Avoid using log filter to modify/enrich log record

The current implementation provides log filter classes which can be used to enrich the log records with correlation IDs. This is a surprising use of a filter since it has a side effect and modifies a log record. For example, when attaching the filter to one handler, another handler may see the modified log record.

According to the documentation (just below https://docs.python.org/3/library/logging.html?highlight=logrecord#logging.LogRecord.getMessage), the intended pattern for custom log record generation is to use a modified log record factory function like this:

old_factory = logging.getLogRecordFactory()

def record_factory(*args, **kwargs):
    record = old_factory(*args, **kwargs)
    record.custom_attribute = 0xdecafbad
    return record

logging.setLogRecordFactory(record_factory)

The only annoying thing here is that this one-off setting of the factory cannot be done using logging.config.

Short of asking app developers to bootstrap the record factory, manually, there may be an alternative whereby the ASGI middleware could be responsible for this. When using a class-based middleware implementation, the middleware’s __init__() constructor may be able to set the log record factory?

[faph]

I will still find some time to play with the log record factory. Just to see if we can simplify the log setup.

[faph]

I guess I’m just thinking out loud whether we can do better than the pragmatic approach of wiring up filters like this…