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encoding/xml: add namespace prefix support in encoder #70944

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encoding/xml: add namespace prefix support in encoder #70944

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186 changes: 122 additions & 64 deletions src/encoding/xml/marshal.go
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Original file line number Diff line number Diff line change
Expand Up @@ -80,8 +80,14 @@ const (
//
// Marshal will return an error if asked to marshal a channel, function, or map.
func Marshal(v any) ([]byte, error) {
nametable := make(map[string]string)
return MarshalWithNametable(v, nametable)
}

func MarshalWithNametable(v any, nametable map[string]string) ([]byte, error) {
var b bytes.Buffer
enc := NewEncoder(&b)
enc.p.nametable = nametable
if err := enc.Encode(v); err != nil {
return nil, err
}
Expand Down Expand Up @@ -130,9 +136,15 @@ type MarshalerAttr interface {
// indented line that starts with prefix and is followed by one or more
// copies of indent according to the nesting depth.
func MarshalIndent(v any, prefix, indent string) ([]byte, error) {
nametable := make(map[string]string)
return MarshalIndentWithNametable(v, nametable, prefix, indent)
}

func MarshalIndentWithNametable(v any, nametable map[string]string, prefix, indent string) ([]byte, error) {
var b bytes.Buffer
enc := NewEncoder(&b)
enc.Indent(prefix, indent)
enc.p.nametable = nametable
if err := enc.Encode(v); err != nil {
return nil, err
}
Expand Down Expand Up @@ -264,6 +276,17 @@ func (enc *Encoder) EncodeToken(t Token) error {
return p.cachedWriteError()
}

func (enc *Encoder) SetNamespace(prefix, url string) {
if enc.p.nametable == nil {
enc.p.nametable = make(map[string]string)
}
enc.p.nametable[url] = prefix
}

func (enc *Encoder) SetNametable(nametable map[string]string) {
enc.p.nametable = nametable
}

// isValidDirective reports whether dir is a valid directive text,
// meaning angle brackets are matched, ignoring comments and strings.
func isValidDirective(dir Directive) bool {
Expand Down Expand Up @@ -318,87 +341,101 @@ func (enc *Encoder) Close() error {
}

type printer struct {
w *bufio.Writer
encoder *Encoder
seq int
indent string
prefix string
depth int
indentedIn bool
putNewline bool
attrNS map[string]string // map prefix -> name space
attrPrefix map[string]string // map name space -> prefix
prefixes []string
tags []Name
closed bool
err error
w *bufio.Writer
encoder *Encoder
seq int
indent string
prefix string
depth int
indentedIn bool
putNewline bool
prefixes []string
tags []Name
closed bool
err error
elementNS map[string]string // map prefix -> name space
elementPrefix map[string]string // map name space -> prefix
nametable map[string]string
}

// createAttrPrefix finds the name space prefix attribute to use for the given name space,
// defining a new prefix if necessary. It returns the prefix.
func (p *printer) createAttrPrefix(url string) string {
if prefix := p.attrPrefix[url]; prefix != "" {
return prefix
func (p *printer) createElementPrefix(url string) (string, bool) {
if url == "" {
return "", true
}
if prefix := p.elementPrefix[url]; prefix != "" {
return prefix, true
}

// The "http://www.w3.org/XML/1998/namespace" name space is predefined as "xml"
// and must be referred to that way.
// (The "http://www.w3.org/2000/xmlns/" name space is also predefined as "xmlns",
// but users should not be trying to use that one directly - that's our job.)
if url == xmlURL {
return xmlPrefix
return xmlPrefix, true
}

// Need to define a new name space.
if p.attrPrefix == nil {
p.attrPrefix = make(map[string]string)
p.attrNS = make(map[string]string)
}

// Pick a name. We try to use the final element of the path
// but fall back to _.
prefix := strings.TrimRight(url, "/")
if i := strings.LastIndex(prefix, "/"); i >= 0 {
prefix = prefix[i+1:]
}
if prefix == "" || !isName([]byte(prefix)) || strings.Contains(prefix, ":") {
prefix = "_"
}
// xmlanything is reserved and any variant of it regardless of
// case should be matched, so:
// (('X'|'x') ('M'|'m') ('L'|'l'))
// See Section 2.3 of https://www.w3.org/TR/REC-xml/
if len(prefix) >= 3 && strings.EqualFold(prefix[:3], "xml") {
prefix = "_" + prefix
}
if p.attrNS[prefix] != "" {
// Name is taken. Find a better one.
for p.seq++; ; p.seq++ {
if id := prefix + "_" + strconv.Itoa(p.seq); p.attrNS[id] == "" {
prefix = id
break
if p.elementPrefix == nil {
p.elementPrefix = make(map[string]string)
p.elementNS = make(map[string]string)
}

