message.py

# coding: utf-8

"""
This module contains the implementation of :class:`can.Message`.

.. note::
    Could use `@dataclass <https://docs.python.org/3.7/library/dataclasses.html>`__
    starting with Python 3.7.
"""

from __future__ import absolute_import, division

import warnings
from copy import deepcopy
from math import isinf, isnan


class Message(object):
    """
    The :class:`~can.Message` object is used to represent CAN messages for
    sending, receiving and other purposes like converting between different
    logging formats.

    Messages can use extended identifiers, be remote or error frames, contain
    data and may be associated to a channel.

    Messages are always compared by identity and never by value, because that
    may introduce unexpected behaviour. See also :meth:`~can.Message.equals`.

    :func:`~copy.copy`/:func:`~copy.deepcopy` is supported as well.

    Messages do not support "dynamic" attributes, meaning any others than the
    documented ones, since it uses :attr:`~object.__slots__`.
    """

    __slots__ = (
        "timestamp",
        "arbitration_id",
        "is_extended_id",
        "is_remote_frame",
        "is_error_frame",
        "channel",
        "dlc",
        "data",
        "is_fd",
        "bitrate_switch",
        "error_state_indicator",
        "__weakref__",              # support weak references to messages
        "_dict"                     # see __getattr__
    )

    def __getattr__(self, key):
        # TODO keep this for a version, in order to not break old code
        # this entire method (as well as the _dict attribute in __slots__ and the __setattr__ method)
        # can be removed in 4.0
        # this method is only called if the attribute was not found elsewhere, like in __slots_
        if key not in self.__slots__:
            raise AttributeError
        try:
            warnings.warn("Custom attributes of messages are deprecated and will be removed in 4.0", DeprecationWarning)
            return self._dict[key]
        except KeyError:
            raise AttributeError("'message' object has no attribute '{}'".format(key))

    def __setattr__(self, key, value):
        # see __getattr__
        try:
            super(Message, self).__setattr__(key, value)
        except AttributeError:
            warnings.warn("Custom attributes of messages are deprecated and will be removed in 4.0", DeprecationWarning)
            self._dict[key] = value

    @property
    def id_type(self):
        # TODO remove in 4.0
        warnings.warn("Message.id_type is deprecated and will be removed in 4.0, use is_extended_id instead", DeprecationWarning)
        return self.is_extended_id

    @id_type.setter
    def id_type(self, value):
        # TODO remove in 4.0
        warnings.warn("Message.id_type is deprecated and will be removed in 4.0, use is_extended_id instead", DeprecationWarning)
        self.is_extended_id = value

    def __init__(self, timestamp=0.0, arbitration_id=0, is_extended_id=None,
                 is_remote_frame=False, is_error_frame=False, channel=None,
                 dlc=None, data=None,
                 is_fd=False, bitrate_switch=False, error_state_indicator=False,
                 extended_id=None, # deprecated in 3.x, TODO remove in 4.x
                 check=False):
        """
        To create a message object, simply provide any of the below attributes
        together with additional parameters as keyword arguments to the constructor.

        :param bool check: By default, the constructor of this class does not strictly check the input.
                           Thus, the caller must prevent the creation of invalid messages or
                           set this parameter to `True`, to raise an Error on invalid inputs.
                           Possible problems include the `dlc` field not matching the length of `data`
                           or creating a message with both `is_remote_frame` and `is_error_frame` set to `True`.

        :raises ValueError: iff `check` is set to `True` and one or more arguments were invalid
        """
        self._dict = dict() # see __getattr__

        self.timestamp = timestamp
        self.arbitration_id = arbitration_id

        if extended_id is not None:
            # TODO remove in 4.0
            warnings.warn("The extended_id parameter is deprecated and will be removed in 4.0, use is_extended_id instead", DeprecationWarning)

        if is_extended_id is not None:
            self.is_extended_id = is_extended_id
        else:
            # Default behaviour is to create extended id messages
            self.is_extended_id = True if extended_id is None else extended_id

        self.is_remote_frame = is_remote_frame
        self.is_error_frame = is_error_frame
        self.channel = channel

        self.is_fd = is_fd
        self.bitrate_switch = bitrate_switch
        self.error_state_indicator = error_state_indicator

        if data is None or is_remote_frame:
            self.data = bytearray()
        elif isinstance(data, bytearray):
            self.data = data
        else:
            try:
                self.data = bytearray(data)
            except TypeError:
                err = "Couldn't create message from {} ({})".format(data, type(data))
                raise TypeError(err)

        if dlc is None:
            self.dlc = len(self.data)
        else:
            self.dlc = dlc

        if check:
            self._check()

    def __str__(self):
        field_strings = ["Timestamp: {0:>15.6f}".format(self.timestamp)]
        if self.is_extended_id:
            arbitration_id_string = "ID: {0:08x}".format(self.arbitration_id)
        else:
            arbitration_id_string = "ID: {0:04x}".format(self.arbitration_id)
        field_strings.append(arbitration_id_string.rjust(12, " "))

        flag_string = " ".join([
            "X" if self.is_extended_id else "S",
            "E" if self.is_error_frame else " ",
            "R" if self.is_remote_frame else " ",
            "F" if self.is_fd else " ",
            "BS" if self.bitrate_switch else "  ",
            "EI" if self.error_state_indicator else "  "
        ])

        field_strings.append(flag_string)

        field_strings.append("DLC: {0:2d}".format(self.dlc))
        data_strings = []
        if self.data is not None:
            for index in range(0, min(self.dlc, len(self.data))):
                data_strings.append("{0:02x}".format(self.data[index]))
        if data_strings:  # if not empty
            field_strings.append(" ".join(data_strings).ljust(24, " "))
        else:
            field_strings.append(" " * 24)

