[Java] Flight fails to handle list vector

[John Peterson]

I believe I'm running into a bug with Flight but I'd like to confirm and
get some advice on a potential fix. I'm not sure where to look or what
could be causing it.

The code in question simply uploads a one-element List<Integer> to the
example server, fetches it from the server, and attempts to append the data
from the server to a new VectorSchemaRoot. It fails in the same way
regardless of whether or not I construct a VectorSchemaRoot instance.

Likewise, the data from the server can't be written out with the JSON
writer, it'll fail in the same way. However, changing the data from a
ListVector to an IntVector causes it to succeed.

Any help would be appreciated.

Thanks,
John

Code in question:
// Set up the server and client
BufferAllocator allocator = new RootAllocator(Long.MAX_VALUE);
Location l = Location.forGrpcInsecure(FlightTestUtil.LOCALHOST, 12233);
ExampleFlightServer server = new ExampleFlightServer(allocator, l);
server.start();
FlightClient client = FlightClient.builder(allocator, l).build();

// Write a one-element List<Integer>
ListVector listVector = ListVector.empty("list", allocator);
UnionListWriter writer = listVector.getWriter();
writer.startList();
writer.integer().writeInt(1);
writer.endList();
writer.setValueCount(1);

// Send that data to the server
VectorSchemaRoot root = VectorSchemaRoot.of(listVector);
ClientStreamListener listener =
client.startPut(FlightDescriptor.path("test"), root, new
AsyncPutListener());
root.setRowCount(1);
listener.putNext();
root.clear();
listener.completed();

// wait for ack to avoid memory leaks.
listener.getResult();

// Attempt to read it back
FlightInfo info = client.getInfo(FlightDescriptor.path("test"));
try (final FlightStream stream =
client.getStream(info.getEndpoints().get(0).getTicket())) {
  VectorSchemaRoot newRoot = stream.getRoot();
  while (stream.next()) {
    // Copying into an entirely new VectorSchemaRoot fails
    try {
      ListVector newList = ListVector.empty("list", allocator);

newList.addOrGetVector(FieldType.nullable(Types.MinorType.INT.getType()));
      VectorSchemaRoot copyRoot = VectorSchemaRoot.of(newList);
      VectorSchemaRootAppender.append(copyRoot, newRoot);
    } catch (IndexOutOfBoundsException e) {
      System.err.println("Expected IOOBE caught");
    }

    // The same is true if we try to copy the data from the server to our
VectorSchemaRoot
    try {
      VectorSchemaRootAppender.append(root, newRoot);
    } catch (IndexOutOfBoundsException e) {
      System.err.println("Expected IOOBE caught again");
      throw e;
    }

    root.clear();
    newRoot.clear();
  }
}