GH-44: Clear signature columns before re-populating in ArrowFlightStatement#executeFlightInfoQuery (#1135)

## Rationale

`ArrowFlightStatement#executeFlightInfoQuery` appends the dataset
schema columns to the statement's `Meta.Signature` without clearing
them, so the column list doubles on every invocation. When the
`FlightInfo` has at least one endpoint, `populateData` overwrites
`signature.columns` from the actual stream schema and hides the
duplication. With an empty endpoint list, that overwrite never
runs. Avatica then refuses the metadata with `Cannot have more columns
with the same name`.

This is a regression introduced in 15.0.0 by the prepared-statement
parameter binding work in
[GH-33475](apache/arrow#38404), which made
`handle.signature` mutable and shared across the `prepareAndExecute` →
`executeFlightInfoQuery` path.

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.
    *