nanny

Records a sliding window of slog events with all log attribute values for remote inspection through HTTP.

usage

	import "github.com/emicklei/nanny"

	...

	nanny.SetupDefault()
	slog.Debug("debug", "hello", "world")

or by composing the setup yourself:

	r := nanny.NewRecorder()

	// recorder captures debug and forwards to existing handler
	h := nanny.NewLogHandler(r, slog.Default().Handler(), slog.LevelDebug) // or nanny.LevelTrace

	// new logger using the nanny handler
	l := slog.New(h) 
	
	// replace the default logger
	slog.SetDefault(l)

	// serve the events
	http.Handle("/nanny", nanny.NewBrowser(r))

Then after starting your HTTP service, you can access /nanny to see and explore your log events.

event groups

Events can be grouped e.g. by function name or for the processing of a specific HTTP request.

	l := slog.Default().With("trace-id", "some-correlation-value")
	l.Debug("var", "key", "value")

Here trace-id is an event group marker. No group markers are set by default. You can change the group keys to whatever you want using the RecorderOptions GroupMarkers. Typically, events are grouped by an external identifier such as a request id or message id. When you click on the group name in the log line, all entries are filtered.

	r := nanny.NewRecorder(nanny.RecorderOptions{
		MaxEvents: 1000,
		MaxEventGroups: 100,
		GroupMarkers:[]string{"trace-id"},
		LogEventGroupOnError: true,
	})

sample record served as JSON

Access the events via /nanny?do=events.

  {
    "t": "2023-11-08T18:15:14.349402+01:00",
    "l": "DEBUG",
    "g" : "some group", 
    "m": "checking...", 
    "a": {
      "bike": {
		"Brand": "Trek",
      	"Model": "Emonda",
      	"Year": "2017"
	  }
    }

field	comment
t	timestamp
l	log level
g	group
m	message
a	attributes

how it works

Your program calls slog.Debug which creates an slog.Record which is sent to the default slog.Handler. If the default handler is a nanny.SlogHandler then the record is first sent to a nanny.Recorder. The nanny.Recorder keeps the last N record copies in memory and adds grouping information to them. Records from the nanny.Recorder are served by the nanny.Browser using an HTTP endpoint.

A nanny.SlogHandler wraps (decorates) another slog.Handler, the fallback handler. Both the nanny.SlogHandler and the fallback handler respond to a certain slog.Level. If the nanny.SlogHandler is enabled for the log level of the record then it is sent to fallback handler. If the fallback handler is enabled for the log level of the record then it is sent to the fallback output. So if the fallback handler is configured for INFO only then the TRACE and DEBUG records are kept by the nanny.Recorder only ; they are not logged to the output of the fallback handler.

considerations

Current implementation does not work when accessing an HTTP load-balanced setup with > 1 instances. This is because the HTML page and event data is fetched in separate HTTP requests; page can be served by instance 1, data could be served by instance 2.

(c) 2024, https://ernestmicklei.com. https://www.stel-it.nl. MIT License.