slogr: add SlogSink

slogr/sloghandler.go

@@ -27,7 +27,10 @@ import (
 )
 
 type slogHandler struct {
+	// May be nil, in which case all logs get discarded.
 	sink logr.LogSink
+	// Non-nil if sink is non-nil and implements SlogSink.
+	slogSink SlogSink
 
 	// groupPrefix collects values from WithGroup calls. It gets added as
 	// prefix to value keys when handling a log record.
@@ -56,6 +59,14 @@ func (l *slogHandler) Enabled(ctx context.Context, level slog.Level) bool {
 }
 
 func (l *slogHandler) Handle(ctx context.Context, record slog.Record) error {
+	if l.slogSink != nil {
+		// Only adjust verbosity level of log entries < slog.LevelError.
+		if record.Level < slog.LevelError {
+			record.Level -= l.levelBias
+		}
+		return l.slogSink.Handle(ctx, record)
+	}
+
 	// No need to check for nil sink here because Handle will only be called
 	// when Enabled returned true.
 
@@ -97,14 +108,20 @@ func (l *slogHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
 	if l.sink == nil || len(attrs) == 0 {
 		return l
 	}
-	kvList := make([]any, 0, 2*len(attrs))
-	for _, attr := range attrs {
-		if attr.Key != "" {
-			kvList = append(kvList, l.addGroupPrefix(attr.Key), attr.Value.Resolve().Any())
+
+	copy := *l
+	if l.slogSink != nil {
+		copy.slogSink = l.slogSink.WithAttrs(attrs)
+		copy.sink = copy.slogSink
+	} else {
+		kvList := make([]any, 0, 2*len(attrs))
+		for _, attr := range attrs {
+			if attr.Key != "" {
+				kvList = append(kvList, l.addGroupPrefix(attr.Key), attr.Value.Resolve().Any())
+			}
 		}
+		copy.sink = l.sink.WithValues(kvList...)
 	}
-	copy := *l
-	copy.sink = l.sink.WithValues(kvList...)
 	return &copy
 }
 
@@ -113,7 +130,12 @@ func (l *slogHandler) WithGroup(name string) slog.Handler {
 		return l
 	}
 	copy := *l
-	copy.groupPrefix = copy.addGroupPrefix(name)
+	if l.slogSink != nil {
+		copy.slogSink = l.slogSink.WithGroup(name)
+		copy.sink = l.slogSink
+	} else {
+		copy.groupPrefix = copy.addGroupPrefix(name)
+	}
 	return &copy
 }
 

slogr/slogr.go

@@ -25,6 +25,7 @@ limitations under the License.
 package slogr
 
 import (
+	"context"
 	"log/slog"
 
 	"github.com/go-logr/logr"
@@ -67,5 +68,40 @@ func NewSlogHandler(logger logr.Logger) slog.Handler {
 		return sink.handler
 	}
 
-	return &slogHandler{sink: logger.GetSink(), levelBias: slog.Level(logger.GetV())}
+	handler := &slogHandler{sink: logger.GetSink(), levelBias: slog.Level(logger.GetV())}
+	if slogSink, ok := handler.sink.(SlogSink); ok {
+		handler.slogSink = slogSink
+	}
+	return handler
+}
+
+// SlogSink is an optional interface that a LogSink can implement to support
+// logging through the slog.Logger or slog.Handler APIs better. It then should
+// also support special slog values like slog.Group. When used as a
+// slog.Handler, the advantages are:
+//
+//   - stack unwinding gets avoided in favor of logging the pre-recorded PC,
+//     as intended by slog
+//   - proper grouping of key/value pairs via WithGroup
+//   - verbosity levels > slog.LevelInfo can be recorded
+//   - less overhead
+//
+// Both APIs (logr.Logger and slog.Logger/Handler) then are supported equally
+// well. Developers can pick whatever API suits them better and/or mix
+// packages which use either API in the same binary with a common logging
+// implementation.
+//
+// This interface is necessary because the type implementing the LogSink
+// interface cannot also implement the slog.Handler interface due to the
+// different prototype of the common Enabled method.
+//
+// An implementation could support both interfaces in two different types, but then
+// additional interfaces would be needed to convert between those types in NewLogr
+// and NewSlogHandler.
+type SlogSink interface {
+	logr.LogSink
+
+	Handle(ctx context.Context, record slog.Record) error
+	WithAttrs(attrs []slog.Attr) SlogSink
+	WithGroup(name string) SlogSink
 }

slogr/slogr_test.go

@@ -21,6 +21,7 @@ package slogr_test
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -106,30 +107,78 @@ func logHelper(logger logr.Logger) {
 	logger.WithCallDepth(1).Info("hello")
 }
 
