console

README

console-slog

A handler for slog that prints colorized logs, similar to zerolog's console writer output without sacrificing performances.

Installation

go get github.com/phsym/console-slog@latest

Example

package main

import (
	"errors"
	"log/slog"
	"os"

	"github.com/phsym/console-slog"
)

func main() {
	logger := slog.New(
		console.NewHandler(os.Stderr, &console.HandlerOptions{Level: slog.LevelDebug}),
	)
	slog.SetDefault(logger)
	slog.Info("Hello world!", "foo", "bar")
	slog.Debug("Debug message")
	slog.Warn("Warning message")
	slog.Error("Error message", "err", errors.New("the error"))

	logger = logger.With("foo", "bar").
		WithGroup("the-group").
		With("bar", "baz")

	logger.Info("group info", "attr", "value")
}

When setting console.HandlerOptions.AddSource to true:

console.NewHandler(os.Stderr, &console.HandlerOptions{Level: slog.LevelDebug, AddSource: true})

Performances

See benchmark file for details.

The handler itself performs quite well compared to std-lib's handlers. It does no allocation:

goos: linux
goarch: amd64
pkg: github.com/phsym/console-slog
cpu: Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz
BenchmarkHandlers/dummy-4               128931026            8.732 ns/op               0 B/op          0 allocs/op
BenchmarkHandlers/console-4               849837              1294 ns/op               0 B/op          0 allocs/op
BenchmarkHandlers/std-text-4              542583              2097 ns/op               4 B/op          2 allocs/op
BenchmarkHandlers/std-json-4              583784              1911 ns/op             120 B/op          3 allocs/op

However, the go 1.21.0 slog.Logger adds some overhead:

goos: linux
goarch: amd64
pkg: github.com/phsym/console-slog
cpu: Intel(R) Core(TM) i5-6300U CPU @ 2.40GHz
BenchmarkLoggers/dummy-4                 1239873             893.2 ns/op             128 B/op          1 allocs/op
BenchmarkLoggers/console-4                483354              2338 ns/op             128 B/op          1 allocs/op
BenchmarkLoggers/std-text-4               368828              3141 ns/op             132 B/op          3 allocs/op
BenchmarkLoggers/std-json-4               393322              2909 ns/op             248 B/op          4 allocs/op

Documentation

Index

• Constants
• Variables
• type ANSIMod
  • func ToANSICode(modes ...int) ANSIMod
  • func (c ANSIMod) String() string
• type Handler
  • func NewHandler(out io.Writer, opts *HandlerOptions) *Handler
  • func (h *Handler) Enabled(_ context.Context, l slog.Level) bool
  • func (h *Handler) Handle(_ context.Context, rec slog.Record) error
  • func (h *Handler) WithAttrs(attrs []slog.Attr) slog.Handler
  • func (h *Handler) WithGroup(name string) slog.Handler
• type HandlerOptions
• type Theme
  • func NewBrightTheme() Theme
  • func NewDefaultTheme() Theme
• type ThemeDef
  • func (t ThemeDef) AttrKey() ANSIMod
  • func (t ThemeDef) AttrValue() ANSIMod
  • func (t ThemeDef) AttrValueError() ANSIMod
  • func (t ThemeDef) Level(level slog.Level) ANSIMod
  • func (t ThemeDef) LevelDebug() ANSIMod
  • func (t ThemeDef) LevelError() ANSIMod
  • func (t ThemeDef) LevelInfo() ANSIMod
  • func (t ThemeDef) LevelWarn() ANSIMod
  • func (t ThemeDef) Message() ANSIMod
  • func (t ThemeDef) MessageDebug() ANSIMod
  • func (t ThemeDef) Name() string
  • func (t ThemeDef) Source() ANSIMod
  • func (t ThemeDef) Timestamp() ANSIMod

