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# Copyright (c) 2019 UAVCAN Consortium
# This software is distributed under the terms of the MIT License.
# Author: Pavel Kirienko <>
import enum
import time
import errno
import typing
import socket
import struct
import select
import asyncio
import logging
import threading
import contextlib
import pyuavcan.transport
from pyuavcan.transport import Timestamp
from import Media, Envelope, FilterConfiguration, FrameFormat
from import DataFrame
# Disable unused ignore warning for this file only because there appears to be no other way to make MyPy
# accept this file both on Windows and GNU/Linux.
# mypy: warn_unused_ignores=False
_logger = logging.getLogger(__name__)
class SocketCANMedia(Media):
This media implementation provides a simple interface for the standard Linux SocketCAN media layer.
If you are testing with a virtual CAN bus and you need CAN FD, you may need to enable it manually
otherwise, you may observe errno 90 "Message too long". Configuration example::
ip link set vcan0 mtu 72
SocketCAN documentation:
def __init__(self, iface_name: str, mtu: int, loop: typing.Optional[asyncio.AbstractEventLoop] = None) -> None:
CAN Classic/FD is selected automatically based on the MTU. It is not possible to use CAN FD with MTU of 8 bytes.
:param iface_name: E.g., ``can0``.
:param mtu: The maximum data field size in bytes. CAN FD is used if this value > 8, Classic CAN otherwise.
This value must belong to Media.VALID_MTU_SET.
:param loop: The event loop to use. Defaults to :func:`asyncio.get_event_loop`.
self._mtu = int(mtu)
if self._mtu not in self.VALID_MTU_SET:
raise ValueError(f"Invalid MTU: {self._mtu} not in {self.VALID_MTU_SET}")
self._iface_name = str(iface_name)
self._loop = loop if loop is not None else asyncio.get_event_loop()
self._is_fd = self._mtu > _NativeFrameDataCapacity.CAN_CLASSIC
self._native_frame_data_capacity = int(
False: _NativeFrameDataCapacity.CAN_CLASSIC,
True: _NativeFrameDataCapacity.CAN_FD,
self._native_frame_size = _FRAME_HEADER_STRUCT.size + self._native_frame_data_capacity
self._sock = _make_socket(iface_name, can_fd=self._is_fd)
self._ctl_main, self._ctl_worker = socket.socketpair() # This is used for controlling the worker thread.
self._closed = False
self._maybe_thread: typing.Optional[threading.Thread] = None
self._loopback_enabled = False
self._ancillary_data_buffer_size = socket.CMSG_SPACE(_TIMEVAL_STRUCT.size) # Used for recvmsg()
def loop(self) -> asyncio.AbstractEventLoop:
return self._loop
def interface_name(self) -> str:
return self._iface_name
def mtu(self) -> int:
return self._mtu
def number_of_acceptance_filters(self) -> int:
512 for SocketCAN.
return 512
def start(self, handler: Media.ReceivedFramesHandler, no_automatic_retransmission: bool) -> None:
if self._maybe_thread is None:
self._maybe_thread = threading.Thread(
target=self._thread_function, name=str(self), args=(handler,), daemon=True
if no_automatic_retransmission:"%s non-automatic retransmission is not supported", self)
raise RuntimeError("The RX frame handler is already set up")
def configure_acceptance_filters(self, configuration: typing.Sequence[FilterConfiguration]) -> None:
if self._closed:
raise pyuavcan.transport.ResourceClosedError(repr(self))
"%s FIXME: acceptance filter configuration is not yet implemented; please submit patches! "
"Requested configuration: %s",
", ".join(map(str, configuration)),
async def send(self, frames: typing.Iterable[Envelope], monotonic_deadline: float) -> int:
num_sent = 0
for f in frames:
if self._closed:
raise pyuavcan.transport.ResourceClosedError(repr(self))
await asyncio.wait_for(
self._loop.sock_sendall(self._sock, self._compile_native_frame(f.frame)),
timeout=monotonic_deadline - self._loop.time(),
except asyncio.TimeoutError:
num_sent += 1
return num_sent
def close(self) -> None:
self._closed = True
if self._ctl_main.fileno() >= 0: # Ignore if already closed.
self._ctl_main.send(b"stop") # The actual data is irrelevant, we just need it to unblock the select().
if self._maybe_thread:
self._maybe_thread = None
self._sock.close() # These are expected to be idempotent.
def _thread_function(self, handler: Media.ReceivedFramesHandler) -> None:
def handler_wrapper(frs: typing.Sequence[typing.Tuple[Timestamp, Envelope]]) -> None:
if not self._closed: # Don't call after closure to prevent race conditions and use-after-close.
except Exception as exc:
_logger.exception("%s: Unhandled exception in the receive handler: %s; lost frames: %s", self, exc, frs)
while not self._closed:
) =, self._ctl_worker), (), (), _SELECT_TIMEOUT)
ts_mono_ns = time.monotonic_ns()
if self._sock in read_ready:
frames: typing.List[typing.Tuple[Timestamp, Envelope]] = []
while True:
except OSError as ex:
if ex.errno != errno.EAGAIN:
self._loop.call_soon_threadsafe(handler_wrapper, frames)
if self._ctl_worker in read_ready:
if self._ctl_worker.recv(1): # pragma: no branch
except Exception as ex: # pragma: no cover
if self._sock.fileno() < 0 or self._ctl_worker.fileno() < 0 or self._ctl_main.fileno() < 0:
self._closed = True
_logger.exception("%s thread failure: %s", self, ex)
time.sleep(1) # Is this an adequate failure management strategy?
