Developer Guide

Clone the golog git repository

git clone ""


A new logger instance is created with InitLogger function. Process identity is given as a parameter.

Mapped Diagnostics Context

The MDCs are key-value pairs, which are included to all log entries by the library. The MDC pairs are logger instance specific.

The idea of the MDC is to define values, which stay the same over multiple log writings. An MDC value set once will appear in all the subsequent logs written with the logger instance.

A logger instance can be shared by several goroutines. Respectively, also the MDC values of the logger instance are then shared by them. When sharing of the MDCs is not desired, separate logger instances should be used.

Log entry format

Each log entry written the library contains

  • Timestamp
  • Logger identity
  • Log entry severity
  • MDC pairs of the logger instance
  • Log message text

Currently the library only supports JSON formatted output written to standard out of the process

Example log output

{“ts”:1551183682974,”crit”:”INFO”,”id”:”myprog”,”mdc”:{“second key”:”other value”,”mykey”:”keyval”},”msg”:”hello world!”}


package main

import (
       mdcloggo ""

func main() {
   logger, _ := mdcloggo.InitLogger("myname")
   logger.MdcAdd("mykey", "keyval")
   logger.Info("Some test logs")

Logging Levels

// ERR is an error level log entry.
  ERR Level = 1
// WARN is a warning level log entry.
  WARN Level = 2
// INFO is an info level log entry.
  INFO Level = 3
// DEBUG is a debug level log entry.
  DEBUG Level = 4

Golog API’s

  1. LevelSet sets the current logging level.
func (l *MdcLogger) LevelSet(level Level)
  1. LevelGet returns the current logging level.
func (l *MdcLogger) LevelGet() Level
  1. MdcAdd adds a new MDC key value pair to the logger.
func (l *MdcLogger) MdcAdd(key string, value string)
  1. MdcRemove removes an MDC key from the logger.
func (l *MdcLogger) MdcRemove(key string)
  1. MdcGet gets the value of an MDC from the logger.
func (l *MdcLogger) MdcGet(key string) (string, bool)

Description: The function returns the value string and a boolean which tells if the key was found or not.

  1. MdcClean removes all MDC keys from the logger.
func (l *MdcLogger) MdcClean()