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Source file src/encoding/xml/marshal.go

     1	// Copyright 2011 The Go Authors. All rights reserved.
     2	// Use of this source code is governed by a BSD-style
     3	// license that can be found in the LICENSE file.
     4	
     5	package xml
     6	
     7	import (
     8		"bufio"
     9		"bytes"
    10		"encoding"
    11		"fmt"
    12		"io"
    13		"reflect"
    14		"strconv"
    15		"strings"
    16	)
    17	
    18	const (
    19		// A generic XML header suitable for use with the output of Marshal.
    20		// This is not automatically added to any output of this package,
    21		// it is provided as a convenience.
    22		Header = `<?xml version="1.0" encoding="UTF-8"?>` + "\n"
    23	)
    24	
    25	// Marshal returns the XML encoding of v.
    26	//
    27	// Marshal handles an array or slice by marshalling each of the elements.
    28	// Marshal handles a pointer by marshalling the value it points at or, if the
    29	// pointer is nil, by writing nothing. Marshal handles an interface value by
    30	// marshalling the value it contains or, if the interface value is nil, by
    31	// writing nothing. Marshal handles all other data by writing one or more XML
    32	// elements containing the data.
    33	//
    34	// The name for the XML elements is taken from, in order of preference:
    35	//     - the tag on the XMLName field, if the data is a struct
    36	//     - the value of the XMLName field of type Name
    37	//     - the tag of the struct field used to obtain the data
    38	//     - the name of the struct field used to obtain the data
    39	//     - the name of the marshalled type
    40	//
    41	// The XML element for a struct contains marshalled elements for each of the
    42	// exported fields of the struct, with these exceptions:
    43	//     - the XMLName field, described above, is omitted.
    44	//     - a field with tag "-" is omitted.
    45	//     - a field with tag "name,attr" becomes an attribute with
    46	//       the given name in the XML element.
    47	//     - a field with tag ",attr" becomes an attribute with the
    48	//       field name in the XML element.
    49	//     - a field with tag ",chardata" is written as character data,
    50	//       not as an XML element.
    51	//     - a field with tag ",cdata" is written as character data
    52	//       wrapped in one or more <![CDATA[ ... ]]> tags, not as an XML element.
    53	//     - a field with tag ",innerxml" is written verbatim, not subject
    54	//       to the usual marshalling procedure.
    55	//     - a field with tag ",comment" is written as an XML comment, not
    56	//       subject to the usual marshalling procedure. It must not contain
    57	//       the "--" string within it.
    58	//     - a field with a tag including the "omitempty" option is omitted
    59	//       if the field value is empty. The empty values are false, 0, any
    60	//       nil pointer or interface value, and any array, slice, map, or
    61	//       string of length zero.
    62	//     - an anonymous struct field is handled as if the fields of its
    63	//       value were part of the outer struct.
    64	//
    65	// If a field uses a tag "a>b>c", then the element c will be nested inside
    66	// parent elements a and b. Fields that appear next to each other that name
    67	// the same parent will be enclosed in one XML element.
    68	//
    69	// See MarshalIndent for an example.
    70	//
    71	// Marshal will return an error if asked to marshal a channel, function, or map.
    72	func Marshal(v interface{}) ([]byte, error) {
    73		var b bytes.Buffer
    74		if err := NewEncoder(&b).Encode(v); err != nil {
    75			return nil, err
    76		}
    77		return b.Bytes(), nil
    78	}
    79	
    80	// Marshaler is the interface implemented by objects that can marshal
    81	// themselves into valid XML elements.
    82	//
    83	// MarshalXML encodes the receiver as zero or more XML elements.
    84	// By convention, arrays or slices are typically encoded as a sequence
    85	// of elements, one per entry.
    86	// Using start as the element tag is not required, but doing so
    87	// will enable Unmarshal to match the XML elements to the correct
    88	// struct field.
    89	// One common implementation strategy is to construct a separate
    90	// value with a layout corresponding to the desired XML and then
    91	// to encode it using e.EncodeElement.
    92	// Another common strategy is to use repeated calls to e.EncodeToken
    93	// to generate the XML output one token at a time.
    94	// The sequence of encoded tokens must make up zero or more valid
    95	// XML elements.
    96	type Marshaler interface {
    97		MarshalXML(e *Encoder, start StartElement) error
    98	}
    99	
   100	// MarshalerAttr is the interface implemented by objects that can marshal
   101	// themselves into valid XML attributes.
   102	//
   103	// MarshalXMLAttr returns an XML attribute with the encoded value of the receiver.
