log

a simple logging library for Go inspired by Dave Cheney's Let's talk about logging blog post.

installation

go get github.com/timbasel/go-log

usage

basic

import "github.com/timbasel/go-log/pkg/log"

func main() {
  // message for the developer debugging the application
  log.Debug("debug message")

  // message for the user running the application
  log.Info("info message")

  // message in case the application encountered an unhandleable error and will terminate after messaging
  // this should effectively only be used in the main.main function after bubbling up the unhandled error
  log.Error("error message")
}

configuration

import "github.com/timbasel/go-log/pkg/log"

func main() {
  // adds locations where the log is written to (by default os.Stdout is set)
  log.SetOutputs(os.Stdout)

  // adds locations with a custom formatter
  log.SetFormattedOutputs(map[io.Writer]log.Formatter{os.Stdout: log.NewRawFormatter()})

  // set if debug messages should be logged (default: false)
  log.SetDebugMode(true)

  // blacklist or whitelist functions and packages from debug output
  log.BlacklistFunctions("main")
  log.WhitelistPackages("github.com/username/project")

  // remove entries from blacklist or whitelist
  log.ClearBlacklist()
}

logger

import "github.com/timbasel/go-log/pkg/log"

func main() {
  logger := log.NewDefaultLogger()

  logger.ClearOutputs()
  logger.SetOutputs(os.Stderr)

  logger.Info("Hello World")
}

formatters

import "github.com/timbasel/go-log/pkg/log"

type CustomFormatter struct{}

func (f *CustomFormatter) Format(level log.Level, msg string) (formattedMsg string) {
  return "> " + msg + " [" + level.String() + "]\n"
}

func ExampleFormatters() {
  logger := log.NewLogger()
  logger.SetDebugMode(true)

  file, _ := ioutil.TempFile("/tmp/", "log_*.json")
  logger.SetFormattedOutputs(map[io.Writer]log.Formatter{
    os.Stdout: &CustomFormatter{},
    os.Stderr: log.NewDefaultFormatter(),
    file:      log.NewJSONFormatter(),
  })

  logger.Debug("Hello World")

  // output to stdout:
  //    > Hello World [DEBUG]
  // output to stderr:
  //    2019-06-03 17:24:10 <log_test.ExampleFormatters> DEBUG: Hello World
  // output to temporary file:
  //    {"function":"ExampleFormatters","level":"DEBUG","msg":"Hello World","package":"github.com/timbasel/go-log/pkg/log_test","time":"2019-06-03T17:23:17+02:00"}
}

license

apache license 2.0 © Tim Basel