Add contextual logger (log.FromContext)

[xnyo]

What this PR does / why we need it:

Adds a contextual logger, retrievable with log.FromContext(ctx)

This is a logger that's similar to log.DefaultLogger, but it's pre-populated with some contextual parameters:

• pluginID
• endpoint
• traceID (if available)
• dsName (if available)
• dsUID (if available)
• uname (if available)

Those are the same attributes logged in Grafana core's contextual logger:

https://github.com/grafana/grafana/blob/50504ba00803a291ea24e8a4a48b14494b97c744/pkg/services/pluginsintegration/clientmiddleware/contextual_logger_middleware.go#L27-L37

For this reason, this is especially useful for decoupling core plugins (replacing contextual logger with plugin sdk contextual logger).

This logger is added to the context.Context by the sdk adapter. This is a similar pattern to what happens in Grafana core (logging middleware).

Usage example:

func (d *Datasource) QueryData(ctx context.Context, req *backend.QueryDataRequest) (*backend.QueryDataResponse, error) {
	log.DefaultLogger.Info("no context", "a", "b")
	log.FromContext(ctx).Info("with context", "a", "b")
	// ...

INFO [10-17|17:23:56] no context                               logger=plugin.grafana-datasourcehttpbackend-datasource a=b
INFO [10-17|17:23:56] with context                             logger=plugin.grafana-datasourcehttpbackend-datasource endpoint=queryData uname=admin a=b dsName="Datasource Http Backend" dsUID=a7e_d3pVk pluginID=grafana-datasourcehttpbackend-datasource

Which issue(s) this PR fixes:

Fixes #755

Special notes for your reviewer:

[marefr]

This looks like a very interesting approach. Great work. Just wonder if, lets say you have an existing logger created with logger.With() and you want to get a contextual logger from that then this approach wouldn't work. Not sure how common this would be though, but that would be how you would use a contextual logger in core grafana.

But maybe, rather than holding a logger in context holding attributes instead, similar to core grafana https://github.com/grafana/grafana/blob/8ac7736c9561d22789298582eb0cd90e3f789774/pkg/infra/log/log.go#L272-L300. WDYT? Lets discuss

[xnyo]

Good point. I think it makes sense to make it similar to core Grafana. I have refactored it so it now stored the attributes in the context rather than the logger directly, and moved FromContext in the logger interface. This can now be used to create sub-loggers from existing ones:

log.DefaultLogger.Info("default logger no context", "a", "b")

log.DefaultLogger.FromContext(ctx).Info("default contextual logger", "c", "d")

svcLogger := log.New().With("service", "myservice")
svcLogger.FromContext(ctx).Info("non-default contextual logger", "e", "f")

👇

INFO [10-18|13:02:35] default logger no context                logger=plugin.grafana-datasourcehttpbackend-datasource a=b
INFO [10-18|13:02:35] default contextual logger                logger=plugin.grafana-datasourcehttpbackend-datasource dsName="Datasource Http Backend" dsUID=a7e_d3pVk endpoint=queryData pluginID=grafana-datasourcehttpbackend-datasource c=d uname=admin
INFO [10-18|13:02:35] non-default contextual logger            logger=plugin.grafana-datasourcehttpbackend-datasource service=myservice dsName="Datasource Http Backend" dsUID=a7e_d3pVk pluginID=grafana-datasourcehttpbackend-datasource e=f endpoint=queryData uname=admin

Regarding ContextualLogProviderFunc which is present in core Grafana: I'm not sure, I haven't implemented it for now. It involves global variables and global state, I think keeping everything in context.Context is better. Also the approach that's implemented in this PR should be enough to handle most use cases. WDYT?

[xnyo]

I decided to implement the contextual logger in the stream_adapter as well. We don't have it in core Grafana for some reason:

https://github.com/grafana/grafana/blob/50504ba00803a291ea24e8a4a48b14494b97c744/pkg/services/pluginsintegration/clientmiddleware/contextual_logger_middleware.go#L59C1-L69

I think it should also be the case for core Grafana, but maybe I am missing something. If there's a reason behind this decision, I will remove it from here. Otherwise I can also open a PR to add it to streaming methods in core Grafana as well

[marefr]

It does make sense 👍 We should probably have it in core grafana as well

[marefr]

LGTM awesome work. Just added a comment, but not a blocker for these changes

[marefr]

FYI for core plugins using the sdk logger we need to provide these contextual attributes as well together with existing https://github.com/grafana/grafana/blob/50504ba00803a291ea24e8a4a48b14494b97c744/pkg/services/pluginsintegration/clientmiddleware/contextual_logger_middleware.go#L59C1-L69 which currently is onyl for the grafana logger :) For now I guess we can duplicate this code to populate attributes for both core grafana logger and sdk logger in core grafana?

Eventually we probably want to include tenant id as well, but we can open a separate issue for that.