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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 xml.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		endDirective = []byte(">")
   182	)
   183	
   184	// EncodeToken writes the given XML token to the stream.
   185	// It returns an error if StartElement and EndElement tokens are not properly matched.
   186	//
   187	// EncodeToken does not call Flush, because usually it is part of a larger operation
   188	// such as Encode or EncodeElement (or a custom Marshaler's MarshalXML invoked
   189	// during those), and those will call Flush when finished.
   190	// Callers that create an Encoder and then invoke EncodeToken directly, without
   191	// using Encode or EncodeElement, need to call Flush when finished to ensure
   192	// that the XML is written to the underlying writer.
   193	//
   194	// EncodeToken allows writing a ProcInst with Target set to "xml" only as the first token
   195	// in the stream.
   196	func (enc *Encoder) EncodeToken(t Token) error {
   197	
   198		p := &enc.p
   199		switch t := t.(type) {
   200		case StartElement:
   201			if err := p.writeStart(&t); err != nil {
   202				return err
   203			}
   204		case EndElement:
   205			if err := p.writeEnd(t.Name); err != nil {
   206				return err
   207			}
   208		case CharData:
   209			escapeText(p, t, false)
   210		case Comment:
   211			if bytes.Contains(t, endComment) {
   212				return fmt.Errorf("xml: EncodeToken of Comment containing --> marker")
   213			}
   214			p.WriteString("<!--")
   215			p.Write(t)
   216			p.WriteString("-->")
   217			return p.cachedWriteError()
   218		case ProcInst:
   219			// First token to be encoded which is also a ProcInst with target of xml
   220			// is the xml declaration.  The only ProcInst where target of xml is allowed.
   221			if t.Target == "xml" && p.Buffered() != 0 {
   222				return fmt.Errorf("xml: EncodeToken of ProcInst xml target only valid for xml declaration, first token encoded")
   223			}
   224			if !isNameString(t.Target) {
   225				return fmt.Errorf("xml: EncodeToken of ProcInst with invalid Target")
   226			}
   227			if bytes.Contains(t.Inst, endProcInst) {
   228				return fmt.Errorf("xml: EncodeToken of ProcInst containing ?> marker")
   229			}
   230			p.WriteString("<?")
   231			p.WriteString(t.Target)
   232			if len(t.Inst) > 0 {
   233				p.WriteByte(' ')
   234				p.Write(t.Inst)
   235			}
   236			p.WriteString("?>")
   237		case Directive:
   238			if !isValidDirective(t) {
   239				return fmt.Errorf("xml: EncodeToken of Directive containing wrong < or > markers")
   240			}
   241			p.WriteString("<!")
   242			p.Write(t)
   243			p.WriteString(">")
   244		default:
   245			return fmt.Errorf("xml: EncodeToken of invalid token type")
   246	
   247		}
   248		return p.cachedWriteError()
   249	}
   250	
   251	// isValidDirective reports whether dir is a valid directive text,
   252	// meaning angle brackets are matched, ignoring comments and strings.
   253	func isValidDirective(dir Directive) bool {
   254		var (
   255			depth     int
   256			inquote   uint8
   257			incomment bool
   258		)
   259		for i, c := range dir {
   260			switch {
   261			case incomment:
   262				if c == '>' {
   263					if n := 1 + i - len(endComment); n >= 0 && bytes.Equal(dir[n:i+1], endComment) {
   264						incomment = false
   265					}
   266				}
   267				// Just ignore anything in comment
   268			case inquote != 0:
   269				if c == inquote {
   270					inquote = 0
   271				}
   272				// Just ignore anything within quotes
   273			case c == '\'' || c == '"':
   274				inquote = c
   275			case c == '<':
   276				if i+len(begComment) < len(dir) && bytes.Equal(dir[i:i+len(begComment)], begComment) {
   277					incomment = true
   278				} else {
   279					depth++
   280				}
   281			case c == '>':
   282				if depth == 0 {
   283					return false
   284				}
   285				depth--
   286			}
   287		}
   288		return depth == 0 && inquote == 0 && !incomment
   289	}
   290	
   291	// Flush flushes any buffered XML to the underlying writer.
