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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 ",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		begComment   = []byte("<!--")
   177		endComment   = []byte("-->")
   178		endProcInst  = []byte("?>")
   179		endDirective = []byte(">")
   180	)
   181	
   182	// EncodeToken writes the given XML token to the stream.
   183	// It returns an error if StartElement and EndElement tokens are not properly matched.
   184	//
   185	// EncodeToken does not call Flush, because usually it is part of a larger operation
   186	// such as Encode or EncodeElement (or a custom Marshaler's MarshalXML invoked
   187	// during those), and those will call Flush when finished.
   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	//
   192	// EncodeToken allows writing a ProcInst with Target set to "xml" only as the first token
   193	// in the stream.
   194	func (enc *Encoder) EncodeToken(t Token) error {
   195	
   196		p := &enc.p
   197		switch t := t.(type) {
   198		case StartElement:
   199			if err := p.writeStart(&t); err != nil {
   200				return err
   201			}
   202		case EndElement:
   203			if err := p.writeEnd(t.Name); err != nil {
   204				return err
   205			}
   206		case CharData:
   207			escapeText(p, t, false)
   208		case Comment:
   209			if bytes.Contains(t, endComment) {
   210				return fmt.Errorf("xml: EncodeToken of Comment containing --> marker")
   211			}
   212			p.WriteString("<!--")
   213			p.Write(t)
   214			p.WriteString("-->")
   215			return p.cachedWriteError()
   216		case ProcInst:
   217			// First token to be encoded which is also a ProcInst with target of xml
   218			// is the xml declaration.  The only ProcInst where target of xml is allowed.
   219			if t.Target == "xml" && p.Buffered() != 0 {
   220				return fmt.Errorf("xml: EncodeToken of ProcInst xml target only valid for xml declaration, first token encoded")
   221			}
   222			if !isNameString(t.Target) {
   223				return fmt.Errorf("xml: EncodeToken of ProcInst with invalid Target")
   224			}
   225			if bytes.Contains(t.Inst, endProcInst) {
   226				return fmt.Errorf("xml: EncodeToken of ProcInst containing ?> marker")
   227			}
   228			p.WriteString("<?")
   229			p.WriteString(t.Target)
   230			if len(t.Inst) > 0 {
   231				p.WriteByte(' ')
   232				p.Write(t.Inst)
   233			}
   234			p.WriteString("?>")
   235		case Directive:
   236			if !isValidDirective(t) {
   237				return fmt.Errorf("xml: EncodeToken of Directive containing wrong < or > markers")
   238			}
   239			p.WriteString("<!")
   240			p.Write(t)
   241			p.WriteString(">")
   242		default:
   243			return fmt.Errorf("xml: EncodeToken of invalid token type")
   244	
   245		}
   246		return p.cachedWriteError()
   247	}
   248	
   249	// isValidDirective reports whether dir is a valid directive text,
   250	// meaning angle brackets are matched, ignoring comments and strings.
   251	func isValidDirective(dir Directive) bool {
   252		var (
   253			depth     int
   254			inquote   uint8
   255			incomment bool
   256		)
   257		for i, c := range dir {
   258			switch {
   259			case incomment:
   260				if c == '>' {
   261					if n := 1 + i - len(endComment); n >= 0 && bytes.Equal(dir[n:i+1], endComment) {
   262						incomment = false
   263					}
   264				}
   265				// Just ignore anything in comment
   266			case inquote != 0:
   267				if c == inquote {
   268					inquote = 0
   269				}
   270				// Just ignore anything within quotes
   271			case c == '\'' || c == '"':
   272				inquote = c
   273			case c == '<':
   274				if i+len(begComment) < len(dir) && bytes.Equal(dir[i:i+len(begComment)], begComment) {
   275					incomment = true
   276				} else {
   277					depth++
   278				}
   279			case c == '>':
   280				if depth == 0 {
   281					return false
   282				}
   283				depth--
   284			}
   285		}
   286		return depth == 0 && inquote == 0 && !incomment
   287	}
   288	
   289	// Flush flushes any buffered XML to the underlying writer.
