Trying to create a MultiSubscriber for a StructArrayTopic, help!

[truher]

Hi,

So I have a set of StructArrayTopics identified by a key prefix, and I want to subscribe to updates for all of them, and I'm having trouble figuring out how to do it.

I tried using a NetworkTableListenerPoller with readQueue(), from which I can get ValueEventData and eventually Value.getRaw(), but I can't find a way to unpack the bytes into the correct array.

Is there a wpistruct array unpacker? or some other way to combine "subscribe to prefix" with "StructArray"?

thanks!

[virtuald]

Do you have a non-python example you can post/link that does what you're looking for?

... but I think these tests do what you're looking for? https://github.com/robotpy/mostrobotpy/blob/main/subprojects/pyntcore/tests/test_struct_topic.py

[truher]

thanks, thats the example I was using, but the version using a poller didn't work. I'll try again I guess.

[virtuald]

If you have a non-python example that works, that would be helpful.

[truher]

I poked at this a bit more and found a way to do it:

What we've done in Java for a long time relies on StructBuffer.readArray(), which doesn't seem to exist in python. So roughly:

NetworkTableInstance inst = NetworkTableInstance.getDefault();
m_poller = new NetworkTableListenerPoller(inst);
m_poller.addListener(
     new MultiSubscriber(inst, new String[] { "foo" }, PubSubOption.keepDuplicates(true)),
     EnumSet.of(NetworkTableEvent.Kind.kValueAll));

...

for (NetworkTableEvent e : m_poller.readQueue()) {
    ValueEventData ve = e.valueData;
    NetworkTableValue v = ve.value;
    byte[] b = v.getRaw();
    Rotation3d[] sights = m_buf.readArray(b);
}                       

Here's an example of using a StructArray subscriber in python, which does the unpacking (but can't subscribe to a prefix):

inst = ntcore.NetworkTableInstance.getDefault()
sub = inst.getStructArrayTopic("foo/1", Datum).subscribe([])

...

queue = sub.readQueue()
item = queue.pop()
value0: Datum = item.value[0]
value1: Datum = item.value[1]

Here's an example that works in python, stepping through the raw array:

inst = ntcore.NetworkTableInstance.getDefault()
poller = ntcore.NetworkTableListenerPoller(inst)
poller.addListener(["foo"], ntcore.EventFlags.kValueAll)

...

queue = poller.readQueue()
event = queue.pop()
item_size = wpistruct.getSize(Datum)
raw_array  =  event.data.value.getRaw()
raw_item_array = [raw_array[i : i + item_size] for i in range(0, len(raw_array), item_size)]
value0: Datum = wpistruct.unpack(Datum, raw_item_array[0])
value1: Datum = wpistruct.unpack(Datum, raw_item_array[1])

So this works fine, it's just that the "listener poller" unpacking is so much clumsier than in the nice clean "subscriber" case.

[virtuald]

Added #107 to remind me to add a pack/unpack array -- it was only added to C++ recently.