Log messages dispatched using the swift-log backend are missing normal swift-log formatting.

[thisisaaronland]

Checklist

• I have read and understood the CONTRIBUTING guide
• I have read the Documentation
• I have searched for a similar issue in the project and found none

Describe the bug

Log messages dispatched using the swift-log backend are missing normal swift-log formatting. Importantly, this might be an issue with our code because we are using CocoaLumberjack in a slightly unusual fashion.

Specifically, we are instantiating a local instance of DDLogHandler.handlerFactory (configured to use a DDFileLogger instance) which is then passed to the Logger.MultiplexLogHandler method:

https://github.com/sfomuseum/swift-sfomuseum-logger/blob/main/Sources/SFOMuseumLogger/SFOMuseumLogger.swift#L48-L64

And:

https://github.com/sfomuseum/swift-sfomuseum-logger/blob/main/Sources/SFOMuseumLogger/SFOMuseumLogger.swift#L78-L93

Messages are logged to the DDFileLogger instance but they are missing the default swift-log premable in addition to any metadata keys assigned to the logger. For example, the StreamLogHandler.standardOutput handler will emit:

2023-10-24T15:25:17-0700 info org.sfomuseum.logger : metadata=debug [sfomuseum_logger] hello world

But the DDFileLogger instance will only emit:

2023/10/24 22:25:17:955  hello world

To Reproduce

$> git clone https://github.com/sfomuseum/swift-sfomuseum-logger.git && cd swift-sfomuseum-logger
$> swift build && ./.build/debug/sfomuseum-logger --logfile true 'hello world'

https://github.com/sfomuseum/swift-sfomuseum-logger/blob/main/Scripts/sfomuseum-logger/SFOMuseumLogger.swift

Expected behavior

For logs written to the DDFileLogger instance to be formatted like this:

2023-10-24T15:25:17-0700 info org.sfomuseum.logger : metadata=debug [sfomuseum_logger] hello world

Environment info

Info	Value
Platform Name	macOS
Platform Version	14.0
CocoaLumberjack Version	3.8.0
Integration Method	Swift Package Manager
Xcode Version	XCode 15.1
Repro rate	100%
Repro project link	https://github.com/sfomuseum/swift-sfomuseum-logger

Additional context

As mentioned, I am open to the possibility that I am just passing incorrect, or incorrect, values to the local cocoaLumberjackHandler method (described above) but if that's the case I am not sure what I am doing wrong and any pointers would be appreciated.

Thanks,

[ffried]

@thisisaaronland First of all a big thanks to you for a very well written issue here! Including a reproduction project and a very detailed explanation. This helps a log to understand what you're trying to do and to help you out!

I've converted this to a discussion in our Q&A section, because you already (correctly) pointed out, that this might be an issue with your setup.

Now to the problem at hand:
This is actually working as designed. In swift-log, formatting is done by the log handler. What you see when using the StreamLogHandler.standardOutput is done here. As soon as you use a different log handler (like the one CocoaLumberjack provides), this code is no longer executed.

You will need to do this formatting yourself using a DDLogFormatter and assign it to the logFormatter property on the DDFileLogger (or any DDLogger for that matter).

If you want consistent formatting, I'd actually recommend not using the Logger.MultiplexLogHandler, but using only CocoaLumberjacks LogHandler instead. Then you can use e.g. DDOSLogger for writing to os_log or use your own DDLogger implementation for writing to stdout. Both of the loggers can use the same log formatter and thus have the same formatting.

Small note, though: If you're using DDOSLogger, make your log formatter configurable to not include the date, because that will always be added by os_log.

Let me know if that helped or if you have any further questions!

[thisisaaronland]

Thanks for your reply. That was exactly what I needed to make things work the way I'd like.