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Source file src/encoding/xml/marshal.go

Documentation: encoding/xml

     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  	// Header is 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 marshaling each of the elements.
    28  // Marshal handles a pointer by marshaling the value it points at or, if the
    29  // pointer is nil, by writing nothing. Marshal handles an interface value by
    30  // marshaling the value it contains or, if the interface value is nil, by
    31  // writing nothing. Marshal handles all other data by writing one or more XML
    32  // elements containing the data.
    33  //
    34  // The name for the XML elements is taken from, in order of preference:
    35  //     - the tag on the XMLName field, if the data is a struct
    36  //     - the value of the XMLName field of type Name
    37  //     - the tag of the struct field used to obtain the data
    38  //     - the name of the struct field used to obtain the data
    39  //     - the name of the marshaled type
    40  //
    41  // The XML element for a struct contains marshaled 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 marshaling procedure.
    55  //     - a field with tag ",comment" is written as an XML comment, not
    56  //       subject to the usual marshaling 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  // If the XML name for a struct field is defined by both the field tag and the
    70  // struct's XMLName field, the names must match.
    71  //
    72  // See MarshalIndent for an example.
    73  //
    74  // Marshal will return an error if asked to marshal a channel, function, or map.
    75  func Marshal(v interface{}) ([]byte, error) {
    76  	var b bytes.Buffer
    77  	if err := NewEncoder(&b).Encode(v); err != nil {
    78  		return nil, err
    79  	}
    80  	return b.Bytes(), nil
    81  }
    82  
    83  // Marshaler is the interface implemented by objects that can marshal
    84  // themselves into valid XML elements.
    85  //
    86  // MarshalXML encodes the receiver as zero or more XML elements.
    87  // By convention, arrays or slices are typically encoded as a sequence
    88  // of elements, one per entry.
    89  // Using start as the element tag is not required, but doing so
    90  // will enable Unmarshal to match the XML elements to the correct
    91  // struct field.
    92  // One common implementation strategy is to construct a separate
    93  // value with a layout corresponding to the desired XML and then
    94  // to encode it using e.EncodeElement.
    95  // Another common strategy is to use repeated calls to e.EncodeToken
    96  // to generate the XML output one token at a time.
    97  // The sequence of encoded tokens must make up zero or more valid
    98  // XML elements.
    99  type Marshaler interface {
   100  	MarshalXML(e *Encoder, start StartElement) error
   101  }
   102  
   103  // MarshalerAttr is the interface implemented by objects that can marshal
   104  // themselves into valid XML attributes.
   105  //
   106  // MarshalXMLAttr returns an XML attribute with the encoded value of the receiver.
   107  // Using name as the attribute name is not required, but doing so
   108  // will enable Unmarshal to match the attribute to the correct
   109  // struct field.
   110  // If MarshalXMLAttr returns the zero attribute Attr{}, no attribute
   111  // will be generated in the output.
   112  // MarshalXMLAttr is used only for struct fields with the
   113  // "attr" option in the field tag.
   114  type MarshalerAttr interface {
   115  	MarshalXMLAttr(name Name) (Attr, error)
   116  }
   117  
   118  // MarshalIndent works like Marshal, but each XML element begins on a new
   119  // indented line that starts with prefix and is followed by one or more
   120  // copies of indent according to the nesting depth.
   121  func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error) {
   122  	var b bytes.Buffer
   123  	enc := NewEncoder(&b)
   124  	enc.Indent(prefix, indent)
   125  	if err := enc.Encode(v); err != nil {
   126  		return nil, err
   127  	}
   128  	return b.Bytes(), nil
   129  }
   130  
   131  // An Encoder writes XML data to an output stream.
   132  type Encoder struct {
   133  	p printer
   134  }
   135  
   136  // NewEncoder returns a new encoder that writes to w.
   137  func NewEncoder(w io.Writer) *Encoder {
   138  	e := &Encoder{printer{Writer: bufio.NewWriter(w)}}
   139  	e.p.encoder = e
   140  	return e
   141  }
   142  
   143  // Indent sets the encoder to generate XML in which each element
   144  // begins on a new indented line that starts with prefix and is followed by
   145  // one or more copies of indent according to the nesting depth.
   146  func (enc *Encoder) Indent(prefix, indent string) {
   147  	enc.p.prefix = prefix
   148  	enc.p.indent = indent
   149  }
   150  
   151  // Encode writes the XML encoding of v to the stream.
   152  //
   153  // See the documentation for Marshal for details about the conversion
   154  // of Go values to XML.
   155  //
   156  // Encode calls Flush before returning.
