codemedic / go-log

Levelled logger for Go; wraps the standard logger.

Go Log

GoLog adds level based logging to logger(s) from standard library.

GoLog's API is designed to be expressive with sensible configuration defaults and to be easy to use.

Installation

go get -u github.com/codemedic/go-log

Getting Started

To get started, import the library and use one of the constructor functions, wrapped with log.Must. Make sure the logger is closed, once you are done with it, using defer l.Close(). Now you are all set to start logging.

Example

package main

import golog "github.com/codemedic/go-log"

func main() {
  // create syslog logger
  l := golog.Must(golog.NewSyslog())
  
  // make sure resources are freed up when we are done
  defer l.Close()

  // hello to the world
  l.Print("hello world!")
}

NOTE
Functions log.Print and log.Printf logs to Debug level by default. It is preferable to use a method that log to a specific level. The level logged to by log.Print and log.Printf can be changed using WithPrintLevel.

You can find more examples here.

Leveled Logging

The methods below provides leveled logging. They follow the same pattern as fmt.Print and fmt.Printf and uses the same format specification.

// Log string message at specific levels
Debug(value ...interface{})
Info(value ...interface{})
Warning(value ...interface{})
Error(value ...interface{})

// Log formatted string message at specific levels, similar to log.Printf from standard library
Debugf(format string, value ...interface{})
Infof(format string, value ...interface{})
Warningf(format string, value ...interface{})
Errorf(format string, value ...interface{})

Example

package main

import (
  "errors"
  golog "github.com/codemedic/go-log"
)

func main() {
  l := golog.Must(golog.NewSyslog())
  defer l.Close()

  l.Debug("debug message")
  l.Debugf("formatted %s message", "debug")

  l.Info("informational message")
  l.Infof("formatted %s message", "informational")

  l.Warning("warning message")
  l.Warningf("formatted %s message", "warning")

  l.Error("error message")
  l.Errorf("formatted %v message", errors.New("error"))
}

Options / Settings

See documentation for all available Options.

Example

package main

import golog "github.com/codemedic/go-log"

func main() {
  l := golog.Must(golog.NewSyslog(
    golog.OptionsMust(golog.Options(
      golog.WithLevelFromEnv("LOG_THRESHOLD", golog.Info),
      golog.WithSourceLocationFromEnv("LOG_CALLER_LOCATION", "short"),
      golog.WithSyslogTag("my-test-app"),
    ))))
  defer l.Close()

  l.Info("hello world!")
}

Standard log handler

Logging via standard logger is handled by default. This is meant for cases where the logging via the standard library is outside your control; a library used in your project for example. Those will be logged at Info level, but this behaviour can be customised using WithStdlogSorter.

Example

package main

import (
  "bytes"
  golog "github.com/codemedic/go-log"
)

func sortStdlog(b []byte) golog.Level {
  switch {
  case bytes.HasPrefix(b, []byte("WARNING")):
    fallthrough
  case bytes.HasPrefix(b, []byte("ERROR")):
    return golog.Warning
  case bytes.HasPrefix(b, []byte("DEBUG")):
    return golog.Disabled
  default:
    return golog.Info
  }
}

func main() {
  l, _ := golog.NewSyslog(golog.WithStdlogSorter(sortStdlog))
  defer l.Close()

  l.Info("hello world!")
}