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Source file src/encoding/xml/marshal.go

  // Copyright 2011 The Go Authors. All rights reserved.
  // Use of this source code is governed by a BSD-style
  // license that can be found in the LICENSE file.
  
  package xml
  
  import (
  	"bufio"
  	"bytes"
  	"encoding"
  	"fmt"
  	"io"
  	"reflect"
  	"strconv"
  	"strings"
  )
  
  const (
  	// A generic XML header suitable for use with the output of Marshal.
  	// This is not automatically added to any output of this package,
  	// it is provided as a convenience.
  	Header = `<?xml version="1.0" encoding="UTF-8"?>` + "\n"
  )
  
  // Marshal returns the XML encoding of v.
  //
  // Marshal handles an array or slice by marshaling each of the elements.
  // Marshal handles a pointer by marshaling the value it points at or, if the
  // pointer is nil, by writing nothing. Marshal handles an interface value by
  // marshaling the value it contains or, if the interface value is nil, by
  // writing nothing. Marshal handles all other data by writing one or more XML
  // elements containing the data.
  //
  // The name for the XML elements is taken from, in order of preference:
  //     - the tag on the XMLName field, if the data is a struct
  //     - the value of the XMLName field of type Name
  //     - the tag of the struct field used to obtain the data
  //     - the name of the struct field used to obtain the data
  //     - the name of the marshaled type
  //
  // The XML element for a struct contains marshaled elements for each of the
  // exported fields of the struct, with these exceptions:
  //     - the XMLName field, described above, is omitted.
  //     - a field with tag "-" is omitted.
  //     - a field with tag "name,attr" becomes an attribute with
  //       the given name in the XML element.
  //     - a field with tag ",attr" becomes an attribute with the
  //       field name in the XML element.
  //     - a field with tag ",chardata" is written as character data,
  //       not as an XML element.
  //     - a field with tag ",cdata" is written as character data
  //       wrapped in one or more <![CDATA[ ... ]]> tags, not as an XML element.
  //     - a field with tag ",innerxml" is written verbatim, not subject
  //       to the usual marshaling procedure.
  //     - a field with tag ",comment" is written as an XML comment, not
  //       subject to the usual marshaling procedure. It must not contain
  //       the "--" string within it.
  //     - a field with a tag including the "omitempty" option is omitted
  //       if the field value is empty. The empty values are false, 0, any
  //       nil pointer or interface value, and any array, slice, map, or
  //       string of length zero.
  //     - an anonymous struct field is handled as if the fields of its
  //       value were part of the outer struct.
  //
  // If a field uses a tag "a>b>c", then the element c will be nested inside
  // parent elements a and b. Fields that appear next to each other that name
  // the same parent will be enclosed in one XML element.
  //
  // See MarshalIndent for an example.
  //
  // Marshal will return an error if asked to marshal a channel, function, or map.
  func Marshal(v interface{}) ([]byte, error) {
  	var b bytes.Buffer
  	if err := NewEncoder(&b).Encode(v); err != nil {
  		return nil, err
  	}
  	return b.Bytes(), nil
  }
  
  // Marshaler is the interface implemented by objects that can marshal
  // themselves into valid XML elements.
  //
  // MarshalXML encodes the receiver as zero or more XML elements.
  // By convention, arrays or slices are typically encoded as a sequence
  // of elements, one per entry.
  // Using start as the element tag is not required, but doing so
  // will enable Unmarshal to match the XML elements to the correct
  // struct field.
  // One common implementation strategy is to construct a separate
  // value with a layout corresponding to the desired XML and then
  // to encode it using e.EncodeElement.
  // Another common strategy is to use repeated calls to e.EncodeToken
  // to generate the XML output one token at a time.
  // The sequence of encoded tokens must make up zero or more valid
  // XML elements.
  type Marshaler interface {
  	MarshalXML(e *Encoder, start StartElement) error
  }
  