   290	// See the EncodeToken documentation for details about when it is necessary.
   291	func (enc *Encoder) Flush() error {
   292		return enc.p.Flush()
   293	}
   294	
   295	type printer struct {
   296		*bufio.Writer
   297		encoder    *Encoder
   298		seq        int
   299		indent     string
   300		prefix     string
   301		depth      int
   302		indentedIn bool
   303		putNewline bool
   304		attrNS     map[string]string // map prefix -> name space
   305		attrPrefix map[string]string // map name space -> prefix
   306		prefixes   []string
   307		tags       []Name
   308	}
   309	
   310	// createAttrPrefix finds the name space prefix attribute to use for the given name space,
   311	// defining a new prefix if necessary. It returns the prefix.
   312	func (p *printer) createAttrPrefix(url string) string {
   313		if prefix := p.attrPrefix[url]; prefix != "" {
   314			return prefix
   315		}
   316	
   317		// The "http://www.w3.org/XML/1998/namespace" name space is predefined as "xml"
   318		// and must be referred to that way.
   319		// (The "http://www.w3.org/2000/xmlns/" name space is also predefined as "xmlns",
   320		// but users should not be trying to use that one directly - that's our job.)
   321		if url == xmlURL {
   322			return "xml"
   323		}
   324	
   325		// Need to define a new name space.
   326		if p.attrPrefix == nil {
   327			p.attrPrefix = make(map[string]string)
   328			p.attrNS = make(map[string]string)
   329		}
   330	
   331		// Pick a name. We try to use the final element of the path
   332		// but fall back to _.
   333		prefix := strings.TrimRight(url, "/")
   334		if i := strings.LastIndex(prefix, "/"); i >= 0 {
   335			prefix = prefix[i+1:]
   336		}
   337		if prefix == "" || !isName([]byte(prefix)) || strings.Contains(prefix, ":") {
   338			prefix = "_"
   339		}
   340		if strings.HasPrefix(prefix, "xml") {
   341			// xmlanything is reserved.
   342			prefix = "_" + prefix
   343		}
   344		if p.attrNS[prefix] != "" {
   345			// Name is taken. Find a better one.
   346			for p.seq++; ; p.seq++ {
   347				if id := prefix + "_" + strconv.Itoa(p.seq); p.attrNS[id] == "" {
   348					prefix = id
   349					break
   350				}
   351			}
   352		}
   353	
   354		p.attrPrefix[url] = prefix
   355		p.attrNS[prefix] = url
   356	
   357		p.WriteString(`xmlns:`)
   358		p.WriteString(prefix)
   359		p.WriteString(`="`)
   360		EscapeText(p, []byte(url))
   361		p.WriteString(`" `)
   362	
   363		p.prefixes = append(p.prefixes, prefix)
   364	
   365		return prefix
   366	}
   367	
   368	// deleteAttrPrefix removes an attribute name space prefix.
   369	func (p *printer) deleteAttrPrefix(prefix string) {
   370		delete(p.attrPrefix, p.attrNS[prefix])
   371		delete(p.attrNS, prefix)
   372	}
   373	
   374	func (p *printer) markPrefix() {
   375		p.prefixes = append(p.prefixes, "")
   376	}
   377	
   378	func (p *printer) popPrefix() {
   379		for len(p.prefixes) > 0 {
   380			prefix := p.prefixes[len(p.prefixes)-1]
   381			p.prefixes = p.prefixes[:len(p.prefixes)-1]
   382			if prefix == "" {
   383				break
   384			}
   385			p.deleteAttrPrefix(prefix)
   386		}
   387	}
   388	
   389	var (
   390		marshalerType     = reflect.TypeOf((*Marshaler)(nil)).Elem()
   391		marshalerAttrType = reflect.TypeOf((*MarshalerAttr)(nil)).Elem()
   392		textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
   393	)
   394	
   395	// marshalValue writes one or more XML elements representing val.
   396	// If val was obtained from a struct field, finfo must have its details.