   292	// See the EncodeToken documentation for details about when it is necessary.
   293	func (enc *Encoder) Flush() error {
   294		return enc.p.Flush()
   295	}
   296	
   297	type printer struct {
   298		*bufio.Writer
   299		encoder    *Encoder
   300		seq        int
   301		indent     string
   302		prefix     string
   303		depth      int
   304		indentedIn bool
   305		putNewline bool
   306		attrNS     map[string]string // map prefix -> name space
   307		attrPrefix map[string]string // map name space -> prefix
   308		prefixes   []string
   309		tags       []Name
   310	}
   311	
   312	// createAttrPrefix finds the name space prefix attribute to use for the given name space,
   313	// defining a new prefix if necessary. It returns the prefix.
   314	func (p *printer) createAttrPrefix(url string) string {
   315		if prefix := p.attrPrefix[url]; prefix != "" {
   316			return prefix
   317		}
   318	
   319		// The "http://www.w3.org/XML/1998/namespace" name space is predefined as "xml"
   320		// and must be referred to that way.
   321		// (The "http://www.w3.org/2000/xmlns/" name space is also predefined as "xmlns",
   322		// but users should not be trying to use that one directly - that's our job.)
   323		if url == xmlURL {
   324			return "xml"
   325		}
   326	
   327		// Need to define a new name space.
   328		if p.attrPrefix == nil {
   329			p.attrPrefix = make(map[string]string)
   330			p.attrNS = make(map[string]string)
   331		}
   332	
   333		// Pick a name. We try to use the final element of the path
   334		// but fall back to _.
   335		prefix := strings.TrimRight(url, "/")
   336		if i := strings.LastIndex(prefix, "/"); i >= 0 {
   337			prefix = prefix[i+1:]
   338		}
   339		if prefix == "" || !isName([]byte(prefix)) || strings.Contains(prefix, ":") {
   340			prefix = "_"
   341		}
   342		if strings.HasPrefix(prefix, "xml") {
   343			// xmlanything is reserved.
   344			prefix = "_" + prefix
   345		}
   346		if p.attrNS[prefix] != "" {
   347			// Name is taken. Find a better one.
   348			for p.seq++; ; p.seq++ {
   349				if id := prefix + "_" + strconv.Itoa(p.seq); p.attrNS[id] == "" {
   350					prefix = id
   351					break
   352				}
   353			}
   354		}
   355	
   356		p.attrPrefix[url] = prefix
   357		p.attrNS[prefix] = url
   358	
   359		p.WriteString(`xmlns:`)
   360		p.WriteString(prefix)
   361		p.WriteString(`="`)
   362		EscapeText(p, []byte(url))
   363		p.WriteString(`" `)
   364	
   365		p.prefixes = append(p.prefixes, prefix)
   366	
   367		return prefix
   368	}
   369	
   370	// deleteAttrPrefix removes an attribute name space prefix.
   371	func (p *printer) deleteAttrPrefix(prefix string) {
   372		delete(p.attrPrefix, p.attrNS[prefix])
   373		delete(p.attrNS, prefix)
   374	}
   375	
   376	func (p *printer) markPrefix() {
   377		p.prefixes = append(p.prefixes, "")
   378	}
   379	
   380	func (p *printer) popPrefix() {
   381		for len(p.prefixes) > 0 {
   382			prefix := p.prefixes[len(p.prefixes)-1]
   383			p.prefixes = p.prefixes[:len(p.prefixes)-1]
   384			if prefix == "" {
   385				break
   386			}
   387			p.deleteAttrPrefix(prefix)
   388		}
   389	}
   390	
   391	var (
   392		marshalerType     = reflect.TypeOf((*Marshaler)(nil)).Elem()
   393		marshalerAttrType = reflect.TypeOf((*MarshalerAttr)(nil)).Elem()
   394		textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
   395	)
   396	
   397	// marshalValue writes one or more XML elements representing val.
   398	// If val was obtained from a struct field, finfo must have its details.