   104	// Using name as the attribute name is not required, but doing so
   105	// will enable Unmarshal to match the attribute to the correct
   106	// struct field.
   107	// If MarshalXMLAttr returns the zero attribute Attr{}, no attribute
   108	// will be generated in the output.
   109	// MarshalXMLAttr is used only for struct fields with the
   110	// "attr" option in the field tag.
   111	type MarshalerAttr interface {
   112		MarshalXMLAttr(name Name) (Attr, error)
   113	}
   114	
   115	// MarshalIndent works like Marshal, but each XML element begins on a new
   116	// indented line that starts with prefix and is followed by one or more
   117	// copies of indent according to the nesting depth.
   118	func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error) {
   119		var b bytes.Buffer
   120		enc := NewEncoder(&b)
   121		enc.Indent(prefix, indent)
   122		if err := enc.Encode(v); err != nil {
   123			return nil, err
   124		}
   125		return b.Bytes(), nil
   126	}
   127	
   128	// An Encoder writes XML data to an output stream.
   129	type Encoder struct {
   130		p printer
   131	}
   132	
   133	// NewEncoder returns a new encoder that writes to w.
   134	func NewEncoder(w io.Writer) *Encoder {
   135		e := &Encoder{printer{Writer: bufio.NewWriter(w)}}
   136		e.p.encoder = e
   137		return e
   138	}
   139	
   140	// Indent sets the encoder to generate XML in which each element
   141	// begins on a new indented line that starts with prefix and is followed by
   142	// one or more copies of indent according to the nesting depth.
   143	func (enc *Encoder) Indent(prefix, indent string) {
   144		enc.p.prefix = prefix
   145		enc.p.indent = indent
   146	}
   147	
   148	// Encode writes the XML encoding of v to the stream.
   149	//
   150	// See the documentation for Marshal for details about the conversion
   151	// of Go values to XML.
   152	//
   153	// Encode calls Flush before returning.
   154	func (enc *Encoder) Encode(v interface{}) error {
   155		err := enc.p.marshalValue(reflect.ValueOf(v), nil, nil)
   156		if err != nil {
   157			return err
   158		}
   159		return enc.p.Flush()
   160	}
   161	
   162	// EncodeElement writes the XML encoding of v to the stream,
   163	// using start as the outermost tag in the encoding.
   164	//
   165	// See the documentation for Marshal for details about the conversion
   166	// of Go values to XML.
   167	//
   168	// EncodeElement calls Flush before returning.
   169	func (enc *Encoder) EncodeElement(v interface{}, start StartElement) error {
   170		err := enc.p.marshalValue(reflect.ValueOf(v), nil, &start)
   171		if err != nil {
   172			return err
   173		}
   174		return enc.p.Flush()
   175	}
   176	
   177	var (
   178		begComment  = []byte("<!--")
   179		endComment  = []byte("-->")
   180		endProcInst = []byte("?>")
   181	)
   182	
   183	// EncodeToken writes the given XML token to the stream.
   184	// It returns an error if StartElement and EndElement tokens are not properly matched.
   185	//
   186	// EncodeToken does not call Flush, because usually it is part of a larger operation
   187	// such as Encode or EncodeElement (or a custom Marshaler's MarshalXML invoked
   188	// during those), and those will call Flush when finished.
   189	// Callers that create an Encoder and then invoke EncodeToken directly, without
   190	// using Encode or EncodeElement, need to call Flush when finished to ensure
   191	// that the XML is written to the underlying writer.
   192	//
   193	// EncodeToken allows writing a ProcInst with Target set to "xml" only as the first token
   194	// in the stream.
   195	func (enc *Encoder) EncodeToken(t Token) error {
   196	
   197		p := &enc.p
   198		switch t := t.(type) {
   199		case StartElement:
   200			if err := p.writeStart(&t); err != nil {
   201				return err
   202			}
   203		case EndElement:
   204			if err := p.writeEnd(t.Name); err != nil {
   205				return err
   206			}
   207		case CharData:
   208			escapeText(p, t, false)
   209		case Comment:
   210			if bytes.Contains(t, endComment) {
   211				return fmt.Errorf("xml: EncodeToken of Comment containing --> marker")
   212			}
   213			p.WriteString("<!--")
   214			p.Write(t)
   215			p.WriteString("-->")
   216			return p.cachedWriteError()
   217		case ProcInst:
   218			// First token to be encoded which is also a ProcInst with target of xml
   219			// is the xml declaration. The only ProcInst where target of xml is allowed.
