From edc2bf7346ea88d8db773535bf62a59dbea4fb20 Mon Sep 17 00:00:00 2001
From: Alex Panchenko <440271+panchenko@users.noreply.github.com>
Date: Fri, 4 Apr 2025 16:09:35 +0200
Subject: [PATCH] stub: Utility method StreamObservers.nextAndComplete() that
 does both onNext and onComplete (#11778)

---
 .../java/io/grpc/stub/StreamObservers.java    | 23 +++++++++---
 .../io/grpc/stub/StreamObserversTest.java     | 35 +++++++++++++++++++
 2 files changed, 54 insertions(+), 4 deletions(-)
 create mode 100644 stub/src/test/java/io/grpc/stub/StreamObserversTest.java

diff --git a/stub/src/main/java/io/grpc/stub/StreamObservers.java b/stub/src/main/java/io/grpc/stub/StreamObservers.java
index 2cc53ea0aa..a421d3eca2 100644
--- a/stub/src/main/java/io/grpc/stub/StreamObservers.java
+++ b/stub/src/main/java/io/grpc/stub/StreamObservers.java
@@ -23,12 +23,21 @@ import java.util.Iterator;
 /**
  * Utility functions for working with {@link StreamObserver} and it's common subclasses like
  * {@link CallStreamObserver}.
- *
- * @deprecated Of questionable utility and generally not used.
  */
-@Deprecated
-@ExperimentalApi("https://github.com/grpc/grpc-java/issues/4694")
 public final class StreamObservers {
+  // Prevent instantiation
+  private StreamObservers() { }
+
+  /**
+   * Utility method to call {@link StreamObserver#onNext(Object)} and
+   * {@link StreamObserver#onCompleted()} on the specified responseObserver.
+   */
+  @ExperimentalApi("https://github.com/grpc/grpc-java/issues/10957")
+  public static <T> void nextAndComplete(StreamObserver<T> responseObserver, T response) {
+    responseObserver.onNext(response);
+    responseObserver.onCompleted();
+  }
+
   /**
    * Copy the values of an {@link Iterator} to the target {@link CallStreamObserver} while properly
    * accounting for outbound flow-control.  After calling this method, {@code target} should no
@@ -40,7 +49,10 @@ public final class StreamObservers {
    *
    * @param source of values expressed as an {@link Iterator}.
    * @param target {@link CallStreamObserver} which accepts values from the source.
+   * @deprecated Of questionable utility and generally not used.
    */
+  @Deprecated
+  @ExperimentalApi("https://github.com/grpc/grpc-java/issues/4694")
   public static <V> void copyWithFlowControl(final Iterator<V> source,
       final CallStreamObserver<V> target) {
     Preconditions.checkNotNull(source, "source");
@@ -80,7 +92,10 @@ public final class StreamObservers {
    *
    * @param source of values expressed as an {@link Iterable}.
    * @param target {@link CallStreamObserver} which accepts values from the source.
+   * @deprecated Of questionable utility and generally not used.
    */
+  @Deprecated
+  @ExperimentalApi("https://github.com/grpc/grpc-java/issues/4694")
   public static <V> void copyWithFlowControl(final Iterable<V> source,
       CallStreamObserver<V> target) {
     Preconditions.checkNotNull(source, "source");
diff --git a/stub/src/test/java/io/grpc/stub/StreamObserversTest.java b/stub/src/test/java/io/grpc/stub/StreamObserversTest.java
new file mode 100644
index 0000000000..86a1aba2e7
--- /dev/null
+++ b/stub/src/test/java/io/grpc/stub/StreamObserversTest.java
@@ -0,0 +1,35 @@
+/*
+ * Copyright 2025 The gRPC Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package io.grpc.stub;
+
+import org.junit.Test;
+import org.mockito.InOrder;
+import org.mockito.Mockito;
+
+public class StreamObserversTest {
+
+  @Test
+  public void nextAndComplete() {
+    @SuppressWarnings("unchecked")
+    StreamObserver<String> observer = Mockito.mock(StreamObserver.class);
+    InOrder inOrder = Mockito.inOrder(observer);
+    StreamObservers.nextAndComplete(observer, "TEST");
+    inOrder.verify(observer).onNext("TEST");
+    inOrder.verify(observer).onCompleted();
+    inOrder.verifyNoMoreInteractions();
+  }
+}