test: client ids should be re-used

google-cloud-spanner/src/main/java/com/google/cloud/spanner/DatabaseClient.java

@@ -24,6 +24,9 @@
  */
 public interface DatabaseClient {
 
+  /** Only for testing */
+  String getClientId();
+
   /**
    * Writes the given mutations atomically to the database.
    *

google-cloud-spanner/src/main/java/com/google/cloud/spanner/DatabaseClientImpl.java

@@ -51,6 +51,10 @@ private enum SessionMode {
     this.pool = pool;
   }
 
+  public String getClientId() {
+    return clientId;
+  }
+
   @VisibleForTesting
   PooledSessionFuture getReadSession() {
     return pool.getReadSession();

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SessionImpl.java

@@ -98,6 +98,10 @@ static interface SessionTransaction {
     this.databaseId = SessionId.of(name).getDatabaseId();
   }
 
+  public String getClientId() {
+    return null;
+  }
+
   @Override
   public String getName() {
     return name;

google-cloud-spanner/src/main/java/com/google/cloud/spanner/SessionPool.java

@@ -1094,6 +1094,10 @@ private void markCheckedOut() {
       this.leakedException = new LeakedSessionException();
     }
 
+    public String getClientId() {
+      return null;
+    }
+
     @Override
     public Timestamp write(Iterable<Mutation> mutations) throws SpannerException {
       try {
@@ -1312,6 +1316,10 @@ private PooledSession(SessionImpl delegate) {
       this.lastUseTime = clock.instant();
     }
 
+    public String getClientId() {
+      return null;
+    }
+
     @Override
     public String toString() {
       return getName();

google-cloud-spanner/src/test/java/com/google/cloud/spanner/it/ITClientIdTest.java

@@ -0,0 +1,62 @@
+/*
+ * Copyright 2020 Google LLC
+ *
+ * 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 com.google.cloud.spanner.it;
+
+import static com.google.common.truth.Truth.assertThat;
+
+import com.google.cloud.spanner.DatabaseClient;
+import com.google.cloud.spanner.DatabaseId;
+import com.google.cloud.spanner.InstanceId;
+import com.google.cloud.spanner.IntegrationTestEnv;
+import com.google.cloud.spanner.Key;
+import com.google.cloud.spanner.ParallelIntegrationTest;
+import com.google.cloud.spanner.Spanner;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
+import org.junit.ClassRule;
+import org.junit.Test;
+import org.junit.experimental.categories.Category;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@Category(ParallelIntegrationTest.class)
+@RunWith(JUnit4.class)
+public class ITClientIdTest {
+  @ClassRule public static IntegrationTestEnv env = new IntegrationTestEnv();
+
+  @Test
+  public void testClientId() throws Exception {
+    Spanner spanner = env.getTestHelper().getClient();
+    InstanceId instanceId = env.getTestHelper().getInstanceId();
+    DatabaseId databaseId = DatabaseId.of(instanceId, "my-database");
+
+    Set<String> ids = new HashSet<>();
+    for (int i = 0; i < 100; i++) {
+      try {
+        DatabaseClient client = spanner.getDatabaseClient(databaseId);
+        ids.add(client.getClientId());
+        client.singleUse().readRow("MyTable", Key.of(0), Arrays.asList("MyColumn"));
+      } catch (Exception e) {
+        // ignore
+      }
+    }
+    // All the database clients have used the same client id.
+    assertThat(ids).hasSize(1);
+    assertThat(ids.iterator().next()).isEqualTo("client-1");
+  }
+}