"""
Contains the ABC bus implementation and its documentation.
"""
from typing import cast, Any, Iterator, List, Optional, Sequence, Tuple, Union
import can.typechecking
from abc import ABC, ABCMeta, abstractmethod
import can
import logging
import threading
from time import time
from enum import Enum, auto
from can.broadcastmanager import ThreadBasedCyclicSendTask, CyclicSendTaskABC
from can.message import Message
LOG = logging.getLogger(__name__)
class BusState(Enum):
"""The state in which a :class:`can.BusABC` can be."""
ACTIVE = auto()
PASSIVE = auto()
ERROR = auto()
[docs]class BusABC(metaclass=ABCMeta):
"""The CAN Bus Abstract Base Class that serves as the basis
for all concrete interfaces.
This class may be used as an iterator over the received messages
and as a context manager for auto-closing the bus when done using it.
Please refer to :ref:`errors` for possible exceptions that may be
thrown by certain operations on this bus.
"""
#: a string describing the underlying bus and/or channel
channel_info = "unknown"
#: Log level for received messages
RECV_LOGGING_LEVEL = 9
@abstractmethod
def __init__(
self,
channel: Any,
can_filters: Optional[can.typechecking.CanFilters] = None,
**kwargs: object
):
"""Construct and open a CAN bus instance of the specified type.
Subclasses should call though this method with all given parameters
as it handles generic tasks like applying filters.
:param channel:
The can interface identifier. Expected type is backend dependent.
:param can_filters:
See :meth:`~can.BusABC.set_filters` for details.
:param dict kwargs:
Any backend dependent configurations are passed in this dictionary
:raises ValueError: If parameters are out of range
:raises can.CanInterfaceNotImplementedError: If the driver cannot be accessed
:raises can.CanInitializationError: If the bus cannot be initialized
"""
self._periodic_tasks: List[_SelfRemovingCyclicTask] = []
self.set_filters(can_filters)
def __str__(self) -> str:
return self.channel_info
[docs] def recv(self, timeout: Optional[float] = None) -> Optional[Message]:
"""Block waiting for a message from the Bus.
:param timeout:
seconds to wait for a message or None to wait indefinitely
:return: ``None`` on timeout or a :class:`Message` object.
:raises can.CanOperationError: If an error occurred while reading
"""
start = time()
time_left = timeout
while True:
# try to get a message
msg, already_filtered = self._recv_internal(timeout=time_left)
# return it, if it matches
if msg and (already_filtered or self._matches_filters(msg)):
LOG.log(self.RECV_LOGGING_LEVEL, "Received: %s", msg)
return msg
# if not, and timeout is None, try indefinitely
elif timeout is None:
continue
# try next one only if there still is time, and with
# reduced timeout
else:
time_left = timeout - (time() - start)
if time_left > 0:
continue
return None
def _recv_internal(
self, timeout: Optional[float]
) -> Tuple[Optional[Message], bool]:
"""
Read a message from the bus and tell whether it was filtered.
This methods may be called by :meth:`~can.BusABC.recv`
to read a message multiple times if the filters set by
:meth:`~can.BusABC.set_filters` do not match and the call has
not yet timed out.
New implementations should always override this method instead of
:meth:`~can.BusABC.recv`, to be able to take advantage of the
software based filtering provided by :meth:`~can.BusABC.recv`
as a fallback. This method should never be called directly.
.. note::
This method is not an `@abstractmethod` (for now) to allow older
external implementations to continue using their existing
:meth:`~can.BusABC.recv` implementation.
.. note::
The second return value (whether filtering was already done) may
change over time for some interfaces, like for example in the
Kvaser interface. Thus it cannot be simplified to a constant value.
:param float timeout: seconds to wait for a message,
see :meth:`~can.BusABC.send`
:return:
1. a message that was read or None on timeout
2. a bool that is True if message filtering has already
been done and else False
:raises can.CanOperationError: If an error occurred while reading
:raises NotImplementedError:
if the bus provides it's own :meth:`~can.BusABC.recv`
implementation (legacy implementation)
"""
raise NotImplementedError("Trying to read from a write only bus?")
[docs] @abstractmethod
def send(self, msg: Message, timeout: Optional[float] = None) -> None:
"""Transmit a message to the CAN bus.