  // MarshalerAttr is the interface implemented by objects that can marshal
  // themselves into valid XML attributes.
  //
  // MarshalXMLAttr returns an XML attribute with the encoded value of the receiver.
  // Using name as the attribute name is not required, but doing so
  // will enable Unmarshal to match the attribute to the correct
  // struct field.
  // If MarshalXMLAttr returns the zero attribute Attr{}, no attribute
  // will be generated in the output.
  // MarshalXMLAttr is used only for struct fields with the
  // "attr" option in the field tag.
  type MarshalerAttr interface {
  	MarshalXMLAttr(name Name) (Attr, error)
  }
  
  // MarshalIndent works like Marshal, but each XML element begins on a new
  // indented line that starts with prefix and is followed by one or more
  // copies of indent according to the nesting depth.
  func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error) {
  	var b bytes.Buffer
  	enc := NewEncoder(&b)
  	enc.Indent(prefix, indent)
  	if err := enc.Encode(v); err != nil {
  		return nil, err
  	}
  	return b.Bytes(), nil
  }
  
  // An Encoder writes XML data to an output stream.
  type Encoder struct {
  	p printer
  }
  
  // NewEncoder returns a new encoder that writes to w.
  func NewEncoder(w io.Writer) *Encoder {
  	e := &Encoder{printer{Writer: bufio.NewWriter(w)}}
  	e.p.encoder = e
  	return e
  }
  
  // Indent sets the encoder to generate XML in which each element
  // begins on a new indented line that starts with prefix and is followed by
  // one or more copies of indent according to the nesting depth.
  func (enc *Encoder) Indent(prefix, indent string) {
  	enc.p.prefix = prefix
  	enc.p.indent = indent
  }
  
  // Encode writes the XML encoding of v to the stream.
  //
  // See the documentation for Marshal for details about the conversion
  // of Go values to XML.
  //
  // Encode calls Flush before returning.
  func (enc *Encoder) Encode(v interface{}) error {
  	err := enc.p.marshalValue(reflect.ValueOf(v), nil, nil)
  	if err != nil {
  		return err
  	}
  	return enc.p.Flush()
  }
  
  // EncodeElement writes the XML encoding of v to the stream,
  // using start as the outermost tag in the encoding.
  //
  // See the documentation for Marshal for details about the conversion
  // of Go values to XML.
  //
  // EncodeElement calls Flush before returning.
  func (enc *Encoder) EncodeElement(v interface{}, start StartElement) error {
  	err := enc.p.marshalValue(reflect.ValueOf(v), nil, &start)
  	if err != nil {
  		return err
  	}
  	return enc.p.Flush()
  }
  
  var (
  	begComment  = []byte("<!--")
  	endComment  = []byte("-->")
  	endProcInst = []byte("?>")
  )
  
  // EncodeToken writes the given XML token to the stream.
  // It returns an error if StartElement and EndElement tokens are not properly matched.
  //
  // EncodeToken does not call Flush, because usually it is part of a larger operation
  // such as Encode or EncodeElement (or a custom Marshaler's MarshalXML invoked
  // during those), and those will call Flush when finished.
  // Callers that create an Encoder and then invoke EncodeToken directly, without
  // using Encode or EncodeElement, need to call Flush when finished to ensure
  // that the XML is written to the underlying writer.
  //
  // EncodeToken allows writing a ProcInst with Target set to "xml" only as the first token
  // in the stream.
  func (enc *Encoder) EncodeToken(t Token) error {
  