   399	func (p *printer) marshalValue(val reflect.Value, finfo *fieldInfo, startTemplate *StartElement) error {
   400		if startTemplate != nil && startTemplate.Name.Local == "" {
   401			return fmt.Errorf("xml: EncodeElement of StartElement with missing name")
   402		}
   403	
   404		if !val.IsValid() {
   405			return nil
   406		}
   407		if finfo != nil && finfo.flags&fOmitEmpty != 0 && isEmptyValue(val) {
   408			return nil
   409		}
   410	
   411		// Drill into interfaces and pointers.
   412		// This can turn into an infinite loop given a cyclic chain,
   413		// but it matches the Go 1 behavior.
   414		for val.Kind() == reflect.Interface || val.Kind() == reflect.Ptr {
   415			if val.IsNil() {
   416				return nil
   417			}
   418			val = val.Elem()
   419		}
   420	
   421		kind := val.Kind()
   422		typ := val.Type()
   423	
   424		// Check for marshaler.
   425		if val.CanInterface() && typ.Implements(marshalerType) {
   426			return p.marshalInterface(val.Interface().(Marshaler), defaultStart(typ, finfo, startTemplate))
   427		}
   428		if val.CanAddr() {
   429			pv := val.Addr()
   430			if pv.CanInterface() && pv.Type().Implements(marshalerType) {
   431				return p.marshalInterface(pv.Interface().(Marshaler), defaultStart(pv.Type(), finfo, startTemplate))
   432			}
   433		}
   434	
   435		// Check for text marshaler.
   436		if val.CanInterface() && typ.Implements(textMarshalerType) {
   437			return p.marshalTextInterface(val.Interface().(encoding.TextMarshaler), defaultStart(typ, finfo, startTemplate))
   438		}
   439		if val.CanAddr() {
   440			pv := val.Addr()
   441			if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   442				return p.marshalTextInterface(pv.Interface().(encoding.TextMarshaler), defaultStart(pv.Type(), finfo, startTemplate))
   443			}
   444		}
   445	
   446		// Slices and arrays iterate over the elements. They do not have an enclosing tag.
   447		if (kind == reflect.Slice || kind == reflect.Array) && typ.Elem().Kind() != reflect.Uint8 {
   448			for i, n := 0, val.Len(); i < n; i++ {
   449				if err := p.marshalValue(val.Index(i), finfo, startTemplate); err != nil {
   450					return err
   451				}
   452			}
   453			return nil
   454		}
   455	
   456		tinfo, err := getTypeInfo(typ)
   457		if err != nil {
   458			return err
   459		}
   460	
   461		// Create start element.
   462		// Precedence for the XML element name is:
   463		// 0. startTemplate
   464		// 1. XMLName field in underlying struct;
   465		// 2. field name/tag in the struct field; and
   466		// 3. type name
   467		var start StartElement
   468	
   469		if startTemplate != nil {
   470			start.Name = startTemplate.Name
   471			start.Attr = append(start.Attr, startTemplate.Attr...)
   472		} else if tinfo.xmlname != nil {
   473			xmlname := tinfo.xmlname
   474			if xmlname.name != "" {
   475				start.Name.Space, start.Name.Local = xmlname.xmlns, xmlname.name
   476			} else if v, ok := xmlname.value(val).Interface().(Name); ok && v.Local != "" {
   477				start.Name = v
   478			}
   479		}
   480		if start.Name.Local == "" && finfo != nil {
   481			start.Name.Space, start.Name.Local = finfo.xmlns, finfo.name
   482		}
   483		if start.Name.Local == "" {
   484			name := typ.Name()
   485			if name == "" {
   486				return &UnsupportedTypeError{typ}
   487			}
   488			start.Name.Local = name
   489		}
   490	
   491		// Attributes
   492		for i := range tinfo.fields {
   493			finfo := &tinfo.fields[i]
   494			if finfo.flags&fAttr == 0 {
   495				continue
   496			}
   497			fv := finfo.value(val)
   498			name := Name{Space: finfo.xmlns, Local: finfo.name}
   499	
   500			if finfo.flags&fOmitEmpty != 0 && isEmptyValue(fv) {
   501				continue
   502			}
   503	
   504			if fv.Kind() == reflect.Interface && fv.IsNil() {
   505				continue
   506			}
   507	
   508			if fv.CanInterface() && fv.Type().Implements(marshalerAttrType) {
