capacitor-pozo-printer/android/src/main/java/com/pozo/printer/UsbPrinter.java

package com.pozo.printer;

import android.content.Context;
import android.hardware.usb.*;
import com.getcapacitor.JSObject;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;

public class UsbPrinter {

  public static List<JSObject> scanDevices(Context context) {
    List<JSObject> result = new ArrayList<>();
    UsbManager manager =
      (UsbManager) context.getSystemService(Context.USB_SERVICE);
    if (manager == null) return result;
    HashMap<String, UsbDevice> devices = manager.getDeviceList();
    for (UsbDevice device : devices.values()) {
      JSObject obj = new JSObject();
      obj.put(
        "name",
        device.getProductName() != null ? device.getProductName() : "USB Device"
      );
      obj.put("address", String.valueOf(device.getDeviceId()));
      result.add(obj);
    }
    return result;
  }

  public static void print(
    Context context,
    byte[] data,
    String deviceIdStr
  ) throws Exception {
    UsbManager manager =
      (UsbManager) context.getSystemService(Context.USB_SERVICE);
    if (manager == null) throw new Exception("USB service not available");

    HashMap<String, UsbDevice> devices = manager.getDeviceList();
    UsbDevice targetDevice = null;

    if (deviceIdStr != null) {
      int deviceId = Integer.parseInt(deviceIdStr);
      for (UsbDevice device : devices.values()) {
        if (device.getDeviceId() == deviceId) {
          targetDevice = device;
          break;
        }
      }
    } else {
      if (!devices.isEmpty()) {
        targetDevice = devices.values().iterator().next();
      }
    }

    if (targetDevice == null) throw new Exception("USB printer not found");
    if (!manager.hasPermission(targetDevice))
      throw new Exception("USB permission denied — prompt user first");

    UsbInterface intf = targetDevice.getInterface(0);
    UsbEndpoint endpoint = null;
    for (int i = 0; i < intf.getEndpointCount(); i++) {
      UsbEndpoint ep = intf.getEndpoint(i);
      if (ep.getDirection() == UsbConstants.USB_DIR_OUT) {
        endpoint = ep;
        break;
      }
    }
    if (endpoint == null) throw new Exception("No OUT endpoint on USB device");

    UsbDeviceConnection connection = manager.openDevice(targetDevice);
    if (connection == null) throw new Exception("Cannot open USB device");

    connection.claimInterface(intf, true);
    try {
      int chunkSize = endpoint.getMaxPacketSize();
      int offset = 0;
      while (offset < data.length) {
        int size = Math.min(chunkSize, data.length - offset);
        byte[] chunk = new byte[size];
        System.arraycopy(data, offset, chunk, 0, size);
        connection.bulkTransfer(endpoint, chunk, size, 5000);
        offset += size;
      }
    } finally {
      connection.releaseInterface(intf);
      connection.close();
    }
  }
}