  	p := &enc.p
  	switch t := t.(type) {
  	case StartElement:
  		if err := p.writeStart(&t); err != nil {
  			return err
  		}
  	case EndElement:
  		if err := p.writeEnd(t.Name); err != nil {
  			return err
  		}
  	case CharData:
  		escapeText(p, t, false)
  	case Comment:
  		if bytes.Contains(t, endComment) {
  			return fmt.Errorf("xml: EncodeToken of Comment containing --> marker")
  		}
  		p.WriteString("<!--")
  		p.Write(t)
  		p.WriteString("-->")
  		return p.cachedWriteError()
  	case ProcInst:
  		// First token to be encoded which is also a ProcInst with target of xml
  		// is the xml declaration. The only ProcInst where target of xml is allowed.
  		if t.Target == "xml" && p.Buffered() != 0 {
  			return fmt.Errorf("xml: EncodeToken of ProcInst xml target only valid for xml declaration, first token encoded")
  		}
  		if !isNameString(t.Target) {
  			return fmt.Errorf("xml: EncodeToken of ProcInst with invalid Target")
  		}
  		if bytes.Contains(t.Inst, endProcInst) {
  			return fmt.Errorf("xml: EncodeToken of ProcInst containing ?> marker")
  		}
  		p.WriteString("<?")
  		p.WriteString(t.Target)
  		if len(t.Inst) > 0 {
  			p.WriteByte(' ')
  			p.Write(t.Inst)
  		}
  		p.WriteString("?>")
  	case Directive:
  		if !isValidDirective(t) {
  			return fmt.Errorf("xml: EncodeToken of Directive containing wrong < or > markers")
  		}
  		p.WriteString("<!")
  		p.Write(t)
  		p.WriteString(">")
  	default:
  		return fmt.Errorf("xml: EncodeToken of invalid token type")
  
  	}
  	return p.cachedWriteError()
  }
  
  // isValidDirective reports whether dir is a valid directive text,
  // meaning angle brackets are matched, ignoring comments and strings.
  func isValidDirective(dir Directive) bool {
  	var (
  		depth     int
  		inquote   uint8
  		incomment bool
  	)
  	for i, c := range dir {
  		switch {
  		case incomment:
  			if c == '>' {
  				if n := 1 + i - len(endComment); n >= 0 && bytes.Equal(dir[n:i+1], endComment) {
  					incomment = false
  				}
  			}
  			// Just ignore anything in comment
  		case inquote != 0:
  			if c == inquote {
  				inquote = 0
  			}
  			// Just ignore anything within quotes
  		case c == '\'' || c == '"':
  			inquote = c
  		case c == '<':
  			if i+len(begComment) < len(dir) && bytes.Equal(dir[i:i+len(begComment)], begComment) {
  				incomment = true
  			} else {
  				depth++
  			}
  		case c == '>':
  			if depth == 0 {
  				return false
  			}
  			depth--
  		}
  	}
  	return depth == 0 && inquote == 0 && !incomment
  }
  
  // Flush flushes any buffered XML to the underlying writer.
  // See the EncodeToken documentation for details about when it is necessary.
  func (enc *Encoder) Flush() error {
  	return enc.p.Flush()
  }
  
  type printer struct {
  	*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
  }
  
  // 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
  	}
  
  	// 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 "xml"
  	}
  
  	// 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 = "_"
  	}
  	if strings.HasPrefix(prefix, "xml") {
  		// xmlanything is reserved.
  		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
  			}
  		}
  	}
  
  	p.attrPrefix[url] = prefix
  	p.attrNS[prefix] = url
  
  	p.WriteString(`xmlns:`)
  	p.WriteString(prefix)
  	p.WriteString(`="`)
  	EscapeText(p, []byte(url))
  	p.WriteString(`" `)
  
  	p.prefixes = append(p.prefixes, prefix)
  
  	return prefix
  }
  
  // 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) markPrefix() {
  	p.prefixes = append(p.prefixes, "")
  }
  
  func (p *printer) popPrefix() {
  	for len(p.prefixes) > 0 {
  		prefix := p.prefixes[len(p.prefixes)-1]
  		p.prefixes = p.prefixes[:len(p.prefixes)-1]
  		if prefix == "" {
  			break
  		}
  		p.deleteAttrPrefix(prefix)
  	}
  }
  
  var (
  	marshalerType     = reflect.TypeOf((*Marshaler)(nil)).Elem()
  	marshalerAttrType = reflect.TypeOf((*MarshalerAttr)(nil)).Elem()
  	textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
  )
  
