blob: 6c7221d5a3895a4b69c1fbcfee750cdfceb2813f [file] [log] [blame]
// Copyright 2022 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package slog_test
import (
// A LevelHandler wraps a Handler with an Enabled method
// that returns false for levels below a minimum.
type LevelHandler struct {
level slog.Leveler
handler slog.Handler
// NewLevelHandler returns a LevelHandler with the given level.
// All methods except Enabled delegate to h.
func NewLevelHandler(level slog.Leveler, h slog.Handler) *LevelHandler {
// Optimization: avoid chains of LevelHandlers.
if lh, ok := h.(*LevelHandler); ok {
h = lh.Handler()
return &LevelHandler{level, h}
// Enabled implements Handler.Enabled by reporting whether
// level is at least as large as h's level.
func (h *LevelHandler) Enabled(_ context.Context, level slog.Level) bool {
return level >= h.level.Level()
// Handle implements Handler.Handle.
func (h *LevelHandler) Handle(ctx context.Context, r slog.Record) error {
return h.handler.Handle(ctx, r)
// WithAttrs implements Handler.WithAttrs.
func (h *LevelHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
return NewLevelHandler(h.level, h.handler.WithAttrs(attrs))
// WithGroup implements Handler.WithGroup.
func (h *LevelHandler) WithGroup(name string) slog.Handler {
return NewLevelHandler(h.level, h.handler.WithGroup(name))
// Handler returns the Handler wrapped by h.
func (h *LevelHandler) Handler() slog.Handler {
return h.handler
// This example shows how to Use a LevelHandler to change the level of an
// existing Handler while preserving its other behavior.
// This example demonstrates increasing the log level to reduce a logger's
// output.
// Another typical use would be to decrease the log level (to LevelDebug, say)
// during a part of the program that was suspected of containing a bug.
func ExampleHandler_levelHandler() {
th := slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{ReplaceAttr: testutil.RemoveTime})
logger := slog.New(NewLevelHandler(slog.LevelWarn, th))
logger.Info("not printed")
// Output:
// level=WARN msg=printed