   220			if t.Target == "xml" && p.Buffered() != 0 {
   221				return fmt.Errorf("xml: EncodeToken of ProcInst xml target only valid for xml declaration, first token encoded")
   222			}
   223			if !isNameString(t.Target) {
   224				return fmt.Errorf("xml: EncodeToken of ProcInst with invalid Target")
   225			}
   226			if bytes.Contains(t.Inst, endProcInst) {
   227				return fmt.Errorf("xml: EncodeToken of ProcInst containing ?> marker")
   228			}
   229			p.WriteString("<?")
   230			p.WriteString(t.Target)
   231			if len(t.Inst) > 0 {
   232				p.WriteByte(' ')
   233				p.Write(t.Inst)
   234			}
   235			p.WriteString("?>")
   236		case Directive:
   237			if !isValidDirective(t) {
   238				return fmt.Errorf("xml: EncodeToken of Directive containing wrong < or > markers")
   239			}
   240			p.WriteString("<!")
   241			p.Write(t)
   242			p.WriteString(">")
   243		default:
   244			return fmt.Errorf("xml: EncodeToken of invalid token type")
   245	
   246		}
   247		return p.cachedWriteError()
   248	}
   249	
   250	// isValidDirective reports whether dir is a valid directive text,
   251	// meaning angle brackets are matched, ignoring comments and strings.
   252	func isValidDirective(dir Directive) bool {
   253		var (
   254			depth     int
   255			inquote   uint8
   256			incomment bool
   257		)
   258		for i, c := range dir {
   259			switch {
   260			case incomment:
   261				if c == '>' {
   262					if n := 1 + i - len(endComment); n >= 0 && bytes.Equal(dir[n:i+1], endComment) {
   263						incomment = false
   264					}
   265				}
   266				// Just ignore anything in comment
   267			case inquote != 0:
   268				if c == inquote {
   269					inquote = 0
   270				}
   271				// Just ignore anything within quotes
   272			case c == '\'' || c == '"':
   273				inquote = c
   274			case c == '<':
   275				if i+len(begComment) < len(dir) && bytes.Equal(dir[i:i+len(begComment)], begComment) {
   276					incomment = true
   277				} else {
   278					depth++
   279				}
   280			case c == '>':
   281				if depth == 0 {
   282					return false
   283				}
   284				depth--
   285			}
   286		}
   287		return depth == 0 && inquote == 0 && !incomment
   288	}
   289	
   290	// Flush flushes any buffered XML to the underlying writer.
   291	// See the EncodeToken documentation for details about when it is necessary.
   292	func (enc *Encoder) Flush() error {
   293		return enc.p.Flush()
   294	}
   295	
   296	type printer struct {
   297		*bufio.Writer
   298		encoder    *Encoder
   299		seq        int
   300		indent     string
   301		prefix     string
   302		depth      int
   303		indentedIn bool
   304		putNewline bool
   305		attrNS     map[string]string // map prefix -> name space
   306		attrPrefix map[string]string // map name space -> prefix
   307		prefixes   []string
   308		tags       []Name
   309	}
   310	
   311	// createAttrPrefix finds the name space prefix attribute to use for the given name space,
   312	// defining a new prefix if necessary. It returns the prefix.
   313	func (p *printer) createAttrPrefix(url string) string {
   314		if prefix := p.attrPrefix[url]; prefix != "" {
   315			return prefix
   316		}
   317	
   318		// The "http://www.w3.org/XML/1998/namespace" name space is predefined as "xml"
   319		// and must be referred to that way.
   320		// (The "http://www.w3.org/2000/xmlns/" name space is also predefined as "xmlns",
   321		// but users should not be trying to use that one directly - that's our job.)
   322		if url == xmlURL {
   323			return "xml"
   324		}
   325	
   326		// Need to define a new name space.
   327		if p.attrPrefix == nil {
   328			p.attrPrefix = make(map[string]string)
   329			p.attrNS = make(map[string]string)
   330		}
   331	
   332		// Pick a name. We try to use the final element of the path
   333		// but fall back to _.
   334		prefix := strings.TrimRight(url, "/")
   335		if i := strings.LastIndex(prefix, "/"); i >= 0 {
   336			prefix = prefix[i+1:]
   337		}
   338		if prefix == "" || !isName([]byte(prefix)) || strings.Contains(prefix, ":") {
   339			prefix = "_"
   340		}
   341		if strings.HasPrefix(prefix, "xml") {
   342			// xmlanything is reserved.
   343			prefix = "_" + prefix
   344		}
   345		if p.attrNS[prefix] != "" {
   346			// Name is taken. Find a better one.