  // marshalValue writes one or more XML elements representing val.
  // If val was obtained from a struct field, finfo must have its details.
  func (p *printer) marshalValue(val reflect.Value, finfo *fieldInfo, startTemplate *StartElement) error {
  	if startTemplate != nil && startTemplate.Name.Local == "" {
  		return fmt.Errorf("xml: EncodeElement of StartElement with missing name")
  	}
  
  	if !val.IsValid() {
  		return nil
  	}
  	if finfo != nil && finfo.flags&fOmitEmpty != 0 && isEmptyValue(val) {
  		return nil
  	}
  
  	// Drill into interfaces and pointers.
  	// This can turn into an infinite loop given a cyclic chain,
  	// but it matches the Go 1 behavior.
  	for val.Kind() == reflect.Interface || val.Kind() == reflect.Ptr {
  		if val.IsNil() {
  			return nil
  		}
  		val = val.Elem()
  	}
  
  	kind := val.Kind()
  	typ := val.Type()
  
  	// Check for marshaler.
  	if val.CanInterface() && typ.Implements(marshalerType) {
  		return p.marshalInterface(val.Interface().(Marshaler), defaultStart(typ, finfo, startTemplate))
  	}
  	if val.CanAddr() {
  		pv := val.Addr()
  		if pv.CanInterface() && pv.Type().Implements(marshalerType) {
  			return p.marshalInterface(pv.Interface().(Marshaler), defaultStart(pv.Type(), finfo, startTemplate))
  		}
  	}
  
  	// Check for text marshaler.
  	if val.CanInterface() && typ.Implements(textMarshalerType) {
  		return p.marshalTextInterface(val.Interface().(encoding.TextMarshaler), defaultStart(typ, finfo, startTemplate))
  	}
  	if val.CanAddr() {
  		pv := val.Addr()
  		if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
  			return p.marshalTextInterface(pv.Interface().(encoding.TextMarshaler), defaultStart(pv.Type(), finfo, startTemplate))
  		}
  	}
  
  	// Slices and arrays iterate over the elements. They do not have an enclosing tag.
  	if (kind == reflect.Slice || kind == reflect.Array) && typ.Elem().Kind() != reflect.Uint8 {
  		for i, n := 0, val.Len(); i < n; i++ {
  			if err := p.marshalValue(val.Index(i), finfo, startTemplate); err != nil {
  				return err
  			}
  		}
  		return nil
  	}
  
  	tinfo, err := getTypeInfo(typ)
  	if err != nil {
  		return err
  	}
  
  	// Create start element.
  	// Precedence for the XML element name is:
  	// 0. startTemplate
  	// 1. XMLName field in underlying struct;
  	// 2. field name/tag in the struct field; and
  	// 3. type name
  	var start StartElement
  
  	if startTemplate != nil {
  		start.Name = startTemplate.Name
  		start.Attr = append(start.Attr, startTemplate.Attr...)
  	} else if tinfo.xmlname != nil {
  		xmlname := tinfo.xmlname
  		if xmlname.name != "" {
  			start.Name.Space, start.Name.Local = xmlname.xmlns, xmlname.name
  		} else if v, ok := xmlname.value(val).Interface().(Name); ok && v.Local != "" {
  			start.Name = v
  		}
  	}
  	if start.Name.Local == "" && finfo != nil {
  		start.Name.Space, start.Name.Local = finfo.xmlns, finfo.name
  	}
  	if start.Name.Local == "" {
  		name := typ.Name()
  		if name == "" {
  			return &UnsupportedTypeError{typ}
  		}
  		start.Name.Local = name
  	}
  
  	// Attributes
  	for i := range tinfo.fields {
  		finfo := &tinfo.fields[i]
  		if finfo.flags&fAttr == 0 {
  			continue
  		}
  		fv := finfo.value(val)
  
  		if finfo.flags&fOmitEmpty != 0 && isEmptyValue(fv) {
  			continue
  		}
  
  		if fv.Kind() == reflect.Interface && fv.IsNil() {
  			continue
  		}
  
  		name := Name{Space: finfo.xmlns, Local: finfo.name}
  		if err := p.marshalAttr(&start, name, fv); err != nil {
  			return err
  		}
  	}
  