-func TestSlogHandler(t *testing.T) {
-	var buffer bytes.Buffer
-	funcrLogger := funcr.NewJSON(func(obj string) {
-		fmt.Fprintln(&buffer, obj)
-	}, funcr.Options{
-		LogTimestamp: true,
-		Verbosity:    10,
-		RenderBuiltinsHook: func(kvList []any) []any {
-			mappedKVList := make([]any, len(kvList))
-			for i := 0; i < len(kvList); i += 2 {
-				key := kvList[i]
-				switch key {
-				case "ts":
-					mappedKVList[i] = "time"
-				default:
-					mappedKVList[i] = key
-				}
-				mappedKVList[i+1] = kvList[i+1]
-			}
-			return mappedKVList
-		},
+func TestJSONHandler(t *testing.T) {
+	testSlog(t, func(buffer *bytes.Buffer) logr.Logger {
+		handler := slog.NewJSONHandler(buffer, nil)
+		sink := testSlogSink{handler: handler}
+		return logr.New(sink)
 	})
-	handler := slogr.NewSlogHandler(funcrLogger)
+}
+
+var _ logr.LogSink = testSlogSink{}
+var _ slogr.SlogSink = testSlogSink{}
+
+// testSlogSink is only used through slog and thus doesn't need to implement the
+// normal LogSink methods.
+type testSlogSink struct {
+	handler slog.Handler
+}
+
+func (s testSlogSink) Init(logr.RuntimeInfo)                  {}
+func (s testSlogSink) Enabled(int) bool                       { return true }
+func (s testSlogSink) Error(error, string, ...interface{})    {}
+func (s testSlogSink) Info(int, string, ...interface{})       {}
+func (s testSlogSink) WithName(string) logr.LogSink           { return s }
+func (s testSlogSink) WithValues(...interface{}) logr.LogSink { return s }
 
+func (s testSlogSink) Handle(ctx context.Context, record slog.Record) error {
+	return s.handler.Handle(ctx, record)
+}
+func (s testSlogSink) WithAttrs(attrs []slog.Attr) slogr.SlogSink {
+	return testSlogSink{handler: s.handler.WithAttrs(attrs)}
+}
+func (s testSlogSink) WithGroup(name string) slogr.SlogSink {
+	return testSlogSink{handler: s.handler.WithGroup(name)}
+}
+
+func TestFuncrHandler(t *testing.T) {
+	testSlog(t, func(buffer *bytes.Buffer) logr.Logger {
+		logger := funcr.NewJSON(func(obj string) {
+			fmt.Fprintln(buffer, obj)
+		}, funcr.Options{
+			LogTimestamp: true,
+			Verbosity:    10,
+			RenderBuiltinsHook: func(kvList []any) []any {
+				mappedKVList := make([]any, len(kvList))
+				for i := 0; i < len(kvList); i += 2 {
+					key := kvList[i]
+					switch key {
+					case "ts":
+						mappedKVList[i] = "time"
+					default:
+						mappedKVList[i] = key
+					}
+					mappedKVList[i+1] = kvList[i+1]
+				}
+				return mappedKVList
+			},
+		})
+		return logger
+	},
+		"a Handler should ignore a zero Record.Time",                     // Time is generated by sink.
+		"a Handler should handle Group attributes",                       // funcr doesn't.
+		"a Handler should inline the Attrs of a group with an empty key", // funcr doesn't know about groups.
+		"a Handler should not output groups for an empty Record",         // Relies on WithGroup. Text may change, see https://go.dev/cl/516155
+		"a Handler should handle the WithGroup method",                   // logHandler does by prefixing keys, which is not what the test expects.
+		"a Handler should handle multiple WithGroup and WithAttr calls",  // Same.
+		"a Handler should call Resolve on attribute values in groups",    // funcr doesn't do that and slogHandler can't do it for it.
+	)
+}
+
+func testSlog(t *testing.T, createLogger func(buffer *bytes.Buffer) logr.Logger, exceptions ...string) {
+	var buffer bytes.Buffer
+	logger := createLogger(&buffer)
+	handler := slogr.NewSlogHandler(logger)
 	err := slogtest.TestHandler(handler, func() []map[string]any {
 		var ms []map[string]any
 		for _, line := range bytes.Split(buffer.Bytes(), []byte{'\n'}) {
@@ -153,15 +202,7 @@ func TestSlogHandler(t *testing.T) {
 			Unwrap() []error
 		}); ok {
 			for _, err := range err.Unwrap() {
-				if !containsOne(err.Error(),
-					"a Handler should ignore a zero Record.Time",                     // Time is generated by sink.
-					"a Handler should handle Group attributes",                       // funcr doesn't.
-					"a Handler should inline the Attrs of a group with an empty key", // funcr doesn't know about groups.
-					"a Handler should not output groups for an empty Record",         // Relies on WithGroup. Text may change, see https://go.dev/cl/516155
-					"a Handler should handle the WithGroup method",                   // logHandler does by prefixing keys, which is not what the test expects.
-					"a Handler should handle multiple WithGroup and WithAttr calls",  // Same.
-					"a Handler should call Resolve on attribute values in groups",    // funcr doesn't do that and slogHandler can't do it for it.
-				) {
+				if !containsOne(err.Error(), exceptions...) {
 					t.Errorf("Unexpected error: %v", err)
 				}
 			}