[Bug] stdin inserts extra 0x06 at start of every write command

[Novakasa]

Describe the bug
It looks like for every PybricksHub.write command, the hub receives an extra 0x06 character in the beginning, using most recent pybricksdev and beta firmware.

Seems like the 0x06 is the Command.WRITE_STDIN const. I would have expected this to be filtered out on the hub side.

Also, PybricksHub.write_line only adds \n as a newline. I'm not sure about this, but I would have expected \r\n since it's also the stdout format. write_line also adds the extra 0x06 at the start

To reproduce
Firmware: Pybricks MicroPython v3.3.0b4 on 2023-04-21; Powered Up City Hub with STM32F030RC
pybricksdev 1.0.0a45

PC program:

import asyncio
from pybricksdev.ble import find_device
from pybricksdev.connections.pybricks import PybricksHub

async def main():
    dev = await find_device()
    print(dev)
    hub = PybricksHub()
    await hub.connect(dev)
    print("connected!")
    await hub.run("ble-server/hub_programs/test_stdin_hub.py", print_output=True, wait=False)
    await asyncio.sleep(0.5)
    print("writing line...")
    await hub.write(b"012345\r\n")
    print("writing line...")
    await hub.write(b"hello\r\n")
    print("writing line...")
    await hub.write(b"\r\n")
    await asyncio.sleep(5.0)
    await hub.disconnect()

    print("OK!")

asyncio.run(main())

hub program:

# NOTE: Run this program with the latest
# firmware provided via https://beta.pybricks.com/

from pybricks.tools import wait

# Standard MicroPython modules
from usys import stdin, stdout
from uselect import poll

keyboard = poll()
keyboard.register(stdin)
buffer = bytearray()

for _ in range(3):
    while True:

        if keyboard.poll(50):
            byte = stdin.buffer.read(1)[0]
            print(byte, end=" ")
            buffer.append(byte)
            if buffer[-2:] == b"\r\n":
                print("\nline received")
                print(str(buffer))
                buffer = bytearray()
                break

wait(100)

Output:

2F:AC:DC:65:90:53: city-blue
connected!
100%|████████████████████████████████████████████████████████████████████████████████████████████████████| 388/388 [00:00<00:00, 1.11kB/s]
writing line...
writing line...
6 48 49 50 51 52 53 13 10
line received
bytearray(b'\x06012345\r\n')
writing line...
6 104 101 108 108 111 13 10
line received
bytearray(b'\x06hello\r\n')
6 13 10 
line received
bytearray(b'\x06\r\n')
OK!

Expected behavior
I am expecting no extra 0x06 at the beginning of stdin for each write command.

[dlech]

for every PybricksHub.write command, the hub receives an extra 0x06 character in the beginning

Thanks for reporting. Not sure how I missed this when testing.

I'm not sure about this, but I would have expected \r\n

I expected the same too, but it caused problems and was changed in pybricks/pybricksdev@a08db5f.