afch-logger

Logger for Azure Function Custom Handler, abusing the undocumented (at least I don't know where) rule of e Function "infering" the log level from stderr.

Usage

You can initialize the log by afch_logger::init. You can also implement your own transforming by implementing afch_logger::Transform trait and passing it to afch_logger::init_transform.

Strategy

For Azure Function Custom Handler, if you print a message to stdout, it will be considered as a Information level log by Azure Function runtime.

If you print a message to stderr, then it will be consider Error if it does not contain warn (case insensitive), otherwise it will be Warning.

So the default strategy is, for error-level log, if warn occurs, base64-encode it, if the encoded string still contains warn, base-encode again, and if the twice-encoded string still contains warn (which should be impossible), log an error explain that the following warning is error, then log it as a warning. For warning-level log, if warn does not occur, add a warning: prefix.