Use original level strings

[j4nk3e]

The level_str breaks the color coding of log levels e.g. in Grafana. Using the original as_str from tracing_core::Level fixes this issue.

[hrxi]

"Original level strings" seems to mean "level strings from tracing_core which have no relation to Loki".

Could the strings be taken from https://grafana.com/docs/grafana/latest/packages_api/data/loglevel/ instead?

Member	Value
alert	"critical"
crit	"critical"
critical	"critical"
dbug	"debug"
debug	"debug"
emerg	"critical"
eror	"error"
err	"error"
error	"error"
fatal	"critical"
info	"info"
information	"info"
informational	"info"
notice	"info"
trace	"trace"
unknown	"unknown"
warn	"warning"
warning	"warning"

So perhaps "trace", "debug", "info", "warning", "error"?

[j4nk3e]

You're right about the tracing_core strings having no relation to Loki, but since there is no best practice for Loki (at least I couldn't find one) and it uses the same string representations as the log package (disregarding the case, see https://docs.rs/log/latest/log/enum.Level.html#variants), I consider it being a standard at least in Rust.

The issue I had with Grafana actually comes from the logs integration, which seems to have a different mapping than what you posted:

Supported expressions	Log level	Color
emerg	critical	purple
fatal	critical	purple
alert	critical	purple
crit	critical	purple
critical	critical	purple
err	error	red
eror	error	red
error	error	red
warn	warning	yellow
warning	warning	yellow
info	info	green
information	info	green
notice	info	green
dbug	debug	blue
debug	debug	blue
trace	trace	light blue
*	unknown	grey

Source: https://grafana.com/docs/grafana/latest/explore/logs-integration/

The string informational is missing here, which also was the root cause of my issue. The coloring works fine with my version, so I assume the case is ignored.

So perhaps "trace", "debug", "info", "warning", "error"?

That would work with the logs integration of Grafana. What would be the benefit of using this mapping (which differs besides the case only in warn vs. warning) in contrast to Level.as_str? Going with Level.as_str is in my opinion the easier implementation, because we don't have to maintain another string mapping (that is not obvious to the user in the first place - I only figured it out after reading the source code of the BackgroundTask implementation) and also matches the default level output of e.g. tracing_subscriber::fmt. Is there maybe some Grafana/Loki/Rust or general best practice I'm not aware of or compatibility issue with different software? Please enlighten me!

[hrxi]

Going with Level.as_str is in my opinion the easier implementation

"easier" is very far back in my list of implementation concerns. First come correctness and sensibility.

I can see the argument that matching the default level output of tracing_subscriber::fmt is good.

I would somehow assume that uppercase is uncommon in structured logs, but that was just a gut feeling not backed by any data. The screenshot in your documentation link does show lowercase log levels. I'll try looking for some other Loki client libraries.

[hrxi]

I only found these:

https://github.com/grafana/loki/blob/31ca108a3cf5bcb87ffeb54d06d6fa4c53e4830d/clients/pkg/promtail/targets/gelf/gelftarget.go#L24-L34

https://github.com/grafana/loki/blob/31ca108a3cf5bcb87ffeb54d06d6fa4c53e4830d/clients/pkg/promtail/targets/journal/journaltarget.go#L363-L383

So maybe go with the lowercased variants of the tracing levels? "error", "warn", "info", "debug", "trace"?

[j4nk3e]

sounds good, I updated the PR

[hrxi]

sounds good, I updated the PR

Sorry, one last thing: Could you update it to use a function again? Currently it lowercases the log level (and even allocates for it) for each log message, which is a bit wasteful.

[hrxi]

Thanks!

[hrxi]

Released a new version tracing-loki 0.2.0 on crates.io.

[j4nk3e]

Thank you!