   397	func (p *printer) marshalValue(val reflect.Value, finfo *fieldInfo, startTemplate *StartElement) error {
   398		if startTemplate != nil && startTemplate.Name.Local == "" {
   399			return fmt.Errorf("xml: EncodeElement of StartElement with missing name")
   400		}
   401	
   402		if !val.IsValid() {
   403			return nil
   404		}
   405		if finfo != nil && finfo.flags&fOmitEmpty != 0 && isEmptyValue(val) {
   406			return nil
   407		}
   408	
   409		// Drill into interfaces and pointers.
   410		// This can turn into an infinite loop given a cyclic chain,
   411		// but it matches the Go 1 behavior.
   412		for val.Kind() == reflect.Interface || val.Kind() == reflect.Ptr {
   413			if val.IsNil() {
   414				return nil
   415			}
   416			val = val.Elem()
   417		}
   418	
   419		kind := val.Kind()
   420		typ := val.Type()
   421	
   422		// Check for marshaler.
   423		if val.CanInterface() && typ.Implements(marshalerType) {
   424			return p.marshalInterface(val.Interface().(Marshaler), defaultStart(typ, finfo, startTemplate))
   425		}
   426		if val.CanAddr() {
   427			pv := val.Addr()
   428			if pv.CanInterface() && pv.Type().Implements(marshalerType) {
   429				return p.marshalInterface(pv.Interface().(Marshaler), defaultStart(pv.Type(), finfo, startTemplate))
   430			}
   431		}
   432	
   433		// Check for text marshaler.
   434		if val.CanInterface() && typ.Implements(textMarshalerType) {
   435			return p.marshalTextInterface(val.Interface().(encoding.TextMarshaler), defaultStart(typ, finfo, startTemplate))
   436		}
   437		if val.CanAddr() {
   438			pv := val.Addr()
   439			if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   440				return p.marshalTextInterface(pv.Interface().(encoding.TextMarshaler), defaultStart(pv.Type(), finfo, startTemplate))
   441			}
   442		}
   443	
   444		// Slices and arrays iterate over the elements. They do not have an enclosing tag.
   445		if (kind == reflect.Slice || kind == reflect.Array) && typ.Elem().Kind() != reflect.Uint8 {
   446			for i, n := 0, val.Len(); i < n; i++ {
   447				if err := p.marshalValue(val.Index(i), finfo, startTemplate); err != nil {
   448					return err
   449				}
   450			}
   451			return nil
   452		}
   453	
   454		tinfo, err := getTypeInfo(typ)
   455		if err != nil {
   456			return err
   457		}
   458	
   459		// Create start element.
   460		// Precedence for the XML element name is:
   461		// 0. startTemplate
   462		// 1. XMLName field in underlying struct;
   463		// 2. field name/tag in the struct field; and
   464		// 3. type name
   465		var start StartElement
   466	
   467		if startTemplate != nil {
   468			start.Name = startTemplate.Name
   469			start.Attr = append(start.Attr, startTemplate.Attr...)
