Access to plain channel which do not parse frames

[splatch]

This might be similar to #20 especially that I began using your code together with netty.
I've successfully integrated your library with Apache PLC4X project under plc4x-transport-socketcan in a way which is working, but still seems semi optimal. Within PLC4X we do usually generate code related to handling of exchanged payloads (frames, structs and such) so we don't need a CANFrame as we have our own representation for that. We're perfectly fine with raw stream of bytes.

For reference you can take a look on:
https://github.com/apache/plc4x/blob/537f4011ef93e09a04446cc520ba16b4a9258d9f/plc4j/transports/socketcan/src/main/java/org/apache/plc4x/java/transport/socketcan/netty/SocketCANChannel.java#L116L121
https://github.com/apache/plc4x/blob/537f4011ef93e09a04446cc520ba16b4a9258d9f/plc4j/transports/socketcan/src/main/java/org/apache/plc4x/java/transport/socketcan/netty/SocketCANChannel.java#L247

These are places where we explicitly touch JavaCAN APIs in which as you can see we just wrap or unwrap payload.

[pschichtel]

Correct me if I'm wrong: You are asking for an even lower-level API that skips the CanFrame wrapper entirely.

[splatch]

Yes, I am asking if you would consider dropping wrapping in one or another implementation of channels entirely. Since plc4x has its own ways for mapping payload there is no point to do it twice. After reading your code and doing complete read-write part I learned that socketcan returns fixed length chunks of data (16 or 72 bytes). I already arranged handling of data padding in plc4x so we're good to go one level down.

Given that your library is compatible with Apache license, has quite nice API it enables us to use socketcan as one of transport options for CAN frames. I didn't work with BDM/iso-tp part of APIs yet. So far we're only on CAN_RAW.

[splatch]

Also, if you will take a look on where we ended up with socketcan-transport it is mapping frame back to byte buffer and then pushing it via old IO support provided by netty to get it parsed by PLC4X payload mapping.

[pschichtel]

If you look here, here and here, you'll see that

ByteBuffer buf = ....;
CanFrame frame = RawCanChannel.read(buf);
assert buf == frame.getBuffer()

holds.

The CanFrame.create*(ByteBuffer) methods, especially createUnsafe just do very basic sanity checking on the buffer. All getters directly poke into the buffer, no parsing is done on the data, so this is already a very thin wrapper.

But still, I can easily just expose the existing readSocket and writeSocket methods, that take a ByteBuffer. That would directly call into JNI and never touch the buffer contents otherwise.

[splatch]

But still, I can easily just expose the existing readSocket and writeSocket methods, that take a ByteBuffer. That would directly call into JNI and never touch the buffer contents otherwise.

That'd be awesome. I looked at these and tried to create PlainChannel in plc4x transport (since raw was already booked) but I've ran into visibility troubles of the method/classes. That's why I come to consult how this could be done. I believe it could play nicely with further work related to netty as plc4x uses netty pipeline to chain "handlers".

[pschichtel]

Would this work for you: 0edb265 ? If so I can backport that to 2.x

[splatch]

Yeah - its gonna definitelly work for plc4x. Thank you very much for exposing these!

[pschichtel]

I just went ahead and released this as 2.3.0.

[pschichtel]

Do you think it would be possible to contribute the netty part of your PLC4X work back as part of #20 ?

[splatch]

I don't think there is a major issue with bringing it to your project, but I have to consult it with others what's their perception on that. The netty part we have pulls some project specific interfaces, but can be safely separated and run independently of PLC4X.