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