Structured Logging Made Easy

Features

• Dependency Free
• Simple and Clean Interface
• Consistent Writer
  • IOWriter, io.Writer wrapper
  • ConsoleWriter, colorful & formatting
  • FileWriter, rotating & effective
  • MultiWriter, multiple level dispatch
  • SyslogWriter, syslog server logging
  • JournalWriter, linux systemd logging
  • EventlogWriter, windows system event
  • AsyncWriter, asynchronously writing
• Third-party Logger Interceptor
  • Logger.Std, (std)log
  • Logger.Grpc, grpclog.LoggerV2
  • Logger.Logr, logr.Logger
• Useful utility function
  • Goid(), the goroutine id matches stack trace
  • NewXID(), create a tracing id
  • Fastrandn(n uint32), fast pseudorandom uint32 in [0,n)
  • IsTerminal(fd uintptr), isatty for golang
  • Printf(fmt string, a ...interface{}), printf logging
• High Performance
  • Significantly faster than all other json loggers.

Interfaces

Logger

// DefaultLogger is the global logger.
var DefaultLogger = Logger{
	Level:      DebugLevel,
	Caller:     0,
	TimeField:  "",
	TimeFormat: "",
	Writer:     &IOWriter{os.Stderr},
}

// A Logger represents an active logging object that generates lines of JSON output to an io.Writer.
type Logger struct {
	// Level defines log levels.
	Level Level

	// Caller determines if adds the file:line of the "caller" key.
	Caller int

	// TimeField defines the time filed name in output.  It uses "time" in if empty.
	TimeField string

	// TimeFormat specifies the time format in output. It uses RFC3339 with millisecond if empty.
	// If set with `TimeFormatUnix`, `TimeFormatUnixMs`, times are formated as UNIX timestamp.
	TimeFormat string

	// Writer specifies the writer of output. It uses a wrapped os.Stderr Writer in if empty.
	Writer Writer
}

ConsoleWriter & FileWriter

// ConsoleWriter parses the JSON input and writes it in a colorized, human-friendly format to Writer.
// IMPORTANT: Don't use ConsoleWriter on critical path of a high concurrency and low latency application.
//
// Default output format:
//     {Time} {Level} {Goid} {Caller} > {Message} {Key}={Value} {Key}={Value}
type ConsoleWriter struct {
	// ColorOutput determines if used colorized output.
	ColorOutput bool

	// QuoteString determines if quoting string values.
	QuoteString bool

	// EndWithMessage determines if output message in the end of line.
	EndWithMessage bool

	// Writer is the output destination. using os.Stderr if empty.
	Writer io.Writer

	// Formatter specifies an optional text formatter for creating a customized output,
	// If it is set, ColorOutput, QuoteString and EndWithMessage will be ignored.
	Formatter func(w io.Writer, args *FormatterArgs) (n int, err error)
}


// FileWriter is an Writer that writes to the specified filename.
type FileWriter struct {
	// Filename is the file to write logs to.  Backup log files will be retained
	// in the same directory.
	Filename string

	// FileMode represents the file's mode and permission bits.  The default
	// mode is 0644
	FileMode os.FileMode

	// MaxSize is the maximum size in bytes of the log file before it gets rotated.
	MaxSize int64

	// MaxBackups is the maximum number of old log files to retain.  The default
	// is to retain all old log files
	MaxBackups int

	// TimeFormat specifies the time format of filename, uses `2006-01-02T15-04-05` as default format.
	// If set with `TimeFormatUnix`, `TimeFormatUnixMs`, times are formated as UNIX timestamp.
	TimeFormat string

	// LocalTime determines if the time used for formatting the timestamps in
	// log files is the computer's local time.  The default is to use UTC time.
	LocalTime bool

	// HostName determines if the hostname used for formatting in log files.
	HostName bool

	// ProcessID determines if the pid used for formatting in log files.
	ProcessID bool

	// EnsureFolder ensures the file directory creation before writing.
	EnsureFolder bool

	// Cleaner specifies an optional cleanup function of log backups after rotation,
	// if not set, the default behavior is to delete more than MaxBackups log files.
	Cleaner func(filename string, maxBackups int, matches []os.FileInfo)
}

Note: FileWriter implements log.Writer and io.Writer interfaces both, it is a drop-in replacement of lumberjack.

