Bugfix using the getMessage method to get a LogRecord msg as a string

[bridgetrossiter]

Pull request to fix a bug in the Ratelimitingfilter.

I noticed a bug when I attempted to call logger.exception(ValueError("This is a error")) . This is because in ratelimitingfilter.py, the log message is extracted from the LogRecord using LogRecord.msg. However, ratelimitingfilter assumes that this msg is always a string. This is not actually the case, particularly when it comes to exceptions.

Documentation on this can be found here: https://docs.python.org/3.9/howto/logging.html#arbitrary-object-messages

For example, change the last test in the code to the following:

def test_log_exception(self):
    logger = logging.getLogger('test')
    handler = logging.StreamHandler()
    ### Added configuration ###
    config = {'match': 'auto'}
    throttle = RateLimitingFilter(rate=1, per=1, burst=1, **config)
    ###########################
    handler.addFilter(throttle)
    logger.addHandler(handler)

    try:
        logger.error('First')
        raise RuntimeError('Expected exception')
    except RuntimeError as e:
        logger.exception(e)  # Should be throttled

And run the tests, you'll see the bug. Ratelimitingfilterfails at any point when it assumes that the msg is a string and attempts to iterate through it, as the LogRecord.msg is actually the RuntimeError exception object and is not iterable.

To fix this bug, I have changed references to LogRecord.msg to LogRecord.getMessage(), which runs str on the message before passing it to you. Details on the method are here: https://docs.python.org/3.9/library/logging.html#logging.LogRecord.getMessage

I have also doubled checked, and even with the changes I still get the full stack trace when logging an exception.

[wkeeling]

Many thanks for the PR! That's a good find on LogRecord.msg when using logger.exception() with auto throttling. Will merge and create a new release containing the fix.