basic ReplaceAttrs support

encoding.go

@@ -3,8 +3,6 @@ package console
 import (
 	"fmt"
 	"log/slog"
-	"path/filepath"
-	"runtime"
 	"time"
 )
 
@@ -75,21 +73,6 @@ func (e encoder) writeTimestamp(buf *buffer, tt time.Time) {
 	}
 }
 
-func (e encoder) writeSource(buf *buffer, pc uintptr, cwd string) {
-	frame, _ := runtime.CallersFrames([]uintptr{pc}).Next()
-	if cwd != "" {
-		if ff, err := filepath.Rel(cwd, frame.File); err == nil {
-			frame.File = ff
-		}
-	}
-	e.withColor(buf, e.opts.Theme.Source(), func() {
-		buf.AppendString(frame.File)
-		buf.AppendByte(':')
-		buf.AppendInt(int64(frame.Line))
-	})
-	e.writeColoredString(buf, " > ", e.opts.Theme.AttrKey())
-}
-
 func (e encoder) writeMessage(buf *buffer, level slog.Level, msg string) {
 	if level >= slog.LevelInfo {
 		e.writeColoredString(buf, msg, e.opts.Theme.Message())
@@ -103,6 +86,18 @@ func (e encoder) writeAttr(buf *buffer, a slog.Attr, group string) {
 	if a.Equal(slog.Attr{}) {
 		return
 	}
+	// Special handling for source attribute.
+	if a.Key == slog.SourceKey {
+		if v, ok := a.Value.Any().(*slog.Source); ok {
+			e.withColor(buf, e.opts.Theme.Source(), func() {
+				buf.AppendString(v.File)
+				buf.AppendByte(':')
+				buf.AppendInt(int64(v.Line))
+			})
+			e.writeColoredString(buf, " > ", e.opts.Theme.AttrKey())
+			return
+		}
+	}
 	value := a.Value.Resolve()
 	if value.Kind() == slog.KindGroup {
 		subgroup := a.Key

example/main.go

@@ -4,13 +4,36 @@ import (
 	"errors"
 	"log/slog"
 	"os"
+	"strings"
 
 	"github.com/phsym/console-slog"
 )
 
 func main() {
 	logger := slog.New(
-		console.NewHandler(os.Stderr, &console.HandlerOptions{Level: slog.LevelDebug, AddSource: true}),
+		console.NewHandler(os.Stderr, &console.HandlerOptions{
+			Level:      slog.LevelDebug,
+			AddSource:  true,
+			TimeFormat: "15:04:05.000000",
+			ReplaceAttr: func(groups []string, a slog.Attr) slog.Attr {
+				if v, ok := a.Value.Any().(*slog.Source); ok {
+					file := v.File
+					parts := strings.Split(v.File, "/")
+					if len(parts) > 0 {
+						file = parts[len(parts)-1]
+					}
+					return slog.Attr{
+						Key: slog.SourceKey,
+						Value: slog.AnyValue(&slog.Source{
+							Function: v.Function,
+							File:     file,
+							Line:     v.Line,
+						}),
+					}
+				}
+				return a
+			},
+		}),
 	)
 	slog.SetDefault(logger)
 	slog.Info("Hello world!", "foo", "bar")

handler.go

@@ -5,6 +5,8 @@ import (
 	"io"
 	"log/slog"
 	"os"
+	"path/filepath"
+	"runtime"
 	"strings"
 	"sync"
 	"time"
@@ -38,6 +40,10 @@ type HandlerOptions struct {
 
 	// Theme defines the colorized output using ANSI escape sequences
 	Theme Theme
+
+	// See [slog.HandlerOptions] for details.
+	// Groups are not supported though.
+	ReplaceAttr func(groups []string, a slog.Attr) slog.Attr
 }
 
 type Handler struct {
@@ -87,11 +93,35 @@ func (h *Handler) Handle(_ context.Context, rec slog.Record) error {
 	h.enc.writeTimestamp(buf, rec.Time)
 	h.enc.writeLevel(buf, rec.Level)
 	if h.opts.AddSource && rec.PC > 0 {
-		h.enc.writeSource(buf, rec.PC, cwd)
+		frame, _ := runtime.CallersFrames([]uintptr{rec.PC}).Next()
+		if cwd != "" {
+			if ff, err := filepath.Rel(cwd, frame.File); err == nil {
+				frame.File = ff
+			}
+		}
+		a := slog.Attr{
+			Key: slog.SourceKey,
+			Value: slog.AnyValue(&slog.Source{
+				Function: frame.Function,
+				File:     frame.File,
+				Line:     frame.Line,
+			}),
+		}
+		if h.opts.ReplaceAttr != nil {
+			a = h.opts.ReplaceAttr(nil, a)
+		}
+		h.enc.writeAttr(
+			buf,
+			a,
+			h.group,
+		)
 	}
 	h.enc.writeMessage(buf, rec.Level, rec.Message)
 	buf.copy(&h.context)
 	rec.Attrs(func(a slog.Attr) bool {
+		if h.opts.ReplaceAttr != nil {
+			a = h.opts.ReplaceAttr(nil, a)
+		}
 		h.enc.writeAttr(buf, a, h.group)
 		return true
 	})

handler_test.go

@@ -26,6 +26,29 @@ func TestHandler_TimeFormat(t *testing.T) {
 	AssertEqual(t, expected, buf.String())
 }
 
+func TestHandler_ReplaceAttr(t *testing.T) {
+	ra := func(groups []string, a slog.Attr) slog.Attr {
+		if a.Key == "test-key" {
+			return slog.Attr{Key: "testkey", Value: a.Value}
+		}
+		if a.Key == "empty" {
+			return slog.Attr{}
+		}
+		return a
+	}
+	buf := bytes.Buffer{}
+	h := NewHandler(&buf, &HandlerOptions{TimeFormat: time.RFC3339Nano, NoColor: true, ReplaceAttr: ra})
+	rec := slog.NewRecord(time.Time{}, slog.LevelInfo, "foobar", 0)
+	rec.AddAttrs(
+		slog.String("test-key", "test-value"),
+		slog.String("empty", "should not be logged"),
+	)
+	AssertNoError(t, h.Handle(context.Background(), rec))
+
+	expected := fmt.Sprintf("INF foobar testkey=test-value\n")
+	AssertEqual(t, expected, buf.String())
+}
+
 // Handlers should not log the time field if it is zero.
 // '- If r.Time is the zero time, ignore the time.'
 // https://pkg.go.dev/log/slog@master#Handler