  	if err := p.writeStart(&start); err != nil {
  		return err
  	}
  
  	if val.Kind() == reflect.Struct {
  		err = p.marshalStruct(tinfo, val)
  	} else {
  		s, b, err1 := p.marshalSimple(typ, val)
  		if err1 != nil {
  			err = err1
  		} else if b != nil {
  			EscapeText(p, b)
  		} else {
  			p.EscapeString(s)
  		}
  	}
  	if err != nil {
  		return err
  	}
  
  	if err := p.writeEnd(start.Name); err != nil {
  		return err
  	}
  
  	return p.cachedWriteError()
  }
  
  // marshalAttr marshals an attribute with the given name and value, adding to start.Attr.
  func (p *printer) marshalAttr(start *StartElement, name Name, val reflect.Value) error {
  	if val.CanInterface() && val.Type().Implements(marshalerAttrType) {
  		attr, err := val.Interface().(MarshalerAttr).MarshalXMLAttr(name)
  		if err != nil {
  			return err
  		}
  		if attr.Name.Local != "" {
  			start.Attr = append(start.Attr, attr)
  		}
  		return nil
  	}
  
  	if val.CanAddr() {
  		pv := val.Addr()
  		if pv.CanInterface() && pv.Type().Implements(marshalerAttrType) {
  			attr, err := pv.Interface().(MarshalerAttr).MarshalXMLAttr(name)
  			if err != nil {
  				return err
  			}
  			if attr.Name.Local != "" {
  				start.Attr = append(start.Attr, attr)
  			}
  			return nil
  		}
  	}
  
  	if val.CanInterface() && val.Type().Implements(textMarshalerType) {
  		text, err := val.Interface().(encoding.TextMarshaler).MarshalText()
  		if err != nil {
  			return err
  		}
  		start.Attr = append(start.Attr, Attr{name, string(text)})
  		return nil
  	}
  
  	if val.CanAddr() {
  		pv := val.Addr()
  		if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
  			text, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
  			if err != nil {
  				return err
  			}
  			start.Attr = append(start.Attr, Attr{name, string(text)})
  			return nil
  		}
  	}
  
  	// Dereference or skip nil pointer, interface values.
  	switch val.Kind() {
  	case reflect.Ptr, reflect.Interface:
  		if val.IsNil() {
  			return nil
  		}
  		val = val.Elem()
  	}
  
  	// Walk slices.
  	if val.Kind() == reflect.Slice && val.Type().Elem().Kind() != reflect.Uint8 {
  		n := val.Len()
  		for i := 0; i < n; i++ {
  			if err := p.marshalAttr(start, name, val.Index(i)); err != nil {
  				return err
  			}
  		}
  		return nil
  	}
  
  	if val.Type() == attrType {
  		start.Attr = append(start.Attr, val.Interface().(Attr))
  		return nil
  	}
  
  	s, b, err := p.marshalSimple(val.Type(), val)
  	if err != nil {
  		return err
  	}
  	if b != nil {
  		s = string(b)
  	}
  	start.Attr = append(start.Attr, Attr{name, s})
  	return nil
  }
  
  // defaultStart returns the default start element to use,
  // given the reflect type, field info, and start template.
  func defaultStart(typ reflect.Type, finfo *fieldInfo, startTemplate *StartElement) StartElement {
  	var start StartElement
  	// Precedence for the XML element name is as above,
  	// except that we do not look inside structs for the first field.
  	if startTemplate != nil {
  		start.Name = startTemplate.Name
  		start.Attr = append(start.Attr, startTemplate.Attr...)
  	} else if finfo != nil && finfo.name != "" {
  		start.Name.Local = finfo.name
  		start.Name.Space = finfo.xmlns
  	} else if typ.Name() != "" {
  		start.Name.Local = typ.Name()
  	} else {
  		// Must be a pointer to a named type,
  		// since it has the Marshaler methods.
  		start.Name.Local = typ.Elem().Name()
  	}
  	return start
  }
  
