✒️ golog

package main

import (
    "github.com/kataras/golog"
)

func main() {
    // Default Output is `os.Stdout`,
    // but you can change it:
    // golog.SetOutput(os.Stderr)

    // Time Format defaults to: "2006/01/02 15:04"
    // you can change it to something else or disable it with:
    // golog.SetTimeFormat("")

    // Level defaults to "info",
    // but you can change it:
    golog.SetLevel("debug")

    golog.Println("This is a raw message, no levels, no colors.")
    golog.Info("This is an info message, with colors (if the output is terminal)")
    golog.Warn("This is a warning message")
    golog.Error("This is an error message")
    golog.Debug("This is a debug message")
    golog.Fatal(`Fatal will exit no matter what,
    but it will also print the log message if logger's Level is >=FatalLevel`)

    // Use any other supported logger through golog, e.g. the new "log/slog":
    // golog.Install(slog.Default())
}

// GetTextForLevel returns the level's (rich) text. 
fatalRichText := golog.GetTextForLevel(golog.FatalLevel, true)

// fatalRichText == "\x1b[41m[FTAL]\x1b[0m"

// ParseLevel returns a Level based on its string name.
level := golog.ParseLevel("debug")

// level == golog.DebugLevel

func init() {
    // Levels contains a map of the log levels and their attributes.
    errorAttrs := golog.Levels[golog.ErrorLevel]

    // Change a log level's text.
    customColorCode := 156
    errorAttrs.SetText("custom text", customColorCode)

    // Get (rich) text per log level.
    enableColors := true
    errorRichText := errorAttrs.Text(enableColors)
}

golog.ErrorText("custom text", 156)

opts := badger.DefaultOptions("./data")
opts.Logger = golog.Child("[badger]").DisableNewLine()

db, err := badger.Open(opts)
// [...]

// Simulate an slog.Logger preparation.
var myLogger = slog.New(slog.NewJSONHandler(os.Stdout, &slog.HandlerOptions{
    Level: slog.LevelDebug,
}))

func main() {
    golog.SetLevel("error")
    golog.Install(myLogger)

    golog.Error("error message")
}

// Simulate a log.Logger preparation.
myLogger := log.New(os.Stdout, "", 0)

golog.SetLevel("error")
golog.Install(myLogger)

golog.Error("error message")

// Simulate a logrus logger preparation.
logrus.SetLevel(logrus.InfoLevel)
logrus.SetFormatter(&logrus.JSONFormatter{})

golog.Install(logrus.StandardLogger())

golog.Debug(`this debug message will not be shown,
    because the logrus level is InfoLevel`)
golog.Error(`this error message will be visible as JSON,
    because of logrus.JSONFormatter`)

import "uuid"

// NewV7 is the one to reach for in logs: v7 UUIDs carry a timestamp in their
// leading bits, so the identifiers sort in the order the lines were written.
golog.SetIDGenerator(uuid.NewV7)

golog.Info("this line has an id of its own")
// [INFO] 2026/08/21 16:04 01a0248d-c937-7ab9-aca1-d9a78c76325d this line has an id of its own

requestID := uuid.NewV7()

reqLogger := golog.Default.Clone().
    SetIDGenerator(func() uuid.UUID { return requestID })

reqLogger.Info("started")  // both lines
reqLogger.Info("finished") // carry the same id

golog.Handle(func(log *golog.Log) bool {
    username, ok := log.Field[string]("username")
    if ok {
        // [...]
    }

    return false
})

import "github.com/kataras/golog"

func main() {
    golog.SetLevel("debug")
    golog.SetFormat("json", "    ") // < --

    // main.go#29
    golog.Debugf("This is a %s with data (debug prints the stacktrace too)", "message", golog.Fields{
        "username": "kataras",
    })
}

golog.RegisterFormatter(new(myFormatter))
golog.SetFormat("myformat", options...)

// Formatter is responsible to print a log to the logger's writer.
type Formatter interface {
	// The name of the formatter.
	String() string
	// Set any options and return a clone,
	// generic. See `Logger.SetFormat`.
	Options(opts ...any) Formatter
	// Writes the "log" to "dest" logger.
	Format(dest io.Writer, log *Log) bool
}

type Handler func(value *Log) (handled bool)

import "encoding/json"

func jsonOutput(l *golog.Log) bool {
    enc := json.NewEncoder(l.Logger.GetLevelOutput(l.Level.String()))
    enc.SetIndent("", "    ")
    err := enc.Encode(l)
    return err == nil
}

import "github.com/kataras/golog"

func main() {
    golog.SetLevel("debug")
    golog.Handle(jsonOutput)

    // main.go#29
    golog.Debugf("This is a %s with data (debug prints the stacktrace too)", "message", golog.Fields{
        "username": "kataras",
    })
}