   347			for p.seq++; ; p.seq++ {
   348				if id := prefix + "_" + strconv.Itoa(p.seq); p.attrNS[id] == "" {
   349					prefix = id
   350					break
   351				}
   352			}
   353		}
   354	
   355		p.attrPrefix[url] = prefix
   356		p.attrNS[prefix] = url
   357	
   358		p.WriteString(`xmlns:`)
   359		p.WriteString(prefix)
   360		p.WriteString(`="`)
   361		EscapeText(p, []byte(url))
   362		p.WriteString(`" `)
   363	
   364		p.prefixes = append(p.prefixes, prefix)
   365	
   366		return prefix
   367	}
   368	
   369	// deleteAttrPrefix removes an attribute name space prefix.
   370	func (p *printer) deleteAttrPrefix(prefix string) {
   371		delete(p.attrPrefix, p.attrNS[prefix])
   372		delete(p.attrNS, prefix)
   373	}
   374	
   375	func (p *printer) markPrefix() {
   376		p.prefixes = append(p.prefixes, "")
   377	}
   378	
   379	func (p *printer) popPrefix() {
   380		for len(p.prefixes) > 0 {
   381			prefix := p.prefixes[len(p.prefixes)-1]
   382			p.prefixes = p.prefixes[:len(p.prefixes)-1]
   383			if prefix == "" {
   384				break
   385			}
   386			p.deleteAttrPrefix(prefix)
   387		}
   388	}
   389	
   390	var (
   391		marshalerType     = reflect.TypeOf((*Marshaler)(nil)).Elem()
   392		marshalerAttrType = reflect.TypeOf((*MarshalerAttr)(nil)).Elem()
   393		textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
   394	)
   395	
   396	// marshalValue writes one or more XML elements representing val.
   397	// If val was obtained from a struct field, finfo must have its details.
   398	func (p *printer) marshalValue(val reflect.Value, finfo *fieldInfo, startTemplate *StartElement) error {
   399		if startTemplate != nil && startTemplate.Name.Local == "" {
   400			return fmt.Errorf("xml: EncodeElement of StartElement with missing name")
   401		}
   402	
   403		if !val.IsValid() {
   404			return nil
   405		}
   406		if finfo != nil && finfo.flags&fOmitEmpty != 0 && isEmptyValue(val) {
   407			return nil
   408		}
   409	
   410		// Drill into interfaces and pointers.
   411		// This can turn into an infinite loop given a cyclic chain,
   412		// but it matches the Go 1 behavior.
   413		for val.Kind() == reflect.Interface || val.Kind() == reflect.Ptr {
   414			if val.IsNil() {
   415				return nil
   416			}
   417			val = val.Elem()
   418		}
   419	
   420		kind := val.Kind()
   421		typ := val.Type()
   422	
   423		// Check for marshaler.
   424		if val.CanInterface() && typ.Implements(marshalerType) {
   425			return p.marshalInterface(val.Interface().(Marshaler), defaultStart(typ, finfo, startTemplate))
   426		}
   427		if val.CanAddr() {
   428			pv := val.Addr()
   429			if pv.CanInterface() && pv.Type().Implements(marshalerType) {
   430				return p.marshalInterface(pv.Interface().(Marshaler), defaultStart(pv.Type(), finfo, startTemplate))
   431			}
   432		}
   433	
   434		// Check for text marshaler.
   435		if val.CanInterface() && typ.Implements(textMarshalerType) {
   436			return p.marshalTextInterface(val.Interface().(encoding.TextMarshaler), defaultStart(typ, finfo, startTemplate))
   437		}
   438		if val.CanAddr() {
   439			pv := val.Addr()
   440			if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   441				return p.marshalTextInterface(pv.Interface().(encoding.TextMarshaler), defaultStart(pv.Type(), finfo, startTemplate))
   442			}
   443		}
   444	
   445		// Slices and arrays iterate over the elements. They do not have an enclosing tag.
   446		if (kind == reflect.Slice || kind == reflect.Array) && typ.Elem().Kind() != reflect.Uint8 {
   447			for i, n := 0, val.Len(); i < n; i++ {
   448				if err := p.marshalValue(val.Index(i), finfo, startTemplate); err != nil {
   449					return err
   450				}
   451			}
   452			return nil
   453		}
   454	
   455		tinfo, err := getTypeInfo(typ)
   456		if err != nil {
   457			return err
   458		}
   459	
   460		// Create start element.