Getting Started

Simple Logging Example

An out of box example.

package main

import (
	"github.com/phuslu/log"
)

func main() {
	log.Info().Str("foo", "bar").Int("number", 42).Msg("hi, phuslog")
	log.Info().Msgf("foo=%s number=%d error=%+v", "bar", 42, "an error")
}

// Output:
//   {"time":"2020-03-22T09:58:41.828Z","level":"info","foo":"bar","number":42,"message":"hi, phuslog"}
//   {"time":"2020-03-22T09:58:41.828Z","level":"info","message":"foo=bar number=42 error=an error"}

Note: By default log writes to os.Stderr

Customize the configuration and formatting:

To customize logger filed name and format.

package main

import (
	"github.com/phuslu/log"
)

func main() {
	log.DefaultLogger = log.Logger{
		Level:      log.InfoLevel,
		Caller:     1,
		TimeField:  "date",
		TimeFormat: "2006-01-02",
		Writer:     &log.IOWriter{os.Stdout},
	}

	log.Info().Str("foo", "bar").Msgf("hello %s", "world")
}

// Output: {"date":"2019-07-04","level":"info","caller":"prog.go:16","foo":"bar","message":"hello world"}

Pretty Console Writer

To log a human-friendly, colorized output, use ConsoleWriter.

if log.IsTerminal(os.Stderr.Fd()) {
	log.DefaultLogger = log.Logger{
		TimeFormat: "15:04:05",
		Caller:     1,
		Writer: &log.ConsoleWriter{
			ColorOutput:    true,
			QuoteString:    true,
			EndWithMessage: true,
		},
	}
}

log.Debug().Int("everything", 42).Str("foo", "bar").Msg("hello world")
log.Info().Int("everything", 42).Str("foo", "bar").Msg("hello world")
log.Warn().Int("everything", 42).Str("foo", "bar").Msg("hello world")
log.Error().Err(errors.New("an error")).Msg("hello world")

Note: pretty logging also works on windows console

Formatting Console Writer

To log with user-defined format(e.g. glog), using ConsoleWriter.Formatter.

log.DefaultLogger = log.Logger{
	Level:      log.InfoLevel,
	Caller:     1,
	TimeFormat: "0102 15:04:05.999999",
	Writer: &log.ConsoleWriter{
		Formatter: func (w io.Writer, a *log.FormatterArgs) (int, error) {
			return fmt.Fprintf(w, "%c%s %s %s] %s\n%s", strings.ToUpper(a.Level)[0],
				a.Time, a.Goid, a.Caller, a.Message, a.Stack)
		},
	},
}

log.Info().Msgf("hello glog %s", "Info")
log.Warn().Msgf("hello glog %s", "Warn")
log.Error().Msgf("hello glog %s", "Error")

// Output:
// I0725 09:59:57.503246 19 console_test.go:183] hello glog Info
// W0725 09:59:57.504247 19 console_test.go:184] hello glog Warn
// E0725 09:59:57.504247 19 console_test.go:185] hello glog Error

Rotating File Writer

To log to a daily-rotating file, use FileWriter.

package main

import (
	"os"
	"path/filepath"
	"time"

	"github.com/phuslu/log"
	"github.com/robfig/cron/v3"
)

func main() {
	logger := log.Logger{
		Level: log.ParseLevel("info"),
		Writer: &log.FileWriter{
			Filename:     "logs/main.log",
			FileMode:     0600,
			MaxSize:      100 * 1024 * 1024,
			MaxBackups:   7,
			EnsureFolder: true,
			LocalTime:    true,
		},
	}

	runner := cron.New(cron.WithLocation(time.Local))
	runner.AddFunc("0 0 * * *", func() { logger.Writer.(*log.FileWriter).Rotate() })
	go runner.Run()

	for {
		time.Sleep(time.Second)
		logger.Info().Msg("hello world")
	}
}

Rotating File Writer within a total size

To rotating log file hourly and keep in a total size, use FileWriter.Cleaner.

package main

import (
	"os"
	"path/filepath"
	"time"

	"github.com/phuslu/log"
	"github.com/robfig/cron/v3"
)

func main() {
	logger := log.Logger{
		Level: log.ParseLevel("info"),
		Writer: &log.FileWriter{
			Filename: "main.log",
			MaxSize:  500 * 1024 * 1024,
			Cleaner:  func(filename string, maxBackups int, matches []os.FileInfo) {
				var dir = filepath.Dir(filename)
				var total int64
				for i := len(matches) - 1; i >= 0; i-- {
					total += matches[i].Size()
					if total > 5*1024*1024*1024 {
						os.Remove(filepath.Join(dir, matches[i].Name()))
					}
				}
			},
		},
	}

	runner := cron.New(cron.WithLocation(time.UTC))
	runner.AddFunc("0 * * * *", func() { logger.Writer.(*log.FileWriter).Rotate() })
	go runner.Run()

	for {
		time.Sleep(time.Second)
		logger.Info().Msg("hello world")
	}
}

Multiple Dispatching Writer

To log to different writers by different levels, use MultiWriter.