        if (self.data is not None) and (self.data.isalnum()):
            field_strings.append("'{}'".format(self.data.decode('utf-8', 'replace')))

        if self.channel is not None:
            try:
                field_strings.append("Channel: {}".format(self.channel))
            except UnicodeEncodeError:
                pass

        return "    ".join(field_strings).strip()

    def __len__(self):
        # return the dlc such that it also works on remote frames
        return self.dlc

    def __bool__(self):
        # For Python 3
        return True

    def __nonzero__(self):
        # For Python 2
        return self.__bool__()

    def __repr__(self):
        args = ["timestamp={}".format(self.timestamp),
                "arbitration_id={:#x}".format(self.arbitration_id),
                "extended_id={}".format(self.is_extended_id)]

        if self.is_remote_frame:
            args.append("is_remote_frame={}".format(self.is_remote_frame))

        if self.is_error_frame:
            args.append("is_error_frame={}".format(self.is_error_frame))

        if self.channel is not None:
            args.append("channel={!r}".format(self.channel))                

        data = ["{:#02x}".format(byte) for byte in self.data]
        args += ["dlc={}".format(self.dlc),
                 "data=[{}]".format(", ".join(data))]

        if self.is_fd:
            args.append("is_fd=True")
            args.append("bitrate_switch={}".format(self.bitrate_switch))
            args.append("error_state_indicator={}".format(self.error_state_indicator))

        return "can.Message({})".format(", ".join(args))

    def __format__(self, format_spec):
        if not format_spec:
            return self.__str__()
        else:
            raise ValueError("non empty format_specs are not supported")

    def __bytes__(self):
        return bytes(self.data)

    def __copy__(self):
        new = Message(
            timestamp=self.timestamp,
            arbitration_id=self.arbitration_id,
            is_extended_id=self.is_extended_id,
            is_remote_frame=self.is_remote_frame,
            is_error_frame=self.is_error_frame,
            channel=self.channel,
            dlc=self.dlc,
            data=self.data,
            is_fd=self.is_fd,
            bitrate_switch=self.bitrate_switch,
            error_state_indicator=self.error_state_indicator
        )
        new._dict.update(self._dict)
        return new

    def __deepcopy__(self, memo):
        new = Message(
            timestamp=self.timestamp,
            arbitration_id=self.arbitration_id,
            is_extended_id=self.is_extended_id,
            is_remote_frame=self.is_remote_frame,
            is_error_frame=self.is_error_frame,
            channel=deepcopy(self.channel, memo),
            dlc=self.dlc,
            data=deepcopy(self.data, memo),
            is_fd=self.is_fd,
            bitrate_switch=self.bitrate_switch,
            error_state_indicator=self.error_state_indicator
        )
        new._dict.update(self._dict)
        return new

    def _check(self):
        """Checks if the message parameters are valid.
        Assumes that the types are already correct.

        :raises ValueError: iff one or more attributes are invalid
        """

        if self.timestamp < 0.0:
            raise ValueError("the timestamp may not be negative")
        if isinf(self.timestamp):
            raise ValueError("the timestamp may not be infinite")
        if isnan(self.timestamp):
            raise ValueError("the timestamp may not be NaN")

        if self.is_remote_frame and self.is_error_frame:
            raise ValueError("a message cannot be a remote and an error frame at the sane time")

        if self.arbitration_id < 0:
            raise ValueError("arbitration IDs may not be negative")

        if self.is_extended_id:
            if 0x20000000 <= self.arbitration_id:
                raise ValueError("Extended arbitration IDs must be less than 2^29")
        elif 0x800 <= self.arbitration_id:
            raise ValueError("Normal arbitration IDs must be less than 2^11")

        if self.dlc < 0:
            raise ValueError("DLC may not be negative")
        if self.is_fd:
            if 64 < self.dlc:
                raise ValueError("DLC was {} but it should be <= 64 for CAN FD frames".format(self.dlc))
        elif 8 < self.dlc:
            raise ValueError("DLC was {} but it should be <= 8 for normal CAN frames".format(self.dlc))

        if self.is_remote_frame:
            if self.data is not None and len(self.data) != 0:
                raise ValueError("remote frames may not carry any data")
        elif self.dlc != len(self.data):
            raise ValueError("the DLC and the length of the data must match up for non remote frames")

        if not self.is_fd:
            if self.bitrate_switch:
                raise ValueError("bitrate switch is only allowed for CAN FD frames")
            if self.error_state_indicator:
                raise ValueError("error state indicator is only allowed for CAN FD frames")

    def equals(self, other, timestamp_delta=1.0e-6):
        """
        Compares a given message with this one.

        :param can.Message other: the message to compare with

        :type timestamp_delta: float or int or None
        :param timestamp_delta: the maximum difference at which two timestamps are
                                still considered equal or None to not compare timestamps

        :rtype: bool
        :return: True iff the given message equals this one
        """
        # see https://github.com/hardbyte/python-can/pull/413 for a discussion
        # on why a delta of 1.0e-6 was chosen
        return (
            # check for identity first and finish fast
            self is other or
            # then check for equality by value
            (
                (
                    timestamp_delta is None or
                    abs(self.timestamp - other.timestamp) <= timestamp_delta
                ) and
                self.arbitration_id == other.arbitration_id and
                self.is_extended_id == other.is_extended_id and
                self.dlc == other.dlc and
                self.data == other.data and
                self.is_remote_frame == other.is_remote_frame and
                self.is_error_frame == other.is_error_frame and
                self.channel == other.channel and
                self.is_fd == other.is_fd and
                self.bitrate_switch == other.bitrate_switch and
                self.error_state_indicator == other.error_state_indicator
            )
        )