  // marshalInterface marshals a Marshaler interface value.
  func (p *printer) marshalInterface(val Marshaler, start StartElement) error {
  	// Push a marker onto the tag stack so that MarshalXML
  	// cannot close the XML tags that it did not open.
  	p.tags = append(p.tags, Name{})
  	n := len(p.tags)
  
  	err := val.MarshalXML(p.encoder, start)
  	if err != nil {
  		return err
  	}
  
  	// Make sure MarshalXML closed all its tags. p.tags[n-1] is the mark.
  	if len(p.tags) > n {
  		return fmt.Errorf("xml: %s.MarshalXML wrote invalid XML: <%s> not closed", receiverType(val), p.tags[len(p.tags)-1].Local)
  	}
  	p.tags = p.tags[:n-1]
  	return nil
  }
  
  // marshalTextInterface marshals a TextMarshaler interface value.
  func (p *printer) marshalTextInterface(val encoding.TextMarshaler, start StartElement) error {
  	if err := p.writeStart(&start); err != nil {
  		return err
  	}
  	text, err := val.MarshalText()
  	if err != nil {
  		return err
  	}
  	EscapeText(p, text)
  	return p.writeEnd(start.Name)
  }
  
  // writeStart writes the given start element.
  func (p *printer) writeStart(start *StartElement) error {
  	if start.Name.Local == "" {
  		return fmt.Errorf("xml: start tag with no name")
  	}
  
  	p.tags = append(p.tags, start.Name)
  	p.markPrefix()
  
  	p.writeIndent(1)
  	p.WriteByte('<')
  	p.WriteString(start.Name.Local)
  
  	if start.Name.Space != "" {
  		p.WriteString(` xmlns="`)
  		p.EscapeString(start.Name.Space)
  		p.WriteByte('"')
  	}
  
  	// Attributes
  	for _, attr := range start.Attr {
  		name := attr.Name
  		if name.Local == "" {
  			continue
  		}
  		p.WriteByte(' ')
  		if name.Space != "" {
  			p.WriteString(p.createAttrPrefix(name.Space))
  			p.WriteByte(':')
  		}
  		p.WriteString(name.Local)
  		p.WriteString(`="`)
  		p.EscapeString(attr.Value)
  		p.WriteByte('"')
  	}
  	p.WriteByte('>')
  	return nil
  }
  
  func (p *printer) writeEnd(name Name) error {
  	if name.Local == "" {
  		return fmt.Errorf("xml: end tag with no name")
  	}
  	if len(p.tags) == 0 || p.tags[len(p.tags)-1].Local == "" {
  		return fmt.Errorf("xml: end tag </%s> without start tag", name.Local)
  	}
  	if top := p.tags[len(p.tags)-1]; top != name {
  		if top.Local != name.Local {
  			return fmt.Errorf("xml: end tag </%s> does not match start tag <%s>", name.Local, top.Local)
  		}
  		return fmt.Errorf("xml: end tag </%s> in namespace %s does not match start tag <%s> in namespace %s", name.Local, name.Space, top.Local, top.Space)
  	}
  	p.tags = p.tags[:len(p.tags)-1]
  
  	p.writeIndent(-1)
  	p.WriteByte('<')
  	p.WriteByte('/')
  	p.WriteString(name.Local)
  	p.WriteByte('>')
  	p.popPrefix()
  	return nil
  }
  
  func (p *printer) marshalSimple(typ reflect.Type, val reflect.Value) (string, []byte, error) {
  	switch val.Kind() {
  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
  		return strconv.FormatInt(val.Int(), 10), nil, nil
  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
  		return strconv.FormatUint(val.Uint(), 10), nil, nil
  	case reflect.Float32, reflect.Float64:
  		return strconv.FormatFloat(val.Float(), 'g', -1, val.Type().Bits()), nil, nil
  	case reflect.String:
  		return val.String(), nil, nil
  	case reflect.Bool:
  		return strconv.FormatBool(val.Bool()), nil, nil
  	case reflect.Array:
  		if typ.Elem().Kind() != reflect.Uint8 {
  			break
  		}
  		// [...]byte
  		var bytes []byte
  		if val.CanAddr() {
  			bytes = val.Slice(0, val.Len()).Bytes()
  		} else {
  			bytes = make([]byte, val.Len())
  			reflect.Copy(reflect.ValueOf(bytes), val)
  		}
  		return "", bytes, nil
  	case reflect.Slice:
  		if typ.Elem().Kind() != reflect.Uint8 {
  			break
  		}
  		// []byte
  		return "", val.Bytes(), nil
  	}
  	return "", nil, &UnsupportedTypeError{typ}
  }
  
  var ddBytes = []byte("--")
  
