Slog TeeHandler with signal for level change

tee_handler_with_signal.go

package main

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"os"
	"os/signal"
	"syscall"
	"time"
)

func main() {
	var level slog.LevelVar
	opts := slog.HandlerOptions{
		Level: &level,
	}
	tee := NewTeeHandler(slog.NewTextHandler(os.Stdout, &opts), slog.NewJSONHandler(os.Stderr, &opts))
	logger := slog.New(tee)

	sigChan := make(chan os.Signal, 1)
	signal.Notify(sigChan, syscall.SIGUSR2)

	go func() {
		for {
			<-sigChan
			currentLevel := level.Level()
			if currentLevel != slog.LevelDebug {
				level.Set(slog.LevelDebug)
			} else {
				level.Set(slog.LevelInfo)
			}
			logger.Info("Log level changed")
		}
	}()

	fmt.Printf("PID is %d\n", os.Getpid())
	fmt.Printf("Send `kill -USR2 %d` signal to toggle log level\n", os.Getpid())
	for {
		logger.Info("this is INFO", "foo", "bar")
		time.Sleep(500 * time.Millisecond)
		logger.Debug("this is DEBUG", "qux", "gazonk")
	}
}

type teeHandler struct {
	handlers []slog.Handler
}

func NewTeeHandler(handlers ...slog.Handler) slog.Handler {
	return &teeHandler{handlers: handlers}
}

func (h *teeHandler) Handle(ctx context.Context, r slog.Record) error {
	var errs []error
	for _, handler := range h.handlers {
		err := handler.Handle(ctx, r)
		errs = append(errs, err)
	}
	return errors.Join(errs...)
}

func (h *teeHandler) Enabled(ctx context.Context, level slog.Level) bool {
	for _, handler := range h.handlers {
		if handler.Enabled(ctx, level) {
			return true
		}
	}
	return false
}

func (h *teeHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
	var tee teeHandler
	for _, handler := range h.handlers {
		handler = handler.WithAttrs(attrs)
		tee.handlers = append(tee.handlers, handler)
	}
	return &tee
}

func (h *teeHandler) WithGroup(name string) slog.Handler {
	var tee teeHandler
	for _, handler := range h.handlers {
		handler = handler.WithGroup(name)
		tee.handlers = append(tee.handlers, handler)
	}
	return &tee
}