   157  func (enc *Encoder) Encode(v interface{}) error {
   158  	err := enc.p.marshalValue(reflect.ValueOf(v), nil, nil)
   159  	if err != nil {
   160  		return err
   161  	}
   162  	return enc.p.Flush()
   163  }
   164  
   165  // EncodeElement writes the XML encoding of v to the stream,
   166  // using start as the outermost tag in the encoding.
   167  //
   168  // See the documentation for Marshal for details about the conversion
   169  // of Go values to XML.
   170  //
   171  // EncodeElement calls Flush before returning.
   172  func (enc *Encoder) EncodeElement(v interface{}, start StartElement) error {
   173  	err := enc.p.marshalValue(reflect.ValueOf(v), nil, &start)
   174  	if err != nil {
   175  		return err
   176  	}
   177  	return enc.p.Flush()
   178  }
   179  
   180  var (
   181  	begComment  = []byte("<!--")
   182  	endComment  = []byte("-->")
   183  	endProcInst = []byte("?>")
   184  )
   185  
   186  // EncodeToken writes the given XML token to the stream.
   187  // It returns an error if StartElement and EndElement tokens are not properly matched.
   188  //
   189  // EncodeToken does not call Flush, because usually it is part of a larger operation
   190  // such as Encode or EncodeElement (or a custom Marshaler's MarshalXML invoked
   191  // during those), and those will call Flush when finished.
   192  // Callers that create an Encoder and then invoke EncodeToken directly, without
   193  // using Encode or EncodeElement, need to call Flush when finished to ensure
   194  // that the XML is written to the underlying writer.
   195  //
   196  // EncodeToken allows writing a ProcInst with Target set to "xml" only as the first token
   197  // in the stream.
   198  func (enc *Encoder) EncodeToken(t Token) error {
   199  
   200  	p := &enc.p
   201  	switch t := t.(type) {
   202  	case StartElement:
   203  		if err := p.writeStart(&t); err != nil {
   204  			return err
   205  		}
   206  	case EndElement:
   207  		if err := p.writeEnd(t.Name); err != nil {
   208  			return err
   209  		}
   210  	case CharData:
   211  		escapeText(p, t, false)
   212  	case Comment:
   213  		if bytes.Contains(t, endComment) {
   214  			return fmt.Errorf("xml: EncodeToken of Comment containing --> marker")
   215  		}
   216  		p.WriteString("<!--")
   217  		p.Write(t)
   218  		p.WriteString("-->")
   219  		return p.cachedWriteError()
   220  	case ProcInst:
   221  		// First token to be encoded which is also a ProcInst with target of xml
   222  		// is the xml declaration. The only ProcInst where target of xml is allowed.
   223  		if t.Target == "xml" && p.Buffered() != 0 {
   224  			return fmt.Errorf("xml: EncodeToken of ProcInst xml target only valid for xml declaration, first token encoded")
   225  		}
   226  		if !isNameString(t.Target) {
   227  			return fmt.Errorf("xml: EncodeToken of ProcInst with invalid Target")
   228  		}
   229  		if bytes.Contains(t.Inst, endProcInst) {
   230  			return fmt.Errorf("xml: EncodeToken of ProcInst containing ?> marker")
   231  		}
   232  		p.WriteString("<?")
   233  		p.WriteString(t.Target)
   234  		if len(t.Inst) > 0 {
   235  			p.WriteByte(' ')
   236  			p.Write(t.Inst)
   237  		}
   238  		p.WriteString("?>")
   239  	case Directive:
   240  		if !isValidDirective(t) {
   241  			return fmt.Errorf("xml: EncodeToken of Directive containing wrong < or > markers")
   242  		}
   243  		p.WriteString("<!")
   244  		p.Write(t)
   245  		p.WriteString(">")
   246  	default:
   247  		return fmt.Errorf("xml: EncodeToken of invalid token type")
   248  
   249  	}
   250  	return p.cachedWriteError()
   251  }
   252  
   253  // isValidDirective reports whether dir is a valid directive text,
   254  // meaning angle brackets are matched, ignoring comments and strings.
   255  func isValidDirective(dir Directive) bool {
   256  	var (
   257  		depth     int
   258  		inquote   uint8
   259  		incomment bool
   260  	)
   261  	for i, c := range dir {
   262  		switch {
   263  		case incomment:
   264  			if c == '>' {
   265  				if n := 1 + i - len(endComment); n >= 0 && bytes.Equal(dir[n:i+1], endComment) {
   266  					incomment = false
   267  				}
   268  			}
   269  			// Just ignore anything in comment
   270  		case inquote != 0:
   271  			if c == inquote {
   272  				inquote = 0
   273  			}
   274  			// Just ignore anything within quotes
   275  		case c == '\'' || c == '"':
   276  			inquote = c
   277  		case c == '<':
   278  			if i+len(begComment) < len(dir) && bytes.Equal(dir[i:i+len(begComment)], begComment) {
   279  				incomment = true
   280  			} else {
   281  				depth++
   282  			}
   283  		case c == '>':
   284  			if depth == 0 {
   285  				return false
   286  			}
   287  			depth--
   288  		}
   289  	}
   290  	return depth == 0 && inquote == 0 && !incomment
   291  }
   292  
   293  // Flush flushes any buffered XML to the underlying writer.
