Missing documentation for Metadata/Tags

[Gaibhne]

Missing documentation for Metadata/Tags

[hagbard]

Ahh ha. You've been exploring the innards then :)

Yes, for a while there was no public API for setting them and they were an internal implementation detail (a way to pass structured data in a mostly safe way from frontend to backend). Since they got used more and more, I decided to expose a "with()" method for setting them, along with using strongly typed keys. However since this was a bit experimental I put it in the Google extension API, not the core API (at least until we were sure it was working as intended).

It can be easily promoted into the core API if it would help (and if you have any feedback on it and how it works, please let me know). See:
https://github.com/google/flogger/blob/master/google/src/main/java/com/google/common/flogger/GoogleLoggingApi.java

You could, as a test, use the GoogleLogger and the "with()" method in its API to set tags.

[hagbard]

I'm looking again at backends and adding a log4j2 backend. Since you mentioned "MDC" (of which I know nothing) I was wondering if you wanted to discuss what that was and how you thought it might work well with Flogger's Metadata. I'd be happy to look at adding it (especially if it can leave metadata more structured when it's handled by the backend).

[Maaartinus]

I know nothing about Metadata., but to me, MDC looks very different. MDC is basically just a public static final ThreadLocal<Map<String, String>>, which you put something in when you start some processing (and remove it afterwards) and - depending on the configuration - it gets printed with every log line automatically. Pretty trivial and pretty useful. I guess, it works with flogger when using a corresponding backend.

[deadmoose]

I've got something cobbled together on my end using a io.grpc.Context and a custom logging backend to do similar. IIRC we'd had mixed luck with MDC because it's very thread-oriented, so it started falling apart for more complicated systems (e.g. we wanted breadcrumbs about the RPC that caused some complex multi-threaded code)

Unfortunately, it's a little awkward arbitrarily dealing with grpc Contexts & core flogger isn't going to want to pull in that kind of dependency. But maybe a way to teach flogger about arbitrary metadata suppliers would simplify doing something like that without going to the extreme of a custom backend?