 
 abstract class AbstractRxJava2SubscriptionTest extends InstrumentationSpecification {
 
-  def "subscription test"() {
+  def "subscribe single test"() {
     when:
     CountDownLatch latch = new CountDownLatch(1)
     runUnderTrace("parent") {
@@ -43,6 +45,32 @@ abstract class AbstractRxJava2SubscriptionTest extends InstrumentationSpecificat
     }
   }
 
+  def "test observable fusion"() {
+    when:
+    CountDownLatch latch = new CountDownLatch(1)
+    runUnderTrace("parent") {
+      Observable<Integer> integerObservable = Observable.just(1, 2, 3, 4)
+      integerObservable.concatMap({
+        return Observable.just(it)
+      }).count().subscribe(new Consumer<Long>() {
+        @Override
+        void accept(Long count) {
+          runInternalSpan("child")
+          latch.countDown()
+        }
+      })
+    }
+    latch.await()
+
+    then:
+    assertTraces(1) {
+      trace(0, 2) {
+        basicSpan(it, 0, "parent")
+        basicSpan(it, 1, "child", span(0))
+      }
+    }
+  }
+
   static class Connection {
     static int query() {
       def span = GlobalOpenTelemetry.getTracer("test").spanBuilder("Connection.query").startSpan()