lgr (version 0.3.2)

EventFilter: Event Filters

Description

Filters can be used for the $set_filter() and $add_filter() methods of Appenders and Loggers. You normally do not need to construct a formal EventFilter object, you can just use any function that has the single argument event or any object that has a filter method.

Modifying LogEvents with Filters

Since LogEvents are R6 objects with reference semantics, Filters can also be abused to modify log events before passing them on. lgr comes with a few preset filters that use this property:

FilterInject$new(..., .list)

... and .list can take any number of named R6 objects that will be injected as custom fields into all LogEvents processed by the Appender/Logger that this filter is attached to. See also with_log_value()

FilterForceLevel$new(level)

Sets the level of all LogEvents processed by the Appender/Logger that this filter is attached to to level. See also with_log_value()

Accessing Appenders and Loggers from Filters

You can use the special function .obj() to access the calling Logger/Appender from within a filter

Examples

# NOT RUN {
# using filters to modify log events
lg <- get_logger("test")

analyse <- function(){
  lg$add_filter(FilterForceLevel$new("info"), "force")
  lg$add_filter(FilterInject$new(type = "analysis"), "inject")
  on.exit(lg$remove_filter(c("force", "inject")))
  lg$debug("a debug message")
  lg$error("an error")
}
analyse()
lg$error("an error")
lg$config(NULL)  # reset config


# using .obj()
lg <- get_logger("test")
f <- function(event) {
  cat("via event$.logger:", event$.logger$threshold, "\n")  #  works for loggers only
  cat("via .obj():      ",.obj()$threshold, "\n") # works for loggers and appenders
  TRUE
}
lg$add_filter(f)
lg$fatal("test")
lg$config(NULL)
# }