Add InstrumenterBuilder.addRequestListener (#5655)

instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/instrumenter/Instrumenter.java

@@ -232,10 +232,11 @@ public class Instrumenter<REQUEST, RESPONSE> {
 
     if (!requestListeners.isEmpty() || !requestMetricListeners.isEmpty()) {
       long endNanos = getNanos(endTime);
-      for (RequestListener requestListener : requestListeners) {
+      // TODO (trask) call end in the reverse order that start was called?
+      for (RequestListener requestListener : requestMetricListeners) {
         requestListener.end(context, attributes, endNanos);
       }
-      for (RequestListener requestListener : requestMetricListeners) {
+      for (RequestListener requestListener : requestListeners) {
         requestListener.end(context, attributes, endNanos);
       }
     }

instrumentation-api/src/main/java/io/opentelemetry/instrumentation/api/instrumenter/InstrumenterBuilder.java

@@ -125,7 +125,13 @@ public final class InstrumenterBuilder<REQUEST, RESPONSE> {
     return this;
   }
 
-  /** Adds a {@link RequestMetrics} whose metrics will be recorded for request start and stop. */
+  /** Adds a {@link RequestListener} which will be called for request start and end. */
+  public InstrumenterBuilder<REQUEST, RESPONSE> addRequestListener(RequestListener listener) {
+    requestListeners.add(listener);
+    return this;
+  }
+
+  /** Adds a {@link RequestMetrics} whose metrics will be recorded for request start and end. */
   @UnstableApi
   public InstrumenterBuilder<REQUEST, RESPONSE> addRequestMetrics(RequestMetrics factory) {
     requestMetricListeners.add(factory.create(meter));

instrumentation-api/src/test/java/io/opentelemetry/instrumentation/api/instrumenter/InstrumenterTest.java

@@ -431,6 +431,38 @@ class InstrumenterTest {
                             .hasParentSpanId("090a0b0c0d0e0f00")));
   }
 
+  @Test
+  void requestListeners() {
+    AtomicReference<Boolean> startContext = new AtomicReference<>();
+    AtomicReference<Boolean> endContext = new AtomicReference<>();
+
+    RequestListener requestListener =
+        new RequestListener() {
+          @Override
+          public Context start(Context context, Attributes startAttributes, long startNanos) {
+            startContext.set(true);
+            return context;
+          }
+
+          @Override
+          public void end(Context context, Attributes endAttributes, long endNanos) {
+            endContext.set(true);
+          }
+        };
+
+    Instrumenter<Map<String, String>, Map<String, String>> instrumenter =
+        Instrumenter.<Map<String, String>, Map<String, String>>builder(
+                otelTesting.getOpenTelemetry(), "test", unused -> "span")
+            .addRequestListener(requestListener)
+            .newServerInstrumenter(new MapGetter());
+
+    Context context = instrumenter.start(Context.root(), REQUEST);
+    instrumenter.end(context, REQUEST, RESPONSE, null);
+
+    assertThat(startContext.get()).isTrue();
+    assertThat(endContext.get()).isTrue();
+  }
+
   @Test
   void requestMetrics() {
     AtomicReference<Context> startContext = new AtomicReference<>();