   461		// Precedence for the XML element name is:
   462		// 0. startTemplate
   463		// 1. XMLName field in underlying struct;
   464		// 2. field name/tag in the struct field; and
   465		// 3. type name
   466		var start StartElement
   467	
   468		if startTemplate != nil {
   469			start.Name = startTemplate.Name
   470			start.Attr = append(start.Attr, startTemplate.Attr...)
   471		} else if tinfo.xmlname != nil {
   472			xmlname := tinfo.xmlname
   473			if xmlname.name != "" {
   474				start.Name.Space, start.Name.Local = xmlname.xmlns, xmlname.name
   475			} else if v, ok := xmlname.value(val).Interface().(Name); ok && v.Local != "" {
   476				start.Name = v
   477			}
   478		}
   479		if start.Name.Local == "" && finfo != nil {
   480			start.Name.Space, start.Name.Local = finfo.xmlns, finfo.name
   481		}
   482		if start.Name.Local == "" {
   483			name := typ.Name()
   484			if name == "" {
   485				return &UnsupportedTypeError{typ}
   486			}
   487			start.Name.Local = name
   488		}
   489	
   490		// Attributes
   491		for i := range tinfo.fields {
   492			finfo := &tinfo.fields[i]
   493			if finfo.flags&fAttr == 0 {
   494				continue
   495			}
   496			fv := finfo.value(val)
   497			name := Name{Space: finfo.xmlns, Local: finfo.name}
   498	
   499			if finfo.flags&fOmitEmpty != 0 && isEmptyValue(fv) {
   500				continue
   501			}
   502	
   503			if fv.Kind() == reflect.Interface && fv.IsNil() {
   504				continue
   505			}
   506	
   507			if fv.CanInterface() && fv.Type().Implements(marshalerAttrType) {
   508				attr, err := fv.Interface().(MarshalerAttr).MarshalXMLAttr(name)
   509				if err != nil {
   510					return err
   511				}
   512				if attr.Name.Local != "" {
   513					start.Attr = append(start.Attr, attr)
   514				}
   515				continue
   516			}
   517	
   518			if fv.CanAddr() {
   519				pv := fv.Addr()
   520				if pv.CanInterface() && pv.Type().Implements(marshalerAttrType) {
   521					attr, err := pv.Interface().(MarshalerAttr).MarshalXMLAttr(name)
   522					if err != nil {
   523						return err
   524					}
   525					if attr.Name.Local != "" {
   526						start.Attr = append(start.Attr, attr)
   527					}
   528					continue
   529				}
   530			}
   531	
   532			if fv.CanInterface() && fv.Type().Implements(textMarshalerType) {
   533				text, err := fv.Interface().(encoding.TextMarshaler).MarshalText()
   534				if err != nil {
   535					return err
   536				}
   537				start.Attr = append(start.Attr, Attr{name, string(text)})
   538				continue
   539			}
   540	
   541			if fv.CanAddr() {
   542				pv := fv.Addr()
   543				if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   544					text, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
   545					if err != nil {
   546						return err
   547					}
   548					start.Attr = append(start.Attr, Attr{name, string(text)})
   549					continue
   550				}
   551			}
   552	
   553			// Dereference or skip nil pointer, interface values.
   554			switch fv.Kind() {
   555			case reflect.Ptr, reflect.Interface:
   556				if fv.IsNil() {
   557					continue
   558				}
   559				fv = fv.Elem()
   560			}
   561	
   562			s, b, err := p.marshalSimple(fv.Type(), fv)
   563			if err != nil {
   564				return err
   565			}
   566			if b != nil {
   567				s = string(b)
   568			}
   569			start.Attr = append(start.Attr, Attr{name, s})
   570		}
   571	
   572		if err := p.writeStart(&start); err != nil {
   573			return err
   574		}
   575	
   576		if val.Kind() == reflect.Struct {
   577			err = p.marshalStruct(tinfo, val)
   578		} else {
   579			s, b, err1 := p.marshalSimple(typ, val)
   580			if err1 != nil {
   581				err = err1
   582			} else if b != nil {
   583				EscapeText(p, b)
   584			} else {
   585				p.EscapeString(s)
   586			}
   587		}
   588		if err != nil {
   589			return err
   590		}
   591	
   592		if err := p.writeEnd(start.Name); err != nil {
   593			return err
   594		}
   595	
   596		return p.cachedWriteError()
   597	}
   598	
   599	// defaultStart returns the default start element to use,
   600	// given the reflect type, field info, and start template.
   601	func defaultStart(typ reflect.Type, finfo *fieldInfo, startTemplate *StartElement) StartElement {
   602		var start StartElement
   603		// Precedence for the XML element name is as above,
   604		// except that we do not look inside structs for the first field.
