example_level_handler_test.go

Documentation: golang.org/x/exp/slog

     1  // Copyright 2022 The Go Authors. All rights reserved.
     2  // Use of this source code is governed by a BSD-style
     3  // license that can be found in the LICENSE file.
     4  
     5  package slog_test
     6  
     7  import (
     8  	"context"
     9  	"os"
    10  
    11  	"golang.org/x/exp/slog"
    12  	"golang.org/x/exp/slog/internal/testutil"
    13  )
    14  
    15  // A LevelHandler wraps a Handler with an Enabled method
    16  // that returns false for levels below a minimum.
    17  type LevelHandler struct {
    18  	level   slog.Leveler
    19  	handler slog.Handler
    20  }
    21  
    22  // NewLevelHandler returns a LevelHandler with the given level.
    23  // All methods except Enabled delegate to h.
    24  func NewLevelHandler(level slog.Leveler, h slog.Handler) *LevelHandler {
    25  	// Optimization: avoid chains of LevelHandlers.
    26  	if lh, ok := h.(*LevelHandler); ok {
    27  		h = lh.Handler()
    28  	}
    29  	return &LevelHandler{level, h}
    30  }
    31  
    32  // Enabled implements Handler.Enabled by reporting whether
    33  // level is at least as large as h's level.
    34  func (h *LevelHandler) Enabled(_ context.Context, level slog.Level) bool {
    35  	return level >= h.level.Level()
    36  }
    37  
    38  // Handle implements Handler.Handle.
    39  func (h *LevelHandler) Handle(ctx context.Context, r slog.Record) error {
    40  	return h.handler.Handle(ctx, r)
    41  }
    42  
    43  // WithAttrs implements Handler.WithAttrs.
    44  func (h *LevelHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
    45  	return NewLevelHandler(h.level, h.handler.WithAttrs(attrs))
    46  }
    47  
    48  // WithGroup implements Handler.WithGroup.
    49  func (h *LevelHandler) WithGroup(name string) slog.Handler {
    50  	return NewLevelHandler(h.level, h.handler.WithGroup(name))
    51  }
    52  
    53  // Handler returns the Handler wrapped by h.
    54  func (h *LevelHandler) Handler() slog.Handler {
    55  	return h.handler
    56  }
    57  
    58  // This example shows how to Use a LevelHandler to change the level of an
    59  // existing Handler while preserving its other behavior.
    60  //
    61  // This example demonstrates increasing the log level to reduce a logger's
    62  // output.
    63  //
    64  // Another typical use would be to decrease the log level (to LevelDebug, say)
    65  // during a part of the program that was suspected of containing a bug.
    66  func ExampleHandler_levelHandler() {
    67  	th := slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{ReplaceAttr: testutil.RemoveTime})
    68  	logger := slog.New(NewLevelHandler(slog.LevelWarn, th))
    69  	logger.Info("not printed")
    70  	logger.Warn("printed")
    71  
    72  	// Output:
    73  	// level=WARN msg=printed
    74  }
    75
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