   509				attr, err := fv.Interface().(MarshalerAttr).MarshalXMLAttr(name)
   510				if err != nil {
   511					return err
   512				}
   513				if attr.Name.Local != "" {
   514					start.Attr = append(start.Attr, attr)
   515				}
   516				continue
   517			}
   518	
   519			if fv.CanAddr() {
   520				pv := fv.Addr()
   521				if pv.CanInterface() && pv.Type().Implements(marshalerAttrType) {
   522					attr, err := pv.Interface().(MarshalerAttr).MarshalXMLAttr(name)
   523					if err != nil {
   524						return err
   525					}
   526					if attr.Name.Local != "" {
   527						start.Attr = append(start.Attr, attr)
   528					}
   529					continue
   530				}
   531			}
   532	
   533			if fv.CanInterface() && fv.Type().Implements(textMarshalerType) {
   534				text, err := fv.Interface().(encoding.TextMarshaler).MarshalText()
   535				if err != nil {
   536					return err
   537				}
   538				start.Attr = append(start.Attr, Attr{name, string(text)})
   539				continue
   540			}
   541	
   542			if fv.CanAddr() {
   543				pv := fv.Addr()
   544				if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   545					text, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
   546					if err != nil {
   547						return err
   548					}
   549					start.Attr = append(start.Attr, Attr{name, string(text)})
   550					continue
   551				}
   552			}
   553	
   554			// Dereference or skip nil pointer, interface values.
   555			switch fv.Kind() {
   556			case reflect.Ptr, reflect.Interface:
   557				if fv.IsNil() {
   558					continue
   559				}
   560				fv = fv.Elem()
   561			}
   562	
   563			s, b, err := p.marshalSimple(fv.Type(), fv)
   564			if err != nil {
   565				return err
   566			}
   567			if b != nil {
   568				s = string(b)
   569			}
   570			start.Attr = append(start.Attr, Attr{name, s})
   571		}
   572	
   573		if err := p.writeStart(&start); err != nil {
   574			return err
   575		}
   576	
   577		if val.Kind() == reflect.Struct {
   578			err = p.marshalStruct(tinfo, val)
   579		} else {
   580			s, b, err1 := p.marshalSimple(typ, val)
   581			if err1 != nil {
   582				err = err1
   583			} else if b != nil {
   584				EscapeText(p, b)
   585			} else {
   586				p.EscapeString(s)
   587			}
   588		}
   589		if err != nil {
   590			return err
   591		}
   592	
   593		if err := p.writeEnd(start.Name); err != nil {
   594			return err
   595		}
   596	
   597		return p.cachedWriteError()
   598	}
   599	
   600	// defaultStart returns the default start element to use,
   601	// given the reflect type, field info, and start template.
   602	func defaultStart(typ reflect.Type, finfo *fieldInfo, startTemplate *StartElement) StartElement {
   603		var start StartElement
   604		// Precedence for the XML element name is as above,
   605		// except that we do not look inside structs for the first field.
   606		if startTemplate != nil {
   607			start.Name = startTemplate.Name
   608			start.Attr = append(start.Attr, startTemplate.Attr...)
   609		} else if finfo != nil && finfo.name != "" {
   610			start.Name.Local = finfo.name
   611			start.Name.Space = finfo.xmlns
   612		} else if typ.Name() != "" {
   613			start.Name.Local = typ.Name()
   614		} else {
   615			// Must be a pointer to a named type,
   616			// since it has the Marshaler methods.
   617			start.Name.Local = typ.Elem().Name()
   618		}
   619		return start
   620	}
   621	
   622	// marshalInterface marshals a Marshaler interface value.
   623	func (p *printer) marshalInterface(val Marshaler, start StartElement) error {
   624		// Push a marker onto the tag stack so that MarshalXML
   625		// cannot close the XML tags that it did not open.
   626		p.tags = append(p.tags, Name{})
   627		n := len(p.tags)
   628	
   629		err := val.MarshalXML(p.encoder, start)
   630		if err != nil {
   631			return err
   632		}
   633	
   634		// Make sure MarshalXML closed all its tags. p.tags[n-1] is the mark.
