Sane logging in go.
Configuration belongs primarily in the environment
It is the job of the consuming application's initiation to redirect stdout and stderr to the appropriate place(s)
e.g. For local work you desire all messages print to the stdout and stderr of your shell. For a production workflow, log messages need to be written and appended to a file, in addition to being printed to the terminal.
In the former scenario nothing needs to be done. But for a production workflow, whatever starts the application process may need to run
your_consuming_application 2>&1 | tee -a some_log_file.log
Log level for the default logger is set to INFO, WARN, and ERROR.
Log level for consuming client application code can be done by passing the severity for a non-default logger along with where stdout and stderr should write to, e.g.:
s := logger.New("", logger.Error | logger.Info, os.Stdout, os.Stderr)
The first precedent to set severity is the mask passed during the creation of a new logger (see Log Level/Severity)
The second precedent are ENV variables prefixed with LOG_LEVEL_. These variables, if defined, will override behavior set through New logger instantiation. If defined and set to something other than 0 that log level will be enabled, vice versa if set to 0. This allows more granular control at runtime of which logging levels are displayed, as the variables can be set completely independently, i.e.:
LOG_LEVEL_ERROR=1 LOG_LEVEL_WARN=0 ...LOG_LEVEL_ERROR=0 LOG_LEVEL_DEBUG=0 LOG_LEVEL_INFO=1 ...LOG_LEVEL_ERROR=0 LOG_LEVEL_DEBUG=0 LOG_LEVEL_INFO=0 LOG_LEVEL_WARN=1 ...
To configure specific loggers, prefix the ENV variable with the same prefix used for that logger. Configuration of log levels set for specific loggers will take priority over non-prefixed LOG_LEVEL_ configuration.
e.g., if you need a renderLogger and a computationalLogger, you might create them like this
renderLogger := logger.New("renderer", logger.DefaultSeverity)
computeLogger := logger.New("computer", logger.DefaultSeverity)
The default severity may be fine for most situations but for testing you may want additional DEBUG log messages from the computeLogger.
In that case, in the ENV of whatever is running tests, you can define
compute_LOG_LEVEL_DEBUG=1
and the computeLogger will additionally show DEBUG messages while the renderLogger will only show messages under the default severity (WARN and ERROR).