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

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