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  //		 - a field implementing Marshaler is written by calling its MarshalXML
		65  //			 method.
		66  //		 - a field implementing encoding.TextMarshaler is written by encoding the
		67  //			 result of its MarshalText method as text.
		68  //
		69  // If a field uses a tag "a>b>c", then the element c will be nested inside
		70  // parent elements a and b. Fields that appear next to each other that name
		71  // the same parent will be enclosed in one XML element.
		72  //
		73  // If the XML name for a struct field is defined by both the field tag and the
		74  // struct's XMLName field, the names must match.
		75  //
		76  // See MarshalIndent for an example.
		77  //
		78  // Marshal will return an error if asked to marshal a channel, function, or map.
		79  func Marshal(v interface{}) ([]byte, error) {
		80  	var b bytes.Buffer
		81  	if err := NewEncoder(&b).Encode(v); err != nil {
		82  		return nil, err
		83  	}
		84  	return b.Bytes(), nil
		85  }
		86  
		87  // Marshaler is the interface implemented by objects that can marshal
		88  // themselves into valid XML elements.
		89  //
		90  // MarshalXML encodes the receiver as zero or more XML elements.
		91  // By convention, arrays or slices are typically encoded as a sequence
		92  // of elements, one per entry.
		93  // Using start as the element tag is not required, but doing so
		94  // will enable Unmarshal to match the XML elements to the correct
		95  // struct field.
		96  // One common implementation strategy is to construct a separate
		97  // value with a layout corresponding to the desired XML and then
		98  // to encode it using e.EncodeElement.
		99  // Another common strategy is to use repeated calls to e.EncodeToken
	 100  // to generate the XML output one token at a time.
	 101  // The sequence of encoded tokens must make up zero or more valid
	 102  // XML elements.
	 103  type Marshaler interface {
	 104  	MarshalXML(e *Encoder, start StartElement) error
	 105  }
	 106  
	 107  // MarshalerAttr is the interface implemented by objects that can marshal
	 108  // themselves into valid XML attributes.
	 109  //
	 110  // MarshalXMLAttr returns an XML attribute with the encoded value of the receiver.
	 111  // Using name as the attribute name is not required, but doing so
	 112  // will enable Unmarshal to match the attribute to the correct
	 113  // struct field.
	 114  // If MarshalXMLAttr returns the zero attribute Attr{}, no attribute
	 115  // will be generated in the output.
	 116  // MarshalXMLAttr is used only for struct fields with the
	 117  // "attr" option in the field tag.
	 118  type MarshalerAttr interface {
	 119  	MarshalXMLAttr(name Name) (Attr, error)
	 120  }
	 121  
	 122  // MarshalIndent works like Marshal, but each XML element begins on a new
	 123  // indented line that starts with prefix and is followed by one or more
	 124  // copies of indent according to the nesting depth.
	 125  func MarshalIndent(v interface{}, prefix, indent string) ([]byte, error) {
	 126  	var b bytes.Buffer
	 127  	enc := NewEncoder(&b)
	 128  	enc.Indent(prefix, indent)
	 129  	if err := enc.Encode(v); err != nil {
	 130  		return nil, err
	 131  	}
	 132  	return b.Bytes(), nil
	 133  }
	 134  
	 135  // An Encoder writes XML data to an output stream.
	 136  type Encoder struct {
	 137  	p printer
	 138  }
	 139  
	 140  // NewEncoder returns a new encoder that writes to w.
	 141  func NewEncoder(w io.Writer) *Encoder {
	 142  	e := &Encoder{printer{Writer: bufio.NewWriter(w)}}
	 143  	e.p.encoder = e
	 144  	return e
	 145  }
	 146  
	 147  // Indent sets the encoder to generate XML in which each element
	 148  // begins on a new indented line that starts with prefix and is followed by
	 149  // one or more copies of indent according to the nesting depth.
	 150  func (enc *Encoder) Indent(prefix, indent string) {
	 151  	enc.p.prefix = prefix
	 152  	enc.p.indent = indent
	 153  }
	 154  
	 155  // Encode writes the XML encoding of v to the stream.