   294  // See the EncodeToken documentation for details about when it is necessary.
   295  func (enc *Encoder) Flush() error {
   296  	return enc.p.Flush()
   297  }
   298  
   299  type printer struct {
   300  	*bufio.Writer
   301  	encoder    *Encoder
   302  	seq        int
   303  	indent     string
   304  	prefix     string
   305  	depth      int
   306  	indentedIn bool
   307  	putNewline bool
   308  	attrNS     map[string]string // map prefix -> name space
   309  	attrPrefix map[string]string // map name space -> prefix
   310  	prefixes   []string
   311  	tags       []Name
   312  }
   313  
   314  // createAttrPrefix finds the name space prefix attribute to use for the given name space,
   315  // defining a new prefix if necessary. It returns the prefix.
   316  func (p *printer) createAttrPrefix(url string) string {
   317  	if prefix := p.attrPrefix[url]; prefix != "" {
   318  		return prefix
   319  	}
   320  
   321  	// The "http://www.w3.org/XML/1998/namespace" name space is predefined as "xml"
   322  	// and must be referred to that way.
   323  	// (The "http://www.w3.org/2000/xmlns/" name space is also predefined as "xmlns",
   324  	// but users should not be trying to use that one directly - that's our job.)
   325  	if url == xmlURL {
   326  		return xmlPrefix
   327  	}
   328  
   329  	// Need to define a new name space.
   330  	if p.attrPrefix == nil {
   331  		p.attrPrefix = make(map[string]string)
   332  		p.attrNS = make(map[string]string)
   333  	}
   334  
   335  	// Pick a name. We try to use the final element of the path
   336  	// but fall back to _.
   337  	prefix := strings.TrimRight(url, "/")
   338  	if i := strings.LastIndex(prefix, "/"); i >= 0 {
   339  		prefix = prefix[i+1:]
   340  	}
   341  	if prefix == "" || !isName([]byte(prefix)) || strings.Contains(prefix, ":") {
   342  		prefix = "_"
   343  	}
   344  	if strings.HasPrefix(prefix, "xml") {
   345  		// xmlanything is reserved.
   346  		prefix = "_" + prefix
   347  	}
   348  	if p.attrNS[prefix] != "" {
   349  		// Name is taken. Find a better one.
   350  		for p.seq++; ; p.seq++ {
   351  			if id := prefix + "_" + strconv.Itoa(p.seq); p.attrNS[id] == "" {
   352  				prefix = id
   353  				break
   354  			}
   355  		}
   356  	}
   357  
   358  	p.attrPrefix[url] = prefix
   359  	p.attrNS[prefix] = url
   360  
   361  	p.WriteString(`xmlns:`)
   362  	p.WriteString(prefix)
   363  	p.WriteString(`="`)
   364  	EscapeText(p, []byte(url))
   365  	p.WriteString(`" `)
   366  
   367  	p.prefixes = append(p.prefixes, prefix)
   368  
   369  	return prefix
   370  }
   371  
   372  // deleteAttrPrefix removes an attribute name space prefix.
   373  func (p *printer) deleteAttrPrefix(prefix string) {
   374  	delete(p.attrPrefix, p.attrNS[prefix])
   375  	delete(p.attrNS, prefix)
   376  }
   377  
   378  func (p *printer) markPrefix() {
   379  	p.prefixes = append(p.prefixes, "")
   380  }
   381  
   382  func (p *printer) popPrefix() {
   383  	for len(p.prefixes) > 0 {
   384  		prefix := p.prefixes[len(p.prefixes)-1]
   385  		p.prefixes = p.prefixes[:len(p.prefixes)-1]
   386  		if prefix == "" {
   387  			break
   388  		}
   389  		p.deleteAttrPrefix(prefix)
   390  	}
   391  }
   392  
   393  var (
   394  	marshalerType     = reflect.TypeOf((*Marshaler)(nil)).Elem()
   395  	marshalerAttrType = reflect.TypeOf((*MarshalerAttr)(nil)).Elem()
   396  	textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
   397  )
   398  
   399  // marshalValue writes one or more XML elements representing val.
   400  // If val was obtained from a struct field, finfo must have its details.
