mpremote rfc2217 telnet connection (rp2040 / Raspberry Pi Pico W)

[scruss]

mpremote connect supports communication over RFC 2217 - Telnet Com Port Control Option. What MicroPython code would I need to be running on a Raspberry Pi Pico W to make this remote connection work, please?

Attempts to use utelnetserver result in failed to access rfc2217://192.168.2.126:23 (it may be in use by another program). If I telnet to the same address using the telnet command, though, I get access to the REPL.

[Josverl]

@scruss, I added that option to support connection to Wokwi that can emulate espxx and rp2 boards in #12500
since i moved off the LoBo ports, i have missed a stable and performant telnet server (on esp32) for remote connections.
I've doe a few tests with telnet servers in MicroPython - but not to my satisfaction.

if you want a direct mpremote connection , it may be possible to just skip Telnet altogether as I mentioned in that PR:
'It would be simple to add support for a straight tcp pipe ( using socket://host:port ) if there is use for that as well.'
I think we just need the device to listen on a known socket , wrap the socket in a stream / IOBase and then dupterm to that stream.

conceptually something like

## completely untested code ##
s = usocket.socket(usocket.AF_INET, usocket.SOCK_STREAM)
s.bind(('0.0.0.0', 4321))
s.listen(1)
while True:
  (clientsocket, address) = s.accept()
  # now do something with the clientsocket
  # pretend this is a streamed filelike object
  stream = uio.IOBase(clientsocket)
  os.dupterm(stream)
## completely untested code ##

need some safeguards and error handling around that , and security will be non-existent

a small mpremote/transport_serial.py patch would be needed to also check for socket://

                if device.startswith("rfc2217://", "socket://"):
                    self.serial = serial.serial_for_url(device, **serial_kwargs)

[scruss]

Ah, thanks. I suspect I'm misunderstanding the intended usage of a rfc2217 connection. I'd hoped it was an alternative to the missing WebREPL support in mpremote

[Josverl]

Hear hear, I'd love to have that work with a telnet server on the device too

[andrewleech]

mpremote webrepl support has been proposed in #14141 using the webrepl websocket.