fix: prevent logger close recursion and unsafe writer closing

io.go

@@ -64,12 +64,18 @@ func (l *Logger) print(level LogLevel, m ...any) {
 	if l.level.n < level.n {
 		return
 	}
+	if len(l.writers) == 0 {
+		return
+	}
 
 	tb := getFullTraceback(0)
 	for _, writer := range l.writers {
+		if writer == nil {
+			continue
+		}
 		err := writer.Print(level, l.prefix, tb, m...)
 		if err != nil {
-			l.Error(err)
+			l.reportWriterError(err)
 		}
 	}
 }
@@ -80,12 +86,28 @@ func (l *Logger) println(level LogLevel, m ...any) {
 	if l.level.n < level.n {
 		return
 	}
+	if len(l.writers) == 0 {
+		return
+	}
 
 	tb := getFullTraceback(0)
+	messages := append(append(make([]any, 0, len(m)+1), m...), "\n")
 	for _, writer := range l.writers {
-		err := writer.Print(level, l.prefix, tb, append(m, "\n")...)
+		if writer == nil {
+			continue
+		}
+		err := writer.Print(level, l.prefix, tb, messages...)
 		if err != nil {
-			l.Error(err)
+			l.reportWriterError(err)
 		}
 	}
 }
+
+// reportWriterError writes internal writer failures directly to stderr to avoid
+// re-entering the same logger path that just failed.
+func (l *Logger) reportWriterError(err error) {
+	if err == nil {
+		return
+	}
+	_, _ = fmt.Fprintf(os.Stderr, "[%s] logger writer error: %v\n", l.prefix, err)
+}

logger.go

@@ -1,6 +1,7 @@
 package slog
 
 import (
+	"errors"
 	"fmt"
 	"io"
 	"strings"
@@ -83,13 +84,18 @@ func (l *Logger) AddWriter(writer LoggerWriter) *Logger {
 	return l
 }
 func (l *Logger) Close() error {
+	var errs []error
 	for _, writer := range l.writers {
+		if writer == nil {
+			continue
+		}
 		err := writer.Close()
 		if err != nil {
-			l.Error(err)
+			errs = append(errs, err)
 		}
 	}
-	return nil
+	l.writers = nil
+	return errors.Join(errs...)
 }
 