   605		if startTemplate != nil {
   606			start.Name = startTemplate.Name
   607			start.Attr = append(start.Attr, startTemplate.Attr...)
   608		} else if finfo != nil && finfo.name != "" {
   609			start.Name.Local = finfo.name
   610			start.Name.Space = finfo.xmlns
   611		} else if typ.Name() != "" {
   612			start.Name.Local = typ.Name()
   613		} else {
   614			// Must be a pointer to a named type,
   615			// since it has the Marshaler methods.
   616			start.Name.Local = typ.Elem().Name()
   617		}
   618		return start
   619	}
   620	
   621	// marshalInterface marshals a Marshaler interface value.
   622	func (p *printer) marshalInterface(val Marshaler, start StartElement) error {
   623		// Push a marker onto the tag stack so that MarshalXML
   624		// cannot close the XML tags that it did not open.
   625		p.tags = append(p.tags, Name{})
   626		n := len(p.tags)
   627	
   628		err := val.MarshalXML(p.encoder, start)
   629		if err != nil {
   630			return err
   631		}
   632	
   633		// Make sure MarshalXML closed all its tags. p.tags[n-1] is the mark.
   634		if len(p.tags) > n {
   635			return fmt.Errorf("xml: %s.MarshalXML wrote invalid XML: <%s> not closed", receiverType(val), p.tags[len(p.tags)-1].Local)
   636		}
   637		p.tags = p.tags[:n-1]
   638		return nil
   639	}
   640	
   641	// marshalTextInterface marshals a TextMarshaler interface value.
   642	func (p *printer) marshalTextInterface(val encoding.TextMarshaler, start StartElement) error {
   643		if err := p.writeStart(&start); err != nil {
   644			return err
   645		}
   646		text, err := val.MarshalText()
   647		if err != nil {
   648			return err
   649		}
   650		EscapeText(p, text)
   651		return p.writeEnd(start.Name)
   652	}
   653	
   654	// writeStart writes the given start element.
   655	func (p *printer) writeStart(start *StartElement) error {
   656		if start.Name.Local == "" {
   657			return fmt.Errorf("xml: start tag with no name")
   658		}
   659	
   660		p.tags = append(p.tags, start.Name)
   661		p.markPrefix()
   662	
   663		p.writeIndent(1)
   664		p.WriteByte('<')
   665		p.WriteString(start.Name.Local)
   666	
   667		if start.Name.Space != "" {
   668			p.WriteString(` xmlns="`)
   669			p.EscapeString(start.Name.Space)
   670			p.WriteByte('"')
   671		}
   672	
   673		// Attributes
   674		for _, attr := range start.Attr {
   675			name := attr.Name
   676			if name.Local == "" {
   677				continue
   678			}
   679			p.WriteByte(' ')
   680			if name.Space != "" {
   681				p.WriteString(p.createAttrPrefix(name.Space))
   682				p.WriteByte(':')
   683			}
   684			p.WriteString(name.Local)
   685			p.WriteString(`="`)
   686			p.EscapeString(attr.Value)
   687			p.WriteByte('"')
   688		}
   689		p.WriteByte('>')
   690		return nil
   691	}
   692	
   693	func (p *printer) writeEnd(name Name) error {
   694		if name.Local == "" {
   695			return fmt.Errorf("xml: end tag with no name")
   696		}
   697		if len(p.tags) == 0 || p.tags[len(p.tags)-1].Local == "" {
   698			return fmt.Errorf("xml: end tag </%s> without start tag", name.Local)
   699		}
   700		if top := p.tags[len(p.tags)-1]; top != name {
   701			if top.Local != name.Local {
   702				return fmt.Errorf("xml: end tag </%s> does not match start tag <%s>", name.Local, top.Local)
   703			}
   704			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)
   705		}
   706		p.tags = p.tags[:len(p.tags)-1]
   707	
   708		p.writeIndent(-1)
   709		p.WriteByte('<')
   710		p.WriteByte('/')
   711		p.WriteString(name.Local)
   712		p.WriteByte('>')
   713		p.popPrefix()
   714		return nil
   715	}
   716	
   717	func (p *printer) marshalSimple(typ reflect.Type, val reflect.Value) (string, []byte, error) {
   718		switch val.Kind() {
   719		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   720			return strconv.FormatInt(val.Int(), 10), nil, nil
   721		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   722			return strconv.FormatUint(val.Uint(), 10), nil, nil
   723		case reflect.Float32, reflect.Float64:
   724			return strconv.FormatFloat(val.Float(), 'g', -1, val.Type().Bits()), nil, nil
   725		case reflect.String:
   726			return val.String(), nil, nil
   727		case reflect.Bool:
   728			return strconv.FormatBool(val.Bool()), nil, nil
