xml: add CopyToken

R=rsc
CC=golang-dev
https://golang.org/cl/634042

src/pkg/xml/xml.go

@@ -55,6 +55,13 @@ type StartElement struct {
 	Attr []Attr
 }
 
+func (e StartElement) Copy() StartElement {
+	attrs := make([]Attr, len(e.Attr))
+	copy(e.Attr, attrs)
+	e.Attr = attrs
+	return e
+}
+
 // An EndElement represents an XML end element.
 type EndElement struct {
 	Name Name
@@ -100,6 +107,23 @@ type readByter interface {
 	ReadByte() (b byte, err os.Error)
 }
 
+// CopyToken returns a copy of a Token.
+func CopyToken(t Token) Token {
+	switch v := t.(type) {
+	case CharData:
+		return v.Copy()
+	case Comment:
+		return v.Copy()
+	case Directive:
+		return v.Copy()
+	case ProcInst:
+		return v.Copy()
+	case StartElement:
+		return v.Copy()
+	}
+	return t
+}
+
 // A Parser represents an XML parser reading a particular input stream.
 // The parser assumes that its input is encoded in UTF-8.
 type Parser struct {
@@ -180,8 +204,8 @@ func NewParser(r io.Reader) *Parser {
 //
 // Slices of bytes in the returned token data refer to the
 // parser's internal buffer and remain valid only until the next
-// call to Token.  To acquire a copy of the bytes, call the token's
-// Copy method.
+// call to Token.  To acquire a copy of the bytes, call CopyToken
+// or the token's Copy method.
 //
 // Token expands self-closing elements such as <br/>
 // into separate start and end elements returned by successive calls.

src/pkg/xml/xml_test.go

@@ -328,3 +328,29 @@ func TestUnquotedAttrs(t *testing.T) {
 		t.Errorf("Unexpected attribute name: %v", attr.Name.Local)
 	}
 }
+
+func TestCopyTokenCharData(t *testing.T) {
+	data := []byte("same data")
+	var tok1 Token = CharData(data)
+	tok2 := CopyToken(tok1)
+	if !reflect.DeepEqual(tok1, tok2) {
+		t.Error("CopyToken(CharData) != CharData")
+	}
+	data[1] = 'o'
+	if reflect.DeepEqual(tok1, tok2) {
+		t.Error("CopyToken(CharData) uses same buffer.")
+	}
+}
+
+func TestCopyTokenStartElement(t *testing.T) {
+	elt := StartElement{Name{"", "hello"}, []Attr{Attr{Name{"", "lang"}, "en"}}}
+	var tok1 Token = elt
+	tok2 := CopyToken(tok1)
+	if !reflect.DeepEqual(tok1, tok2) {
+		t.Error("CopyToken(StartElement) != StartElement")
+	}
+	elt.Attr[0] = Attr{Name{"", "lang"}, "de"}
+	if reflect.DeepEqual(tok1, tok2) {
+		t.Error("CopyToken(CharData) uses same buffer.")
+	}
+}