device_wrapping.py

# Copyright 2017 Google Inc. All Rights Reserved.

# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at

#     http://www.apache.org/licenses/LICENSE-2.0

# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
"""OpenHTF base plugs for thinly wrapping existing device abstractions.

Sometimes you already have a Python interface to a device or instrument; you
just need to put that interface in plug form to get it into your test phase.
Device-wrapping plugs are your friends in such times.
"""

import functools
import types

from openhtf.core import base_plugs


def short_repr(obj, max_len=40):
  """Returns a short, term-friendly string representation of the object.

  Args:
    obj: An object for which to return a string representation.
    max_len: Maximum length of the returned string. Longer reprs will be turned
      into a brief descriptive string giving the type and length of obj.
  """
  obj_repr = repr(obj)
  if len(obj_repr) <= max_len:
    return obj_repr
  return '<{} of length {}>'.format(type(obj).__name__, len(obj_repr))


class DeviceWrappingPlugNotFullyInitializedError(base_plugs.InvalidPlugError):
  """Raised if DeviceWrappingPlug instances do not have _device set.

  Generally a by a subclass __init__ failing to call the superclass __init__.
  """


class DeviceWrappingPlug(base_plugs.BasePlug):
  """A base plug for wrapping existing device abstractions.

  Attribute access is delegated to the _device attribute, which is normally set
  by passing some device instance to the constructor of this base class.
  Subclasses can use the @conf.inject_positional_args decorator on their
  constructors to get any configuration needed to construct the inner device
  instance.

  Example:
    class BleSnifferPlug(DeviceWrappingPlug):
      ...
      @conf.inject_positional_args
      def __init__(self, ble_sniffer_host, ble_sniffer_port):
        super(BleSnifferPlug, self).__init__(
            ble_sniffer.BleSniffer(ble_sniffer_host, ble_sniffer_port))
        ...

  Because not all third-party device and instrument control libraries can be
  counted on to do sufficient logging, some debug logging is provided here in
  the plug layer to show which attributes were called and with what arguments.

  Raises:
    base_plugs.InvalidPlugError: The _device attribute has the value None
        when attribute access is attempted.
  """

  verbose = True  # overwrite on subclass to disable logging_wrapper.

  def __init__(self, device):
    """Constructor.

    Args:
      device: The device to wrap; must not be None.
    """
    super(DeviceWrappingPlug, self).__init__()
    self._device = device
    if hasattr(self._device, 'tearDown') and self.uses_base_tear_down():
      self.logger.warning(
          'Wrapped device %s implements a tearDown method, '
          'but using the no-op BasePlug tearDown method.', type(self._device))

  def __setattr__(self, name, value):
    if (name == '_device' or '_device' not in self.__dict__ or
        name in self.__dict__):
      super(DeviceWrappingPlug, self).__setattr__(name, value)
    else:
      setattr(self._device, name, value)

  def __getattr__(self, attr):
    if attr == '_device':
      # _device was not found in the instance attributes.
      raise DeviceWrappingPlugNotFullyInitializedError(
          f'{type(self)} must set _device. This is genally done in __init__ by '
          'calling super().__init__(device)')

    if self._device is None:
      raise base_plugs.InvalidPlugError(
          'DeviceWrappingPlug instances must set the _device attribute.')
    attribute = getattr(self._device, attr)

    if not self.verbose or not isinstance(attribute, types.MethodType):
      return attribute

    # Attribute callable; return a wrapper that logs calls with args and kwargs.
    functools.wraps(attribute, assigned=('__name__', '__doc__'))

    def logging_wrapper(*args, **kwargs):
      """Wraps a callable with a logging statement."""
      args_strings = tuple(short_repr(arg) for arg in args)
      kwargs_strings = tuple(('%s=%s' % (key, short_repr(val))
                              for key, val in kwargs.items()))
      log_line = '%s calling "%s" on device.' % (type(self).__name__, attr)
      if args_strings or kwargs_strings:
        log_line += ' Args: \n  %s' % (', '.join(args_strings + kwargs_strings))
      self.logger.debug(log_line)
      return attribute(*args, **kwargs)

    return logging_wrapper