log.DefaultLogger.Writer = &log.MultiWriter{
	InfoWriter:    &log.FileWriter{Filename: "main.INFO", MaxSize: 100<<20},
	WarnWriter:    &log.FileWriter{Filename: "main.WARNING", MaxSize: 100<<20},
	ErrorWriter:   &log.FileWriter{Filename: "main.ERROR", MaxSize: 100<<20},
	ConsoleWriter: &log.ConsoleWriter{ColorOutput: true},
	ConsoleLevel:  log.ErrorLevel,
}

log.Info().Int("number", 42).Str("foo", "bar").Msg("a info log")
log.Warn().Int("number", 42).Str("foo", "bar").Msg("a warn log")
log.Error().Int("number", 42).Str("foo", "bar").Msg("a error log")

Multiple Combined Logger:

To logging to different logger as you want, use below idiom.

package main

import (
	"github.com/phuslu/log"
)

var logger = struct {
	Console log.Logger
	Access  log.Logger
	Data    log.Logger
}{
	Console: log.Logger{
		TimeFormat: "15:04:05",
		Caller:     1,
		Writer: &log.ConsoleWriter{
			ColorOutput:    true,
			EndWithMessage: true,
		},
	},
	Access: log.Logger{
		Level: log.InfoLevel,
		Writer: &log.FileWriter{
			Filename:   "access.log",
			MaxSize:    50 * 1024 * 1024,
			MaxBackups: 7,
			LocalTime:  false,
		},
	},
	Data: log.Logger{
		Level: log.InfoLevel,
		Writer: &log.FileWriter{
			Filename:   "data.log",
			MaxSize:    50 * 1024 * 1024,
			MaxBackups: 7,
			LocalTime:  false,
		},
	},
}

func main() {
	logger.Console.Info().Msgf("hello world")
	logger.Access.Log().Msgf("handle request")
	logger.Data.Log().Msgf("some data")
}

SyslogWriter & JournalWriter & EventlogWriter

To log to a syslog server, using SyslogWriter.

log.DefaultLogger.Writer = &log.SyslogWriter{
	// Network : "unixgram",
	// Address : "/run/systemd/journal/syslog",
	Network : "tcp",
	Address : "192.168.0.2:601",
	Tag     : "",
	Marker  : "@cee:",
	Dial    : net.Dial,
}

log.Info().Msg("hi")

// Output: <6>Oct 5 16:25:38 [237]: @cee:{"time":"2020-10-05T16:25:38.026Z","level":"info","message":"hi"}

To log to linux systemd journald, using JournalWriter.

log.DefaultLogger.Writer = &log.JournalWriter{}

log.Info().Int("number", 42).Str("foo", "bar").Msg("hello world")

To log to windows system event, using EventlogWriter.

log.DefaultLogger.Writer = &log.EventlogWriter{
	Source: ".NET Runtime",
	ID:     1000,
}

log.Info().Int("number", 42).Str("foo", "bar").Msg("hello world")

AsyncWriter

To logging asynchronously for performance stability, use AsyncWriter.

logger := log.Logger{
	Level:  log.InfoLevel,
	Writer: &log.AsyncWriter{
		ChannelSize: 100,
		Writer:      &log.FileWriter{
			Filename:   "main.log",
			FileMode:   0600,
			MaxSize:    50*1024*1024,
			MaxBackups: 7,
			LocalTime:  false,
		},
	},
}

logger.Info().Int("number", 42).Str("foo", "bar").Msg("a async info log")
logger.Warn().Int("number", 42).Str("foo", "bar").Msg("a async warn log")
logger.Writer.(io.Closer).Close()

Note: To flush data and quit safely, call AsyncWriter.Close() explicitly.

