Provide or document how to create an asynchronous interface

[Sitin]

This is a suggested improvement.

Right now the library has only synchronous interface but the nusb used under the hood is async-first. It would be nice to have an option to use this library in asynchronous environments with minimal (or no) overhead from extra threads.

It seeams that in order to provide such functionality we need to add AsyncReader / AsyncWriter and probably an asynchronous version of CdcSerial. The USB manager and intent checking part may also require some changes.

[wuwbobo2021]

"It seeams that in order to provide such functionality we need to add AsyncReader / AsyncWriter and probably an asynchronous version of CdcSerial."

I hadn't considered adding such feature because serialport and a few other crates don't provide it (except serial2-tokio). Do you have a realistic use case?

"The USB manager and intent checking part may also require some changes." I don't think so.

PS: busy fixing a bug in Slint UI (issue 7203), I will not implement the asynchronous interface for this crate soon.

[Sitin]

There are several use cases that comes into my mind. The Rinf for Flutter is asynchronous by default and Tauri has async option. Both of them can use asynchronous API for Android serial connection.

As far as I am concerned, my own library for MavLink provides both sync and async interfaces and I want to support Android out of the box for both API flavours.

Still, I do understand why you may not want to go into this direction. Supporting two types of API is extremely labourious.

[wuwbobo2021]

I've released a new version of my crate which allows taking nusb transfer queues from the serial handler. AsyncReader / AsyncWriter will probably be added after the release of nusb 0.2.0.

[wuwbobo2021]

A reminder of existing problems in the released version 0.2.2:

The possible crate-level open function can return a result of Vec<Box<dyn UsbSerial>> instead of Box<dyn UsbSerial> to support multiple serial interfaces of the USB device.

The UsbSerial trait sealer should be changed to make it dyn compatible after supporting other serial adapters. Also note that CdcSerial::set_config can be marked as deprecated.

Trait UsbSerial should have a required function take_queues(&mut self) aside from into_queues(self), to reserve the possiblility of hardware flow control after turning it into a possible Box<dyn AsyncUsbSerial>. SyncReader and SyncWriter should be wrapped by Option in serial driver implementations.

I can't find any implementation in the original usb-serial-for-android that uses hardware flow control within synchronous read and write, though.

Struct AsyncUsbSerialImpl<T: UsbSerial> (should it be private?) which implements trait AsyncUsbSerial can be added to be used by the possible crate-level open_async(dev_info: &DeviceInfo) -> Result<Box<dyn AsyncUsbSerial>, Error>. Convertion from T: UsbSerial to AsyncUsbSerialImpl will be possible.