fix: return EmptyQueryResponse for empty statements (#126)

Empty SQL statements should cause the server to return an EmptyQueryResponse instead of a CommandCompleteResponse. See https://www.postgresql.org/docs/14/protocol-message-formats.html

Author: olavloite

src/main/java/com/google/cloud/spanner/pgadapter/wireoutput/EmptyQueryResponse.java

@@ -0,0 +1,42 @@
+// Copyright 2022 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.pgadapter.wireoutput;
+
+import java.io.DataOutputStream;
+import java.text.MessageFormat;
+
+public class EmptyQueryResponse extends WireOutput {
+ public EmptyQueryResponse(DataOutputStream output) {
+ super(output, 4);
+ }
+
+ @Override
+ protected void sendPayload() throws Exception {}
+
+ @Override
+ public byte getIdentifier() {
+ return 'I';
+ }
+
+ @Override
+ protected String getMessageName() {
+ return "EmptyQueryResponse";
+ }
+
+ @Override
+ protected String getPayloadString() {
+ return new MessageFormat("Length: {0}").format(new Object[] {this.length});
+ }
+}

src/main/java/com/google/cloud/spanner/pgadapter/wireprotocol/QueryMessage.java

@@ -27,6 +27,7 @@
 import com.google.cloud.spanner.pgadapter.statements.MatcherStatement;
 import com.google.cloud.spanner.pgadapter.utils.StatementParser;
 import com.google.cloud.spanner.pgadapter.wireoutput.CopyInResponse;
+import com.google.cloud.spanner.pgadapter.wireoutput.EmptyQueryResponse;
 import com.google.cloud.spanner.pgadapter.wireoutput.ErrorResponse;
 import com.google.cloud.spanner.pgadapter.wireoutput.ErrorResponse.State;
 import com.google.cloud.spanner.pgadapter.wireoutput.ReadyResponse;
@@ -121,6 +122,8 @@ public void handleQuery() throws Exception {
 
  // Return early as we do not respond with CommandComplete after a COPY command.
  return;
+ } else if ("".equals(this.statement.getCommandTag(index))) {
+ new EmptyQueryResponse(outputStream).send();
  } else {
  if (this.statement.containsResultSet(index)) {
  new RowDescriptionResponse(

src/test/java/com/google/cloud/spanner/pgadapter/JdbcSimpleModeMockServerTest.java

@@ -104,6 +104,25 @@ public void testEmptyStatement() throws SQLException {
  assertEquals(0, mockSpanner.countRequestsOfType(ExecuteSqlRequest.class));
  }
 
+ @Test
+ public void testEmptyStatementFollowedByNonEmptyStatement() throws SQLException {
+ try (Connection connection = DriverManager.getConnection(createUrl())) {
+ try (Statement statement = connection.createStatement()) {
+ // Execute should return false for the first statement.
+ assertFalse(statement.execute(""));
+
+ assertTrue(statement.execute("SELECT 1"));
+ try (ResultSet resultSet = statement.getResultSet()) {
+ assertTrue(resultSet.next());
+ assertEquals(1L, resultSet.getLong(1));
+ assertFalse(resultSet.next());
+ }
+ assertFalse(statement.getMoreResults());
+ }
+ }
+ assertEquals(1, mockSpanner.countRequestsOfType(ExecuteSqlRequest.class));
+ }
+
  @Test
  public void testWrongDialect() {
  // Let the mock server respond with the Google SQL dialect instead of PostgreSQL. The