Oak internally has all of it's debug and logging calls go through the dlog package. This package exports the function SetLogger which users can use to override default logging behavior. If the user does nothing, a default logger will be used.
The default logger in dlog will simultaneously write to file and fmt.Print incoming log statements. It will attempt to create a log file with a name matching the current time when oak is run, in a logs directory relative to where oak is run from. If this directory does not exist, no logs will be written to file.
The default logger supports four levels of logging: Verb, Info, Warn, and Error, and will only display (but will still write to file) messages that contain a customizable string filter. The error level and string filter are set through oak.SetupConfig.
Users are able to replace the default logger with anything that satsfies one of two interfaces-- it can either satisfy dlog.Logger, which supports four-level logging, or it can satisfy dlog.FullLogger which has additional utilities along with file creation, logging just to file, and setting debug filter and level. If the input to SetLogger does not satisfy dlog.FullLogger, these additional operations will become NOPs.