	 156  //
	 157  // See the documentation for Marshal for details about the conversion
	 158  // of Go values to XML.
	 159  //
	 160  // Encode calls Flush before returning.
	 161  func (enc *Encoder) Encode(v interface{}) error {
	 162  	err := enc.p.marshalValue(reflect.ValueOf(v), nil, nil)
	 163  	if err != nil {
	 164  		return err
	 165  	}
	 166  	return enc.p.Flush()
	 167  }
	 168  
	 169  // EncodeElement writes the XML encoding of v to the stream,
	 170  // using start as the outermost tag in the encoding.
	 171  //
	 172  // See the documentation for Marshal for details about the conversion
	 173  // of Go values to XML.
	 174  //
	 175  // EncodeElement calls Flush before returning.
	 176  func (enc *Encoder) EncodeElement(v interface{}, start StartElement) error {
	 177  	err := enc.p.marshalValue(reflect.ValueOf(v), nil, &start)
	 178  	if err != nil {
	 179  		return err
	 180  	}
	 181  	return enc.p.Flush()
	 182  }
	 183  
	 184  var (
	 185  	begComment	= []byte("<!--")
	 186  	endComment	= []byte("-->")
	 187  	endProcInst = []byte("?>")
	 188  )
	 189  
	 190  // EncodeToken writes the given XML token to the stream.
	 191  // It returns an error if StartElement and EndElement tokens are not properly matched.
	 192  //
	 193  // EncodeToken does not call Flush, because usually it is part of a larger operation
	 194  // such as Encode or EncodeElement (or a custom Marshaler's MarshalXML invoked
	 195  // during those), and those will call Flush when finished.
	 196  // Callers that create an Encoder and then invoke EncodeToken directly, without
	 197  // using Encode or EncodeElement, need to call Flush when finished to ensure
	 198  // that the XML is written to the underlying writer.
	 199  //
	 200  // EncodeToken allows writing a ProcInst with Target set to "xml" only as the first token
	 201  // in the stream.
	 202  func (enc *Encoder) EncodeToken(t Token) error {
	 203  
	 204  	p := &enc.p
	 205  	switch t := t.(type) {
	 206  	case StartElement:
	 207  		if err := p.writeStart(&t); err != nil {
	 208  			return err
	 209  		}
	 210  	case EndElement:
	 211  		if err := p.writeEnd(t.Name); err != nil {
	 212  			return err
	 213  		}
	 214  	case CharData:
	 215  		escapeText(p, t, false)
	 216  	case Comment:
	 217  		if bytes.Contains(t, endComment) {
	 218  			return fmt.Errorf("xml: EncodeToken of Comment containing --> marker")
	 219  		}
	 220  		p.WriteString("<!--")
	 221  		p.Write(t)
	 222  		p.WriteString("-->")
	 223  		return p.cachedWriteError()
	 224  	case ProcInst:
	 225  		// First token to be encoded which is also a ProcInst with target of xml
	 226  		// is the xml declaration. The only ProcInst where target of xml is allowed.
	 227  		if t.Target == "xml" && p.Buffered() != 0 {
	 228  			return fmt.Errorf("xml: EncodeToken of ProcInst xml target only valid for xml declaration, first token encoded")
	 229  		}
	 230  		if !isNameString(t.Target) {
	 231  			return fmt.Errorf("xml: EncodeToken of ProcInst with invalid Target")
	 232  		}
	 233  		if bytes.Contains(t.Inst, endProcInst) {
	 234  			return fmt.Errorf("xml: EncodeToken of ProcInst containing ?> marker")
	 235  		}
	 236  		p.WriteString("<?")
	 237  		p.WriteString(t.Target)
	 238  		if len(t.Inst) > 0 {
	 239  			p.WriteByte(' ')
	 240  			p.Write(t.Inst)
	 241  		}
	 242  		p.WriteString("?>")
	 243  	case Directive:
	 244  		if !isValidDirective(t) {
	 245  			return fmt.Errorf("xml: EncodeToken of Directive containing wrong < or > markers")
	 246  		}
	 247  		p.WriteString("<!")