   470		} else if tinfo.xmlname != nil {
   471			xmlname := tinfo.xmlname
   472			if xmlname.name != "" {
   473				start.Name.Space, start.Name.Local = xmlname.xmlns, xmlname.name
   474			} else if v, ok := xmlname.value(val).Interface().(Name); ok && v.Local != "" {
   475				start.Name = v
   476			}
   477		}
   478		if start.Name.Local == "" && finfo != nil {
   479			start.Name.Space, start.Name.Local = finfo.xmlns, finfo.name
   480		}
   481		if start.Name.Local == "" {
   482			name := typ.Name()
   483			if name == "" {
   484				return &UnsupportedTypeError{typ}
   485			}
   486			start.Name.Local = name
   487		}
   488	
   489		// Attributes
   490		for i := range tinfo.fields {
   491			finfo := &tinfo.fields[i]
   492			if finfo.flags&fAttr == 0 {
   493				continue
   494			}
   495			fv := finfo.value(val)
   496			name := Name{Space: finfo.xmlns, Local: finfo.name}
   497	
   498			if finfo.flags&fOmitEmpty != 0 && isEmptyValue(fv) {
   499				continue
   500			}
   501	
   502			if fv.Kind() == reflect.Interface && fv.IsNil() {
   503				continue
   504			}
   505	
   506			if fv.CanInterface() && fv.Type().Implements(marshalerAttrType) {
   507				attr, err := fv.Interface().(MarshalerAttr).MarshalXMLAttr(name)
   508				if err != nil {
   509					return err
   510				}
   511				if attr.Name.Local != "" {
   512					start.Attr = append(start.Attr, attr)
   513				}
   514				continue
   515			}
   516	
   517			if fv.CanAddr() {
   518				pv := fv.Addr()
   519				if pv.CanInterface() && pv.Type().Implements(marshalerAttrType) {
   520					attr, err := pv.Interface().(MarshalerAttr).MarshalXMLAttr(name)
   521					if err != nil {
   522						return err
   523					}
   524					if attr.Name.Local != "" {
   525						start.Attr = append(start.Attr, attr)
   526					}
   527					continue
   528				}
   529			}
   530	
   531			if fv.CanInterface() && fv.Type().Implements(textMarshalerType) {
   532				text, err := fv.Interface().(encoding.TextMarshaler).MarshalText()
   533				if err != nil {
   534					return err
   535				}
   536				start.Attr = append(start.Attr, Attr{name, string(text)})
   537				continue
   538			}
   539	
   540			if fv.CanAddr() {
   541				pv := fv.Addr()
   542				if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   543					text, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
   544					if err != nil {
   545						return err
   546					}
   547					start.Attr = append(start.Attr, Attr{name, string(text)})
   548					continue
   549				}
   550			}
   551	
   552			// Dereference or skip nil pointer, interface values.
   553			switch fv.Kind() {
   554			case reflect.Ptr, reflect.Interface:
   555				if fv.IsNil() {
   556					continue
   557				}
   558				fv = fv.Elem()
   559			}
   560	
   561			s, b, err := p.marshalSimple(fv.Type(), fv)
   562			if err != nil {
   563				return err
   564			}
   565			if b != nil {
   566				s = string(b)
   567			}
   568			start.Attr = append(start.Attr, Attr{name, s})
   569		}
   570	
   571		if err := p.writeStart(&start); err != nil {
   572			return err
   573		}
   574	
   575		if val.Kind() == reflect.Struct {
   576			err = p.marshalStruct(tinfo, val)
   577		} else {
   578			s, b, err1 := p.marshalSimple(typ, val)
   579			if err1 != nil {
   580				err = err1
   581			} else if b != nil {
   582				EscapeText(p, b)
   583			} else {
   584				p.EscapeString(s)
   585			}
   586		}
   587		if err != nil {
   588			return err
   589		}
   590	
   591		if err := p.writeEnd(start.Name); err != nil {
   592			return err
   593		}
   594	
   595		return p.cachedWriteError()
   596	}
   597	
   598	// defaultStart returns the default start element to use,
   599	// given the reflect type, field info, and start template.
   600	func defaultStart(typ reflect.Type, finfo *fieldInfo, startTemplate *StartElement) StartElement {
   601		var start StartElement
   602		// Precedence for the XML element name is as above,
   603		// except that we do not look inside structs for the first field.
   604		if startTemplate != nil {
   605			start.Name = startTemplate.Name
   606			start.Attr = append(start.Attr, startTemplate.Attr...)
   607		} else if finfo != nil && finfo.name != "" {
   608			start.Name.Local = finfo.name
   609			start.Name.Space = finfo.xmlns
   610		} else if typ.Name() != "" {
   611			start.Name.Local = typ.Name()
   612		} else {
   613			// Must be a pointer to a named type,
   614			// since it has the Marshaler methods.
   615			start.Name.Local = typ.Elem().Name()
   616		}
   617		return start
   618	}
   619	
   620	// marshalInterface marshals a Marshaler interface value.
   621	func (p *printer) marshalInterface(val Marshaler, start StartElement) error {
   622		// Push a marker onto the tag stack so that MarshalXML
   623		// cannot close the XML tags that it did not open.
