How to use the AnyPointer type?

Hi,

I have a Request struct with the following schema:

struct Request {
	timestamp @0: UInt64;
	payload @1: AnyPointer;
}

The payload can either be a capnp.Data struct filled from a Node.js Buffer, or another user-defined struct (let’s say a Todo struct for example). How am I supposed to create a message with such payload?

I tried the following:

const msg = new capnp.Message();
const req = msg.initRoot(Request);
req.setTimestamp(capnp.Uint64.fromNumber(0));

// With a capnp.Data struct:
const payload = capnp.Struct.initStructAt(0, capnp.Data, req);
payload.copyBuffer(Buffer.from("coucou"));
req.setPayload(payload);
// or with a Todo struct:
const payload = capnp.Struct.initStrutAt(0, Todo, req);
payload.setText("Masterize capnp-ts");
payload.setDone(false);
res.setPayload(payload);

The payload is transmitted but the timestamp field seems corrupted when I set the payload. So, what is the correct way to fill this AnyPointer payload field?

[jonathan-roy]

I finally found a very hacky way to fill the capnp.Data struct. First, I created a DataBox struct with the following schema:

@0x915f3367709de788;
  
struct DataBox {
        value @0 :Data;
}

Then I use it like this:

const msg = new capnp.Message();
const dataBox = msg.initRoot(DataBox);
dataBox.initValue(yourReadyData.length);
const payload = dataBox.getValue();
payload.copyBuffer(yourReadyData);
req.setPayload(payload);

It is obviously not ideal so I won’t close this issue, but it seems to work.

[ndisidore]

Sorry for the necro thread, but this still seems to be an issue: this could definitely be user error, but as far as I can tell a few data types (Data & AnyPointer are the ones tested) are near impossible to use because copyBuffer has some fundamental issues in that it assumes your destination buffer is (at least) the right size.

In my setup, I’m working with a protobuf struct like

struct MyStruct {
  value @0 :Data;
}

Accompanying JS code looks like

const prepopulatedBuffer = new TextEncoder().encode('test')

const msg = new capnp.Message()
const myStruct = msg.initRoot(MyStruct)
const data = new capnp.Message().initRoot(capnp.Data)
...

I’d like to copy an externally populated Uint8Array prepopulatedBuffer to data. However, passing both the raw Uint8Array and the Uint8Array as an ArrayBuffer (via prepopulatedBuffer.buffer) don’t accomplish this because copyBuffer truncates based on the destination size (which I haven’t found a way to not be 0 yet) and results in the same behavior @jonathan-roy was seeing.