	 248  		p.Write(t)
	 249  		p.WriteString(">")
	 250  	default:
	 251  		return fmt.Errorf("xml: EncodeToken of invalid token type")
	 252  
	 253  	}
	 254  	return p.cachedWriteError()
	 255  }
	 256  
	 257  // isValidDirective reports whether dir is a valid directive text,
	 258  // meaning angle brackets are matched, ignoring comments and strings.
	 259  func isValidDirective(dir Directive) bool {
	 260  	var (
	 261  		depth		 int
	 262  		inquote	 uint8
	 263  		incomment bool
	 264  	)
	 265  	for i, c := range dir {
	 266  		switch {
	 267  		case incomment:
	 268  			if c == '>' {
	 269  				if n := 1 + i - len(endComment); n >= 0 && bytes.Equal(dir[n:i+1], endComment) {
	 270  					incomment = false
	 271  				}
	 272  			}
	 273  			// Just ignore anything in comment
	 274  		case inquote != 0:
	 275  			if c == inquote {
	 276  				inquote = 0
	 277  			}
	 278  			// Just ignore anything within quotes
	 279  		case c == '\'' || c == '"':
	 280  			inquote = c
	 281  		case c == '<':
	 282  			if i+len(begComment) < len(dir) && bytes.Equal(dir[i:i+len(begComment)], begComment) {
	 283  				incomment = true
	 284  			} else {
	 285  				depth++
	 286  			}
	 287  		case c == '>':
	 288  			if depth == 0 {
	 289  				return false
	 290  			}
	 291  			depth--
	 292  		}
	 293  	}
	 294  	return depth == 0 && inquote == 0 && !incomment
	 295  }
	 296  
	 297  // Flush flushes any buffered XML to the underlying writer.
	 298  // See the EncodeToken documentation for details about when it is necessary.
	 299  func (enc *Encoder) Flush() error {
	 300  	return enc.p.Flush()
	 301  }
	 302  
	 303  type printer struct {
	 304  	*bufio.Writer
	 305  	encoder		*Encoder
	 306  	seq				int
	 307  	indent		 string
	 308  	prefix		 string
	 309  	depth			int
	 310  	indentedIn bool
	 311  	putNewline bool
	 312  	attrNS		 map[string]string // map prefix -> name space
	 313  	attrPrefix map[string]string // map name space -> prefix
	 314  	prefixes	 []string
	 315  	tags			 []Name
	 316  }
	 317  
	 318  // createAttrPrefix finds the name space prefix attribute to use for the given name space,
	 319  // defining a new prefix if necessary. It returns the prefix.
	 320  func (p *printer) createAttrPrefix(url string) string {
	 321  	if prefix := p.attrPrefix[url]; prefix != "" {
	 322  		return prefix
	 323  	}
	 324  
	 325  	// The "http://www.w3.org/XML/1998/namespace" name space is predefined as "xml"
	 326  	// and must be referred to that way.
	 327  	// (The "http://www.w3.org/2000/xmlns/" name space is also predefined as "xmlns",
	 328  	// but users should not be trying to use that one directly - that's our job.)
	 329  	if url == xmlURL {
	 330  		return xmlPrefix
	 331  	}
	 332  
	 333  	// Need to define a new name space.
	 334  	if p.attrPrefix == nil {
	 335  		p.attrPrefix = make(map[string]string)
	 336  		p.attrNS = make(map[string]string)
	 337  	}
	 338  
	 339  	// Pick a name. We try to use the final element of the path
	 340  	// but fall back to _.