  // indirect drills into interfaces and pointers, returning the pointed-at value.
  // If it encounters a nil interface or pointer, indirect returns that nil value.
  // This can turn into an infinite loop given a cyclic chain,
  // but it matches the Go 1 behavior.
  func indirect(vf reflect.Value) reflect.Value {
  	for vf.Kind() == reflect.Interface || vf.Kind() == reflect.Ptr {
  		if vf.IsNil() {
  			return vf
  		}
  		vf = vf.Elem()
  	}
  	return vf
  }
  
  func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
  	s := parentStack{p: p}
  	for i := range tinfo.fields {
  		finfo := &tinfo.fields[i]
  		if finfo.flags&fAttr != 0 {
  			continue
  		}
  		vf := finfo.value(val)
  
  		switch finfo.flags & fMode {
  		case fCDATA, fCharData:
  			emit := EscapeText
  			if finfo.flags&fMode == fCDATA {
  				emit = emitCDATA
  			}
  			if err := s.trim(finfo.parents); err != nil {
  				return err
  			}
  			if vf.CanInterface() && vf.Type().Implements(textMarshalerType) {
  				data, err := vf.Interface().(encoding.TextMarshaler).MarshalText()
  				if err != nil {
  					return err
  				}
  				if err := emit(p, data); err != nil {
  					return err
  				}
  				continue
  			}
  			if vf.CanAddr() {
  				pv := vf.Addr()
  				if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
  					data, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
  					if err != nil {
  						return err
  					}
  					if err := emit(p, data); err != nil {
  						return err
  					}
  					continue
  				}
  			}
  
  			var scratch [64]byte
  			vf = indirect(vf)
  			switch vf.Kind() {
  			case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
  				if err := emit(p, strconv.AppendInt(scratch[:0], vf.Int(), 10)); err != nil {
  					return err
  				}
  			case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
  				if err := emit(p, strconv.AppendUint(scratch[:0], vf.Uint(), 10)); err != nil {
  					return err
  				}
  			case reflect.Float32, reflect.Float64:
  				if err := emit(p, strconv.AppendFloat(scratch[:0], vf.Float(), 'g', -1, vf.Type().Bits())); err != nil {
  					return err
  				}
  			case reflect.Bool:
  				if err := emit(p, strconv.AppendBool(scratch[:0], vf.Bool())); err != nil {
  					return err
  				}
  			case reflect.String:
  				if err := emit(p, []byte(vf.String())); err != nil {
  					return err
  				}
  			case reflect.Slice:
  				if elem, ok := vf.Interface().([]byte); ok {
  					if err := emit(p, elem); err != nil {
  						return err
  					}
  				}
  			}
  			continue
  
  		case fComment:
  			if err := s.trim(finfo.parents); err != nil {
  				return err
  			}
  			vf = indirect(vf)
  			k := vf.Kind()
  			if !(k == reflect.String || k == reflect.Slice && vf.Type().Elem().Kind() == reflect.Uint8) {
  				return fmt.Errorf("xml: bad type for comment field of %s", val.Type())
  			}
  			if vf.Len() == 0 {
  				continue
  			}
  			p.writeIndent(0)
  			p.WriteString("<!--")
  			dashDash := false
  			dashLast := false
  			switch k {
  			case reflect.String:
  				s := vf.String()
  				dashDash = strings.Contains(s, "--")
  				dashLast = s[len(s)-1] == '-'
  				if !dashDash {
  					p.WriteString(s)
  				}
  			case reflect.Slice:
  				b := vf.Bytes()
  				dashDash = bytes.Contains(b, ddBytes)
  				dashLast = b[len(b)-1] == '-'
  				if !dashDash {
  					p.Write(b)
  				}
  			default:
  				panic("can't happen")
  			}
  			if dashDash {
  				return fmt.Errorf(`xml: comments must not contain "--"`)
  			}
  			if dashLast {
  				// "--->" is invalid grammar. Make it "- -->"
  				p.WriteByte(' ')
  			}
  			p.WriteString("-->")
  			continue
  
