GH-44: Clear signature columns before re-populating in ArrowFlightStatement#executeFlightInfoQuery

ArrowFlightStatement#executeFlightInfoQuery appended the dataset schema
columns to the statement's reused Meta.Signature without first clearing
them, doubling the column list on every invocation. When the FlightInfo
has at least one endpoint, ArrowFlightJdbcVectorSchemaRootResultSet
overwrites signature.columns from the actual stream schema and hides
the duplication. With an empty endpoint list — reported against both
Rust- and Denodo-based Flight SQL servers — that overwrite never runs
and ResultSetMetaData#getColumnCount() reports 2x the schema width.

Regression introduced in 15.0.0 (GH-33475 prepared-statement parameter
binding) when handle.signature became mutable across executions.

Adds a regression test that registers a mock query with no endpoints
and asserts ResultSetMetaData#getColumnCount() matches the schema.

Closes #44.

Author: hkad98

flight/flight-sql-jdbc-core/src/main/java/org/apache/arrow/driver/jdbc/ArrowFlightStatement.java

@@ -52,6 +52,7 @@ public FlightInfo executeFlightInfoQuery() throws SQLException {
     }
 
     final Schema resultSetSchema = preparedStatement.getDataSetSchema();
+    signature.columns.clear();
     signature.columns.addAll(
         ConvertUtils.convertArrowFieldsToColumnMetaDataList(resultSetSchema.getFields()));
     setSignature(signature);

flight/flight-sql-jdbc-core/src/test/java/org/apache/arrow/driver/jdbc/ResultSetMetadataTest.java

@@ -220,4 +220,23 @@ public void testShouldIsSearchable() throws SQLException {
   public void testShouldGetColumnTypesFromOutOfBoundIndex() {
     assertThrows(IndexOutOfBoundsException.class, () -> metadata.getColumnType(4));
   }
+
+  /**
+   * Regression test for <a href="https://github.com/apache/arrow-java/issues/44">issue #44</a>:
+   * {@code ArrowFlightStatement#executeFlightInfoQuery} appends schema columns to the reused {@code
+   * Meta.Signature} without clearing the existing list. When the result has at least one endpoint,
+   * the {@code FlightStream} consumption path overwrites {@code signature.columns} from the actual
+   * stream schema and hides the duplication. With an empty endpoint list — the scenario reported
+   * against both Rust- and Denodo-based Flight SQL servers — that overwrite never runs and {@code
+   * ResultSetMetaData#getColumnCount()} reports double the schema width.
+   */
+  @Test
+  public void testShouldNotDuplicateColumnsWhenFlightInfoHasNoEndpoints() throws SQLException {
+    try (Connection conn = FLIGHT_SERVER_TEST_EXTENSION.getConnection(false);
+        Statement st = conn.createStatement();
+        ResultSet rs =
+            st.executeQuery(CoreMockedSqlProducers.LEGACY_REGULAR_NO_ENDPOINTS_SQL_CMD)) {
+      assertThat(rs.getMetaData().getColumnCount(), equalTo(1));
+    }
+  }
 }

flight/flight-sql-jdbc-core/src/test/java/org/apache/arrow/driver/jdbc/utils/CoreMockedSqlProducers.java

@@ -67,6 +67,8 @@ public final class CoreMockedSqlProducers {
   public static final String LEGACY_METADATA_SQL_CMD = "SELECT * FROM METADATA";
   public static final String LEGACY_CANCELLATION_SQL_CMD = "SELECT * FROM TAKES_FOREVER";
   public static final String LEGACY_REGULAR_WITH_EMPTY_SQL_CMD = "SELECT * FROM TEST_EMPTIES";
+  public static final String LEGACY_REGULAR_NO_ENDPOINTS_SQL_CMD =
+      "SELECT * FROM TEST_NO_ENDPOINTS";
 
   public static final String UUID_SQL_CMD = "SELECT * FROM UUID_TABLE";
   public static final String UUID_PREPARED_SELECT_SQL_CMD =
@@ -100,12 +102,22 @@ public static MockFlightSqlProducer getLegacyProducer() {
     addLegacyMetadataSqlCmdSupport(producer);
     addLegacyCancellationSqlCmdSupport(producer);
     addQueryWithEmbeddedEmptyRoot(producer);
+    addQueryWithNoEndpoints(producer);
     addUuidSqlCmdSupport(producer);
     addUuidPreparedSelectSqlCmdSupport(producer);
     addUuidPreparedUpdateSqlCmdSupport(producer);
     return producer;
   }
 
+  private static void addQueryWithNoEndpoints(final MockFlightSqlProducer producer) {
+    final Schema querySchema =
+        new Schema(
+            ImmutableList.of(
+                new Field("ID", new FieldType(true, new ArrowType.Int(64, true), null), null)));
+    producer.addSelectQuery(
+        LEGACY_REGULAR_NO_ENDPOINTS_SQL_CMD, querySchema, Collections.emptyList());
+  }
+
   /**
    * Gets a {@link MockFlightSqlProducer} configured with UUID test data.
    *