   635		if len(p.tags) > n {
   636			return fmt.Errorf("xml: %s.MarshalXML wrote invalid XML: <%s> not closed", receiverType(val), p.tags[len(p.tags)-1].Local)
   637		}
   638		p.tags = p.tags[:n-1]
   639		return nil
   640	}
   641	
   642	// marshalTextInterface marshals a TextMarshaler interface value.
   643	func (p *printer) marshalTextInterface(val encoding.TextMarshaler, start StartElement) error {
   644		if err := p.writeStart(&start); err != nil {
   645			return err
   646		}
   647		text, err := val.MarshalText()
   648		if err != nil {
   649			return err
   650		}
   651		EscapeText(p, text)
   652		return p.writeEnd(start.Name)
   653	}
   654	
   655	// writeStart writes the given start element.
   656	func (p *printer) writeStart(start *StartElement) error {
   657		if start.Name.Local == "" {
   658			return fmt.Errorf("xml: start tag with no name")
   659		}
   660	
   661		p.tags = append(p.tags, start.Name)
   662		p.markPrefix()
   663	
   664		p.writeIndent(1)
   665		p.WriteByte('<')
   666		p.WriteString(start.Name.Local)
   667	
   668		if start.Name.Space != "" {
   669			p.WriteString(` xmlns="`)
   670			p.EscapeString(start.Name.Space)
   671			p.WriteByte('"')
   672		}
   673	
   674		// Attributes
   675		for _, attr := range start.Attr {
   676			name := attr.Name
   677			if name.Local == "" {
   678				continue
   679			}
   680			p.WriteByte(' ')
   681			if name.Space != "" {
   682				p.WriteString(p.createAttrPrefix(name.Space))
   683				p.WriteByte(':')
   684			}
   685			p.WriteString(name.Local)
   686			p.WriteString(`="`)
   687			p.EscapeString(attr.Value)
   688			p.WriteByte('"')
   689		}
   690		p.WriteByte('>')
   691		return nil
   692	}
   693	
   694	func (p *printer) writeEnd(name Name) error {
   695		if name.Local == "" {
   696			return fmt.Errorf("xml: end tag with no name")
   697		}
   698		if len(p.tags) == 0 || p.tags[len(p.tags)-1].Local == "" {
   699			return fmt.Errorf("xml: end tag </%s> without start tag", name.Local)
   700		}
   701		if top := p.tags[len(p.tags)-1]; top != name {
   702			if top.Local != name.Local {
   703				return fmt.Errorf("xml: end tag </%s> does not match start tag <%s>", name.Local, top.Local)
   704			}
   705			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)
   706		}
   707		p.tags = p.tags[:len(p.tags)-1]
   708	
   709		p.writeIndent(-1)
   710		p.WriteByte('<')
   711		p.WriteByte('/')
   712		p.WriteString(name.Local)
   713		p.WriteByte('>')
   714		p.popPrefix()
   715		return nil
   716	}
   717	
   718	func (p *printer) marshalSimple(typ reflect.Type, val reflect.Value) (string, []byte, error) {
   719		switch val.Kind() {
   720		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   721			return strconv.FormatInt(val.Int(), 10), nil, nil
   722		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   723			return strconv.FormatUint(val.Uint(), 10), nil, nil
   724		case reflect.Float32, reflect.Float64:
   725			return strconv.FormatFloat(val.Float(), 'g', -1, val.Type().Bits()), nil, nil
   726		case reflect.String:
   727			return val.String(), nil, nil
   728		case reflect.Bool:
   729			return strconv.FormatBool(val.Bool()), nil, nil
   730		case reflect.Array:
   731			if typ.Elem().Kind() != reflect.Uint8 {
   732				break
   733			}
   734			// [...]byte
   735			var bytes []byte
   736			if val.CanAddr() {
   737				bytes = val.Slice(0, val.Len()).Bytes()
   738			} else {
   739				bytes = make([]byte, val.Len())
   740				reflect.Copy(reflect.ValueOf(bytes), val)
   741			}
   742			return "", bytes, nil
   743		case reflect.Slice:
   744			if typ.Elem().Kind() != reflect.Uint8 {
   745				break
   746			}
   747			// []byte
   748			return "", val.Bytes(), nil
   749		}
   750		return "", nil, &UnsupportedTypeError{typ}
   751	}
   752	
   753	var ddBytes = []byte("--")
   754	
   755	func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
   756		s := parentStack{p: p}
   757		for i := range tinfo.fields {
   758			finfo := &tinfo.fields[i]
   759			if finfo.flags&fAttr != 0 {
   760				continue
   761			}
   762			vf := finfo.value(val)
   763	
   764			// Dereference or skip nil pointer, interface values.