	 341  	prefix := strings.TrimRight(url, "/")
	 342  	if i := strings.LastIndex(prefix, "/"); i >= 0 {
	 343  		prefix = prefix[i+1:]
	 344  	}
	 345  	if prefix == "" || !isName([]byte(prefix)) || strings.Contains(prefix, ":") {
	 346  		prefix = "_"
	 347  	}
	 348  	// xmlanything is reserved and any variant of it regardless of
	 349  	// case should be matched, so:
	 350  	//		(('X'|'x') ('M'|'m') ('L'|'l'))
	 351  	// See Section 2.3 of https://www.w3.org/TR/REC-xml/
	 352  	if len(prefix) >= 3 && strings.EqualFold(prefix[:3], "xml") {
	 353  		prefix = "_" + prefix
	 354  	}
	 355  	if p.attrNS[prefix] != "" {
	 356  		// Name is taken. Find a better one.
	 357  		for p.seq++; ; p.seq++ {
	 358  			if id := prefix + "_" + strconv.Itoa(p.seq); p.attrNS[id] == "" {
	 359  				prefix = id
	 360  				break
	 361  			}
	 362  		}
	 363  	}
	 364  
	 365  	p.attrPrefix[url] = prefix
	 366  	p.attrNS[prefix] = url
	 367  
	 368  	p.WriteString(`xmlns:`)
	 369  	p.WriteString(prefix)
	 370  	p.WriteString(`="`)
	 371  	EscapeText(p, []byte(url))
	 372  	p.WriteString(`" `)
	 373  
	 374  	p.prefixes = append(p.prefixes, prefix)
	 375  
	 376  	return prefix
	 377  }
	 378  
	 379  // deleteAttrPrefix removes an attribute name space prefix.
	 380  func (p *printer) deleteAttrPrefix(prefix string) {
	 381  	delete(p.attrPrefix, p.attrNS[prefix])
	 382  	delete(p.attrNS, prefix)
	 383  }
	 384  
	 385  func (p *printer) markPrefix() {
	 386  	p.prefixes = append(p.prefixes, "")
	 387  }
	 388  
	 389  func (p *printer) popPrefix() {
	 390  	for len(p.prefixes) > 0 {
	 391  		prefix := p.prefixes[len(p.prefixes)-1]
	 392  		p.prefixes = p.prefixes[:len(p.prefixes)-1]
	 393  		if prefix == "" {
	 394  			break
	 395  		}
	 396  		p.deleteAttrPrefix(prefix)
	 397  	}
	 398  }
	 399  
	 400  var (
	 401  	marshalerType		 = reflect.TypeOf((*Marshaler)(nil)).Elem()
	 402  	marshalerAttrType = reflect.TypeOf((*MarshalerAttr)(nil)).Elem()
	 403  	textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
	 404  )
	 405  
	 406  // marshalValue writes one or more XML elements representing val.
	 407  // If val was obtained from a struct field, finfo must have its details.
	 408  func (p *printer) marshalValue(val reflect.Value, finfo *fieldInfo, startTemplate *StartElement) error {
	 409  	if startTemplate != nil && startTemplate.Name.Local == "" {
	 410  		return fmt.Errorf("xml: EncodeElement of StartElement with missing name")
	 411  	}
	 412  
	 413  	if !val.IsValid() {
	 414  		return nil
	 415  	}
	 416  	if finfo != nil && finfo.flags&fOmitEmpty != 0 && isEmptyValue(val) {
	 417  		return nil
	 418  	}
	 419  
	 420  	// Drill into interfaces and pointers.
	 421  	// This can turn into an infinite loop given a cyclic chain,
	 422  	// but it matches the Go 1 behavior.
	 423  	for val.Kind() == reflect.Interface || val.Kind() == reflect.Ptr {
	 424  		if val.IsNil() {
	 425  			return nil
	 426  		}
	 427  		val = val.Elem()
	 428  	}
	 429  
	 430  	kind := val.Kind()
	 431  	typ := val.Type()
	 432  
	 433  	// Check for marshaler.
	 434  	if val.CanInterface() && typ.Implements(marshalerType) {
	 435  		return p.marshalInterface(val.Interface().(Marshaler), defaultStart(typ, finfo, startTemplate))
	 436  	}
	 437  	if val.CanAddr() {
	 438  		pv := val.Addr()
	 439  		if pv.CanInterface() && pv.Type().Implements(marshalerType) {
	 440  			return p.marshalInterface(pv.Interface().(Marshaler), defaultStart(pv.Type(), finfo, startTemplate))
	 441  		}
	 442  	}
	 443  
	 444  	// Check for text marshaler.