   624		p.tags = append(p.tags, Name{})
   625		n := len(p.tags)
   626	
   627		err := val.MarshalXML(p.encoder, start)
   628		if err != nil {
   629			return err
   630		}
   631	
   632		// Make sure MarshalXML closed all its tags. p.tags[n-1] is the mark.
   633		if len(p.tags) > n {
   634			return fmt.Errorf("xml: %s.MarshalXML wrote invalid XML: <%s> not closed", receiverType(val), p.tags[len(p.tags)-1].Local)
   635		}
   636		p.tags = p.tags[:n-1]
   637		return nil
   638	}
   639	
   640	// marshalTextInterface marshals a TextMarshaler interface value.
   641	func (p *printer) marshalTextInterface(val encoding.TextMarshaler, start StartElement) error {
   642		if err := p.writeStart(&start); err != nil {
   643			return err
   644		}
   645		text, err := val.MarshalText()
   646		if err != nil {
   647			return err
   648		}
   649		EscapeText(p, text)
   650		return p.writeEnd(start.Name)
   651	}
   652	
   653	// writeStart writes the given start element.
   654	func (p *printer) writeStart(start *StartElement) error {
   655		if start.Name.Local == "" {
   656			return fmt.Errorf("xml: start tag with no name")
   657		}
   658	
   659		p.tags = append(p.tags, start.Name)
   660		p.markPrefix()
   661	
   662		p.writeIndent(1)
   663		p.WriteByte('<')
   664		p.WriteString(start.Name.Local)
   665	
   666		if start.Name.Space != "" {
   667			p.WriteString(` xmlns="`)
   668			p.EscapeString(start.Name.Space)
   669			p.WriteByte('"')
   670		}
   671	
   672		// Attributes
   673		for _, attr := range start.Attr {
   674			name := attr.Name
   675			if name.Local == "" {
   676				continue
   677			}
   678			p.WriteByte(' ')
   679			if name.Space != "" {
   680				p.WriteString(p.createAttrPrefix(name.Space))
   681				p.WriteByte(':')
   682			}
   683			p.WriteString(name.Local)
   684			p.WriteString(`="`)
   685			p.EscapeString(attr.Value)
   686			p.WriteByte('"')
   687		}
   688		p.WriteByte('>')
   689		return nil
   690	}
   691	
   692	func (p *printer) writeEnd(name Name) error {
   693		if name.Local == "" {
   694			return fmt.Errorf("xml: end tag with no name")
   695		}
   696		if len(p.tags) == 0 || p.tags[len(p.tags)-1].Local == "" {
   697			return fmt.Errorf("xml: end tag </%s> without start tag", name.Local)
   698		}
   699		if top := p.tags[len(p.tags)-1]; top != name {
   700			if top.Local != name.Local {
   701				return fmt.Errorf("xml: end tag </%s> does not match start tag <%s>", name.Local, top.Local)
   702			}
   703			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)
   704		}
   705		p.tags = p.tags[:len(p.tags)-1]
   706	
   707		p.writeIndent(-1)
   708		p.WriteByte('<')
   709		p.WriteByte('/')
   710		p.WriteString(name.Local)
   711		p.WriteByte('>')
   712		p.popPrefix()
   713		return nil
   714	}
   715	
   716	func (p *printer) marshalSimple(typ reflect.Type, val reflect.Value) (string, []byte, error) {
   717		switch val.Kind() {
   718		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   719			return strconv.FormatInt(val.Int(), 10), nil, nil
   720		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   721			return strconv.FormatUint(val.Uint(), 10), nil, nil
   722		case reflect.Float32, reflect.Float64:
   723			return strconv.FormatFloat(val.Float(), 'g', -1, val.Type().Bits()), nil, nil
   724		case reflect.String:
   725			return val.String(), nil, nil
   726		case reflect.Bool:
   727			return strconv.FormatBool(val.Bool()), nil, nil
   728		case reflect.Array:
   729			if typ.Elem().Kind() != reflect.Uint8 {
   730				break
   731			}
   732			// [...]byte
   733			var bytes []byte
   734			if val.CanAddr() {
   735				bytes = val.Slice(0, val.Len()).Bytes()
   736			} else {
   737				bytes = make([]byte, val.Len())
   738				reflect.Copy(reflect.ValueOf(bytes), val)
   739			}
   740			return "", bytes, nil
   741		case reflect.Slice:
   742			if typ.Elem().Kind() != reflect.Uint8 {
   743				break
   744			}
   745			// []byte
   746			return "", val.Bytes(), nil
   747		}
   748		return "", nil, &UnsupportedTypeError{typ}
   749	}
   750	
   751	var ddBytes = []byte("--")
   752	
   753	func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
   754		s := parentStack{p: p}
   755		for i := range tinfo.fields {
   756			finfo := &tinfo.fields[i]
   757			if finfo.flags&fAttr != 0 {
   758				continue
   759			}
   760			vf := finfo.value(val)
   761	
   762			// Dereference or skip nil pointer, interface values.
