USB Printer Not Displayed When Bluetooth Permissions Denied

[fedog-ops]

Description

When using the "Find a printer" feature, the app enters an indefinite search state if Bluetooth is turned off or if the user denies Bluetooth permissions. This happens even when a Star Micronics TSP100IIIU printer is physically connected via a USB-to-iOS cable.

The USB-connected printer only appears and is recognised if Bluetooth is enabled or if the user grants Bluetooth access — which should not be a requirement for wired printer discovery.

Your device where the bug occurs

• Device:
  iPad 10th gen
• OS:
  iOS 18.1
• Version
  1.10.0

Your printer

• Model Names:
  TSP100IIIU
• Firmware Version:
  Unknown
• Interface:
  Usb

Your development environment

react-native run-ios --device "iPad"
react-native run-ios --device "iPad" --mode Release

To Reproduce

  export enum InterfaceType {
    Unknown = 'Unknown',
    Lan = 'Lan',
    Bluetooth = 'Bluetooth',
    BluetoothLE = 'BluetoothLE',
    Usb = 'Usb'
    }

  static async portDiscovery(type: Array<InterfaceType>) {
    try {
      const printers: Array<{ id: string; name: string }> = [];

      const manager = await StarDeviceDiscoveryManagerFactory.create(type);

      manager.discoveryTime = 1000;

      manager.onPrinterFound = (printer: StarPrinter) => {
        printers.push({
          id: `${printer.connectionSettings.identifier}|${printer.connectionSettings.interfaceType}`,
          name: printer.information?.model || "Unknown Printer",
        });
      };

      await new Promise<void>((resolve) => {
        manager.onDiscoveryFinished = () => {
          resolve();
        };

        manager.startDiscovery();
      });

      return printers;
    } catch (error) {
      console.debug(`Error initialising printer discovery: ${String(error)}`);
      throw new Error("Unable to find any printers. Please try again");
    }
  }

Steps:

• Connect the TSP100IIIU printer via USB to iPad.
• Open the app and navigate to the "Find a printer" screen.
• When prompted for Bluetooth access, choose "Don't Allow".
  Alternatively, disable Bluetooth in iOS settings before launching the app.
• Observe: the discovery process hangs indefinitely and does not list the USB printer.

Expected behavior

The USB-connected TSP100IIIU printer should be discovered and returned in the array, regardless of Bluetooth state or permission.

Screenshots

Video A – Demonstrating the issue
https://github.com/user-attachments/assets/210cdbbe-dfbb-4458-8c20-b10e1755ad3f

Screenshot A – Expected result

[can-miki]

Please confirm whether there are any error messages for startDiscovery().

When discovery is performed via the all interface and Bluetooth cannot be used, a BluetoothUnavailable error occurs, so the discovery would fail.
If, at the time of performing discovery, there are interfaces on the host device that cannot be used due to its settings, please remove those and start discovery.

[fedog-ops]

In my case, startDiscovery() does not throw any error. Discovery just hangs silently, with no crash or console output, and stopDiscovery() has no effect. My try/catch never catches an error, and manager.discoveryTime = 1000 seems to be ignored.

It seems that the discovery time isn’t applied when there’s an internal Bluetooth issue, which makes the process appear to hang indefinitely. One workaround I’ve considered is wrapping discovery in a promise with setTimeout to manually control the discovery time.

I understand that removing Bluetooth from interfaceType would avoid this. However, since the library already handles the Bluetooth permission prompt automatically and remembers the permission state, it seems like it could also detect when Bluetooth isn’t available and throw the proper error instead of failing silently.