self._closed = True
_logger.debug("%s thread is about to exit", self)
def _read_frame(self, ts_mono_ns: int) -> typing.Tuple[Timestamp, Envelope]:
while True:
data, ancdata, msg_flags, _addr = self._sock.recvmsg(
self._native_frame_size, self._ancillary_data_buffer_size
assert msg_flags & socket.MSG_TRUNC == 0, "The data buffer is not large enough"
assert msg_flags & socket.MSG_CTRUNC == 0, "The ancillary data buffer is not large enough"
loopback = bool(msg_flags & socket.MSG_CONFIRM)
ts_system_ns = 0
for cmsg_level, cmsg_type, cmsg_data in ancdata:
if cmsg_level == socket.SOL_SOCKET and cmsg_type == _SO_TIMESTAMP:
sec, usec = _TIMEVAL_STRUCT.unpack(cmsg_data)
ts_system_ns = (sec * 1_000_000 + usec) * 1000
assert False, f"Unexpected ancillary data: {cmsg_level}, {cmsg_type}, {cmsg_data!r}"
assert ts_system_ns > 0, "Missing the timestamp; does the driver support timestamping?"
timestamp = Timestamp(system_ns=ts_system_ns, monotonic_ns=ts_mono_ns)
out = SocketCANMedia._parse_native_frame(data)
if out is not None:
return timestamp, Envelope(out, loopback=loopback)
def _compile_native_frame(self, source: DataFrame) -> bytes:
flags = _CANFD_BRS if self._is_fd else 0
ident = source.identifier | (_CAN_EFF_FLAG if source.format == FrameFormat.EXTENDED else 0)
header = _FRAME_HEADER_STRUCT.pack(ident, len(, flags)
out = header +, b"\x00")
assert len(out) == self._native_frame_size
return out
def _parse_native_frame(source: bytes) -> typing.Optional[DataFrame]:
header_size = _FRAME_HEADER_STRUCT.size
ident_raw, data_length, _flags = _FRAME_HEADER_STRUCT.unpack(source[:header_size])
if (ident_raw & _CAN_RTR_FLAG) or (ident_raw & _CAN_ERR_FLAG): # Unsupported format, ignore silently
_logger.debug("Unsupported CAN frame dropped; raw SocketCAN ID is %08x", ident_raw)
return None
frame_format = FrameFormat.EXTENDED if ident_raw & _CAN_EFF_FLAG else FrameFormat.BASE
data = source[header_size : header_size + data_length]
assert len(data) == data_length
ident = ident_raw & _CAN_EFF_MASK
return DataFrame(frame_format, ident, bytearray(data))
def _set_loopback_enabled(self, enable: bool) -> None:
if enable != self._loopback_enabled:
self._sock.setsockopt(socket.SOL_CAN_RAW, socket.CAN_RAW_RECV_OWN_MSGS, int(enable)) # type: ignore
self._loopback_enabled = enable
def list_available_interface_names() -> typing.Iterable[str]:
import re
import subprocess
proc ="ip link show", check=True, timeout=1, text=True, shell=True, capture_output=True)
return re.findall(r"\d+?: ([a-z0-9]+?): <[^>]*UP[^>]*>.*\n *link/can", proc.stdout)
except Exception as ex:
"Could not scrape the output of `ip link show`, using the fallback method: %s", ex, exc_info=True
with open("/proc/net/dev") as f:
out = [line.split(":")[0].strip() for line in f if ":" in line and "can" in line]
return sorted(out, key=lambda x: "can" in x, reverse=True)
class _NativeFrameDataCapacity(enum.IntEnum):
CAN_FD = 64
# struct can_frame {
# canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
# __u8 can_dlc; /* data length code: 0 .. 8 */
# __u8 data[8] __attribute__((aligned(8)));
# };
# struct canfd_frame {
# canid_t can_id; /* 32 bit CAN_ID + EFF/RTR/ERR flags */
# __u8 len; /* frame payload length in byte */
# __u8 flags; /* additional flags for CAN FD */
# __u8 __res0; /* reserved / padding */
# __u8 __res1; /* reserved / padding */
# __u8 data[CANFD_MAX_DLEN] __attribute__((aligned(8)));
# };
_FRAME_HEADER_STRUCT = struct.Struct("=IBB2x") # Using standard size because the native definition relies on stdint.h
_TIMEVAL_STRUCT = struct.Struct("@Ll") # Using native size because the native definition uses plain integers
# From the Linux kernel; not exposed via the Python's socket module
_CAN_EFF_FLAG = 0x80000000
_CAN_RTR_FLAG = 0x40000000
_CAN_ERR_FLAG = 0x20000000
def _make_socket(iface_name: str, can_fd: bool) -> socket.SocketType:
s = socket.socket(socket.PF_CAN, socket.SOCK_RAW, socket.CAN_RAW) # type: ignore
s.setsockopt(socket.SOL_SOCKET, _SO_TIMESTAMP, 1) # timestamping
if can_fd:
s.setsockopt(socket.SOL_CAN_RAW, socket.CAN_RAW_FD_FRAMES, 1) # type: ignore
if 0 != s.getsockopt(socket.SOL_SOCKET, socket.SO_ERROR):
raise OSError("Could not configure the socket: getsockopt(SOL_SOCKET, SO_ERROR) != 0")
except BaseException:
with contextlib.suppress(Exception):
return s