   401  func (p *printer) marshalValue(val reflect.Value, finfo *fieldInfo, startTemplate *StartElement) error {
   402  	if startTemplate != nil && startTemplate.Name.Local == "" {
   403  		return fmt.Errorf("xml: EncodeElement of StartElement with missing name")
   404  	}
   405  
   406  	if !val.IsValid() {
   407  		return nil
   408  	}
   409  	if finfo != nil && finfo.flags&fOmitEmpty != 0 && isEmptyValue(val) {
   410  		return nil
   411  	}
   412  
   413  	// Drill into interfaces and pointers.
   414  	// This can turn into an infinite loop given a cyclic chain,
   415  	// but it matches the Go 1 behavior.
   416  	for val.Kind() == reflect.Interface || val.Kind() == reflect.Ptr {
   417  		if val.IsNil() {
   418  			return nil
   419  		}
   420  		val = val.Elem()
   421  	}
   422  
   423  	kind := val.Kind()
   424  	typ := val.Type()
   425  
   426  	// Check for marshaler.
   427  	if val.CanInterface() && typ.Implements(marshalerType) {
   428  		return p.marshalInterface(val.Interface().(Marshaler), defaultStart(typ, finfo, startTemplate))
   429  	}
   430  	if val.CanAddr() {
   431  		pv := val.Addr()
   432  		if pv.CanInterface() && pv.Type().Implements(marshalerType) {
   433  			return p.marshalInterface(pv.Interface().(Marshaler), defaultStart(pv.Type(), finfo, startTemplate))
   434  		}
   435  	}
   436  
   437  	// Check for text marshaler.
   438  	if val.CanInterface() && typ.Implements(textMarshalerType) {
   439  		return p.marshalTextInterface(val.Interface().(encoding.TextMarshaler), defaultStart(typ, finfo, startTemplate))
   440  	}
   441  	if val.CanAddr() {
   442  		pv := val.Addr()
   443  		if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   444  			return p.marshalTextInterface(pv.Interface().(encoding.TextMarshaler), defaultStart(pv.Type(), finfo, startTemplate))
   445  		}
   446  	}
   447  
   448  	// Slices and arrays iterate over the elements. They do not have an enclosing tag.
   449  	if (kind == reflect.Slice || kind == reflect.Array) && typ.Elem().Kind() != reflect.Uint8 {
   450  		for i, n := 0, val.Len(); i < n; i++ {
   451  			if err := p.marshalValue(val.Index(i), finfo, startTemplate); err != nil {
   452  				return err
   453  			}
   454  		}
   455  		return nil
   456  	}
   457  
   458  	tinfo, err := getTypeInfo(typ)
   459  	if err != nil {
   460  		return err
   461  	}
   462  
   463  	// Create start element.
   464  	// Precedence for the XML element name is:
   465  	// 0. startTemplate
   466  	// 1. XMLName field in underlying struct;
   467  	// 2. field name/tag in the struct field; and
   468  	// 3. type name
   469  	var start StartElement
   470  
   471  	if startTemplate != nil {
   472  		start.Name = startTemplate.Name
   473  		start.Attr = append(start.Attr, startTemplate.Attr...)
   474  	} else if tinfo.xmlname != nil {
   475  		xmlname := tinfo.xmlname
   476  		if xmlname.name != "" {
   477  			start.Name.Space, start.Name.Local = xmlname.xmlns, xmlname.name
   478  		} else if v, ok := xmlname.value(val).Interface().(Name); ok && v.Local != "" {
   479  			start.Name = v
   480  		}
   481  	}
   482  	if start.Name.Local == "" && finfo != nil {
   483  		start.Name.Space, start.Name.Local = finfo.xmlns, finfo.name
   484  	}
   485  	if start.Name.Local == "" {
   486  		name := typ.Name()
   487  		if name == "" {
   488  			return &UnsupportedTypeError{typ}
   489  		}
   490  		start.Name.Local = name
   491  	}
   492  
   493  	// Attributes
   494  	for i := range tinfo.fields {
   495  		finfo := &tinfo.fields[i]
   496  		if finfo.flags&fAttr == 0 {
   497  			continue
   498  		}
   499  		fv := finfo.value(val)
   500  
   501  		if finfo.flags&fOmitEmpty != 0 && isEmptyValue(fv) {
   502  			continue
   503  		}
   504  
   505  		if fv.Kind() == reflect.Interface && fv.IsNil() {
   506  			continue
   507  		}
   508  
   509  		name := Name{Space: finfo.xmlns, Local: finfo.name}
   510  		if err := p.marshalAttr(&start, name, fv); err != nil {
   511  			return err
   512  		}
   513  	}
   514  
   515  	if err := p.writeStart(&start); err != nil {
   516  		return err
   517  	}
   518  
   519  	if val.Kind() == reflect.Struct {
   520  		err = p.marshalStruct(tinfo, val)
   521  	} else {
   522  		s, b, err1 := p.marshalSimple(typ, val)
   523  		if err1 != nil {
   524  			err = err1
   525  		} else if b != nil {
   526  			EscapeText(p, b)
   527  		} else {
   528  			p.EscapeString(s)
   529  		}
   530  	}
   531  	if err != nil {
   532  		return err
   533  	}
   534  
   535  	if err := p.writeEnd(start.Name); err != nil {
   536  		return err
   537  	}
   538  
   539  	return p.cachedWriteError()
   540  }
   541  
   542  // marshalAttr marshals an attribute with the given name and value, adding to start.Attr.