   763			switch vf.Kind() {
   764			case reflect.Ptr, reflect.Interface:
   765				if !vf.IsNil() {
   766					vf = vf.Elem()
   767				}
   768			}
   769	
   770			switch finfo.flags & fMode {
   771			case fCharData:
   772				if err := s.trim(finfo.parents); err != nil {
   773					return err
   774				}
   775				if vf.CanInterface() && vf.Type().Implements(textMarshalerType) {
   776					data, err := vf.Interface().(encoding.TextMarshaler).MarshalText()
   777					if err != nil {
   778						return err
   779					}
   780					Escape(p, data)
   781					continue
   782				}
   783				if vf.CanAddr() {
   784					pv := vf.Addr()
   785					if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   786						data, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
   787						if err != nil {
   788							return err
   789						}
   790						Escape(p, data)
   791						continue
   792					}
   793				}
   794				var scratch [64]byte
   795				switch vf.Kind() {
   796				case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   797					Escape(p, strconv.AppendInt(scratch[:0], vf.Int(), 10))
   798				case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   799					Escape(p, strconv.AppendUint(scratch[:0], vf.Uint(), 10))
   800				case reflect.Float32, reflect.Float64:
   801					Escape(p, strconv.AppendFloat(scratch[:0], vf.Float(), 'g', -1, vf.Type().Bits()))
   802				case reflect.Bool:
   803					Escape(p, strconv.AppendBool(scratch[:0], vf.Bool()))
   804				case reflect.String:
   805					if err := EscapeText(p, []byte(vf.String())); err != nil {
   806						return err
   807					}
   808				case reflect.Slice:
   809					if elem, ok := vf.Interface().([]byte); ok {
   810						if err := EscapeText(p, elem); err != nil {
   811							return err
   812						}
   813					}
   814				}
   815				continue
   816	
   817			case fComment:
   818				if err := s.trim(finfo.parents); err != nil {
   819					return err
   820				}
   821				k := vf.Kind()
   822				if !(k == reflect.String || k == reflect.Slice && vf.Type().Elem().Kind() == reflect.Uint8) {
   823					return fmt.Errorf("xml: bad type for comment field of %s", val.Type())
   824				}
   825				if vf.Len() == 0 {
   826					continue
   827				}
   828				p.writeIndent(0)
   829				p.WriteString("<!--")
   830				dashDash := false
   831				dashLast := false
   832				switch k {
   833				case reflect.String:
   834					s := vf.String()
   835					dashDash = strings.Index(s, "--") >= 0
   836					dashLast = s[len(s)-1] == '-'
   837					if !dashDash {
   838						p.WriteString(s)
   839					}
   840				case reflect.Slice:
   841					b := vf.Bytes()
   842					dashDash = bytes.Index(b, ddBytes) >= 0
   843					dashLast = b[len(b)-1] == '-'
   844					if !dashDash {
   845						p.Write(b)
   846					}
   847				default:
   848					panic("can't happen")
   849				}
   850				if dashDash {
   851					return fmt.Errorf(`xml: comments must not contain "--"`)
   852				}
   853				if dashLast {
   854					// "--->" is invalid grammar. Make it "- -->"
   855					p.WriteByte(' ')
   856				}
   857				p.WriteString("-->")
   858				continue
   859	
   860			case fInnerXml:
   861				iface := vf.Interface()
   862				switch raw := iface.(type) {
   863				case []byte:
   864					p.Write(raw)
   865					continue
   866				case string:
   867					p.WriteString(raw)
   868					continue
   869				}
   870	
   871			case fElement, fElement | fAny:
   872				if err := s.trim(finfo.parents); err != nil {
   873					return err
   874				}