	 445  	if val.CanInterface() && typ.Implements(textMarshalerType) {
	 446  		return p.marshalTextInterface(val.Interface().(encoding.TextMarshaler), defaultStart(typ, finfo, startTemplate))
	 447  	}
	 448  	if val.CanAddr() {
	 449  		pv := val.Addr()
	 450  		if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
	 451  			return p.marshalTextInterface(pv.Interface().(encoding.TextMarshaler), defaultStart(pv.Type(), finfo, startTemplate))
	 452  		}
	 453  	}
	 454  
	 455  	// Slices and arrays iterate over the elements. They do not have an enclosing tag.
	 456  	if (kind == reflect.Slice || kind == reflect.Array) && typ.Elem().Kind() != reflect.Uint8 {
	 457  		for i, n := 0, val.Len(); i < n; i++ {
	 458  			if err := p.marshalValue(val.Index(i), finfo, startTemplate); err != nil {
	 459  				return err
	 460  			}
	 461  		}
	 462  		return nil
	 463  	}
	 464  
	 465  	tinfo, err := getTypeInfo(typ)
	 466  	if err != nil {
	 467  		return err
	 468  	}
	 469  
	 470  	// Create start element.
	 471  	// Precedence for the XML element name is:
	 472  	// 0. startTemplate
	 473  	// 1. XMLName field in underlying struct;
	 474  	// 2. field name/tag in the struct field; and
	 475  	// 3. type name
	 476  	var start StartElement
	 477  
	 478  	if startTemplate != nil {
	 479  		start.Name = startTemplate.Name
	 480  		start.Attr = append(start.Attr, startTemplate.Attr...)
	 481  	} else if tinfo.xmlname != nil {
	 482  		xmlname := tinfo.xmlname
	 483  		if xmlname.name != "" {
	 484  			start.Name.Space, start.Name.Local = xmlname.xmlns, xmlname.name
	 485  		} else {
	 486  			fv := xmlname.value(val, dontInitNilPointers)
	 487  			if v, ok := fv.Interface().(Name); ok && v.Local != "" {
	 488  				start.Name = v
	 489  			}
	 490  		}
	 491  	}
	 492  	if start.Name.Local == "" && finfo != nil {
	 493  		start.Name.Space, start.Name.Local = finfo.xmlns, finfo.name
	 494  	}
	 495  	if start.Name.Local == "" {
	 496  		name := typ.Name()
	 497  		if name == "" {
	 498  			return &UnsupportedTypeError{typ}
	 499  		}
	 500  		start.Name.Local = name
	 501  	}
	 502  
	 503  	// Attributes
	 504  	for i := range tinfo.fields {
	 505  		finfo := &tinfo.fields[i]
	 506  		if finfo.flags&fAttr == 0 {
	 507  			continue
	 508  		}
	 509  		fv := finfo.value(val, dontInitNilPointers)
	 510  
	 511  		if finfo.flags&fOmitEmpty != 0 && isEmptyValue(fv) {
	 512  			continue
	 513  		}
	 514  
	 515  		if fv.Kind() == reflect.Interface && fv.IsNil() {
	 516  			continue
	 517  		}
	 518  
	 519  		name := Name{Space: finfo.xmlns, Local: finfo.name}
	 520  		if err := p.marshalAttr(&start, name, fv); err != nil {
	 521  			return err
	 522  		}
	 523  	}
	 524  
	 525  	if err := p.writeStart(&start); err != nil {
	 526  		return err
	 527  	}
	 528  
	 529  	if val.Kind() == reflect.Struct {
	 530  		err = p.marshalStruct(tinfo, val)
	 531  	} else {
	 532  		s, b, err1 := p.marshalSimple(typ, val)
	 533  		if err1 != nil {
	 534  			err = err1
	 535  		} else if b != nil {
	 536  			EscapeText(p, b)
	 537  		} else {
	 538  			p.EscapeString(s)
	 539  		}
	 540  	}
	 541  	if err != nil {
	 542  		return err
	 543  	}
	 544  
	 545  	if err := p.writeEnd(start.Name); err != nil {
	 546  		return err
	 547  	}
	 548  
	 549  	return p.cachedWriteError()
	 550  }
	 551  
	 552  // marshalAttr marshals an attribute with the given name and value, adding to start.Attr.