   543  func (p *printer) marshalAttr(start *StartElement, name Name, val reflect.Value) error {
   544  	if val.CanInterface() && val.Type().Implements(marshalerAttrType) {
   545  		attr, err := val.Interface().(MarshalerAttr).MarshalXMLAttr(name)
   546  		if err != nil {
   547  			return err
   548  		}
   549  		if attr.Name.Local != "" {
   550  			start.Attr = append(start.Attr, attr)
   551  		}
   552  		return nil
   553  	}
   554  
   555  	if val.CanAddr() {
   556  		pv := val.Addr()
   557  		if pv.CanInterface() && pv.Type().Implements(marshalerAttrType) {
   558  			attr, err := pv.Interface().(MarshalerAttr).MarshalXMLAttr(name)
   559  			if err != nil {
   560  				return err
   561  			}
   562  			if attr.Name.Local != "" {
   563  				start.Attr = append(start.Attr, attr)
   564  			}
   565  			return nil
   566  		}
   567  	}
   568  
   569  	if val.CanInterface() && val.Type().Implements(textMarshalerType) {
   570  		text, err := val.Interface().(encoding.TextMarshaler).MarshalText()
   571  		if err != nil {
   572  			return err
   573  		}
   574  		start.Attr = append(start.Attr, Attr{name, string(text)})
   575  		return nil
   576  	}
   577  
   578  	if val.CanAddr() {
   579  		pv := val.Addr()
   580  		if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   581  			text, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
   582  			if err != nil {
   583  				return err
   584  			}
   585  			start.Attr = append(start.Attr, Attr{name, string(text)})
   586  			return nil
   587  		}
   588  	}
   589  
   590  	// Dereference or skip nil pointer, interface values.
   591  	switch val.Kind() {
   592  	case reflect.Ptr, reflect.Interface:
   593  		if val.IsNil() {
   594  			return nil
   595  		}
   596  		val = val.Elem()
   597  	}
   598  
   599  	// Walk slices.
   600  	if val.Kind() == reflect.Slice && val.Type().Elem().Kind() != reflect.Uint8 {
   601  		n := val.Len()
   602  		for i := 0; i < n; i++ {
   603  			if err := p.marshalAttr(start, name, val.Index(i)); err != nil {
   604  				return err
   605  			}
   606  		}
   607  		return nil
   608  	}
   609  
   610  	if val.Type() == attrType {
   611  		start.Attr = append(start.Attr, val.Interface().(Attr))
   612  		return nil
   613  	}
   614  
   615  	s, b, err := p.marshalSimple(val.Type(), val)
   616  	if err != nil {
   617  		return err
   618  	}
   619  	if b != nil {
   620  		s = string(b)
   621  	}
   622  	start.Attr = append(start.Attr, Attr{name, s})
   623  	return nil
   624  }
   625  
   626  // defaultStart returns the default start element to use,
   627  // given the reflect type, field info, and start template.
   628  func defaultStart(typ reflect.Type, finfo *fieldInfo, startTemplate *StartElement) StartElement {
   629  	var start StartElement
   630  	// Precedence for the XML element name is as above,
   631  	// except that we do not look inside structs for the first field.
   632  	if startTemplate != nil {
   633  		start.Name = startTemplate.Name
   634  		start.Attr = append(start.Attr, startTemplate.Attr...)
   635  	} else if finfo != nil && finfo.name != "" {
   636  		start.Name.Local = finfo.name
   637  		start.Name.Space = finfo.xmlns
   638  	} else if typ.Name() != "" {
   639  		start.Name.Local = typ.Name()
   640  	} else {
   641  		// Must be a pointer to a named type,
   642  		// since it has the Marshaler methods.
   643  		start.Name.Local = typ.Elem().Name()
   644  	}
   645  	return start
   646  }
   647  
   648  // marshalInterface marshals a Marshaler interface value.
   649  func (p *printer) marshalInterface(val Marshaler, start StartElement) error {
   650  	// Push a marker onto the tag stack so that MarshalXML
   651  	// cannot close the XML tags that it did not open.