   875				if len(finfo.parents) > len(s.stack) {
   876					if vf.Kind() != reflect.Ptr && vf.Kind() != reflect.Interface || !vf.IsNil() {
   877						if err := s.push(finfo.parents[len(s.stack):]); err != nil {
   878							return err
   879						}
   880					}
   881				}
   882			}
   883			if err := p.marshalValue(vf, finfo, nil); err != nil {
   884				return err
   885			}
   886		}
   887		s.trim(nil)
   888		return p.cachedWriteError()
   889	}
   890	
   891	// return the bufio Writer's cached write error
   892	func (p *printer) cachedWriteError() error {
   893		_, err := p.Write(nil)
   894		return err
   895	}
   896	
   897	func (p *printer) writeIndent(depthDelta int) {
   898		if len(p.prefix) == 0 && len(p.indent) == 0 {
   899			return
   900		}
   901		if depthDelta < 0 {
   902			p.depth--
   903			if p.indentedIn {
   904				p.indentedIn = false
   905				return
   906			}
   907			p.indentedIn = false
   908		}
   909		if p.putNewline {
   910			p.WriteByte('\n')
   911		} else {
   912			p.putNewline = true
   913		}
   914		if len(p.prefix) > 0 {
   915			p.WriteString(p.prefix)
   916		}
   917		if len(p.indent) > 0 {
   918			for i := 0; i < p.depth; i++ {
   919				p.WriteString(p.indent)
   920			}
   921		}
   922		if depthDelta > 0 {
   923			p.depth++
   924			p.indentedIn = true
   925		}
   926	}
   927	
   928	type parentStack struct {
   929		p     *printer
   930		stack []string
   931	}
   932	
   933	// trim updates the XML context to match the longest common prefix of the stack
   934	// and the given parents.  A closing tag will be written for every parent
   935	// popped.  Passing a zero slice or nil will close all the elements.
   936	func (s *parentStack) trim(parents []string) error {
   937		split := 0
   938		for ; split < len(parents) && split < len(s.stack); split++ {
   939			if parents[split] != s.stack[split] {
   940				break
   941			}
   942		}
   943		for i := len(s.stack) - 1; i >= split; i-- {
   944			if err := s.p.writeEnd(Name{Local: s.stack[i]}); err != nil {
   945				return err
   946			}
   947		}
   948		s.stack = s.stack[:split]
   949		return nil
   950	}
   951	
   952	// push adds parent elements to the stack and writes open tags.
   953	func (s *parentStack) push(parents []string) error {
   954		for i := 0; i < len(parents); i++ {
   955			if err := s.p.writeStart(&StartElement{Name: Name{Local: parents[i]}}); err != nil {
   956				return err
   957			}
   958		}
   959		s.stack = append(s.stack, parents...)
   960		return nil
   961	}
   962	
   963	// A MarshalXMLError is returned when Marshal encounters a type
   964	// that cannot be converted into XML.
   965	type UnsupportedTypeError struct {
   966		Type reflect.Type
   967	}
   968	
   969	func (e *UnsupportedTypeError) Error() string {
   970		return "xml: unsupported type: " + e.Type.String()
   971	}
   972	
   973	func isEmptyValue(v reflect.Value) bool {
   974		switch v.Kind() {
   975		case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
   976			return v.Len() == 0
   977		case reflect.Bool:
   978			return !v.Bool()
   979		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   980			return v.Int() == 0
   981		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   982			return v.Uint() == 0
   983		case reflect.Float32, reflect.Float64:
   984			return v.Float() == 0
   985		case reflect.Interface, reflect.Ptr:
   986			return v.IsNil()
   987		}
   988		return false
   989	}
   990	

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