// Get the prefix from the nametable
prefix := p.nametable[url]
if prefix == "" {
// Pick a name. We try to use the final element of the path
// but fall back to _.
prefix = strings.TrimRight(url, "/")
if i := strings.LastIndex(prefix, "/"); i >= 0 {
prefix = prefix[i+1:]
}
if prefix == "" || !isName([]byte(prefix)) || strings.Contains(prefix, ":") {
prefix = "_"
}

// xmlanything is reserved and any variant of it regardless of
// case should be matched, so:
// (('X'|'x') ('M'|'m') ('L'|'l'))
// See Section 2.3 of https://www.w3.org/TR/REC-xml/
if len(prefix) >= 3 && strings.EqualFold(prefix[:3], "xml") {
prefix = "_" + prefix
}
if p.elementNS[prefix] != "" {
for p.seq++; ; p.seq++ {
if id := prefix + "_" + strconv.Itoa(p.seq); p.elementNS[id] == "" {
prefix = id
break
}
}
}
}

p.attrPrefix[url] = prefix
p.attrNS[prefix] = url

p.WriteString(`xmlns:`)
p.WriteString(prefix)
p.WriteString(`="`)
EscapeText(p, []byte(url))
p.WriteString(`" `)

p.elementPrefix[url] = prefix
p.elementNS[prefix] = url
p.prefixes = append(p.prefixes, prefix)

return prefix
return prefix, false
}

// deleteAttrPrefix removes an attribute name space prefix.
func (p *printer) deleteAttrPrefix(prefix string) {
delete(p.attrPrefix, p.attrNS[prefix])
delete(p.attrNS, prefix)
func (p *printer) deleteElementPrefix(prefix string) {
delete(p.elementPrefix, p.elementNS[prefix])
delete(p.elementNS, prefix)
}

// createAttrPrefix finds the name space prefix attribute to use for the given name space,
// defining a new prefix if necessary. It returns the prefix.
func (p *printer) createAttrPrefix(url string) string {
prefix, found := p.createElementPrefix(url)

if !found {
p.WriteString(`xmlns:`)
p.WriteString(prefix)
p.WriteString(`="`)
EscapeText(p, []byte(url))
p.WriteString(`" `)
}

return prefix
}

func (p *printer) markPrefix() {
Expand All @@ -412,7 +449,7 @@ func (p *printer) popPrefix() {
if prefix == "" {
break
}
p.deleteAttrPrefix(prefix)
p.deleteElementPrefix(prefix)
}
}

Expand Down Expand Up @@ -726,12 +763,24 @@ func (p *printer) writeStart(start *StartElement) error {
p.tags = append(p.tags, start.Name)
p.markPrefix()

prefix, prefixFound := p.createElementPrefix(start.Name.Space)

p.writeIndent(1)
p.WriteByte('<')
if prefix != "" {
p.WriteString(prefix)
p.WriteByte(':')
}
p.WriteString(start.Name.Local)

if start.Name.Space != "" {
p.WriteString(` xmlns="`)
if start.Name.Space != "" && !prefixFound {
p.WriteString(" xmlns")
if prefix != "" {
p.WriteByte(':')
p.WriteString(prefix)
}
p.WriteByte('=')
p.WriteByte('"')
p.EscapeString(start.Name.Space)
p.WriteByte('"')
}
Expand Down Expand Up @@ -771,9 +820,18 @@ func (p *printer) writeEnd(name Name) error {
}
p.tags = p.tags[:len(p.tags)-1]

prefix := ""
if name.Space != "" {
prefix = p.elementPrefix[name.Space]
}

p.writeIndent(-1)
p.WriteByte('<')
p.WriteByte('/')
if prefix != "" {
p.WriteString(prefix)
p.WriteByte(':')
}
p.WriteString(name.Local)
p.WriteByte('>')
p.popPrefix()
Expand Down