StdLog & Logr & Grpc Interceptor

Using wrapped loggers for stdlog/grpc/logr.

package main

import (
	stdLog "log"
	"github.com/go-logr/logr"
	"github.com/phuslu/log"
	"google.golang.org/grpc/grpclog"
)

func main() {
	ctx := log.NewContext(nil).Str("tag", "hi log").Value()

	var stdlog *stdLog.Logger = log.DefaultLogger.Std(log.InfoLevel, ctx, "prefix ", stdLog.LstdFlags)
	stdlog.Print("hello from stdlog Print")
	stdlog.Println("hello from stdlog Println")
	stdlog.Printf("hello from stdlog %s", "Printf")

	var grpclog grpclog.LoggerV2 = log.DefaultLogger.Grpc(ctx)
	grpclog.Infof("hello %s", "grpclog Infof message")
	grpclog.Errorf("hello %s", "grpclog Errorf message")

	var logrLog logr.Logger = log.DefaultLogger.Logr(ctx)
	logrLog = logrLog.WithName("a_named_logger").WithValues("a_key", "a_value")
	logrLog.Info("hello", "foo", "bar", "number", 42)
	logrLog.Error(errors.New("this is a error"), "hello", "foo", "bar", "number", 42)
}

User-defined Data Structure

To log with user-defined struct effectively, implements MarshalObject.

package main

import (
	"github.com/phuslu/log"
)

type User struct {
	ID   int
	Name string
	Pass string
}

func (u *User) MarshalObject(e *log.Entry) {
	e.Int("id", u.ID).Str("name", u.Name).Str("password", "***")
}

func main() {
	log.Info().Object("user", &User{1, "neo", "123456"}).Msg("")
	log.Info().EmbedObject(&User{2, "john", "abc"}).Msg("")
}

// Output:
//   {"time":"2020-07-12T05:03:43.949Z","level":"info","user":{"id":1,"name":"neo","password":"***"}}
//   {"time":"2020-07-12T05:03:43.949Z","level":"info","id":2,"name":"john","password":"***"}

Contextual Fields

To add preserved key:value pairs to each entry, use NewContext.

ctx := log.NewContext(nil).Str("ctx_str", "a ctx str").Value()

logger := log.Logger{Level: log.InfoLevel}
logger.Debug().Context(ctx).Int("no0", 0).Msg("zero")
logger.Info().Context(ctx).Int("no1", 1).Msg("first")
logger.Info().Context(ctx).Int("no2", 2).Msg("second")

// Output:
//   {"time":"2020-07-12T05:03:43.949Z","level":"info","ctx_str":"a ctx str","no1":1,"message":"first"}
//   {"time":"2020-07-12T05:03:43.949Z","level":"info","ctx_str":"a ctx str","no2":2,"message":"second"}

High Performance

The most common benchmarks(disable/normal/interface/printf/caller) with zap/zerolog, which runs on github actions:

// go test -v -cpu=4 -run=none -bench=. -benchtime=10s -benchmem log_test.go
package main

import (
	"io/ioutil"
	"testing"

	"github.com/phuslu/log"
	"github.com/rs/zerolog"
	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
)

var msg = "The quick brown fox jumps over the lazy dog"
var obj = struct {Rate string; Low int; High float32}{"15", 16, 123.2}

func BenchmarkDisableZap(b *testing.B) {
	logger := zap.New(zapcore.NewCore(
		zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig()),
		zapcore.AddSync(ioutil.Discard),
		zapcore.InfoLevel,
	))
	for i := 0; i < b.N; i++ {
		logger.Debug(msg, zap.String("rate", "15"), zap.Int("low", 16), zap.Float32("high", 123.2))
	}
}

func BenchmarkNormalZap(b *testing.B) {
	logger := zap.New(zapcore.NewCore(
		zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig()),
		zapcore.AddSync(ioutil.Discard),
		zapcore.InfoLevel,
	))
	for i := 0; i < b.N; i++ {
		logger.Info(msg, zap.String("rate", "15"), zap.Int("low", 16), zap.Float32("high", 123.2))
	}
}

func BenchmarkInterfaceZap(b *testing.B) {
	logger := zap.New(zapcore.NewCore(
		zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig()),
		zapcore.AddSync(ioutil.Discard),
		zapcore.InfoLevel,
	)).Sugar()
	for i := 0; i < b.N; i++ {
		logger.Infow(msg, "object", &obj)
	}
}

func BenchmarkPrintfZap(b *testing.B) {
	logger := zap.New(zapcore.NewCore(
		zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig()),
		zapcore.AddSync(ioutil.Discard),
		zapcore.InfoLevel,
	)).Sugar()
	for i := 0; i < b.N; i++ {
		logger.Infof("rate=%s low=%d high=%f msg=%s", "15", 16, 123.2, msg)
	}
}