  		case fInnerXml:
  			vf = indirect(vf)
  			iface := vf.Interface()
  			switch raw := iface.(type) {
  			case []byte:
  				p.Write(raw)
  				continue
  			case string:
  				p.WriteString(raw)
  				continue
  			}
  
  		case fElement, fElement | fAny:
  			if err := s.trim(finfo.parents); err != nil {
  				return err
  			}
  			if len(finfo.parents) > len(s.stack) {
  				if vf.Kind() != reflect.Ptr && vf.Kind() != reflect.Interface || !vf.IsNil() {
  					if err := s.push(finfo.parents[len(s.stack):]); err != nil {
  						return err
  					}
  				}
  			}
  		}
  		if err := p.marshalValue(vf, finfo, nil); err != nil {
  			return err
  		}
  	}
  	s.trim(nil)
  	return p.cachedWriteError()
  }
  
  // return the bufio Writer's cached write error
  func (p *printer) cachedWriteError() error {
  	_, err := p.Write(nil)
  	return err
  }
  
  func (p *printer) writeIndent(depthDelta int) {
  	if len(p.prefix) == 0 && len(p.indent) == 0 {
  		return
  	}
  	if depthDelta < 0 {
  		p.depth--
  		if p.indentedIn {
  			p.indentedIn = false
  			return
  		}
  		p.indentedIn = false
  	}
  	if p.putNewline {
  		p.WriteByte('\n')
  	} else {
  		p.putNewline = true
  	}
  	if len(p.prefix) > 0 {
  		p.WriteString(p.prefix)
  	}
  	if len(p.indent) > 0 {
  		for i := 0; i < p.depth; i++ {
  			p.WriteString(p.indent)
  		}
  	}
  	if depthDelta > 0 {
  		p.depth++
  		p.indentedIn = true
  	}
  }
  
  type parentStack struct {
  	p     *printer
  	stack []string
  }
  
  // trim updates the XML context to match the longest common prefix of the stack
  // and the given parents. A closing tag will be written for every parent
  // popped. Passing a zero slice or nil will close all the elements.
  func (s *parentStack) trim(parents []string) error {
  	split := 0
  	for ; split < len(parents) && split < len(s.stack); split++ {
  		if parents[split] != s.stack[split] {
  			break
  		}
  	}
  	for i := len(s.stack) - 1; i >= split; i-- {
  		if err := s.p.writeEnd(Name{Local: s.stack[i]}); err != nil {
  			return err
  		}
  	}
  	s.stack = s.stack[:split]
  	return nil
  }
  
  // push adds parent elements to the stack and writes open tags.
  func (s *parentStack) push(parents []string) error {
  	for i := 0; i < len(parents); i++ {
  		if err := s.p.writeStart(&StartElement{Name: Name{Local: parents[i]}}); err != nil {
  			return err
  		}
  	}
  	s.stack = append(s.stack, parents...)
  	return nil
  }
  
  // A MarshalXMLError is returned when Marshal encounters a type
  // that cannot be converted into XML.
  type UnsupportedTypeError struct {
  	Type reflect.Type
  }
  
  func (e *UnsupportedTypeError) Error() string {
  	return "xml: unsupported type: " + e.Type.String()
  }
  
  func isEmptyValue(v reflect.Value) bool {
  	switch v.Kind() {
  	case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
  		return v.Len() == 0
  	case reflect.Bool:
  		return !v.Bool()
  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
  		return v.Int() == 0
  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
  		return v.Uint() == 0
  	case reflect.Float32, reflect.Float64:
  		return v.Float() == 0
  	case reflect.Interface, reflect.Ptr:
  		return v.IsNil()
  	}
  	return false
  }
  

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