   652  	p.tags = append(p.tags, Name{})
   653  	n := len(p.tags)
   654  
   655  	err := val.MarshalXML(p.encoder, start)
   656  	if err != nil {
   657  		return err
   658  	}
   659  
   660  	// Make sure MarshalXML closed all its tags. p.tags[n-1] is the mark.
   661  	if len(p.tags) > n {
   662  		return fmt.Errorf("xml: %s.MarshalXML wrote invalid XML: <%s> not closed", receiverType(val), p.tags[len(p.tags)-1].Local)
   663  	}
   664  	p.tags = p.tags[:n-1]
   665  	return nil
   666  }
   667  
   668  // marshalTextInterface marshals a TextMarshaler interface value.
   669  func (p *printer) marshalTextInterface(val encoding.TextMarshaler, start StartElement) error {
   670  	if err := p.writeStart(&start); err != nil {
   671  		return err
   672  	}
   673  	text, err := val.MarshalText()
   674  	if err != nil {
   675  		return err
   676  	}
   677  	EscapeText(p, text)
   678  	return p.writeEnd(start.Name)
   679  }
   680  
   681  // writeStart writes the given start element.
   682  func (p *printer) writeStart(start *StartElement) error {
   683  	if start.Name.Local == "" {
   684  		return fmt.Errorf("xml: start tag with no name")
   685  	}
   686  
   687  	p.tags = append(p.tags, start.Name)
   688  	p.markPrefix()
   689  
   690  	p.writeIndent(1)
   691  	p.WriteByte('<')
   692  	p.WriteString(start.Name.Local)
   693  
   694  	if start.Name.Space != "" {
   695  		p.WriteString(` xmlns="`)
   696  		p.EscapeString(start.Name.Space)
   697  		p.WriteByte('"')
   698  	}
   699  
   700  	// Attributes
   701  	for _, attr := range start.Attr {
   702  		name := attr.Name
   703  		if name.Local == "" {
   704  			continue
   705  		}
   706  		p.WriteByte(' ')
   707  		if name.Space != "" {
   708  			p.WriteString(p.createAttrPrefix(name.Space))
   709  			p.WriteByte(':')
   710  		}
   711  		p.WriteString(name.Local)
   712  		p.WriteString(`="`)
   713  		p.EscapeString(attr.Value)
   714  		p.WriteByte('"')
   715  	}
   716  	p.WriteByte('>')
   717  	return nil
   718  }
   719  
   720  func (p *printer) writeEnd(name Name) error {
   721  	if name.Local == "" {
   722  		return fmt.Errorf("xml: end tag with no name")
   723  	}
   724  	if len(p.tags) == 0 || p.tags[len(p.tags)-1].Local == "" {
   725  		return fmt.Errorf("xml: end tag </%s> without start tag", name.Local)
   726  	}
   727  	if top := p.tags[len(p.tags)-1]; top != name {
   728  		if top.Local != name.Local {
   729  			return fmt.Errorf("xml: end tag </%s> does not match start tag <%s>", name.Local, top.Local)
   730  		}
   731  		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)
   732  	}
   733  	p.tags = p.tags[:len(p.tags)-1]
   734  
   735  	p.writeIndent(-1)
   736  	p.WriteByte('<')
   737  	p.WriteByte('/')
   738  	p.WriteString(name.Local)
   739  	p.WriteByte('>')
   740  	p.popPrefix()
   741  	return nil
   742  }
   743  
   744  func (p *printer) marshalSimple(typ reflect.Type, val reflect.Value) (string, []byte, error) {
   745  	switch val.Kind() {
   746  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   747  		return strconv.FormatInt(val.Int(), 10), nil, nil
   748  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   749  		return strconv.FormatUint(val.Uint(), 10), nil, nil
   750  	case reflect.Float32, reflect.Float64:
   751  		return strconv.FormatFloat(val.Float(), 'g', -1, val.Type().Bits()), nil, nil
   752  	case reflect.String:
   753  		return val.String(), nil, nil
   754  	case reflect.Bool:
   755  		return strconv.FormatBool(val.Bool()), nil, nil
   756  	case reflect.Array:
   757  		if typ.Elem().Kind() != reflect.Uint8 {
   758  			break
   759  		}
   760  		// [...]byte
   761  		var bytes []byte
   762  		if val.CanAddr() {
   763  			bytes = val.Slice(0, val.Len()).Bytes()
   764  		} else {
   765  			bytes = make([]byte, val.Len())
   766  			reflect.Copy(reflect.ValueOf(bytes), val)
   767  		}
   768  		return "", bytes, nil
   769  	case reflect.Slice:
   770  		if typ.Elem().Kind() != reflect.Uint8 {
   771  			break
   772  		}
   773  		// []byte
   774  		return "", val.Bytes(), nil
   775  	}
   776  	return "", nil, &UnsupportedTypeError{typ}
   777  }
   778  
   779  var ddBytes = []byte("--")
   780  
   781  // indirect drills into interfaces and pointers, returning the pointed-at value.
