Add slog log bridge

[pellared]

Add slog.Handler log bridge

• The bridge factory should accept a logger provider and set the name of the bridge (e.g. go.opentelemetry.io/contrib/bridges/sloghandler) and its version as instrumentation scope
• The bridge should not make any heap allocation when the application emits a log using slog with up to 5 non-complex (no slices, no maps) attributes. There should be "zero allocation" unit tests for this.
• Calling WithGroup should result in nesting the attributes in a https://pkg.go.dev/go.opentelemetry.io/otel/log#Map so that it has similar behavior to slog.JSONHandler. See: https://go.dev/play/p/bjJp7A-56bf
• The bridge needs to have benchmarks

Additional resources:

• You can find a prototype implementation here: https://github.com/pellared/opentelemetry-go/blob/147762ffb5c4394417b3f973274cc570723db79b/log/internal/slog.go (from Logs Bridge API prototype opentelemetry-go#4725)
• A guide on writing custom slog.Handler: https://github.com/golang/example/blob/master/slog-handler-guide/README.md
• More resources on slog: https://go.dev/wiki/Resources-for-slog

[jpkrohling]

Recommended reading:

https://github.com/golang/example/blob/master/slog-handler-guide/README.md
https://opentelemetry.io/docs/specs/otel/ (especially the Bridge API part)

And perhaps before that, I'd also recommend getting familiar with OpenTelemetry, if you aren't already:
https://opentelemetry.io/docs/what-is-opentelemetry/

It might also help to understand what OpenTelemetry is by taking a look at the demo:
https://github.com/open-telemetry/opentelemetry-demo

[Sanket-0510]

I would like to start working over this to get the better and in depth understanding of open-telemetry/community#1865

Till now what I've understood is that too configure a logging handler for slog logging library in go.

The flow goes like this

1. Select the atleast one logging library to bridge with OTel logger and exporter. ( in our case right now we are using Slog we can use any other third party logging library in go in that sense)
2. Now here comes the use of Bridge API and its architecture which goes like this
   Logger Provider (in our case slog) ---> ( get the logs from slog logger ) ----> logger ------> (emit the logs ) -----> log Record

Am I on the correct path?

[MrAlias]

SIG meeting notes: plan is to add this bridge to contrib.

[jpkrohling]

I've added this to the scope of a few internships, such as LFX and Outreachy. Please, talk to me before working on this one.

[pellared]

@jpkrohling I updated the description to make the issue more open for new contributors. However, we may want to start working on it sooner to be able to showcase it at KubeCon EU 2024.

[jpkrohling]

I think the LFX announcement happens today, and we'll start working on that right away.

[pellared]

We are already starting working on it 🚀

[pellared]

@jba, we have an initial version of otelslog.Handler here: https://github.com/open-telemetry/opentelemetry-go-contrib/tree/main/bridges/otelslog. GoDoc: https://pkg.go.dev/go.opentelemetry.io/contrib/bridges/otelslog. Are you willing to review it?

You can simply create a new GitHub issue with your feedback or even add some comments here.

You can also review and add comments here: #5314 as this is the PR that introduced most of the implementation.

[jba]

Thanks for including me. I made a couple of performance-related comments on the PR, not really important.
I didn't dig too deeply but everything looks good to me.

[Nikola-Milovic]

I am combing through the current version of the slog bridge code and I couldn't figure out the intended way to set the log level

In slog.Handler we can use the slog.HandlerOptions

slog.HandlerOptions{
	Level: level,
}

While in otelslog.NewHandler we can set the source, version, provider and the schema url.

Did I overlook some API?

[scorpionknifes]

I am combing through the current version of the slog bridge code and I couldn't figure out the intended way to set the log level

In slog.Handler we can use the slog.HandlerOptions

slog.HandlerOptions{

	Level: level,

}

While in otelslog.NewHandler we can set the source, version, provider and the schema url.

Did I overlook some API?

The current log level is set here and cannot be set manually

opentelemetry-go-contrib/bridges/otelslog/handler.go

Line 190 in 00786cc

const sevOffset = slog.Level(log.SeverityDebug) - slog.LevelDebug

It's designed to map the following

opentelemetry-go-contrib/bridges/otelslog/handler.go

Lines 19 to 25 in 00786cc

	// The Level is transformed by using the static offset to the OpenTelemetry
	// Severity types. For example:
	//
	// - [slog.LevelDebug] is transformed to [log.SeverityDebug]
	// - [slog.LevelInfo] is transformed to [log.SeverityInfo]
	// - [slog.LevelWarn] is transformed to [log.SeverityWarn]
	// - [slog.LevelError] is transformed to [log.SeverityError]

What's your use case that the above mapping doesn't work for you?

[Nikola-Milovic]

@scorpionknifes The mapping is fine, my question was how to control the minimum log level. I usually disable the LevelDebug in production. Eg setting the handler option for the level, which doesn't seem to be available with the bridge

slog.HandlerOptions{
	Level: slog.LevelInfo,
}

[scorpionknifes]

@scorpionknifes The mapping is fine, my question was how to control the minimum log level. I usually disable the LevelDebug in production. Eg setting the handler option for the level, which doesn't seem to be available with the bridge

slog.HandlerOptions{

	Level: slog.LevelInfo,

}

There is a similar conversation about a different bridge, this should help: #6283 (comment)

[pellared]

@Nikola-Milovic, PTAL at https://pkg.go.dev/go.opentelemetry.io/contrib/processors/minsev

You can also make your own slog.Handler wrapper if you do not want to make the filtering on the SDK level.