Add support for using slog for log output

Allows containerd logs to use the default slog logger if configured.
Ensures that when formatting is set, such as through a default
configuration, if the slog format as well previously set.

Signed-off-by: Derek McGowan <derek@mcg.dev>

Author: dmcgowan

context.go

@@ -40,6 +40,7 @@ package log
 import (
 	"context"
 	"fmt"
+	"log/slog"
 
 	"github.com/sirupsen/logrus"
 )
@@ -127,6 +128,9 @@ func SetLevel(level string) error {
 	}
 
 	L.Logger.SetLevel(lvl)
+	if slogOut != nil {
+		slogLevel.Set(logrusToSlogLevel(lvl))
+	}
 	return nil
 }
 
@@ -155,15 +159,26 @@ func SetFormat(format OutputFormat) error {
 			TimestampFormat: RFC3339NanoFixed,
 			FullTimestamp:   true,
 		})
-		return nil
 	case JSONFormat:
 		L.Logger.SetFormatter(&logrus.JSONFormatter{
 			TimestampFormat: RFC3339NanoFixed,
 		})
-		return nil
 	default:
 		return fmt.Errorf("unknown log format: %s", format)
 	}
+
+	if slogOut != nil {
+		var handler slog.Handler
+		switch format {
+		case TextFormat:
+			handler = slog.NewTextHandler(slogOut, &slog.HandlerOptions{Level: slogLevel})
+		case JSONFormat:
+			handler = slog.NewJSONHandler(slogOut, &slog.HandlerOptions{Level: slogLevel})
+		}
+		slog.SetDefault(slog.New(handler))
+	}
+
+	return nil
 }
 
 // WithLogger returns a new context with the provided logger. Use in

slog.go

@@ -0,0 +1,87 @@
+/*
+   Copyright The containerd Authors.
+
+   Licensed under the Apache License, Version 2.0 (the "License");
+   you may not use this file except in compliance with the License.
+   You may obtain a copy of the License at
+
+       http://www.apache.org/licenses/LICENSE-2.0
+
+   Unless required by applicable law or agreed to in writing, software
+   distributed under the License is distributed on an "AS IS" BASIS,
+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+   See the License for the specific language governing permissions and
+   limitations under the License.
+*/
+
+package log
+
+import (
+	"context"
+	"io"
+	"log/slog"
+
+	"github.com/sirupsen/logrus"
+)
+
+// slogOut is used to set the slog logger when setting output format.
+var slogOut io.Writer
+
+// slogLevel is used to control the slog handler's level when slog output is active.
+var slogLevel = &slog.LevelVar{}
+
+func UseSlog() {
+	L.Logger.SetNoLock()
+	L.Logger.AddHook(slogHook{})
+	slogOut = L.Logger.Out
+	L.Logger.SetOutput(io.Discard)
+}
+
+type slogHook struct{}
+
+func (hook slogHook) Levels() []logrus.Level {
+	return logrus.AllLevels
+}
+
+func logrusToSlogLevel(l logrus.Level) slog.Level {
+	switch l {
+	case logrus.PanicLevel:
+		return slog.LevelError + 4
+	case logrus.FatalLevel:
+		return slog.LevelError + 2
+	case logrus.ErrorLevel:
+		return slog.LevelError
+	case logrus.WarnLevel:
+		return slog.LevelWarn
+	case logrus.DebugLevel:
+		return slog.LevelDebug
+	case logrus.TraceLevel:
+		return slog.LevelDebug - 4
+	default:
+		return slog.LevelInfo
+	}
+}
+
+func (hook slogHook) Fire(entry *logrus.Entry) error {
+	level := logrusToSlogLevel(entry.Level)
+
+	handler := slog.Default().Handler()
+
+	ctx := entry.Context
+	if ctx == nil {
+		ctx = context.Background()
+	}
+
+	if !handler.Enabled(ctx, level) {
+		return nil
+	}
+
+	record := slog.NewRecord(entry.Time, level, entry.Message, 0)
+
+	// Convert logrus fields to slog attributes.
+	for k, v := range entry.Data {
+		record.AddAttrs(slog.Any(k, v))
+	}
+
+	return handler.Handle(ctx, record)
+}