   729		case reflect.Array:
   730			if typ.Elem().Kind() != reflect.Uint8 {
   731				break
   732			}
   733			// [...]byte
   734			var bytes []byte
   735			if val.CanAddr() {
   736				bytes = val.Slice(0, val.Len()).Bytes()
   737			} else {
   738				bytes = make([]byte, val.Len())
   739				reflect.Copy(reflect.ValueOf(bytes), val)
   740			}
   741			return "", bytes, nil
   742		case reflect.Slice:
   743			if typ.Elem().Kind() != reflect.Uint8 {
   744				break
   745			}
   746			// []byte
   747			return "", val.Bytes(), nil
   748		}
   749		return "", nil, &UnsupportedTypeError{typ}
   750	}
   751	
   752	var ddBytes = []byte("--")
   753	
   754	func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
   755		s := parentStack{p: p}
   756		for i := range tinfo.fields {
   757			finfo := &tinfo.fields[i]
   758			if finfo.flags&fAttr != 0 {
   759				continue
   760			}
   761			vf := finfo.value(val)
   762	
   763			// Dereference or skip nil pointer, interface values.
   764			switch vf.Kind() {
   765			case reflect.Ptr, reflect.Interface:
   766				if !vf.IsNil() {
   767					vf = vf.Elem()
   768				}
   769			}
   770	
   771			switch finfo.flags & fMode {
   772			case fCDATA, fCharData:
   773				emit := EscapeText
   774				if finfo.flags&fMode == fCDATA {
   775					emit = emitCDATA
   776				}
   777				if err := s.trim(finfo.parents); err != nil {
   778					return err
   779				}
   780				if vf.CanInterface() && vf.Type().Implements(textMarshalerType) {
   781					data, err := vf.Interface().(encoding.TextMarshaler).MarshalText()
   782					if err != nil {
   783						return err
   784					}
   785					if err := emit(p, data); err != nil {
   786						return err
   787					}
   788					continue
   789				}
   790				if vf.CanAddr() {
   791					pv := vf.Addr()
   792					if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   793						data, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
   794						if err != nil {
   795							return err
   796						}
   797						if err := emit(p, data); err != nil {
   798							return err
   799						}
   800						continue
   801					}
   802				}
   803				var scratch [64]byte
   804				switch vf.Kind() {
   805				case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   806					if err := emit(p, strconv.AppendInt(scratch[:0], vf.Int(), 10)); err != nil {
   807						return err
   808					}
   809				case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   810					if err := emit(p, strconv.AppendUint(scratch[:0], vf.Uint(), 10)); err != nil {
   811						return err
   812					}
   813				case reflect.Float32, reflect.Float64:
   814					if err := emit(p, strconv.AppendFloat(scratch[:0], vf.Float(), 'g', -1, vf.Type().Bits())); err != nil {
   815						return err
   816					}
   817				case reflect.Bool:
   818					if err := emit(p, strconv.AppendBool(scratch[:0], vf.Bool())); err != nil {
   819						return err
   820					}
   821				case reflect.String:
   822					if err := emit(p, []byte(vf.String())); err != nil {
   823						return err
   824					}
   825				case reflect.Slice:
   826					if elem, ok := vf.Interface().([]byte); ok {
   827						if err := emit(p, elem); err != nil {
   828							return err
   829						}
   830					}
   831				}
   832				continue
   833	
   834			case fComment:
   835				if err := s.trim(finfo.parents); err != nil {
   836					return err
   837				}
   838				k := vf.Kind()
   839				if !(k == reflect.String || k == reflect.Slice && vf.Type().Elem().Kind() == reflect.Uint8) {
   840					return fmt.Errorf("xml: bad type for comment field of %s", val.Type())
   841				}
   842				if vf.Len() == 0 {
   843					continue
   844				}
   845				p.writeIndent(0)
   846				p.WriteString("<!--")
   847				dashDash := false
   848				dashLast := false
   849				switch k {
   850				case reflect.String:
   851					s := vf.String()
   852					dashDash = strings.Contains(s, "--")
   853					dashLast = s[len(s)-1] == '-'
   854					if !dashDash {
   855						p.WriteString(s)
   856					}
   857				case reflect.Slice:
   858					b := vf.Bytes()
   859					dashDash = bytes.Contains(b, ddBytes)
   860					dashLast = b[len(b)-1] == '-'
   861					if !dashDash {
   862						p.Write(b)
   863					}