 func (l *Logger) CreateTextWriter(w io.Writer) *LoggerTextWriter {

logger_test.go

@@ -0,0 +1,170 @@
+package slog
+
+import (
+	"bytes"
+	"errors"
+	"os"
+	"testing"
+)
+
+type stubLoggerWriter struct {
+	printErr   error
+	closeErr   error
+	printCalls int
+	closeCalls int
+}
+
+func (w *stubLoggerWriter) Close() error {
+	w.closeCalls++
+	return w.closeErr
+}
+
+func (w *stubLoggerWriter) Write(p []byte) (int, error) {
+	return len(p), nil
+}
+
+func (w *stubLoggerWriter) Print(_ LogLevel, _ string, _ []*MethodTraceback, _ ...any) error {
+	w.printCalls++
+	return w.printErr
+}
+
+func TestLoggerCloseReturnsJoinedErrorsWithoutRelogging(t *testing.T) {
+	firstErr := errors.New("first close failed")
+	secondErr := errors.New("second close failed")
+	first := &stubLoggerWriter{closeErr: firstErr}
+	second := &stubLoggerWriter{closeErr: secondErr}
+
+	logger := CreateLogger().AddWriters(first, second)
+	err := logger.Close()
+	if !errors.Is(err, firstErr) {
+		t.Fatalf("Close() error should include first writer error, got %v", err)
+	}
+	if !errors.Is(err, secondErr) {
+		t.Fatalf("Close() error should include second writer error, got %v", err)
+	}
+	if first.printCalls != 0 || second.printCalls != 0 {
+		t.Fatalf("Close() should not log through writers again, got print calls first=%d second=%d", first.printCalls, second.printCalls)
+	}
+	if first.closeCalls != 1 || second.closeCalls != 1 {
+		t.Fatalf("Close() should close each writer once, got close calls first=%d second=%d", first.closeCalls, second.closeCalls)
+	}
+	if err := logger.Close(); err != nil {
+		t.Fatalf("second Close() should be a no-op, got %v", err)
+	}
+}
+
+func TestLoggerPrintDoesNotRecurseOnWriterError(t *testing.T) {
+	oldStderr := os.Stderr
+	stderrFile, err := os.CreateTemp(t.TempDir(), "stderr")
+	if err != nil {
+		t.Fatalf("CreateTemp() error = %v", err)
+	}
+	os.Stderr = stderrFile
+	t.Cleanup(func() {
+		os.Stderr = oldStderr
+		_ = stderrFile.Close()
+	})
+
+	bad := &stubLoggerWriter{printErr: errors.New("print failed")}
+	good := &stubLoggerWriter{}
+
+	logger := CreateLogger().AddWriters(bad, good)
+	logger.Error("boom")
+
+	if bad.printCalls != 1 {
+		t.Fatalf("bad writer should be called once, got %d", bad.printCalls)
+	}
+	if good.printCalls != 1 {
+		t.Fatalf("good writer should be called once, got %d", good.printCalls)
+	}
+}
+
+func TestCreateTextWriterCloseOnNonCloserIsNoOp(t *testing.T) {
+	writer := CreateTextWriter(&bytes.Buffer{}, false, false)
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+}
+
+func TestCreateTextWriterDoesNotCloseExternalCloser(t *testing.T) {
+	file, err := os.CreateTemp(t.TempDir(), "text-writer")
+	if err != nil {
+		t.Fatalf("CreateTemp() error = %v", err)
+	}
+	t.Cleanup(func() {
+		_ = file.Close()
+	})
+
+	writer := CreateTextWriter(file, false, false)
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+	if _, err := file.WriteString("still open"); err != nil {
+		t.Fatalf("CreateTextWriter() should not close external writers, got %v", err)
+	}
+}
+
+func TestCreateJsonWriterCloseOnNonCloserIsNoOp(t *testing.T) {
+	writer := CreateJsonWriter(&bytes.Buffer{}, false)
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+}
+
+func TestCreateJsonWriterDoesNotCloseExternalCloser(t *testing.T) {
+	file, err := os.CreateTemp(t.TempDir(), "json-writer")
+	if err != nil {
+		t.Fatalf("CreateTemp() error = %v", err)
+	}
+	t.Cleanup(func() {
+		_ = file.Close()
+	})
+
+	writer := CreateJsonWriter(file, false)
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+	if _, err := file.WriteString("still open"); err != nil {
+		t.Fatalf("CreateJsonWriter() should not close external writers, got %v", err)
+	}
+}
+
+func TestCreateTextStdoutWriterDoesNotCloseStdout(t *testing.T) {
+	stdoutFile := swapStdout(t)
+
+	writer := CreateTextStdoutWriter(false, false)
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+	if _, err := stdoutFile.WriteString("still open"); err != nil {
+		t.Fatalf("stdout writer Close() should not close stdout, got %v", err)
+	}
+}
+
+func TestCreateJsonStdoutWriterDoesNotCloseStdout(t *testing.T) {
+	stdoutFile := swapStdout(t)
+
+	writer := CreateJsonStdoutWriter(false)
+	if err := writer.Close(); err != nil {
+		t.Fatalf("Close() error = %v", err)
+	}
+	if _, err := stdoutFile.WriteString("still open"); err != nil {
+		t.Fatalf("stdout writer Close() should not close stdout, got %v", err)
+	}
+}
+
+func swapStdout(t *testing.T) *os.File {
+	t.Helper()
+
+	oldStdout := os.Stdout
+	stdoutFile, err := os.CreateTemp(t.TempDir(), "stdout")
+	if err != nil {
+		t.Fatalf("CreateTemp() error = %v", err)
+	}
+	os.Stdout = stdoutFile
+	t.Cleanup(func() {
+		os.Stdout = oldStdout
+		_ = stdoutFile.Close()
+	})
+	return stdoutFile
+}

