blob: c9e4ec924f24a38308591802bf4cea1f71143e9b [file] [log] [blame]
// Copyright 2015 The LUCI Authors.
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
package gologger
import (
gol ""
// StdFormat is a preferred logging format to use.
// It is compatible with logging format used by luci-py. The zero after %{pid}
// is "thread ID" which is unavailable in go.
const StdFormat = `[%{level:.1s}%{time:2006-01-02T15:04:05.000000Z07:00} ` +
`%{pid} 0 %{shortfile}] %{message}`
// StdFormatWithColor is same as StdFormat, except with fancy colors.
// Use it when logging to terminal. Note that StdConfig will pick it
// automatically if it detects that given io.Writer is an os.File and it
// is a terminal. See PickStdFormat().
const StdFormatWithColor = `%{color}[%{level:.1s}%{time:2006-01-02T15:04:05.000000Z07:00} ` +
`%{pid} 0 %{shortfile}]%{color:reset} %{message}`
// PickStdFormat returns StdFormat for non terminal-backed files or
// StdFormatWithColor for io.Writers that are io.Files backed by a terminal.
// Used by default StdConfig.
func PickStdFormat(w io.Writer) string {
if file, _ := w.(*os.File); file != nil {
if terminal.IsTerminal(int(file.Fd())) {
return StdFormatWithColor
return StdFormat
// StdConfig defines default logger configuration.
// It logs to Stderr using default logging format compatible with luci-py, see
// StdFormat.
// Call StdConfig.Use(ctx) to install it as a default context logger.
var StdConfig = LoggerConfig{Out: os.Stderr}
// LoggerConfig owns a go-logging logger, configured in some way.
// Despite its name it is not a configuration. It is a stateful object that
// lazy-initializes go-logging logger on a first use.
// If you are using os.File as Out, you are responsible for closing it when you
// are done with logging.
type LoggerConfig struct {
Out io.Writer // where to write the log to, required
Format string // how to format the log, default is PickStdFormat(Out)
Logger *gol.Logger // if set, will be used as is, overrides everything else
initOnce sync.Once
w *goLoggerWrapper
// NewLogger returns new go-logging based logger bound to the given context.
// It will use logging level and fields specified in the context. Pass 'nil' as
// a context to completely disable context-related checks. Note that default
// context (e.g. context.Background()) is configured for Info logging level, not
// Debug.
// lc.NewLogger is in fact logging.Factory and can be used in SetFactory.
// All loggers produced by LoggerConfig share single underlying go-logging
// Logger instance.
func (lc *LoggerConfig) NewLogger(c context.Context) logging.Logger {
lc.initOnce.Do(func() {
logger := lc.Logger
if logger == nil {
fmt := lc.Format
if fmt == "" {
fmt = PickStdFormat(lc.Out)
// Leveled formatted file backend.
backend := gol.AddModuleLevel(
gol.NewLogBackend(lc.Out, "", 0),
backend.SetLevel(gol.DEBUG, "")
logger = gol.MustGetLogger("")
lc.w = &goLoggerWrapper{l: logger}
ret := &loggerImpl{goLoggerWrapper: lc.w}
if c != nil {
ret.level = logging.GetLevel(c)
if fields := logging.GetFields(c); len(fields) > 0 {
ret.fields = fields.String()
return ret
// Use registers go-logging based logger as default logger of the context.
func (lc *LoggerConfig) Use(c context.Context) context.Context {
return logging.SetFactory(c, lc.NewLogger)