Implement HttpServerResponseCustomizer support for Akka-http

instrumentation/akka/akka-http-10.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/akkahttp/server/AkkaFlowWrapper.java

@@ -9,6 +9,7 @@
 import static io.opentelemetry.javaagent.instrumentation.akkahttp.server.AkkaHttpServerSingletons.errorResponse;
 import static io.opentelemetry.javaagent.instrumentation.akkahttp.server.AkkaHttpServerSingletons.instrumenter;
 
+import akka.http.javadsl.model.HttpHeader;
 import akka.http.scaladsl.model.HttpRequest;
 import akka.http.scaladsl.model.HttpResponse;
 import akka.stream.Attributes;
@@ -22,8 +23,10 @@
 import akka.stream.stage.GraphStageLogic;
 import io.opentelemetry.context.Context;
 import io.opentelemetry.context.Scope;
+import io.opentelemetry.javaagent.bootstrap.http.HttpServerResponseCustomizerHolder;
 import java.util.ArrayDeque;
 import java.util.Deque;
+import java.util.List;
 
 public class AkkaFlowWrapper
     extends GraphStage<BidiShape<HttpResponse, HttpResponse, HttpRequest, HttpRequest>> {
@@ -134,6 +137,17 @@ public void onPush() {
                 // this may happen on a different thread from the one that opened the scope
                 // actor instrumentation will take care of the leaked scopes
                 tracingRequest.scope.close();
+
+                // akka response is immutable so the customizer just captures the added headers
+                AkkaHttpResponseMutator responseMutator = new AkkaHttpResponseMutator();
+                HttpServerResponseCustomizerHolder.getCustomizer()
+                    .customize(tracingRequest.context, response, responseMutator);
+                // build a new response with the added headers
+                List<HttpHeader> headers = responseMutator.getHeaders();
+                if (!headers.isEmpty()) {
+                  response = (HttpResponse) response.addHeaders(headers);
+                }
+
                 instrumenter().end(tracingRequest.context, tracingRequest.request, response, null);
               }
               push(responseOut, response);

instrumentation/akka/akka-http-10.0/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/akkahttp/server/AkkaHttpResponseMutator.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.javaagent.instrumentation.akkahttp.server;
+
+import akka.http.javadsl.model.HttpHeader;
+import akka.http.javadsl.model.HttpResponse;
+import akka.http.javadsl.model.headers.RawHeader;
+import io.opentelemetry.javaagent.bootstrap.http.HttpServerResponseMutator;
+import java.util.ArrayList;
+import java.util.List;
+
+final class AkkaHttpResponseMutator implements HttpServerResponseMutator<HttpResponse> {
+
+  private final List<HttpHeader> headers = new ArrayList<>();
+
+  @Override
+  public void appendHeader(HttpResponse response, String name, String value) {
+    headers.add(RawHeader.create(name, value));
+  }
+
+  List<HttpHeader> getHeaders() {
+    return headers;
+  }
+}

instrumentation/akka/akka-http-10.0/javaagent/src/test/scala/io/opentelemetry/javaagent/instrumentation/akkahttp/AbstractHttpServerInstrumentationTest.scala

@@ -14,7 +14,7 @@ import io.opentelemetry.instrumentation.testing.junit.http.{
 
 import java.util
 import java.util.Collections
-import java.util.function.Function
+import java.util.function.{Function, Predicate}
 
 abstract class AbstractHttpServerInstrumentationTest
     extends AbstractHttpServerTest[Object] {
@@ -29,5 +29,11 @@ abstract class AbstractHttpServerInstrumentationTest
           Collections.emptySet()
       }
     )
+    options.setHasResponseCustomizer(
+      new Predicate[ServerEndpoint] {
+        override def test(t: ServerEndpoint): Boolean =
+          t != ServerEndpoint.EXCEPTION
+      }
+    )
   }
 }