Gologshim runtime controlled handler

gologshim/gologshim.go

@@ -40,49 +40,50 @@ var lvlToLower = map[slog.Level]slog.Value{
 	slog.LevelError: slog.StringValue("error"),
 }
 
-// goLogBridge detects go-log's slog bridge via duck typing, without import dependency
-type goLogBridge interface {
-	GoLogBridge()
+var defaultHandler atomic.Pointer[slog.Handler]
+
+// SetDefaultHandler allows an application to change the underlying handler used
+// by gologshim as long as it's changed *before* the first log by the logger.
+func SetDefaultHandler(handler slog.Handler) {
+	defaultHandler.Store(&handler)
 }
 
-// lazyBridgeHandler delays bridge detection until first log call to handle init order issues
-type lazyBridgeHandler struct {
+// dynamicHandler delays bridge detection until first log call to handle init order issues
+type dynamicHandler struct {
 	system  string
 	config  *Config
 	once    sync.Once
-	handler atomic.Pointer[slog.Handler]
+	handler slog.Handler
 }
 
-func (h *lazyBridgeHandler) ensureHandler() slog.Handler {
-	if handler := h.handler.Load(); handler != nil {
-		return *handler
-	}
-
+func (h *dynamicHandler) ensureHandler() slog.Handler {
 	h.once.Do(func() {
-		var handler slog.Handler
-		if bridge, ok := slog.Default().Handler().(goLogBridge); ok {
-			attrs := make([]slog.Attr, 0, 1+len(h.config.labels))
-			attrs = append(attrs, slog.String("logger", h.system))
-			attrs = append(attrs, h.config.labels...)
-			handler = bridge.(slog.Handler).WithAttrs(attrs)
+		if hPtr := defaultHandler.Load(); hPtr != nil {
+			h.handler = *hPtr
 		} else {
-			handler = h.createFallbackHandler()
+			h.handler = h.createFallbackHandler()
 		}
-		h.handler.Store(&handler)
+		attrs := make([]slog.Attr, 0, 1+len(h.config.labels))
+		attrs = append(attrs, slog.String("logger", h.system))
+		attrs = append(attrs, h.config.labels...)
+		h.handler = h.handler.WithAttrs(attrs)
 	})
 
-	return *h.handler.Load()
+	return h.handler
 }
 
-func (h *lazyBridgeHandler) createFallbackHandler() slog.Handler {
+func (h *dynamicHandler) createFallbackHandler() slog.Handler {
 	opts := &slog.HandlerOptions{
 		Level:     h.config.LevelForSystem(h.system),
 		AddSource: h.config.addSource,
 		ReplaceAttr: func(_ []string, a slog.Attr) slog.Attr {
-			if a.Key == slog.TimeKey {
+			switch a.Key {
+			case slog.TimeKey:
+				// ipfs go-log uses "ts" for time
 				a.Key = "ts"
-			} else if a.Key == slog.LevelKey {
+			case slog.LevelKey:
 				if lvl, ok := a.Value.Any().(slog.Level); ok {
+					// ipfs go-log uses lowercase level names
 					if s, ok := lvlToLower[lvl]; ok {
 						a.Value = s
 					}
@@ -91,31 +92,26 @@ func (h *lazyBridgeHandler) createFallbackHandler() slog.Handler {
 			return a
 		},
 	}
-	var handler slog.Handler
 	if h.config.format == logFormatText {
-		handler = slog.NewTextHandler(os.Stderr, opts)
-	} else {
-		handler = slog.NewJSONHandler(os.Stderr, opts)
+		return slog.NewTextHandler(os.Stderr, opts)
 	}
-	attrs := make([]slog.Attr, 1+len(h.config.labels))
-	attrs[0] = slog.String("logger", h.system)
-	copy(attrs[1:], h.config.labels)
-	return handler.WithAttrs(attrs)
+
+	return slog.NewJSONHandler(os.Stderr, opts)
 }
 
-func (h *lazyBridgeHandler) Enabled(ctx context.Context, lvl slog.Level) bool {
+func (h *dynamicHandler) Enabled(ctx context.Context, lvl slog.Level) bool {
 	return h.ensureHandler().Enabled(ctx, lvl)
 }
 
-func (h *lazyBridgeHandler) Handle(ctx context.Context, r slog.Record) error {
+func (h *dynamicHandler) Handle(ctx context.Context, r slog.Record) error {
 	return h.ensureHandler().Handle(ctx, r)
 }
 
-func (h *lazyBridgeHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
+func (h *dynamicHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
 	return h.ensureHandler().WithAttrs(attrs)
 }
 
-func (h *lazyBridgeHandler) WithGroup(name string) slog.Handler {
+func (h *dynamicHandler) WithGroup(name string) slog.Handler {
 	return h.ensureHandler().WithGroup(name)
 }
 
@@ -126,18 +122,7 @@ func (h *lazyBridgeHandler) WithGroup(name string) slog.Handler {
 // fallback level to warn.
 func Logger(system string) *slog.Logger {
 	c := ConfigFromEnv()
-
-	// If go-log bridge available, use it immediately
-	if _, ok := slog.Default().Handler().(goLogBridge); ok {
-		attrs := make([]slog.Attr, 0, 1+len(c.labels))
-		attrs = append(attrs, slog.String("logger", system))
-		attrs = append(attrs, c.labels...)
-		h := slog.Default().Handler().WithAttrs(attrs)
-		return slog.New(h)
-	}
-
-	// Use lazy handler for init order issues
-	return slog.New(&lazyBridgeHandler{
+	return slog.New(&dynamicHandler{
 		system: system,
 		config: c,
 	})

gologshim/gologshim_test.go

@@ -6,18 +6,20 @@ import (
 	"log/slog"
 	"os"
 	"strings"
+	"sync"
 	"testing"
 )
 
 // mockBridge simulates go-log's slog bridge for testing duck typing detection
 type mockBridge struct {
+	sync.Mutex
 	slog.Handler
 	logs *bytes.Buffer
 }
 
-func (m *mockBridge) GoLogBridge() {}
-
 func (m *mockBridge) Handle(_ context.Context, r slog.Record) error {
+	m.Lock()
+	defer m.Unlock()
 	m.logs.WriteString(r.Message)
 	m.logs.WriteString("\n")
 	return nil
@@ -44,7 +46,7 @@ func TestGoLogBridgeDetection(t *testing.T) {
 			Handler: slog.NewTextHandler(&buf, nil),
 			logs:    &buf,
 		}
-		slog.SetDefault(slog.New(bridge))
+		SetDefaultHandler(bridge)
 
 		// Create logger - should detect bridge
 		log := Logger("test-subsystem")
@@ -92,12 +94,16 @@ func TestLazyBridgeInitialization(t *testing.T) {
 		Handler: slog.NewTextHandler(&bridgeBuf, nil),
 		logs:    &bridgeBuf,
 	}
-	slog.SetDefault(slog.New(bridge))
+	SetDefaultHandler(bridge)
 
+	// Log in goroutine to detect races
+	go log.Info("lazy init message")
 	// First log call should detect the bridge via lazy initialization
 	log.Info("lazy init message")
 
+	bridge.Lock()
 	output := bridgeBuf.String()
+	bridge.Unlock()
 	if !strings.Contains(output, "lazy init message") {
 		t.Errorf("Lazy handler should have detected bridge, got: %s", output)
 	}