   765			switch vf.Kind() {
   766			case reflect.Ptr, reflect.Interface:
   767				if !vf.IsNil() {
   768					vf = vf.Elem()
   769				}
   770			}
   771	
   772			switch finfo.flags & fMode {
   773			case fCDATA, fCharData:
   774				emit := EscapeText
   775				if finfo.flags&fMode == fCDATA {
   776					emit = emitCDATA
   777				}
   778				if err := s.trim(finfo.parents); err != nil {
   779					return err
   780				}
   781				if vf.CanInterface() && vf.Type().Implements(textMarshalerType) {
   782					data, err := vf.Interface().(encoding.TextMarshaler).MarshalText()
   783					if err != nil {
   784						return err
   785					}
   786					if err := emit(p, data); err != nil {
   787						return err
   788					}
   789					continue
   790				}
   791				if vf.CanAddr() {
   792					pv := vf.Addr()
   793					if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   794						data, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
   795						if err != nil {
   796							return err
   797						}
   798						if err := emit(p, data); err != nil {
   799							return err
   800						}
   801						continue
   802					}
   803				}
   804				var scratch [64]byte
   805				switch vf.Kind() {
   806				case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   807					if err := emit(p, strconv.AppendInt(scratch[:0], vf.Int(), 10)); err != nil {
   808						return err
   809					}
   810				case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   811					if err := emit(p, strconv.AppendUint(scratch[:0], vf.Uint(), 10)); err != nil {
   812						return err
   813					}
   814				case reflect.Float32, reflect.Float64:
   815					if err := emit(p, strconv.AppendFloat(scratch[:0], vf.Float(), 'g', -1, vf.Type().Bits())); err != nil {
   816						return err
   817					}
   818				case reflect.Bool:
   819					if err := emit(p, strconv.AppendBool(scratch[:0], vf.Bool())); err != nil {
   820						return err
   821					}
   822				case reflect.String:
   823					if err := emit(p, []byte(vf.String())); err != nil {
   824						return err
   825					}
   826				case reflect.Slice:
   827					if elem, ok := vf.Interface().([]byte); ok {
   828						if err := emit(p, elem); err != nil {
   829							return err
   830						}
   831					}
   832				}
   833				continue
   834	
   835			case fComment:
   836				if err := s.trim(finfo.parents); err != nil {
   837					return err
   838				}
   839				k := vf.Kind()
   840				if !(k == reflect.String || k == reflect.Slice && vf.Type().Elem().Kind() == reflect.Uint8) {
   841					return fmt.Errorf("xml: bad type for comment field of %s", val.Type())
   842				}
   843				if vf.Len() == 0 {
   844					continue
   845				}
   846				p.writeIndent(0)
   847				p.WriteString("<!--")
   848				dashDash := false
   849				dashLast := false
   850				switch k {
   851				case reflect.String:
   852					s := vf.String()
   853					dashDash = strings.Index(s, "--") >= 0
   854					dashLast = s[len(s)-1] == '-'
   855					if !dashDash {
   856						p.WriteString(s)
   857					}
   858				case reflect.Slice:
   859					b := vf.Bytes()
   860					dashDash = bytes.Index(b, ddBytes) >= 0
   861					dashLast = b[len(b)-1] == '-'
   862					if !dashDash {
   863						p.Write(b)
   864					}
   865				default:
   866					panic("can't happen")
   867				}
   868				if dashDash {
   869					return fmt.Errorf(`xml: comments must not contain "--"`)
   870				}
   871				if dashLast {
   872					// "--->" is invalid grammar. Make it "- -->"
   873					p.WriteByte(' ')
   874				}
   875				p.WriteString("-->")
   876				continue
   877	
   878			case fInnerXml:
   879				iface := vf.Interface()
   880				switch raw := iface.(type) {
   881				case []byte:
   882					p.Write(raw)
   883					continue
