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// This is a logger implementation that supports multiple log levels,
// multiple output destinations with configurable formats and levels
// for each. It also supports granular output configuration to get
// more detailed logging for specific files/packages. Timber includes
// support for standard XML or JSON config files to get you started
// quickly. It's also easy to configure in code if you want to DIY.
// Basic use:
// import "timber"
// timber.LoadConfiguration("timber.xml")
// timber.Debug("Debug message!")
// IMPORTANT: timber has not default destination configured so log messages
// will be dropped until a destination is configured
// It can be used as a drop-in replacement for the standard logger
// by changing the log import statement from:
// import "log"
// to
// import log "timber"
// It can also be used as the output of the standard logger with
// log.SetFlags(0)
// log.SetOutput(timber.Global)
// Configuration in code is also simple:
// timber.AddLogger(timber.ConfigLogger{
// LogWriter: new(timber.ConsoleWriter),
// Level: timber.DEBUG,
// Formatter: timber.NewPatFormatter("[%D %T] [%L] %S %M"),
// })
// XML Config file:
// <logging>
// <filter enabled="true">
// <tag>stdout</tag>
// <type>console</type>
// <level>DEBUG</level>
// </filter>
// <filter enabled="true">
// <tag>file</tag>
// <type>file</type>
// <level>FINEST</level>
// <granular>
// <level>INFO</level>
// <path>path/to/package.FunctionName</path>
// </granular>
// <granular>
// <level>WARNING</level>
// <path>path/to/package</path>
// </granular>
// <property name="filename">log/server.log</property>
// <property name="format">server [%D %T] [%L] %M</property>
// </filter>
// <filter enabled="false">
// <tag>syslog</tag>
// <type>socket</type>
// <level>FINEST</level>
// <property name="protocol">unixgram</property>
// <property name="endpoint">/dev/log</property>
// <format name="pattern">%L %M</property>
// </filter>
// </logging>
// The <tag> is ignored.
// To configure the pattern formatter all filters accept:
// <format name="pattern">[%D %T] %L %M</format>
// Pattern format specifiers (not the same as log4go!):
// %T - Time: 17:24:05.333
// %t - Time: 17:24:05 HH:MM:SS
// %D - Date: 2011-12-25 yyyy-mm-dd
// %d - Date: 2011/12/25 yyyy/mm/dd
// %S - Source: full runtime.Caller line and line number
// %s - Short Source: just file and line number
// %x - Extra Short Source: just file without .go suffix
// %M - Message
// %% - Percent sign
// %P - Caller Path: packagePath.CallingFunctionName
// %p - Caller Path: packagePath
// the string number prefixes are allowed e.g.: %10s will pad the source field to 10 spaces
// pattern defaults to %M
// Both log4go synatax of <property name="format"> and new <format name=type> are supported
// the property syntax will only ever support the pattern formatter
// To configure granulars:
// - Create one or many <granular> within a filter
// - Define a <level> and <path> within, where path can be path to package or path to
// package.FunctionName. Function name definitions override package paths.
// Code Architecture:
// A MultiLogger <logging> which consists of many ConfigLoggers <filter>. ConfigLoggers have three properties:
// LogWriter <type>, Level (as a threshold) <level> and LogFormatter <format>.
// In practice, this means that you define ConfigLoggers with a LogWriter (where the log prints to
// eg. socket, file, stdio etc), the Level threshold, and a LogFormatter which formats the message
// before writing. Because the LogFormatters and LogWriters are simple interfaces, it is easy to
// write your own custom implementations.
// Once configured, you only deal with the "Logger" interface and use the log methods in your code
// The motivation for this package grew from a need to make some changes to the functionality of
// log4go (which had already been integrated into a larger project). I tried to maintain compatiblity
// with log4go for the interface and configuration. The main issue I had with log4go was that each of
// logger types had incisistent and incompatible configuration. I looked at contributing changes to
// log4go, but I would have needed to break existing use cases so I decided to do a rewrite from scratch.
