PyUSBBackend Linux Kernel Management - fix Resource Busy USBError

doc/USB_Linux.md

@@ -0,0 +1,29 @@
+# USB
+
+## LibUSB
+
+libusb - Check Linux/Windows install Guides for this
+
+- On Ubuntu this is likely already installed.
+
+## Permissions
+
+If you are on Linux, you may need to add a UDEV Rule to allow the Printer to be accessed by your User.
+
+Rule: `/etc/udev/rules.d/99-brother-ptp700.rules`
+
+```bash
+SUBSYSTEMS=="usb", GROUP="plugdev", ACTION=="add", ATTRS{idVendor}==<VENDOR_ID>, ATTRS{idProduct}==<PRODUCT_ID>, MODE="0660"
+```
+
+This sets the owner of the device node to root:usbusers rather than root:root
+
+Ensure that the User is in the `plu gdev` group : `sudo usermod -aG plugdev <USER>`
+
+## Brother P-Touch
+
+Note: If your printer has a 'PLite' mode, you need to disable it if you want to print via USB. Make sure that the corresponding LED is not lit by holding the button down until it turns off.
+
+Get VendorID : `lsusb | grep -i Brother | awk '{print $6}' | cut -d':' -f1`
+
+Get ProductID: `lsusb | grep -i Brother | awk '{print $6}' | cut -d':' -f2`

labelprinterkit/backends/usb.py

@@ -1,4 +1,5 @@
 from __future__ import annotations
+
 from time import sleep
 
 import usb.core
@@ -8,26 +9,67 @@
 
 
 class PyUSBBackend(BaseBackend):
-    def __init__(self):
-        dev = usb.core.find(custom_match=self.is_usb_printer)
+    """Assumes only a SINGLE USB Printer / Brother Device is Attached"""
+
+    def __init__(self) -> None:
+        self._dev = PyUSBBackend.get_device()
+
+    @staticmethod
+    def get_device() -> usb.core.Device:
+        """Get the PyUSB Device for a USB Printer"""
+        dev = usb.core.find(custom_match=PyUSBBackend.is_usb_printer)
         if dev is None:
-            raise OSError('Device not found')
-        self._dev = dev
+            raise OSError("No Printer Found")
+        return dev
 
     @staticmethod
     def is_usb_printer(dev) -> bool:
+        """Check if the Device is a USB Printer - by Device Class or Interface Class"""
         if dev.bDeviceClass == 7:
             return True
         for cfg in dev:
             if usb.util.find_descriptor(cfg, bInterfaceClass=7) is not None:
                 return True
         return False
 
-    def write(self, data: bytes):
+    @staticmethod
+    def is_brother_manufacturer(dev) -> bool:
+        """Check if the Device is a Brother Printer - by Manufacturer"""
+        try:
+            manufacturer = usb.util.get_string(dev, dev.iManufacturer)
+        except (usb.core.USBError, ValueError):
+            manufacturer = None
+
+        if manufacturer == "Brother":
+            return True
+        return False
+
+    def detach_from_kernel(self) -> None:
+        """
+        Detach the given Device from the Kernel - allowing PyUSB Exclusive Access
+        Required for: usb.core.USBError: [Errno 16] Resource busy
+        """
+        self._dev.reset()
+
+        interface = self._dev[0].interfaces()[0].bInterfaceNumber
+        if self._dev.is_kernel_driver_active(interface):
+            try:
+                self._dev.detach_kernel_driver(interface)
+            except usb.core.USBError:
+                pass
+
+        self._dev.set_configuration()
+
+        self.refresh()
+
+    def refresh(self) -> None:
+        self._dev = PyUSBBackend.get_device()
+
+    def write(self, data: bytes) -> None:
         self._dev.write(0x2, data)
 
     def read(self, count: int) -> bytes | None:
-        for i in range(0, 3):
+        for _ in range(0, 3):
             data = self._dev.read(0x81, count)
             if data:
                 return data