   782  // If it encounters a nil interface or pointer, indirect returns that nil value.
   783  // This can turn into an infinite loop given a cyclic chain,
   784  // but it matches the Go 1 behavior.
   785  func indirect(vf reflect.Value) reflect.Value {
   786  	for vf.Kind() == reflect.Interface || vf.Kind() == reflect.Ptr {
   787  		if vf.IsNil() {
   788  			return vf
   789  		}
   790  		vf = vf.Elem()
   791  	}
   792  	return vf
   793  }
   794  
   795  func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
   796  	s := parentStack{p: p}
   797  	for i := range tinfo.fields {
   798  		finfo := &tinfo.fields[i]
   799  		if finfo.flags&fAttr != 0 {
   800  			continue
   801  		}
   802  		vf := finfo.value(val)
   803  
   804  		switch finfo.flags & fMode {
   805  		case fCDATA, fCharData:
   806  			emit := EscapeText
   807  			if finfo.flags&fMode == fCDATA {
   808  				emit = emitCDATA
   809  			}
   810  			if err := s.trim(finfo.parents); err != nil {
   811  				return err
   812  			}
   813  			if vf.CanInterface() && vf.Type().Implements(textMarshalerType) {
   814  				data, err := vf.Interface().(encoding.TextMarshaler).MarshalText()
   815  				if err != nil {
   816  					return err
   817  				}
   818  				if err := emit(p, data); err != nil {
   819  					return err
   820  				}
   821  				continue
   822  			}
   823  			if vf.CanAddr() {
   824  				pv := vf.Addr()
   825  				if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   826  					data, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
   827  					if err != nil {
   828  						return err
   829  					}
   830  					if err := emit(p, data); err != nil {
   831  						return err
   832  					}
   833  					continue
   834  				}
   835  			}
   836  
   837  			var scratch [64]byte
   838  			vf = indirect(vf)
   839  			switch vf.Kind() {
   840  			case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   841  				if err := emit(p, strconv.AppendInt(scratch[:0], vf.Int(), 10)); err != nil {
   842  					return err
   843  				}
   844  			case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   845  				if err := emit(p, strconv.AppendUint(scratch[:0], vf.Uint(), 10)); err != nil {
   846  					return err
   847  				}
   848  			case reflect.Float32, reflect.Float64:
   849  				if err := emit(p, strconv.AppendFloat(scratch[:0], vf.Float(), 'g', -1, vf.Type().Bits())); err != nil {
   850  					return err
   851  				}
   852  			case reflect.Bool:
   853  				if err := emit(p, strconv.AppendBool(scratch[:0], vf.Bool())); err != nil {
   854  					return err
   855  				}
   856  			case reflect.String:
   857  				if err := emit(p, []byte(vf.String())); err != nil {
   858  					return err
   859  				}
   860  			case reflect.Slice:
   861  				if elem, ok := vf.Interface().([]byte); ok {
   862  					if err := emit(p, elem); err != nil {
   863  						return err
   864  					}
   865  				}
   866  			}
   867  			continue
   868  
   869  		case fComment:
   870  			if err := s.trim(finfo.parents); err != nil {
   871  				return err
   872  			}
   873  			vf = indirect(vf)
   874  			k := vf.Kind()
   875  			if !(k == reflect.String || k == reflect.Slice && vf.Type().Elem().Kind() == reflect.Uint8) {
   876  				return fmt.Errorf("xml: bad type for comment field of %s", val.Type())
   877  			}
   878  			if vf.Len() == 0 {
   879  				continue
   880  			}
   881  			p.writeIndent(0)
   882  			p.WriteString("<!--")
   883  			dashDash := false
   884  			dashLast := false
   885  			switch k {
   886  			case reflect.String:
   887  				s := vf.String()
   888  				dashDash = strings.Contains(s, "--")
   889  				dashLast = s[len(s)-1] == '-'
   890  				if !dashDash {
   891  					p.WriteString(s)
   892  				}
   893  			case reflect.Slice:
   894  				b := vf.Bytes()
   895  				dashDash = bytes.Contains(b, ddBytes)
   896  				dashLast = b[len(b)-1] == '-'
   897  				if !dashDash {
   898  					p.Write(b)
   899  				}
   900  			default:
   901  				panic("can't happen")
   902  			}
   903  			if dashDash {
   904  				return fmt.Errorf(`xml: comments must not contain "--"`)
   905  			}
   906  			if dashLast {