   864				default:
   865					panic("can't happen")
   866				}
   867				if dashDash {
   868					return fmt.Errorf(`xml: comments must not contain "--"`)
   869				}
   870				if dashLast {
   871					// "--->" is invalid grammar. Make it "- -->"
   872					p.WriteByte(' ')
   873				}
   874				p.WriteString("-->")
   875				continue
   876	
   877			case fInnerXml:
   878				iface := vf.Interface()
   879				switch raw := iface.(type) {
   880				case []byte:
   881					p.Write(raw)
   882					continue
   883				case string:
   884					p.WriteString(raw)
   885					continue
   886				}
   887	
   888			case fElement, fElement | fAny:
   889				if err := s.trim(finfo.parents); err != nil {
   890					return err
   891				}
   892				if len(finfo.parents) > len(s.stack) {
   893					if vf.Kind() != reflect.Ptr && vf.Kind() != reflect.Interface || !vf.IsNil() {
   894						if err := s.push(finfo.parents[len(s.stack):]); err != nil {
   895							return err
   896						}
   897					}
   898				}
   899			}
   900			if err := p.marshalValue(vf, finfo, nil); err != nil {
   901				return err
   902			}
   903		}
   904		s.trim(nil)
   905		return p.cachedWriteError()
   906	}
   907	
   908	// return the bufio Writer's cached write error
   909	func (p *printer) cachedWriteError() error {
   910		_, err := p.Write(nil)
   911		return err
   912	}
   913	
   914	func (p *printer) writeIndent(depthDelta int) {
   915		if len(p.prefix) == 0 && len(p.indent) == 0 {
   916			return
   917		}
   918		if depthDelta < 0 {
   919			p.depth--
   920			if p.indentedIn {
   921				p.indentedIn = false
   922				return
   923			}
   924			p.indentedIn = false
   925		}
   926		if p.putNewline {
   927			p.WriteByte('\n')
   928		} else {
   929			p.putNewline = true
   930		}
   931		if len(p.prefix) > 0 {
   932			p.WriteString(p.prefix)
   933		}
   934		if len(p.indent) > 0 {
   935			for i := 0; i < p.depth; i++ {
   936				p.WriteString(p.indent)
   937			}
   938		}
   939		if depthDelta > 0 {
   940			p.depth++
   941			p.indentedIn = true
   942		}
   943	}
   944	
   945	type parentStack struct {
   946		p     *printer
   947		stack []string
   948	}
   949	
   950	// trim updates the XML context to match the longest common prefix of the stack
   951	// and the given parents. A closing tag will be written for every parent
   952	// popped. Passing a zero slice or nil will close all the elements.
   953	func (s *parentStack) trim(parents []string) error {
   954		split := 0
   955		for ; split < len(parents) && split < len(s.stack); split++ {
   956			if parents[split] != s.stack[split] {
   957				break
   958			}
   959		}
   960		for i := len(s.stack) - 1; i >= split; i-- {
   961			if err := s.p.writeEnd(Name{Local: s.stack[i]}); err != nil {
   962				return err
   963			}
   964		}
   965		s.stack = s.stack[:split]
   966		return nil
   967	}
   968	
   969	// push adds parent elements to the stack and writes open tags.
   970	func (s *parentStack) push(parents []string) error {
   971		for i := 0; i < len(parents); i++ {
   972			if err := s.p.writeStart(&StartElement{Name: Name{Local: parents[i]}}); err != nil {
   973				return err
   974			}
   975		}
   976		s.stack = append(s.stack, parents...)
   977		return nil
   978	}
   979	
   980	// A MarshalXMLError is returned when Marshal encounters a type
   981	// that cannot be converted into XML.
   982	type UnsupportedTypeError struct {
   983		Type reflect.Type
   984	}
   985	
   986	func (e *UnsupportedTypeError) Error() string {
   987		return "xml: unsupported type: " + e.Type.String()
   988	}
   989	
   990	func isEmptyValue(v reflect.Value) bool {
   991		switch v.Kind() {
   992		case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
   993			return v.Len() == 0
   994		case reflect.Bool:
   995			return !v.Bool()
   996		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   997			return v.Int() == 0
   998		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   999			return v.Uint() == 0
  1000		case reflect.Float32, reflect.Float64:
  1001			return v.Float() == 0
  1002		case reflect.Interface, reflect.Ptr:
  1003			return v.IsNil()
  1004		}
  1005		return false
  1006	}
  1007	

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