func BenchmarkCallerZap(b *testing.B) {
	logger := zap.New(zapcore.NewCore(
		zapcore.NewJSONEncoder(zap.NewProductionEncoderConfig()),
		zapcore.AddSync(ioutil.Discard),
		zapcore.InfoLevel),
		zap.AddCaller(),
	)
	for i := 0; i < b.N; i++ {
		logger.Info(msg, zap.String("rate", "15"), zap.Int("low", 16), zap.Float32("high", 123.2))
	}
}

func BenchmarkDisableZeroLog(b *testing.B) {
	zerolog.SetGlobalLevel(zerolog.InfoLevel)
	logger := zerolog.New(ioutil.Discard).With().Timestamp().Logger()
	for i := 0; i < b.N; i++ {
		logger.Debug().Str("rate", "15").Int("low", 16).Float32("high", 123.2).Msg(msg)
	}
}

func BenchmarkNormalZeroLog(b *testing.B) {
	logger := zerolog.New(ioutil.Discard).With().Timestamp().Logger()
	for i := 0; i < b.N; i++ {
		logger.Info().Str("rate", "15").Int("low", 16).Float32("high", 123.2).Msg(msg)
	}
}

func BenchmarkInterfaceZeroLog(b *testing.B) {
	logger := zerolog.New(ioutil.Discard).With().Timestamp().Logger()
	for i := 0; i < b.N; i++ {
		logger.Info().Interface("object", &obj).Msg(msg)
	}
}

func BenchmarkPrintfZeroLog(b *testing.B) {
	logger := zerolog.New(ioutil.Discard).With().Timestamp().Logger()
	for i := 0; i < b.N; i++ {
		logger.Info().Msgf("rate=%s low=%d high=%f msg=%s", "15", 16, 123.2, msg)
	}
}

func BenchmarkCallerZeroLog(b *testing.B) {
	logger := zerolog.New(ioutil.Discard).With().Caller().Timestamp().Logger()
	for i := 0; i < b.N; i++ {
		logger.Info().Str("rate", "15").Int("low", 16).Float32("high", 123.2).Msg(msg)
	}
}

func BenchmarkDisablePhusLog(b *testing.B) {
	logger := log.Logger{Level: log.InfoLevel, Writer: log.IOWriter{ioutil.Discard}}
	for i := 0; i < b.N; i++ {
		logger.Debug().Str("rate", "15").Int("low", 16).Float32("high", 123.2).Msg(msg)
	}
}

func BenchmarkNormalPhusLog(b *testing.B) {
	logger := log.Logger{Writer: log.IOWriter{ioutil.Discard}}
	for i := 0; i < b.N; i++ {
		logger.Info().Str("rate", "15").Int("low", 16).Float32("high", 123.2).Msg(msg)
	}
}

func BenchmarkInterfacePhusLog(b *testing.B) {
	logger := log.Logger{Writer: log.IOWriter{ioutil.Discard}}
	for i := 0; i < b.N; i++ {
		logger.Info().Interface("object", &obj).Msg(msg)
	}
}

func BenchmarkPrintfPhusLog(b *testing.B) {
	logger := log.Logger{Writer: log.IOWriter{ioutil.Discard}}
	for i := 0; i < b.N; i++ {
		logger.Info().Msgf("rate=%s low=%d high=%f msg=%s", "15", 16, 123.2, msg)
	}
}

func BenchmarkCallerPhusLog(b *testing.B) {
	logger := log.Logger{Caller: 1, Writer: log.IOWriter{ioutil.Discard}}
	for i := 0; i < b.N; i++ {
		logger.Info().Str("rate", "15").Int("low", 16).Float32("high", 123.2).Msg(msg)
	}
}

A Performance result as below, for daily benchmark results see github actions

BenchmarkDisableZap-4         	84149790	       138 ns/op	     192 B/op	       1 allocs/op
BenchmarkNormalZap-4          	 8281590	      1459 ns/op	     192 B/op	       1 allocs/op
BenchmarkInterfaceZap-4       	 6159080	      1924 ns/op	     208 B/op	       2 allocs/op
BenchmarkPrintfZap-4          	 6664330	      1846 ns/op	      96 B/op	       2 allocs/op
BenchmarkCallerZap-4          	 3661080	      3280 ns/op	     440 B/op	       4 allocs/op