   907  				// "--->" is invalid grammar. Make it "- -->"
   908  				p.WriteByte(' ')
   909  			}
   910  			p.WriteString("-->")
   911  			continue
   912  
   913  		case fInnerXml:
   914  			vf = indirect(vf)
   915  			iface := vf.Interface()
   916  			switch raw := iface.(type) {
   917  			case []byte:
   918  				p.Write(raw)
   919  				continue
   920  			case string:
   921  				p.WriteString(raw)
   922  				continue
   923  			}
   924  
   925  		case fElement, fElement | fAny:
   926  			if err := s.trim(finfo.parents); err != nil {
   927  				return err
   928  			}
   929  			if len(finfo.parents) > len(s.stack) {
   930  				if vf.Kind() != reflect.Ptr && vf.Kind() != reflect.Interface || !vf.IsNil() {
   931  					if err := s.push(finfo.parents[len(s.stack):]); err != nil {
   932  						return err
   933  					}
   934  				}
   935  			}
   936  		}
   937  		if err := p.marshalValue(vf, finfo, nil); err != nil {
   938  			return err
   939  		}
   940  	}
   941  	s.trim(nil)
   942  	return p.cachedWriteError()
   943  }
   944  
   945  // return the bufio Writer's cached write error
   946  func (p *printer) cachedWriteError() error {
   947  	_, err := p.Write(nil)
   948  	return err
   949  }
   950  
   951  func (p *printer) writeIndent(depthDelta int) {
   952  	if len(p.prefix) == 0 && len(p.indent) == 0 {
   953  		return
   954  	}
   955  	if depthDelta < 0 {
   956  		p.depth--
   957  		if p.indentedIn {
   958  			p.indentedIn = false
   959  			return
   960  		}
   961  		p.indentedIn = false
   962  	}
   963  	if p.putNewline {
   964  		p.WriteByte('\n')
   965  	} else {
   966  		p.putNewline = true
   967  	}
   968  	if len(p.prefix) > 0 {
   969  		p.WriteString(p.prefix)
   970  	}
   971  	if len(p.indent) > 0 {
   972  		for i := 0; i < p.depth; i++ {
   973  			p.WriteString(p.indent)
   974  		}
   975  	}
   976  	if depthDelta > 0 {
   977  		p.depth++
   978  		p.indentedIn = true
   979  	}
   980  }
   981  
   982  type parentStack struct {
   983  	p     *printer
   984  	stack []string
   985  }
   986  
   987  // trim updates the XML context to match the longest common prefix of the stack
   988  // and the given parents. A closing tag will be written for every parent
   989  // popped. Passing a zero slice or nil will close all the elements.
   990  func (s *parentStack) trim(parents []string) error {
   991  	split := 0
   992  	for ; split < len(parents) && split < len(s.stack); split++ {
   993  		if parents[split] != s.stack[split] {
   994  			break
   995  		}
   996  	}
   997  	for i := len(s.stack) - 1; i >= split; i-- {
   998  		if err := s.p.writeEnd(Name{Local: s.stack[i]}); err != nil {
   999  			return err
  1000  		}
  1001  	}
  1002  	s.stack = s.stack[:split]
  1003  	return nil
  1004  }
  1005  
  1006  // push adds parent elements to the stack and writes open tags.
  1007  func (s *parentStack) push(parents []string) error {
  1008  	for i := 0; i < len(parents); i++ {
  1009  		if err := s.p.writeStart(&StartElement{Name: Name{Local: parents[i]}}); err != nil {
  1010  			return err
  1011  		}
  1012  	}
  1013  	s.stack = append(s.stack, parents...)
  1014  	return nil
  1015  }
  1016  
  1017  // UnsupportedTypeError is returned when Marshal encounters a type
  1018  // that cannot be converted into XML.
  1019  type UnsupportedTypeError struct {
  1020  	Type reflect.Type
  1021  }
  1022  
  1023  func (e *UnsupportedTypeError) Error() string {
  1024  	return "xml: unsupported type: " + e.Type.String()
  1025  }
  1026  
  1027  func isEmptyValue(v reflect.Value) bool {
  1028  	switch v.Kind() {
  1029  	case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
  1030  		return v.Len() == 0
  1031  	case reflect.Bool:
  1032  		return !v.Bool()
  1033  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
  1034  		return v.Int() == 0
  1035  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
  1036  		return v.Uint() == 0
  1037  	case reflect.Float32, reflect.Float64:
  1038  		return v.Float() == 0
  1039  	case reflect.Interface, reflect.Ptr:
  1040  		return v.IsNil()
  1041  	}
  1042  	return false
  1043  }
  1044  

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