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slogr: restore original backend when converting back and forth #210

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Aug 23, 2023
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27 changes: 25 additions & 2 deletions slogr/sloghandler.go
Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,11 @@ var _ slog.Handler = &slogHandler{}
// groupSeparator is used to concatenate WithGroup names and attribute keys.
const groupSeparator = "."

// GetLevel is used for black box unit testing.
func (l *slogHandler) GetLevel() slog.Level {
return l.levelBias
}

func (l *slogHandler) Enabled(ctx context.Context, level slog.Level) bool {
return l.sink != nil && (level >= slog.LevelError || l.sink.Enabled(l.levelFromSlog(level)))
}
Expand All @@ -62,14 +67,32 @@ func (l *slogHandler) Handle(ctx context.Context, record slog.Record) error {
return true
})
if record.Level >= slog.LevelError {
l.sink.Error(nil, record.Message, kvList...)
l.sinkWithCallDepth().Error(nil, record.Message, kvList...)
} else {
level := l.levelFromSlog(record.Level)
l.sink.Info(level, record.Message, kvList...)
l.sinkWithCallDepth().Info(level, record.Message, kvList...)
}
return nil
}

// sinkWithCallDepth adjusts the stack unwinding so that when Error or Info
// are called by Handle, code in slog gets skipped.
//
// This offset currently (Go 1.21.0) works for calls through
// slog.New(NewSlogHandler(...)). There's no guarantee that the call
// chain won't change. Wrapping the handler will also break unwinding. It's
// still better than not adjusting at all....
//
// This cannot be done when constructing the handler because NewLogr needs
// access to the original sink without this adjustment. A second copy would
// work, but then WithAttrs would have to be called for both of them.
func (l *slogHandler) sinkWithCallDepth() logr.LogSink {
if sink, ok := l.sink.(logr.CallDepthLogSink); ok {
return sink.WithCallDepth(2)
}
return l.sink
}

func (l *slogHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
if l.sink == nil || len(attrs) == 0 {
return l
Expand Down
15 changes: 10 additions & 5 deletions slogr/slogr.go
Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,12 @@ import (
// The logr verbosity level is mapped to slog levels such that V(0) becomes
// slog.LevelInfo and V(4) becomes slog.LevelDebug.
func NewLogr(handler slog.Handler) logr.Logger {
if handler, ok := handler.(*slogHandler); ok {
if handler.sink == nil {
return logr.Discard()
}
return logr.New(handler.sink).V(int(handler.levelBias))
}
return logr.New(&slogSink{handler: handler})
}

Expand All @@ -57,10 +63,9 @@ func NewLogr(handler slog.Handler) logr.Logger {
// slog.New(NewSlogHandler(logger)).Info(...) -> logger.GetSink().Info(level=0, ...)
// slog.New(NewSlogHandler(logger.V(4))).Info(...) -> logger.GetSink().Info(level=4, ...)
func NewSlogHandler(logger logr.Logger) slog.Handler {
// This offset currently (Go 1.21.0) works for slog.New(NewSlogHandler(...)).Info.
// There's no guarantee that the call chain won't change and wrapping
// the handler will also break unwinding, but it's still better than not
// adjusting at all.
logger = logger.WithCallDepth(2)
if sink, ok := logger.GetSink().(*slogSink); ok && logger.GetV() == 0 {
return sink.handler
}

return &slogHandler{sink: logger.GetSink(), levelBias: slog.Level(logger.GetV())}
}
35 changes: 35 additions & 0 deletions slogr/slogr_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -24,6 +24,7 @@ import (
"encoding/json"
"errors"
"fmt"
"io"
"log/slog"
"os"
"path"
Expand Down Expand Up @@ -184,3 +185,37 @@ func TestDiscard(t *testing.T) {
logger := slog.New(slogr.NewSlogHandler(logr.Discard()))
logger.WithGroup("foo").With("x", 1).Info("hello")
}

func TestConversion(t *testing.T) {
d := logr.Discard()
d2 := slogr.NewLogr(slogr.NewSlogHandler(d))
expectEqual(t, d, d2)

e := logr.Logger{}
e2 := slogr.NewLogr(slogr.NewSlogHandler(e))
expectEqual(t, e, e2)

f := funcr.New(func(prefix, args string) {}, funcr.Options{})
f2 := slogr.NewLogr(slogr.NewSlogHandler(f))
expectEqual(t, f, f2)

text := slog.NewTextHandler(io.Discard, nil)
text2 := slogr.NewSlogHandler(slogr.NewLogr(text))
expectEqual(t, text, text2)

text3 := slogr.NewSlogHandler(slogr.NewLogr(text).V(1))
if handler, ok := text3.(interface {
GetLevel() slog.Level
}); ok {
expectEqual(t, handler.GetLevel(), slog.Level(1))
} else {
t.Errorf("Expected a slogHandler which implements V(1), got instead: %T %+v", text3, text3)
}
}

func expectEqual(t *testing.T, expected, actual any) {
if expected != actual {
t.Helper()
t.Errorf("Expected %T %+v, got instead: %T %+v", expected, expected, actual, actual)
}
}
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