BLF reader CAN_MESSAGE and CAN_MESSAGE2 incomplete

[pratik-mahamuni]

Describe the bug

The class BLFReader from can.io.blf is implemented using Toby Lorenz's Vector_BLF. The implementation for reading CAN messages especially for CAN_MESSAGE and CAN_MESSAGE2 is incorrect.

In this library

The code in this library related to this is as follows:

if obj_type in (CAN_MESSAGE, CAN_MESSAGE2):
    channel, flags, dlc, can_id, can_data = unpack_can_msg(data, pos)
    yield Message(
        timestamp=timestamp,
        arbitration_id=can_id & 0x1FFFFFFF,
        is_extended_id=bool(can_id & CAN_MSG_EXT),
        is_remote_frame=bool(flags & REMOTE_FLAG),
        is_rx=not bool(flags & DIR),
        dlc=dlc,
        data=can_data[:dlc],
        channel=channel - 1,
    )

data=can_data[:dlc] uses the data length code to slice data bytes.

In Vector_BLF

For CAN_MESSAGE:

void CanMessage::read(AbstractFile & is) {
    ObjectHeader::read(is);
    is.read(reinterpret_cast<char *>(&channel), sizeof(channel));
    is.read(reinterpret_cast<char *>(&flags), sizeof(flags));
    is.read(reinterpret_cast<char *>(&dlc), sizeof(dlc));
    is.read(reinterpret_cast<char *>(&id), sizeof(id));
    is.read(reinterpret_cast<char *>(data.data()), static_cast<std::streamsize>(data.size()));
}

For CAN_MESSAGE2:

void CanMessage2::read(AbstractFile & is) {
    ObjectHeader::read(is);
    is.read(reinterpret_cast<char *>(&channel), sizeof(channel));
    is.read(reinterpret_cast<char *>(&flags), sizeof(flags));
    is.read(reinterpret_cast<char *>(&dlc), sizeof(dlc));
    is.read(reinterpret_cast<char *>(&id), sizeof(id));
    data.resize(objectSize - calculateObjectSize()); // all remaining data
    is.read(reinterpret_cast<char *>(data.data()), static_cast<std::streamsize>(data.size()));
    is.read(reinterpret_cast<char *>(&frameLength), sizeof(frameLength));
    is.read(reinterpret_cast<char *>(&bitCount), sizeof(bitCount));
    is.read(reinterpret_cast<char *>(&reservedCanMessage1), sizeof(reservedCanMessage1));
    is.read(reinterpret_cast<char *>(&reservedCanMessage2), sizeof(reservedCanMessage2));
}

Both versions have a is.read(reinterpret_cast<char *>(data.data()), static_cast<std::streamsize>(data.size())); that does not slice the data based on DLC.

To Reproduce

Instantiate the BLFReader class:

data = BLFReader(blffile_path)

Expected behavior

Bytes extracted from the data should be 8 bytes

bytearray(b'\xff\x00\xff\x00\x00\x00\x08\x00')

In the current version:

Bytes extracted from the data are 3 bytes because of the DLC slicing

bytearray(b'\xff\x00\xff')

This causes errors in decoding the data using cantools which reads the length of data as 8 bytes from the DBC file.

Additional context

OS and version: Ubuntu 22.04
Python version: 3.10.12
python-can version: 4.4.2
python-can interface/s (if applicable):

[zariiii9003]

python-can behaves correctly. According to your blf, there are only 3 valid bytes in your message. So this is either an issue with your ECU or your dbc file. Either way, cantools has a allow_truncated parameter for this.