Complex Vector Examples?

[Johnny Sheeley]

I'm trying to build flatbuffers using a schema like this:

struct Header1 {

...

}

table Event {

  header1: Header1;

  ...

  headerChecksum: ulong;

  body: [ubyte];

  bodyChecksum:ulong;

}

table EventTable {

  events: [Event];

}

I see the basic Monster example in the codebase, and a reference to more complex vector usage, but I am running into an IndexOutOfBoundsException when I try to deserialize. Are there more in-depth examples of how this works? Here's a simplified version of how I'm building:

public byte[] serialize(List<EventData>Events){

         byte[] eventBytes = getBytesFromEvents(events);

    FlatBufferBuilder fbb = new FlatBufferBuilder();

    EventTable.startEventsVector(fbb, events.size());

    for (byte b : eventBytes) {

      fbb.addByte(b);

    }

    int eventsEnd = fbb.endVector();

    EventTable.startEventTable(fbb);

    EventTable.addEvents(fbb, eventsEnd);

    int end = EventTable.endEventTable(fbb);

    EventTable.finishEventTableBuffer(fbb, end);

    return fbb.sizedByteArray();

}

public byte[] getBytesFromEvents(List<EventData>Events){

  FlatBufferBuilder fbb = new FlatBufferBuilder();

  for (Map<String, Object> event : events) {

    Map<String, Object> bodyMap = clean(event);

    byte[] body = bodySerializer.serialize(bodyMap);

    int bodyOffset = Event.createBodyVector(fbb, body);

    Event.startEvent(fbb);

    // Headers

    Event.addHeader1(fbb, createHeader1(fbb, event);

    // ...

    // Body

    Event.addBody(fbb, bodyOffset);

    Event.addBodyChecksum(fbb, checksum.getValue());

  }

  return fbb.sizedByteArray();

}

And to deserialize:

EventTable eventRoot = EventTable.getRootAsEventTable(ByteBuffer.wrap(bytes));

Any tips/complex samples that may be helpful?

Thanks!

Johnny

[Johnny Sheeley]

Had totally misread things with a half-awake brain. Have it working successfully like so:

         FlatBufferBuilder fbb = new FlatBufferBuilder();

    int[] eventOffsets = addEventsToBuffer(fbb, events);

    int eventVectorOffset = EventContainer.createEventsVector(fbb, eventOffsets);

    EventContainer.startEventContainer(fbb);

    EventContainer.addEvents(fbb, eventVectorOffset);

    int end = EventContainer.endEventContainer(fbb);

    EventContainer.finishEventContainerBuffer(fbb, end);

    return fbb.sizedByteArray();

[Wouter van Oortmerssen]

Yup, the last one looks correct!

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[Johnny Sheeley]

One thing that I ran into when adding multiple events was I had to add this check, which doesn't make sense to me:

https://gist.github.com/sheeley/38fd734010401af716c2#file-sample-java-L26-L33

Does that make sense to you? With this check, things appear to serialize/deserialize correctly, but I'm concerned that it doesn't seem like it should need to happen in certain cases but not others.

[Wouter van Oortmerssen]

That definitely shouldn't be needed. That code makes assumptions about alignment and how things are put into a FlatBuffer, and may break. If you want to checksum your headers, you're better off doing that entirely outside the realm of the FlatBuffer serialized data.

[Johnny Sheeley]

Will make changes, then! Thanks for the feedback.