suggestion: allow optional `tz` parameter for `timestamp_fmt` in Layout(s)

[mmuurr]

Sometimes it's helpful to have logs across disparate machines output timestamps with the same TZ offset.

Currently, the best way to do this is:

• Not do it at all, but set the timestamp_fmt string to something like %FT%T%z, a proper ISO8601 with TZ offset (%z).
• Change the default TZ of the R session (either from within R or prior to launching the R process from the shell; the latter approach is somewhat error-prone and dependent on how different OSes and Linux distros manage timezones).

But(!), base::format.POSIXct includes a tz parameter; here's the signature:

format.POSIXct <-  function(x, format = "", tz = "", usetz = FALSE, ...)

... and lgr's default Layouts simply delegate to that function.

I wonder if it'd be possible to pass on the tz argument, or perhaps even more generally simply 'pass the dots' and allow timestamp_tz setters to specify a dots (...) arg that is captured, stored, then spliced into the eventual format.POSIXct dispatch.

Only a suggestion :-) ... and thanks much for all the work you've put into lgr, it's quite nice!

[s-fleck]

So you want Layouts to be able to convert between different timezones?

So getting timezones right is kinda tricky, and I think general best practice would be to log everything in UTC, especially if you work across several systems in different timezones. I understand that It would be more convenient if lgr supported converting timezones directly, but if it did that should probably be at global level - so that all Appenders log in the same timezone.

I will leave this open, but It might be a while before I get around to work on lgr again because I'm kinda tied up in other projects at the moment.

[GitForrest]

I agree that UTC is the best timezone to use for logging timestamps. Is there a recommended approach to configuring the lgr package to log everything in UTC? Currently the lgr package seems to be writing to the local timezone by default.

[s-fleck]

No there is not. I'd really like to improve timezone handling in lgr but it seems to be a problem that is a bit convoluted and I'm not yet sure how to go about it.

You COULD attach a filter to the logger as a workaround if you really need UTC timestamps right now, but this is probably something I should support natively:

lg <- lgr::get_logger("test/logger")
lg$add_filter(function(event){
  attr(event$timestamp, "tzone") <- "UTC"
  TRUE
}, "UTCify")

lg$info("Test")

[GitForrest]

I think I found another workaround that may interest you.

Below I simply set the Sys.timezone() to 'UTC' and all timestamps using Sys.time() will be returned in the 'UTC' timezone with appropriate offset from my local time.

`
#### EXAMPLE #####

library(lgr)

# get a logger object
lg <- lgr::get_logger(name = "logger")

lg$set_threshold('info')

# set up logger to write to the console
lg$set_appenders(list(cons = lgr::AppenderConsole$new()))

# Not certain what this does, yet follows all examples in the package
# documentation.
lg$set_propagate(FALSE)

# set the formatting of the logging events
format_string <- paste0("%t - %L: %m")

lg$appenders$cons$layout$set_fmt(format_string)
lg$appenders$cons$layout$set_timestamp_fmt("%Y-%m-%d %H:%M:%OS3")


print(Sys.timezone())
lg$info("Some message with local timestamp")

# Ensure the Sys.time() will return timestamp in UTC
Sys.setenv(TZ = 'UTC')
print(Sys.timezone())

lg$info("Some message with UTC timestamp")

`

OUTPUT

[1] "America/New_York"
2021-10-25 15:07:05.372 - INFO : Some message with local timestamp
[1] "UTC"
2021-10-25 19:07:05.383 - INFO : Some message with UTC timestamp

[s-fleck]

lgr$set_propagate(FALSE) makes it so that the log messages are not propageted to the logger parents. In a real-world Scenario you usually want propagate to be TRUE (the default), but it makes sense for examples to keep the exemple-loggers "isolated" form your "real" R-Session!

I am not sure what Sys.setenv(TZ = 'UTC') does, but I guess the least it does is changing the timezone for your whole R-Session, which is a fine solution if that is what you really want!