Add an optional context field to capture the filename and line number

[ccll]

Often it's useful to capture the filename and line number in the log, to help finding the location where this log entry is generated.

zap have this feature:

... "caller":"hello/main.go:221" ...

zerolog should support this too, may be in an optional context field like Timestamp()?

[rs]

Yes, we could add that as optional features. Those are costly operations which IMHO don't add much value.

[Ullaakut]

@ccll You can add this feature to your logger with a custom hook by using runtime.Caller, it's pretty straightforward and I don't think it really makes sense to have it as a feature in ZeroLog itself as it's clearly making the logging slower.

If you want advice on how to implement it, I can help.

[ccll]

@Ullaakut Thanks for the advice, I'll definitely try that.
Closing now.

[OptimisticLock]

@Ullaakut please do post the snip with runtime.Caller if you would.

[Ullaakut]

Hi @OptimisticLock. Something like that should work.

type LineInfoHook struct{}

func (h LineInfoHook) Run(e *zerolog.Event, l zerolog.Level, msg string) {
	_, file, line, ok := runtime.Caller(0)
	if ok {
		e.Str("file", file)
		e.Int("line", line)
	}
}

or if you want it in a single field:

type LineInfoHook struct{}

func (h LineInfoHook) Run(e *zerolog.Event, l zerolog.Level, msg string) {
	_, file, line, ok := runtime.Caller(0)
	if ok {
		e.Str("line", fmt.Sprintf("%s:%d", file, line))
	}
}

See https://github.com/rs/zerolog/blob/master/log_example_test.go for examples with hooks.
See the runtime package docs for more info about the Caller func.

[adbenitez]

Hi @OptimisticLock. Something like that should work.

it doesn't work, it prints the like where runtime.Caller(0) is called inside the hook, not the line where the logging happened

[Ullaakut]

My bad, indeed it shouldn't have been 0. Anyway, since then, the Caller() method has been added to zerolog to achieve this. Once again though, keep in mind that IIRC, this slows down the logger a great deal.