Fix ASC Reader start time

[Tian-Jionglu]

to get correct absolute timestamp

[Tian-Jionglu]

An example.asc:

date Thu May 16 06:16:50.884 pm 2024 base hex timestamps absolute internal events logged // version 8.2.0 Begin Triggerblock Thu May 16 06:16:50.884 pm 2024 0.000000 Start der Messung 594680.670773 CANFD 1 Rx 168 1 0 8 08 95 0b 80 00 00 00 00 00 0 0 3000 0 0 0 0 0 594680.670873 CANFD 2 Rx 121 1 0 8 08 35 0b 00 00 00 00 00 00 0 0 3000 0 0 0 0 0 594680.670895 5 1af Rx d 8 d3 0b 1c 6a 00 00 00 00 End TriggerBlock 

In release-4.4.0 branch io/asc.py snipped:

 if trigger_match := ASC_TRIGGER_REGEX.match(line): datetime_str = trigger_match.group("datetime_string") self.start_time = ( 0.0 if self.relative_timestamp else self._datetime_to_timestamp(datetime_str) ) continue 

here, self.relative_timestamp is always True, therefor self.start_time is always 0.0. (What is relative_timestamp stand for? no records found in ASC files)
As a result, msg.timestamp can't get correct value with code snipped

timestamp = float(_timestamp) + self.start_time 

Besides, 2 more changes to unify ASCReader with other Reader(BLFReader):

1. move _extract_header to __init__, to make it possible to get start_timestamp via reader.start_timestamp;
2. add attribution start_timestamp as BLFReader;

To reproduce the issue, use the code below to read the example.asc

from datetime import datetime, timedelta import can if __name__ == '__main__': log_file = "example.asc" with can.LogReader(log_file) as reader: print(datetime.fromtimestamp(reader.start_time)) for msg in reader: print("{}\t{}\t{}".format( datetime.fromtimestamp(msg.timestamp), msg.channel + 1, msg.data) ) 

[Tian-Jionglu]

At present, tests below failed:

FAILED test/logformats_test.py::TestAscFileFormat::test_read_can_and_canfd_error_frames - AssertionError: messages are unequal: FAILED test/logformats_test.py::TestAscFileFormat::test_read_can_fd_message - AssertionError: messages are unequal: FAILED test/logformats_test.py::TestAscFileFormat::test_read_can_fd_message_64 - AssertionError: messages are unequal: FAILED test/logformats_test.py::TestAscFileFormat::test_read_can_fd_remote_message - AssertionError: messages are unequal: FAILED test/logformats_test.py::TestAscFileFormat::test_read_can_message - AssertionError: messages are unequal: FAILED test/logformats_test.py::TestAscFileFormat::test_read_can_remote_message - AssertionError: messages are unequal: 

This is because it is asserted between relative and absolute timestamps.

For example, snipped codes in test/logformats_test.py:

 def test_read_can_and_canfd_error_frames(self): expected_messages = [ can.Message(timestamp=2.501000, channel=0, is_error_frame=True), can.Message(timestamp=3.501000, channel=0, is_error_frame=True), can.Message(timestamp=4.501000, channel=1, is_error_frame=True), can.Message( timestamp=30.806898, channel=4, is_rx=False, is_error_frame=True, is_fd=True, ), ] actual = self._read_log_file("test_CanErrorFrames.asc") self.assertMessagesEqual(actual, expected_messages) 

here actual are absolute timestamps, but expected_messages relative.

To solve this, we can delete start_timestamp when reading messages in can/io/asc.py:

 def __iter__(self) -> Generator[Message, None, None]: for _line in self.file: line = _line.strip() if not ASC_MESSAGE_REGEX.match(line): # line might be a comment, chip status, # J1939 message or some other unsupported event continue msg_kwargs: Dict[str, Union[float, bool, int]] ={} try: _timestamp, channel, rest_of_message = line.split(None, 2) timestamp = float(_timestamp) + self.start_timestamp 

just do + self.start_timestamp

From my side, this change is correct. Users can get absolute timestamp in their own scripts.
But..., it would be not unified with BLFReader.
Please take a review about this point, thanks.