   884				case string:
   885					p.WriteString(raw)
   886					continue
   887				}
   888	
   889			case fElement, fElement | fAny:
   890				if err := s.trim(finfo.parents); err != nil {
   891					return err
   892				}
   893				if len(finfo.parents) > len(s.stack) {
   894					if vf.Kind() != reflect.Ptr && vf.Kind() != reflect.Interface || !vf.IsNil() {
   895						if err := s.push(finfo.parents[len(s.stack):]); err != nil {
   896							return err
   897						}
   898					}
   899				}
   900			}
   901			if err := p.marshalValue(vf, finfo, nil); err != nil {
   902				return err
   903			}
   904		}
   905		s.trim(nil)
   906		return p.cachedWriteError()
   907	}
   908	
   909	// return the bufio Writer's cached write error
   910	func (p *printer) cachedWriteError() error {
   911		_, err := p.Write(nil)
   912		return err
   913	}
   914	
   915	func (p *printer) writeIndent(depthDelta int) {
   916		if len(p.prefix) == 0 && len(p.indent) == 0 {
   917			return
   918		}
   919		if depthDelta < 0 {
   920			p.depth--
   921			if p.indentedIn {
   922				p.indentedIn = false
   923				return
   924			}
   925			p.indentedIn = false
   926		}
   927		if p.putNewline {
   928			p.WriteByte('\n')
   929		} else {
   930			p.putNewline = true
   931		}
   932		if len(p.prefix) > 0 {
   933			p.WriteString(p.prefix)
   934		}
   935		if len(p.indent) > 0 {
   936			for i := 0; i < p.depth; i++ {
   937				p.WriteString(p.indent)
   938			}
   939		}
   940		if depthDelta > 0 {
   941			p.depth++
   942			p.indentedIn = true
   943		}
   944	}
   945	
   946	type parentStack struct {
   947		p     *printer
   948		stack []string
   949	}
   950	
   951	// trim updates the XML context to match the longest common prefix of the stack
   952	// and the given parents.  A closing tag will be written for every parent
   953	// popped.  Passing a zero slice or nil will close all the elements.
   954	func (s *parentStack) trim(parents []string) error {
   955		split := 0
   956		for ; split < len(parents) && split < len(s.stack); split++ {
   957			if parents[split] != s.stack[split] {
   958				break
   959			}
   960		}
   961		for i := len(s.stack) - 1; i >= split; i-- {
   962			if err := s.p.writeEnd(Name{Local: s.stack[i]}); err != nil {
   963				return err
   964			}
   965		}
   966		s.stack = s.stack[:split]
   967		return nil
   968	}
   969	
   970	// push adds parent elements to the stack and writes open tags.
   971	func (s *parentStack) push(parents []string) error {
   972		for i := 0; i < len(parents); i++ {
   973			if err := s.p.writeStart(&StartElement{Name: Name{Local: parents[i]}}); err != nil {
   974				return err
   975			}
   976		}
   977		s.stack = append(s.stack, parents...)
   978		return nil
   979	}
   980	
   981	// A MarshalXMLError is returned when Marshal encounters a type
   982	// that cannot be converted into XML.
   983	type UnsupportedTypeError struct {
   984		Type reflect.Type
   985	}
   986	
   987	func (e *UnsupportedTypeError) Error() string {
   988		return "xml: unsupported type: " + e.Type.String()
   989	}
   990	
   991	func isEmptyValue(v reflect.Value) bool {
   992		switch v.Kind() {
   993		case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
   994			return v.Len() == 0
   995		case reflect.Bool:
   996			return !v.Bool()
   997		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   998			return v.Int() == 0
   999		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
  1000			return v.Uint() == 0
  1001		case reflect.Float32, reflect.Float64:
  1002			return v.Float() == 0
  1003		case reflect.Interface, reflect.Ptr:
  1004			return v.IsNil()
  1005		}
  1006		return false
  1007	}
  1008	

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