Override this method to enable the transmit path.
:param Message msg: A message object.
:param timeout:
If > 0, wait up to this many seconds for message to be ACK'ed or
for transmit queue to be ready depending on driver implementation.
If timeout is exceeded, an exception will be raised.
Might not be supported by all interfaces.
None blocks indefinitely.
:raises can.CanOperationError: If an error occurred while sending
"""
raise NotImplementedError("Trying to write to a readonly bus?")
[docs] def send_periodic(
self,
msgs: Union[Message, Sequence[Message]],
period: float,
duration: Optional[float] = None,
store_task: bool = True,
) -> can.broadcastmanager.CyclicSendTaskABC:
"""Start sending messages at a given period on this bus.
The task will be active until one of the following conditions are met:
- the (optional) duration expires
- the Bus instance goes out of scope
- the Bus instance is shutdown
- :meth:`BusABC.stop_all_periodic_tasks()` is called
- the task's :meth:`CyclicTask.stop()` method is called.
:param msgs:
Message(s) to transmit
:param period:
Period in seconds between each message
:param duration:
Approximate duration in seconds to continue sending messages. If
no duration is provided, the task will continue indefinitely.
:param store_task:
If True (the default) the task will be attached to this Bus instance.
Disable to instead manage tasks manually.
:return:
A started task instance. Note the task can be stopped (and depending on
the backend modified) by calling the task's :meth:`stop` method.
.. note::
Note the duration before the messages stop being sent may not
be exactly the same as the duration specified by the user. In
general the message will be sent at the given rate until at
least **duration** seconds.
.. note::
For extremely long running Bus instances with many short lived
tasks the default api with ``store_task==True`` may not be
appropriate as the stopped tasks are still taking up memory as they
are associated with the Bus instance.
"""
if isinstance(msgs, Message):
msgs = [msgs]
elif isinstance(msgs, Sequence):
# A Sequence does not necessarily provide __bool__ we need to use len()
if len(msgs) == 0:
raise ValueError("Must be a sequence at least of length 1")
else:
raise ValueError("Must be either a message or a sequence of messages")
# Create a backend specific task; will be patched to a _SelfRemovingCyclicTask later
task = cast(
_SelfRemovingCyclicTask,
self._send_periodic_internal(msgs, period, duration),
)
# we wrap the task's stop method to also remove it from the Bus's list of tasks
periodic_tasks = self._periodic_tasks
original_stop_method = task.stop
def wrapped_stop_method(remove_task: bool = True) -> None:
nonlocal task, periodic_tasks, original_stop_method
if remove_task:
try:
periodic_tasks.remove(task)
except ValueError:
pass # allow the task to be already removed
original_stop_method()
task.stop = wrapped_stop_method # type: ignore
if store_task:
self._periodic_tasks.append(task)
return task
def _send_periodic_internal(
self,
msgs: Union[Sequence[Message], Message],
period: float,
duration: Optional[float] = None,
) -> can.broadcastmanager.CyclicSendTaskABC:
"""Default implementation of periodic message sending using threading.
Override this method to enable a more efficient backend specific approach.
:param msgs:
Messages to transmit
:param period:
Period in seconds between each message
:param duration:
The duration between sending each message at the given rate. If
no duration is provided, the task will continue indefinitely.
:return:
A started task instance. Note the task can be stopped (and
depending on the backend modified) by calling the :meth:`stop`
method.
"""
if not hasattr(self, "_lock_send_periodic"):
# Create a send lock for this bus, but not for buses which override this method
self._lock_send_periodic = ( # pylint: disable=attribute-defined-outside-init
threading.Lock()
)
task = ThreadBasedCyclicSendTask(
self, self._lock_send_periodic, msgs, period, duration
)
return task
[docs] def stop_all_periodic_tasks(self, remove_tasks: bool = True) -> None:
"""Stop sending any messages that were started using **bus.send_periodic**.
.. note::
The result is undefined if a single task throws an exception while being stopped.
:param remove_tasks:
Stop tracking the stopped tasks.
