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"""Common routines and base driver class for HID-based meters.
"""
__author__ = 'Diego Elio Pettenò'
__email__ = 'flameeyes@flameeyes.com'
__copyright__ = 'Copyright © 2017, Diego Elio Pettenò'
__license__ = 'MIT'
import logging
import os
try:
from typing import BinaryIO, Optional, Text
except ImportError:
pass
from glucometerutils import exceptions
class HidDevice:
"""A device speaking USB HID protocol driver base.
This class does not implement an actual driver by itself, but provides an
easier access to the boilerplate code required for speaking USB HID.
This helper wraps around an optional dependency on hidapi library: if
present the driver will auto-detect the device, if not the device path needs
to be provided and should point to a device implementing Linux's hidraw
interface.
The following constants can be set by the actual drivers:
USB_VENDOR_ID: (int) USB vendor ID for the device.
USB_PRODUCT_ID: (int) USB product ID for the device.
If the VID/PID pair is not provided, the driver will require a device path
to be used.
Optional parameters available:
TIMEOUT_MS: (int, default: 0) the read timeout in milliseconds, used
for hidapi reads only. If < 1, hidapi will be provided no timeout.
"""
USB_VENDOR_ID = None # type: int
USB_PRODUCT_ID = None # type: int
TIMEOUT_MS = 0 # type: int
def __init__(self, device):
# type: (Optional[Text]) -> None
if None in (self.USB_VENDOR_ID, self.USB_PRODUCT_ID) and not device:
raise exceptions.CommandLineError(
'--device parameter is required, should point to a /dev/hidraw '
'device node representing the meter.')
# If the user passed a device path that does not exist, raise an
# error. This is to avoid writing to a file instead of to a device node.
if device and not os.path.exists(device):
raise exceptions.ConnectionFailed(
message='Path %s does not exist.' % device)
# If the user passed a device, try opening it.
if device:
self.handle_ = open(device, 'w+b') # type: Optional[BinaryIO]
else:
self.handle_ = None
logging.info(
'No --device parameter provided, using hidapi library.')
try:
import hid
self.hidapi_handle_ = hid.device()
self.hidapi_handle_.open(
self.USB_VENDOR_ID, self.USB_PRODUCT_ID)
except ImportError:
raise exceptions.ConnectionFailed(
message='Missing requied "hidapi" module.')
except OSError as e:
raise exceptions.ConnectionFailed(
message='Unable to connect to meter: %s.' % e)
def _write(self, report):
# type: (bytes) -> None
"""Writes a report to the HID handle."""
if self.handle_:
written = self.handle_.write(report)
else:
written = self.hidapi_handle_.write(report)
if written < 0:
raise exceptions.CommandError()
def _read(self, size=64):
# type: (int) -> bytes
"""Read a report from the HID handle.
This is important as it handles the one incompatible interface between
hidraw devices and hidapi handles.
"""
if self.handle_:
return bytes(self.handle_.read(size))
return bytes(self.hidapi_handle_.read(
size, timeout_ms=self.TIMEOUT_MS))
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