Example on Ubuntu 22.10 throws `errno = 22`

[Schwusch]

Running the example on Ubuntu 22.10 with Flutter 3.7.0-1.2.pre gives this error on startup:

══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY╞═══════════════════════════════════════════════════════════
The following SerialPortError was thrown building Builder(dirty):
Invalid argument, errno = 22

The relevant error-causing widget was:
  Builder
  Builder:file:///home/schwusch/development/flutter_libserialport/example/lib/main.dart:52:17

When the exception was thrown, this was the stack:
#0      Util.call (package:libserialport/src/util.dart:39:7)
#1      Util.toInt (package:libserialport/src/util.dart:77:16)
#2      _SerialPortImpl.busNumber (package:libserialport/src/port.dart:284:17)
#3      _ExampleAppState.build.<anonymous closure>
(package:flutter_libserialport_example/main.dart:59:52)
#4      Builder.build (package:flutter/src/widgets/basic.dart:7448:48)

Running flutter --version:

Flutter 3.7.0-1.2.pre • channel beta • https://github.com/flutter/flutter.git
Framework • revision c29b09b878 (2 weeks ago) • 2022-12-19 18:30:12 -0600
Engine • revision 8c99b0feaf
Tools • Dart 2.19.0 (build 2.19.0-444.2.beta) • DevTools 2.20.0

[Schwusch]

When skimming through old issues, I saw the trick with LIBSERIALPORT_DEBUG=1, and this is the output:

sp: sp_get_port_by_name(/dev/ttyS4, 0x7f48e80c4990) called.
sp: Building structure for port /dev/ttyS4.
sp: get_port_details returning SP_OK.
sp: sp_get_port_by_name returning SP_OK.
sp: sp_get_port_description(0x7f48e847dde0) called.
sp: sp_get_port_description returning ttyS4.
sp: sp_get_port_transport(0x7f48e847dde0) called.
sp: sp_get_port_transport returning 0.
sp: sp_get_port_usb_bus_address(0x7f48e847dde0) called.
sp: sp_get_port_usb_bus_address returning SP_ERR_ARG: Port does not use USB transport.
sp: sp_last_error_message() called.
sp: sp_last_error_message returning Invalid argument.
sp: sp_free_error_message(Invalid argument) called.
sp: sp_free_error_message returning.
sp: sp_last_error_code() called.
sp: sp_last_error_code returning 22.
sp: sp_last_error_message() called.
sp: sp_last_error_message returning Invalid argument.
sp: sp_free_error_message(Invalid argument) called.
sp: sp_free_error_message returning.
sp: sp_last_error_code() called.
sp: sp_last_error_code returning 22.

[mateen-demah]

@Schwusch did you find a fix or workaround for this error? Facing the problem here.

[Schwusch]

@mateen-demah I did port the Golang serial library function for getting a more valid list of ports, but abandoned that code in favour of just filtering on vendor/product ID. I seriously considered porting all of Golangs serial library in order to have a pure Dart implementation (no libserialport dependency). Maybe at some point in the future.

[mateen-demah]

@mateen-demah I did port the Golang serial library function for getting a more valid list of ports, but abandoned that code in favour of just filtering on vendor/product ID. I seriously considered porting all of Golangs serial library in order to have a pure Dart implementation (no libserialport dependency). Maybe at some point in the future.

@Schwusch how did you do that? From the example app, you'd have create a SerialPort object to get access to the vendor/product ID. And the error occurs at the point of SerialPort object creation.

[Schwusch]

My use case was to present the user with a list of available ports to choose from, and that is possible without instantiating a SerialPort object, by enumerating the files in the /dev directory like they do it in go-serial. After that, you can instantiate the object with the chosen name SerialPort(name);. Also, it is a good idea to wrap the instantiation with a try-catch :)

[Schwusch]

Also, you can read the vid/pid from the file system

[mateen-demah]

Thanks @Schwusch I'll try that out. In my case, I don't just want to present the ports so I really need that object.

[mingpepe]

When skimming through old issues, I saw the trick with LIBSERIALPORT_DEBUG=1, and this is the output:

sp: sp_get_port_by_name(/dev/ttyS4, 0x7f48e80c4990) called.
sp: Building structure for port /dev/ttyS4.
sp: get_port_details returning SP_OK.
sp: sp_get_port_by_name returning SP_OK.
sp: sp_get_port_description(0x7f48e847dde0) called.
sp: sp_get_port_description returning ttyS4.
sp: sp_get_port_transport(0x7f48e847dde0) called.
sp: sp_get_port_transport returning 0.
sp: sp_get_port_usb_bus_address(0x7f48e847dde0) called.
sp: sp_get_port_usb_bus_address returning SP_ERR_ARG: Port does not use USB transport.
sp: sp_last_error_message() called.
sp: sp_last_error_message returning Invalid argument.
sp: sp_free_error_message(Invalid argument) called.
sp: sp_free_error_message returning.
sp: sp_last_error_code() called.
sp: sp_last_error_code returning 22.
sp: sp_last_error_message() called.
sp: sp_last_error_message returning Invalid argument.
sp: sp_free_error_message(Invalid argument) called.
sp: sp_free_error_message returning.
sp: sp_last_error_code() called.
sp: sp_last_error_code returning 22.

Seems like your serial port is not USB type, hence no bus number can be provided. Possible throw an exception from here, then trace code can find that the library just complain about it's type when getting bus number. https://github.com/jpnurmi/libserialport.dart/blob/main/lib/src/port.dart#L285 https://github.com/martinling/libserialport/blob/master/serialport.c#L172

[mateen-demah]

Thanks @mingpepe . For my usecase I'm only interested in USB devices so I put a try block around the port creation code and just skipped when something went wrong. Worked like a charm; all the USB devices showed up.