BenchmarkDisableZeroLog-4     	788723734	        14.7 ns/op	       0 B/op	       0 allocs/op
BenchmarkNormalZeroLog-4      	15282351	       768 ns/op	       0 B/op	       0 allocs/op
BenchmarkInterfaceZeroLog-4   	10396608	      1163 ns/op	      48 B/op	       1 allocs/op
BenchmarkPrintfZeroLog-4      	 8954383	      1360 ns/op	      96 B/op	       2 allocs/op
BenchmarkCallerZeroLog-4      	 3586092	      3563 ns/op	     264 B/op	       3 allocs/op

BenchmarkDisablePhusLog-4     	932239788	        13.1 ns/op	       0 B/op	       0 allocs/op
BenchmarkNormalPhusLog-4      	25032302	       449 ns/op	       0 B/op	       0 allocs/op
BenchmarkInterfacePhusLog-4   	14000850	       837 ns/op	       0 B/op	       0 allocs/op
BenchmarkPrintfPhusLog-4      	13794639	       851 ns/op	      16 B/op	       1 allocs/op
BenchmarkCallerPhusLog-4      	 8207911	      1434 ns/op	     216 B/op	       2 allocs/op

This library uses the following special techniques to achieve better performance,

1. handwriting time formatting
2. manual inlining
3. unrolled functions

A Real World Example

The example starts a geoip http server which supports change log level dynamically

package main

import (
	"encoding/json"
	"fmt"
	"net"
	"net/http"
	"os"

	"github.com/phuslu/iploc"
	"github.com/phuslu/log"
)

type Config struct {
	Listen struct {
		Tcp string
	}
	Log struct {
		Level   string
		Maxsize int64
		Backups int
	}
}

type Handler struct {
	Config       *Config
	AccessLogger log.Logger
}

func (h *Handler) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
	reqID := log.NewXID()
	remoteIP, _, _ := net.SplitHostPort(req.RemoteAddr)
	geo := iploc.Country(net.ParseIP(remoteIP))

	h.AccessLogger.Log().
		Xid("req_id", reqID).
		Str("host", req.Host).
		Bytes("geo", geo).
		Str("remote_ip", remoteIP).
		Str("request_uri", req.RequestURI).
		Str("user_agent", req.UserAgent()).
		Str("referer", req.Referer()).
		Msg("access log")

	switch req.RequestURI {
	case "/debug", "/info", "/warn", "/error":
		log.DefaultLogger.SetLevel(log.ParseLevel(req.RequestURI[1:]))
	default:
		fmt.Fprintf(rw, `{"req_id":"%s","ip":"%s","geo":"%s"}`, reqID, remoteIP, geo)
	}
}

func main() {
	config := new(Config)
	err := json.Unmarshal([]byte(`{
		"listen": {
			"tcp": ":8080"
		},
		"log": {
			"level": "debug",
			"maxsize": 1073741824,
			"backups": 5
		}
	}`), config)
	if err != nil {
		log.Fatal().Msgf("json.Unmarshal error: %+v", err)
	}

	handler := &Handler{
		Config: config,
		AccessLogger: log.Logger{
			Writer: &log.FileWriter{
				Filename:   "access.log",
				MaxSize:    config.Log.Maxsize,
				MaxBackups: config.Log.Backups,
				LocalTime:  true,
			},
		},
	}

	if log.IsTerminal(os.Stderr.Fd()) {
		log.DefaultLogger = log.Logger{
			Level:      log.ParseLevel(config.Log.Level),
			Caller:     1,
			TimeFormat: "15:04:05",
			Writer: &log.ConsoleWriter{
				ColorOutput:    true,
				EndWithMessage: true,
			},
		}
		handler.AccessLogger = log.DefaultLogger
	} else {
		log.DefaultLogger = log.Logger{
			Level: log.ParseLevel(config.Log.Level),
			Writer: &log.FileWriter{
				Filename:   "main.log",
				MaxSize:    config.Log.Maxsize,
				MaxBackups: config.Log.Backups,
				LocalTime:  true,
			},
		}
	}

	server := &http.Server{
		Addr:     config.Listen.Tcp,
		ErrorLog: log.DefaultLogger.Std(log.ErrorLevel, nil, "", 0),
		Handler:  handler,
	}

	log.Fatal().Err(server.ListenAndServe()).Msg("listen failed")
}

Acknowledgment

This log is heavily inspired by zerolog, glog, gjson and lumberjack.