fix(httpclient): ensure proper closure of HttpClient in shutdown method

Fixes #7388

Author: felixbarny

exporters/sender/jdk/src/main/java/io/opentelemetry/exporter/sender/jdk/internal/JdkHttpSender.java

@@ -390,6 +390,13 @@ public CompletableResultCode shutdown() {
     if (managedExecutor) {
       executorService.shutdown();
     }
+    if (AutoCloseable.class.isInstance(client)) {
+      try {
+        AutoCloseable.class.cast(client).close();
+      } catch (Exception e) {
+        return CompletableResultCode.ofExceptionalFailure(e);
+      }
+    }
     return CompletableResultCode.ofSuccess();
   }
 }

exporters/sender/jdk/src/test/java/io/opentelemetry/exporter/sender/jdk/internal/JdkHttpSenderTest.java

@@ -18,6 +18,7 @@
 import io.opentelemetry.exporter.internal.marshal.Serializer;
 import io.opentelemetry.sdk.common.export.RetryPolicy;
 import java.io.IOException;
+import java.lang.reflect.Method;
 import java.net.ConnectException;
 import java.net.ServerSocket;
 import java.net.http.HttpClient;
@@ -29,6 +30,7 @@
 import org.assertj.core.api.InstanceOfAssertFactories;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.condition.EnabledForJreRange;
 import org.junit.jupiter.api.extension.ExtendWith;
 import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
@@ -66,6 +68,16 @@ void setup() throws IOException, InterruptedException {
             null);
   }
 
+  @Test
+  @EnabledForJreRange(
+      minVersion = 21,
+      disabledReason = "HttpClient#close has been added in Java 21")
+  void testShutdown() throws Exception {
+    sender.shutdown();
+    Method close = HttpClient.class.getMethod("close");
+    close.invoke(verify(mockHttpClient));
+  }
+
   @Test
   void sendInternal_RetryableConnectTimeoutException() throws IOException, InterruptedException {
     assertThatThrownBy(() -> sender.sendInternal(new NoOpMarshaler()))