Feat[pool]: add safer strings.Builder pool

pool/strings.go

@@ -0,0 +1,112 @@
+package pool
+
+import (
+	"errors"
+	"strings"
+	"sync"
+)
+
+var ErrBufferReturned = errors.New("buffer already returned")
+
+type String struct {
+	*strings.Builder
+	*sync.Once
+}
+
+func (s String) String() string {
+	if s.Builder == nil {
+		return ""
+	}
+	return s.Builder.String()
+}
+
+func (s String) Reset() error {
+	if s.Builder == nil {
+		return ErrBufferReturned
+	}
+	s.Builder.Reset()
+	return nil
+}
+
+func (s String) WriteString(str string) (int, error) {
+	if s.Builder == nil {
+		return 0, ErrBufferReturned
+	}
+	return s.Builder.WriteString(str)
+}
+
+func (s String) Len() int {
+	if s.Builder == nil {
+		return 0
+	}
+	return s.Builder.Len()
+}
+
+func (s String) Write(p []byte) (int, error) {
+	if s.Builder == nil {
+		return 0, ErrBufferReturned
+	}
+	return s.Builder.Write(p)
+}
+
+func (s String) WriteRune(r rune) (int, error) {
+	if s.Builder == nil {
+		return 0, ErrBufferReturned
+	}
+	return s.Builder.WriteRune(r)
+}
+
+func (s String) WriteByte(c byte) error {
+	if s.Builder == nil {
+		return ErrBufferReturned
+	}
+	return s.Builder.WriteByte(c)
+}
+
+func (s String) Grow(n int) error {
+	if s.Builder == nil {
+		return ErrBufferReturned
+	}
+	s.Builder.Grow(n)
+	return nil
+}
+
+func (s String) Cap() int {
+	if s.Builder == nil {
+		return 0
+	}
+	return s.Builder.Cap()
+}
+
+type StringFactory struct {
+	pool *sync.Pool
+}
+
+// NewStringFactory creates a new strings.Builder pool.
+func NewStringFactory() StringFactory {
+	return StringFactory{
+		pool: &sync.Pool{
+			New: func() any { return new(strings.Builder) },
+		},
+	}
+}
+
+// Put returns a strings.Builder back into to the pool after resetting it.
+func (sf StringFactory) Put(buf *String) error {
+	var err = ErrBufferReturned
+	buf.Do(func() {
+		_ = buf.Reset()
+		sf.pool.Put(buf.Builder)
+		buf.Builder = nil
+		err = nil
+	})
+	return err
+}
+
+// Get returns a strings.Builder from the pool.
+func (sf StringFactory) Get() *String {
+	return &String{
+		sf.pool.Get().(*strings.Builder),
+		&sync.Once{},
+	}
+}

pool/strings_test.go

@@ -0,0 +1,95 @@
+package pool
+
+import (
+	"testing"
+)
+
+func TestStringFactory(t *testing.T) {
+	s := NewStringFactory()
+	buf := s.Get()
+	if _, err := buf.WriteString("hello"); err != nil {
+		t.Fatal(err)
+	}
+	if buf.String() != "hello" {
+		t.Fatal("unexpected string")
+	}
+	if err := buf.WriteByte(' '); err != nil {
+		t.Fatal(err)
+	}
+	if buf.String() != "hello " {
+		t.Fatalf("unexpected string: %s", buf.String())
+	}
+	if _, err := buf.WriteRune('w'); err != nil {
+		t.Fatal(err)
+	}
+	if buf.String() != "hello w" {
+		t.Fatalf("unexpected string: %s", buf.String())
+	}
+	if _, err := buf.Write([]byte("orld")); err != nil {
+		t.Fatal(err)
+	}
+	if err := buf.Grow(1); err != nil {
+		t.Fatal(err)
+	}
+	if buf.Cap() == 0 {
+		t.Fatal("expected capacity, got 0")
+	}
+	if err := buf.Reset(); err != nil {
+		t.Fatal(err)
+	}
+	if buf.String() != "" {
+		t.Fatalf("unexpected string: %s", buf.String())
+	}
+	if err := s.Put(buf); err != nil {
+		t.Fatal(err)
+	}
+	if err := s.Put(buf); err == nil {
+		t.Fatal("expected error")
+	}
+	if s.Get().Len() > 0 {
+		t.Fatalf("StringFactory.Put() did not reset the buffer")
+	}
+	if err := s.Put(buf); err == nil {
+		t.Fatalf("StringFactory.Put() should have returned an error after already returning the buffer")
+	}
+	if err := buf.Grow(10); err == nil {
+		t.Fatalf("StringFactory.Grow() should not work after returning the buffer")
+	}
+	if buf.Cap() != 0 {
+		t.Fatalf("StringFactory.Cap() should return 0 after returning the buffer")
+	}
+	got := s.Get()
+	if got.String() != "" {
+		t.Fatalf("should have gotten a clean buffer")
+	}
+	if err := s.Put(got); err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if _, err := got.WriteString("a"); err == nil {
+		t.Fatalf("should not be able to write to a returned buffer")
+	}
+	if _, err := got.WriteRune('a'); err == nil {
+		t.Fatalf("should not be able to write to a returned buffer")
+	}
+	if err := got.WriteByte('a'); err == nil {
+		t.Fatalf("should not be able to write to a returned buffer")
+	}
+	if _, err := got.Write([]byte("a")); err == nil {
+		t.Fatalf("should not be able to write to a returned buffer")
+	}
+	if err := got.Reset(); err == nil {
+		t.Fatalf("should not be able to reset a returned buffer")
+	}
+	if str := got.String(); str != "" {
+		t.Fatalf("should not be able to get string from a returned buffer")
+	}
+	if got.Len() != 0 {
+		t.Fatalf("should not be able to write to a returned buffer")
+	}
+	if got = s.Get(); got.Len() > 0 {
+		t.Fatalf("StringFactory.Put() did not reset the buffer")
+	}
+	if got.Cap() != 0 {
+		t.Fatalf("StringFactory.Put() did not reset the buffer")
+	}
+}