open() fails with NetworkError: Unable to claim interface

[mibcat]

Hi !
I like to use the linked npm package in an Angular application but I'm not able to open the serial port.

This is the test code:

    // implementation with web-serial-polyfill lib
    this.comPort = await serial.requestPort();
    if (this.comPort) {
      console.log(this.comPort);
      await this.comPort.open();
      console.log(this.comPort);
    }

The requestPort() function is working (permission access dialog is shown and populated with the device):

SerialPort {serialOptions_: {…}, device_: USBDevice}
device_: USBDevice {configurations: Array(1), deviceClass: 2, deviceProtocol: 0, deviceSubclass: 2, deviceVersionMajor: 2, …}
serialOptions_: {baudrate: 115200, databits: 8, stopbits: 1, parity: "none", buffersize: 255, …}
transferInterface_: USBInterface {alternates: Array(1), claimed: false, interfaceNumber: 1, alternate: null}
__proto__: Object

but the following open() function always fails:

core.js:4197 ERROR Error: Uncaught (in promise): Error: Error setting up device: NetworkError: Unable to claim interface.
Error: Error setting up device: NetworkError: Unable to claim interface.
    at SerialPort.open (serial.js:88)
    at resolvePromise (zone-evergreen.js:798)
    at zone-evergreen.js:705
    at rejected (tslib.es6.js:72)
    at ZoneDelegate.invoke (zone-evergreen.js:364)
    at Object.onInvoke (core.js:27430)
    at ZoneDelegate.invoke (zone-evergreen.js:363)
    at Zone.run (zone-evergreen.js:123)
    at zone-evergreen.js:857
    at ZoneDelegate.invokeTask (zone-evergreen.js:399)
    at Object.onInvokeTask (core.js:27418)

What's the exact meaning of "Unable to claim interface" ?
The device shouldn't be blocked by an other application. It's listed under /dev/ttyACM0 and I can open it with a serial terminal program like cutecom without problems.

Thanks for any help !

Best regards,
Michael.

[reillyeon]

This library is a polyfill for the Serial API on platforms which do not have drivers for a USB serial port. If your system is detecting the device and creating /dev/ttyACM0 then you can use the real Serial API implementation in your browser. Enable it for development purposes using chrome://flags/#enable-experimental-web-platform-features or sign up for the Origin Trial here: https://developers.chrome.com/origintrials/#/view_trial/2992641952387694593

#10 tracks work to make the polyfill and browser implementations integrate more seamlessly.

[mibcat]

OK - thanks for your feedback.

[helder-a-reis]

Hi, I am using this library to open a Serial connection on an Angular app running Chrome for Android and I'm getting a similar error. I was able to connect to the equipment using the WebUSB API, but that didn't provide the Serial connection, and the Serial API is not supported on Android, as far as I understand (even if enabling experimental features).
Should this library work for my use case? Thanks in advance. My code:

`import * as Serial from 'web-serial-polyfill';

public async connectSerial() {
    try {
        this.port = await Serial.serial.requestPort({ usbVendorId: 1546 });
        await this.port.open({ baudRate: 9600 });
        console.log(this.port);
    } catch (err) {
        console.error('There was an error opening the serial port:', err);
    }
}

`

[reillyeon]

If you are hitting an error claiming an interface on Android you are probably running into the case where the Android system has loaded a driver for the device even though it doesn't provide an API for applications to use that driver. We're looking at a solution for this in Chromium issue 1099521 but haven't had time to finish the implementation.