Constants

const (
	Reset = iota
	Bold
	Faint
	Italic
	Underline
	CrossedOut = 9
)

const (
	Black = iota + 30
	Red
	Green
	Yellow
	Blue
	Magenta
	Cyan
	Gray
)

const (
	BrightBlack = iota + 90
	BrightRed
	BrightGreen
	BrightYellow
	BrightBlue
	BrightMagenta
	BrightCyan
	White
)

Variables

var ResetMod = ToANSICode(Reset)

Types

type ANSIMod

type ANSIMod string

func ToANSICode

func ToANSICode(modes ...int) ANSIMod

func (ANSIMod) String

func (c ANSIMod) String() string

type Handler

type Handler struct {
	// contains filtered or unexported fields
}

func NewHandler

func NewHandler(out io.Writer, opts *HandlerOptions) *Handler

NewHandler creates a Handler that writes to w, using the given options. If opts is nil, the default options are used.

func (*Handler) Enabled

func (h *Handler) Enabled(_ context.Context, l slog.Level) bool

Enabled implements slog.Handler.

func (*Handler) Handle

func (h *Handler) Handle(_ context.Context, rec slog.Record) error

Handle implements slog.Handler.

func (*Handler) WithAttrs

func (h *Handler) WithAttrs(attrs []slog.Attr) slog.Handler

WithAttrs implements slog.Handler.

func (*Handler) WithGroup

func (h *Handler) WithGroup(name string) slog.Handler

WithGroup implements slog.Handler.

type HandlerOptions

type HandlerOptions struct {
	// AddSource causes the handler to compute the source code position
	// of the log statement and add a SourceKey attribute to the output.
	AddSource bool

	// Level reports the minimum record level that will be logged.
	// The handler discards records with lower levels.
	// If Level is nil, the handler assumes LevelInfo.
	// The handler calls Level.Level for each record processed;
	// to adjust the minimum level dynamically, use a LevelVar.
	Level slog.Leveler

	// Disable colorized output
	NoColor bool

	// TimeFormat is the format used for time.DateTime
	TimeFormat string

	// Theme defines the colorized output using ANSI escape sequences
	Theme Theme
}

HandlerOptions are options for a ConsoleHandler. A zero HandlerOptions consists entirely of default values.

type Theme

type Theme interface {
	Name() string
	Timestamp() ANSIMod
	Source() ANSIMod

	Message() ANSIMod
	MessageDebug() ANSIMod
	AttrKey() ANSIMod
	AttrValue() ANSIMod
	AttrValueError() ANSIMod
	LevelError() ANSIMod
	LevelWarn() ANSIMod
	LevelInfo() ANSIMod
	LevelDebug() ANSIMod
	Level(level slog.Level) ANSIMod
}

func NewBrightTheme

func NewBrightTheme() Theme

func NewDefaultTheme

func NewDefaultTheme() Theme

type ThemeDef

type ThemeDef struct {
	// contains filtered or unexported fields
}

func (ThemeDef) AttrKey

func (t ThemeDef) AttrKey() ANSIMod

func (ThemeDef) AttrValue

func (t ThemeDef) AttrValue() ANSIMod

func (ThemeDef) AttrValueError

func (t ThemeDef) AttrValueError() ANSIMod

func (ThemeDef) Level

func (t ThemeDef) Level(level slog.Level) ANSIMod

func (ThemeDef) LevelDebug

func (t ThemeDef) LevelDebug() ANSIMod

func (ThemeDef) LevelError

func (t ThemeDef) LevelError() ANSIMod

func (ThemeDef) LevelInfo

func (t ThemeDef) LevelInfo() ANSIMod

func (ThemeDef) LevelWarn

func (t ThemeDef) LevelWarn() ANSIMod

func (ThemeDef) Message

func (t ThemeDef) Message() ANSIMod

func (ThemeDef) MessageDebug

func (t ThemeDef) MessageDebug() ANSIMod

func (ThemeDef) Name

func (t ThemeDef) Name() string

func (ThemeDef) Source

func (t ThemeDef) Source() ANSIMod

func (ThemeDef) Timestamp

func (t ThemeDef) Timestamp() ANSIMod