package timber
import (
type Level int
// Log levels
const (
NONE Level = iota // NONE to be used for standard go log impl's
// Default level passed to runtime.Caller by Timber, add to this if you wrap Timber in your own logging code
const DefaultFileDepth int = 3
// What gets printed for each Log level
var LevelStrings = [...]string{"", "FNST", "FINE", "DEBG", "TRAC", "INFO", "WARN", "EROR", "CRIT"}
// Full level names
var LongLevelStrings = []string{
// Return a given level string as the actual Level value
func getLevel(lvlString string) Level {
for idx, str := range LongLevelStrings {
if str == lvlString {
return Level(idx)
return Level(0)
// This explicitly defines the contract for a logger
// Not really useful except for documentation for
// writing an separate implementation
type Logger interface {
// match log4go interface to drop-in replace
Finest(arg0 interface{}, args ...interface{})
Fine(arg0 interface{}, args ...interface{})
Debug(arg0 interface{}, args ...interface{})
Trace(arg0 interface{}, args ...interface{})
Info(arg0 interface{}, args ...interface{})
Warn(arg0 interface{}, args ...interface{}) error
Error(arg0 interface{}, args ...interface{}) error
Critical(arg0 interface{}, args ...interface{}) error
Log(lvl Level, arg0 interface{}, args ...interface{})
// support standard log too
Print(v ...interface{})
Printf(format string, v ...interface{})
Println(v ...interface{})
Panic(v ...interface{})
Panicf(format string, v ...interface{})
Panicln(v ...interface{})
Fatal(v ...interface{})
Fatalf(format string, v ...interface{})
Fatalln(v ...interface{})
// Not used
type LoggerConfig interface {
// When set, messages with level < lvl will be ignored. It's up to the implementor to keep the contract or not
SetLevel(lvl Level)
// Set the formatter for the log
SetFormatter(formatter LogFormatter)
// Interface required for a log writer endpoint. It's more or less a
// io.WriteCloser with no errors allowed to be returned and string
// instead of []byte.
// TODO: Maybe this should just be a standard io.WriteCloser?
type LogWriter interface {
LogWrite(msg string)
// This packs up all the message data and metadata. This structure
// will be passed to the LogFormatter
type LogRecord struct {
Level Level
Timestamp time.Time
SourceFile string
SourceLine int
Message string
FuncPath string
PackagePath string
// Format a log message before writing
type LogFormatter interface {
Format(rec *LogRecord) string
// Container a single log format/destination
type ConfigLogger struct {
LogWriter LogWriter
// Messages with level < Level will be ignored. It's up to the implementor to keep the contract or not
Level Level
Formatter LogFormatter
Granulars map[string]Level
// Allow logging to multiple places
type MultiLogger interface {
// returns an int that identifies the logger for future calls to SetLevel and SetFormatter
AddLogger(logger ConfigLogger) int
// dynamically change level or format
SetLevel(index int, lvl Level)
SetFormatter(index int, formatter LogFormatter)
// Implementation
// The Timber instance is the concrete implementation of the logger interfaces.
// New instances may be created, but usually you'll just want to use the default
// instance in Global
// NOTE: I don't supporting the log4go special handling of the first parameter based on type
// mainly cuz I don't think it's particularly useful (I kept passing a data string as the first
// param and expecting a Println-like output but that would always break expecting a format string)
// I also don't support the passing of the closure stuff
type Timber struct {
writerConfigChan chan timberConfig
recordChan chan *LogRecord
hasLogger bool
closeLatch *sync.Once
blackHole chan int
// This value is passed to runtime.Caller to get the file name/line and may require
// tweaking if you want to wrap the logger
FileDepth int
type timberAction int
const (
actionAdd timberAction = iota
type timberConfig struct {
Action timberAction // type of config action
Index int // only for modify
Cfg ConfigLogger // used for modify or add
Ret chan int // only used for add
// Creates a new Timber logger that is ready to be configured
// With no subsequent configuration, nothing will be logged
func NewTimber() *Timber {
t := new(Timber)
t.writerConfigChan = make(chan timberConfig)
t.recordChan = make(chan *LogRecord, 300)
t.FileDepth = DefaultFileDepth
t.closeLatch = &sync.Once{}
t.blackHole = make(chan int)
go t.asyncLumberJack()
return t
func (t *Timber) asyncLumberJack() {
var loggers []ConfigLogger = make([]ConfigLogger, 0, 2)
loopIt := true
for loopIt {
select {
case rec := <-t.recordChan:
sendToLoggers(loggers, rec)
case cfg := <-t.writerConfigChan:
switch cfg.Action {
case actionAdd:
loggers = append(loggers, cfg.Cfg)
cfg.Ret <- (len(loggers) - 1)
case actionModify:
case actionQuit:
loopIt = false
defer func() {
cfg.Ret <- 0
} // select
} // for
// drain the log channel before closing
for rec := range t.recordChan {
sendToLoggers(loggers, rec)
func sendToLogger(rec *LogRecord, granLevel Level, formatted string, cLog ConfigLogger) bool {
if rec.Level >= granLevel || granLevel == 0 {
if formatted == "" {
formatted = cLog.Formatter.Format(rec)
return true
return false
func sendToLoggers(loggers []ConfigLogger, rec *LogRecord) {
formatted := ""
for _, cLog := range loggers {
// Find any function level definitions.