"""
for task in self._periodic_tasks:
# we cannot let `task.stop()` modify `self._periodic_tasks` while we are
# iterating over it (#634)
task.stop(remove_task=False)
if remove_tasks:
self._periodic_tasks.clear()
[docs] def __iter__(self) -> Iterator[Message]:
"""Allow iteration on messages as they are received.
>>> for msg in bus:
... print(msg)
:yields:
:class:`Message` msg objects.
"""
while True:
msg = self.recv(timeout=1.0)
if msg is not None:
yield msg
@property
def filters(self) -> Optional[can.typechecking.CanFilters]:
"""
Modify the filters of this bus. See :meth:`~can.BusABC.set_filters`
for details.
"""
return self._filters
@filters.setter
def filters(self, filters: Optional[can.typechecking.CanFilters]) -> None:
self.set_filters(filters)
[docs] def set_filters(
self, filters: Optional[can.typechecking.CanFilters] = None
) -> None:
"""Apply filtering to all messages received by this Bus.
All messages that match at least one filter are returned.
If `filters` is `None` or a zero length sequence, all
messages are matched.
Calling without passing any filters will reset the applied
filters to ``None``.
:param filters:
A iterable of dictionaries each containing a "can_id",
a "can_mask", and an optional "extended" key.
>>> [{"can_id": 0x11, "can_mask": 0x21, "extended": False}]
A filter matches, when
``<received_can_id> & can_mask == can_id & can_mask``.
If ``extended`` is set as well, it only matches messages where
``<received_is_extended> == extended``. Else it matches every
messages based only on the arbitration ID and mask.
"""
self._filters = filters or None
self._apply_filters(self._filters)
def _apply_filters(self, filters: Optional[can.typechecking.CanFilters]) -> None:
"""
Hook for applying the filters to the underlying kernel or
hardware if supported/implemented by the interface.
:param filters:
See :meth:`~can.BusABC.set_filters` for details.
"""
def _matches_filters(self, msg: Message) -> bool:
"""Checks whether the given message matches at least one of the
current filters. See :meth:`~can.BusABC.set_filters` for details
on how the filters work.
This method should not be overridden.
:param msg:
the message to check if matching
:return: whether the given message matches at least one filter
"""
# if no filters are set, all messages are matched
if self._filters is None:
return True
for _filter in self._filters:
# check if this filter even applies to the message
if "extended" in _filter:
_filter = cast(can.typechecking.CanFilterExtended, _filter)
if _filter["extended"] != msg.is_extended_id:
continue
# then check for the mask and id
can_id = _filter["can_id"]
can_mask = _filter["can_mask"]
# basically, we compute
# `msg.arbitration_id & can_mask == can_id & can_mask`
# by using the shorter, but equivalent from below:
if (can_id ^ msg.arbitration_id) & can_mask == 0:
return True
# nothing matched
return False
[docs] def flush_tx_buffer(self) -> None:
"""Discard every message that may be queued in the output buffer(s)."""
[docs] def shutdown(self) -> None:
"""
Called to carry out any interface specific cleanup required
in shutting down a bus.
"""
self.stop_all_periodic_tasks()
def __enter__(self):
return self
def __exit__(self, exc_type, exc_val, exc_tb):
self.shutdown()
@property
def state(self) -> BusState:
"""
Return the current state of the hardware
"""
return BusState.ACTIVE
@state.setter
def state(self, new_state: BusState) -> None:
"""
Set the new state of the hardware
"""
raise NotImplementedError("Property is not implemented.")
@staticmethod
def _detect_available_configs() -> List[can.typechecking.AutoDetectedConfig]:
"""Detect all configurations/channels that this interface could
currently connect with.
This might be quite time consuming.
May not to be implemented by every interface on every platform.
:return: an iterable of dicts, each being a configuration suitable
for usage in the interface's bus constructor.
"""
raise NotImplementedError()
[docs] def fileno(self) -> int:
raise NotImplementedError("fileno is not implemented using current CAN bus")
class _SelfRemovingCyclicTask(CyclicSendTaskABC, ABC):
"""Removes itself from a bus.
Only needed for typing :meth:`Bus._periodic_tasks`. Do not instantiate.
"""
def stop( # pylint: disable=arguments-differ
self, remove_task: bool = True
) -> None:
raise NotImplementedError()