fix: iterate over async result set in sync (#416)

Iterating over an AsyncResultSet using a standard while (rs.next()) loop would fail after the last row was consumed.

Author: olavloite

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

@@ -559,7 +559,7 @@ public boolean next() throws SpannerException {
  this.state = State.SYNC;
  }
  boolean res = delegateResultSet.next();
- currentRow = delegateResultSet.getCurrentRowAsStruct();
+ currentRow = res ? delegateResultSet.getCurrentRowAsStruct() : null;
  return res;
  }
 

google-cloud-spanner/src/test/java/com/google/cloud/spanner/DatabaseClientImplTest.java

@@ -225,6 +225,19 @@ public CallbackResponse cursorReady(AsyncResultSet resultSet) {
  assertThat(rowCount.get()).isEqualTo(1);
  }
 
+ @Test
+ public void singleUseAsyncWithoutCallback() throws Exception {
+ DatabaseClient client =
+ spanner.getDatabaseClient(DatabaseId.of(TEST_PROJECT, TEST_INSTANCE, TEST_DATABASE));
+ int rowCount = 0;
+ try (AsyncResultSet rs = client.singleUse().executeQueryAsync(SELECT1)) {
+ while (rs.next()) {
+ rowCount++;
+ }
+ }
+ assertThat(rowCount).isEqualTo(1);
+ }
+
  @Test
  public void singleUseBound() {
  DatabaseClient client =