gLevel, ok := cLog.Granulars[rec.FuncPath]
if ok {
sendToLogger(rec, gLevel, formatted, cLog)
// Find any package level definitions.
gLevel, ok = cLog.Granulars[rec.PackagePath]
if ok {
sendToLogger(rec, gLevel, formatted, cLog)
// Use default definition
sendToLogger(rec, cLog.Level, formatted, cLog)
func closeAllWriters(cls []ConfigLogger) {
for _, cLog := range cls {
// MultiLogger interface
func (t *Timber) AddLogger(logger ConfigLogger) int {
tcChan := make(chan int, 1) // buffered
tc := timberConfig{Action: actionAdd, Cfg: logger, Ret: tcChan}
t.writerConfigChan <- tc
return <-tcChan
// MultiLogger interface
func (t *Timber) Close() {
t.closeLatch.Do(func() {
tcChan := make(chan int)
tc := timberConfig{Action: actionQuit, Ret: tcChan}
t.writerConfigChan <- tc
<-tcChan // block for cloosing
// Not yet implemented
func (t *Timber) SetLevel(index int, lvl Level) {
// Not yet implemented
func (t *Timber) SetFormatter(index int, formatter LogFormatter) {
// Logger interface
func (t *Timber) prepareAndSend(lvl Level, msg string, depth int) {
select {
case <-t.blackHole:
// the blackHole always blocks until we close
// then it always succeeds so we avoid writing
// to the closed channel
t.recordChan <- t.prepare(lvl, msg, depth+1)
func (t *Timber) prepare(lvl Level, msg string, depth int) *LogRecord {
now := time.Now()
pc, file, line, _ := runtime.Caller(depth)
funcPath := "_"
packagePath := "_"
me := runtime.FuncForPC(pc)
if me != nil {
funcPath = me.Name()
packagePath = splitPackage(funcPath)
return &LogRecord{
Level: lvl,
Timestamp: now,
SourceFile: file,
SourceLine: line,
Message: msg,
FuncPath: funcPath,
PackagePath: packagePath,
// This function allows a Timber instance to be used in the standard library
// log.SetOutput(). It is not a general Writer interface and assumes one
// message per call to Write. All messages are send at level INFO
func (t *Timber) Write(p []byte) (n int, err error) {
t.prepareAndSend(INFO, string(bytes.TrimSpace(p)), 4)
return len(p), nil
func (t *Timber) Finest(arg0 interface{}, args ...interface{}) {
t.prepareAndSend(FINEST, fmt.Sprintf(arg0.(string), args...), t.FileDepth)
func (t *Timber) Fine(arg0 interface{}, args ...interface{}) {
t.prepareAndSend(FINE, fmt.Sprintf(arg0.(string), args...), t.FileDepth)
func (t *Timber) Debug(arg0 interface{}, args ...interface{}) {
t.prepareAndSend(DEBUG, fmt.Sprintf(arg0.(string), args...), t.FileDepth)
func (t *Timber) Trace(arg0 interface{}, args ...interface{}) {
t.prepareAndSend(TRACE, fmt.Sprintf(arg0.(string), args...), t.FileDepth)
func (t *Timber) Info(arg0 interface{}, args ...interface{}) {
t.prepareAndSend(INFO, fmt.Sprintf(arg0.(string), args...), t.FileDepth)
func (t *Timber) Warn(arg0 interface{}, args ...interface{}) error {
msg := fmt.Sprintf(arg0.(string), args...)
t.prepareAndSend(WARNING, msg, t.FileDepth)
return errors.New(msg)
func (t *Timber) Error(arg0 interface{}, args ...interface{}) error {
msg := fmt.Sprintf(arg0.(string), args...)