writers.go

@@ -1,7 +1,6 @@
 package slog
 
 import (
-	"bufio"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -20,17 +19,13 @@ type LoggerWriter interface {
 type LoggerTextWriter struct {
 	LoggerWriter
 	writer         io.Writer
+	closer         io.Closer
 	printTraceback bool
 	printTime      bool
 }
 
 func (w *LoggerTextWriter) Write(p []byte) (n int, err error) {
-	n, err = w.writer.Write(p)
-	if err != nil {
-		return n, err
-	}
-	err = bufio.NewWriter(w.writer).Flush()
-	return n, err
+	return w.writer.Write(p)
 }
 func (w *LoggerTextWriter) Print(level LogLevel, prefix string, _ []*MethodTraceback, messages ...any) error {
 	s := BuildString(level, prefix, w.printTime, w.printTraceback, messages...)
@@ -38,13 +33,17 @@ func (w *LoggerTextWriter) Print(level LogLevel, prefix string, _ []*MethodTrace
 	return err
 }
 func (w *LoggerTextWriter) Close() error {
-	return w.writer.(io.Closer).Close()
+	if w.closer == nil {
+		return nil
+	}
+	return w.closer.Close()
 }
 
 // LoggerJsonWriter write into writer JSON
 type LoggerJsonWriter struct {
 	LoggerWriter
 	writer io.Writer
+	closer io.Closer
 	pretty bool
 }
 type LoggerJsonMessage struct {
@@ -56,12 +55,7 @@ type LoggerJsonMessage struct {
 }
 
 func (w *LoggerJsonWriter) Write(data []byte) (int, error) {
-	n, err := w.writer.Write(data)
-	if err != nil {
-		return n, err
-	}
-	err = bufio.NewWriter(w.writer).Flush()
-	return n, err
+	return w.writer.Write(data)
 }
 func (w *LoggerJsonWriter) Print(level LogLevel, prefix string, traceback []*MethodTraceback, messages ...any) error {
 	msg := Map(messages, func(el any) string {
@@ -98,7 +92,10 @@ func (w *LoggerJsonWriter) Print(level LogLevel, prefix string, traceback []*Met
 	return err
 }
 func (w *LoggerJsonWriter) Close() error {
-	return w.writer.(io.Closer).Close()
+	if w.closer == nil {
+		return nil
+	}
+	return w.closer.Close()
 }
 
 func CreateTextWriter(w io.Writer, printTraceback, printTime bool) *LoggerTextWriter {
@@ -116,10 +113,14 @@ func CreateTextFileWriter(path string, printTraceback, printTime bool) (*LoggerT
 	if err != nil {
 		return nil, err
 	}
-	return CreateTextWriter(file, printTraceback, printTime), nil
+	writer := CreateTextWriter(file, printTraceback, printTime)
+	writer.closer = file
+	return writer, nil
 }
 func CreateTextStdoutWriter(printTraceback, printTime bool) *LoggerTextWriter {
-	return CreateTextWriter(os.Stdout, printTraceback, printTime)
+	writer := CreateTextWriter(os.Stdout, printTraceback, printTime)
+	writer.closer = nil
+	return writer
 }
 
 func CreateJsonWriter(w io.Writer, pretty bool) *LoggerJsonWriter {
@@ -129,7 +130,9 @@ func CreateJsonWriter(w io.Writer, pretty bool) *LoggerJsonWriter {
 	return writer
 }
 func CreateJsonStdoutWriter(pretty bool) *LoggerJsonWriter {
-	return CreateJsonWriter(os.Stdout, pretty)
+	writer := CreateJsonWriter(os.Stdout, pretty)
+	writer.closer = nil
+	return writer
 }
 func CreateJsonFileWriter(path string, pretty bool) (*LoggerJsonWriter, error) {
 	err := os.MkdirAll(filepath.Dir(path), os.ModePerm)
@@ -140,5 +143,7 @@ func CreateJsonFileWriter(path string, pretty bool) (*LoggerJsonWriter, error) {
 	if err != nil {
 		return nil, err
 	}
-	return CreateJsonWriter(file, pretty), nil
+	writer := CreateJsonWriter(file, pretty)
+	writer.closer = file
+	return writer, nil
 }