t.prepareAndSend(ERROR, msg, t.FileDepth)
return errors.New(msg)
func (t *Timber) Critical(arg0 interface{}, args ...interface{}) error {
msg := fmt.Sprintf(arg0.(string), args...)
t.prepareAndSend(CRITICAL, msg, t.FileDepth)
return errors.New(msg)
func (t *Timber) Log(lvl Level, arg0 interface{}, args ...interface{}) {
t.prepareAndSend(lvl, fmt.Sprintf(arg0.(string), args...), t.FileDepth)
// Print won't work well with a pattern_logger because it explicitly adds
// its own \n; so you'd have to write your own formatter to remove it
func (t *Timber) Print(v ...interface{}) {
t.prepareAndSend(DEBUG, fmt.Sprint(v...), t.FileDepth)
func (t *Timber) Printf(format string, v ...interface{}) {
t.prepareAndSend(DEBUG, fmt.Sprintf(format, v...), t.FileDepth)
// Println won't work well either with a pattern_logger because it explicitly adds
// its own \n; so you'd have to write your own formatter to not have 2 \n's
func (t *Timber) Println(v ...interface{}) {
t.prepareAndSend(DEBUG, fmt.Sprintln(v...), t.FileDepth)
func (t *Timber) Panic(v ...interface{}) {
msg := fmt.Sprint(v...)
t.prepareAndSend(CRITICAL, msg, t.FileDepth)
func (t *Timber) Panicf(format string, v ...interface{}) {
msg := fmt.Sprintf(format, v...)
t.prepareAndSend(CRITICAL, msg, t.FileDepth)
func (t *Timber) Panicln(v ...interface{}) {
msg := fmt.Sprintln(v...)
t.prepareAndSend(CRITICAL, msg, t.FileDepth)
func (t *Timber) Fatal(v ...interface{}) {
msg := fmt.Sprint(v...)
t.prepareAndSend(CRITICAL, msg, t.FileDepth)
func (t *Timber) Fatalf(format string, v ...interface{}) {
msg := fmt.Sprintf(format, v...)
t.prepareAndSend(CRITICAL, msg, t.FileDepth)
func (t *Timber) Fatalln(v ...interface{}) {
msg := fmt.Sprintln(v...)
t.prepareAndSend(CRITICAL, msg, t.FileDepth)
// Default Instance
// Default Timber Instance (used for all the package level function calls)
var Global = NewTimber()
// Simple wrappers for Logger interface
func Finest(arg0 interface{}, args ...interface{}) { Global.Finest(arg0, args...) }
func Fine(arg0 interface{}, args ...interface{}) { Global.Fine(arg0, args...) }
func Debug(arg0 interface{}, args ...interface{}) { Global.Debug(arg0, args...) }
func Trace(arg0 interface{}, args ...interface{}) { Global.Trace(arg0, args...) }
func Info(arg0 interface{}, args ...interface{}) { Global.Info(arg0, args...) }
func Warn(arg0 interface{}, args ...interface{}) error { return Global.Warn(arg0, args...) }
func Error(arg0 interface{}, args ...interface{}) error { return Global.Error(arg0, args...) }
func Critical(arg0 interface{}, args ...interface{}) error { return Global.Critical(arg0, args...) }
func Log(lvl Level, arg0 interface{}, args ...interface{}) { Global.Log(lvl, arg0, args...) }
func Print(v ...interface{}) { Global.Print(v...) }
func Printf(format string, v ...interface{}) { Global.Printf(format, v...) }
func Println(v ...interface{}) { Global.Println(v...) }
func Panic(v ...interface{}) { Global.Panic(v...) }
func Panicf(format string, v ...interface{}) { Global.Panicf(format, v...) }
func Panicln(v ...interface{}) { Global.Panicln(v...) }
func Fatal(v ...interface{}) { Global.Fatal(v...) }
func Fatalf(format string, v ...interface{}) { Global.Fatalf(format, v...) }
func Fatalln(v ...interface{}) { Global.Fatalln(v...) }
func AddLogger(logger ConfigLogger) int { return Global.AddLogger(logger) }
func Close() { Global.Close() }
func LoadConfiguration(filename string) { Global.LoadConfig(filename) }
func LoadXMLConfiguration(filename string) { Global.LoadXMLConfig(filename) }
func LoadJSONConfiguration(filename string) { Global.LoadJSONConfig(filename) }