	 553  func (p *printer) marshalAttr(start *StartElement, name Name, val reflect.Value) error {
	 554  	if val.CanInterface() && val.Type().Implements(marshalerAttrType) {
	 555  		attr, err := val.Interface().(MarshalerAttr).MarshalXMLAttr(name)
	 556  		if err != nil {
	 557  			return err
	 558  		}
	 559  		if attr.Name.Local != "" {
	 560  			start.Attr = append(start.Attr, attr)
	 561  		}
	 562  		return nil
	 563  	}
	 564  
	 565  	if val.CanAddr() {
	 566  		pv := val.Addr()
	 567  		if pv.CanInterface() && pv.Type().Implements(marshalerAttrType) {
	 568  			attr, err := pv.Interface().(MarshalerAttr).MarshalXMLAttr(name)
	 569  			if err != nil {
	 570  				return err
	 571  			}
	 572  			if attr.Name.Local != "" {
	 573  				start.Attr = append(start.Attr, attr)
	 574  			}
	 575  			return nil
	 576  		}
	 577  	}
	 578  
	 579  	if val.CanInterface() && val.Type().Implements(textMarshalerType) {
	 580  		text, err := val.Interface().(encoding.TextMarshaler).MarshalText()
	 581  		if err != nil {
	 582  			return err
	 583  		}
	 584  		start.Attr = append(start.Attr, Attr{name, string(text)})
	 585  		return nil
	 586  	}
	 587  
	 588  	if val.CanAddr() {
	 589  		pv := val.Addr()
	 590  		if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
	 591  			text, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
	 592  			if err != nil {
	 593  				return err
	 594  			}
	 595  			start.Attr = append(start.Attr, Attr{name, string(text)})
	 596  			return nil
	 597  		}
	 598  	}
	 599  
	 600  	// Dereference or skip nil pointer, interface values.
	 601  	switch val.Kind() {
	 602  	case reflect.Ptr, reflect.Interface:
	 603  		if val.IsNil() {
	 604  			return nil
	 605  		}
	 606  		val = val.Elem()
	 607  	}
	 608  
	 609  	// Walk slices.
	 610  	if val.Kind() == reflect.Slice && val.Type().Elem().Kind() != reflect.Uint8 {
	 611  		n := val.Len()
	 612  		for i := 0; i < n; i++ {
	 613  			if err := p.marshalAttr(start, name, val.Index(i)); err != nil {
	 614  				return err
	 615  			}
	 616  		}
	 617  		return nil
	 618  	}
	 619  
	 620  	if val.Type() == attrType {
	 621  		start.Attr = append(start.Attr, val.Interface().(Attr))
	 622  		return nil
	 623  	}
	 624  
	 625  	s, b, err := p.marshalSimple(val.Type(), val)
	 626  	if err != nil {
	 627  		return err
	 628  	}
	 629  	if b != nil {
	 630  		s = string(b)
	 631  	}
	 632  	start.Attr = append(start.Attr, Attr{name, s})
	 633  	return nil
	 634  }
	 635  
	 636  // defaultStart returns the default start element to use,
	 637  // given the reflect type, field info, and start template.
	 638  func defaultStart(typ reflect.Type, finfo *fieldInfo, startTemplate *StartElement) StartElement {
	 639  	var start StartElement
	 640  	// Precedence for the XML element name is as above,
	 641  	// except that we do not look inside structs for the first field.
	 642  	if startTemplate != nil {
	 643  		start.Name = startTemplate.Name
	 644  		start.Attr = append(start.Attr, startTemplate.Attr...)
	 645  	} else if finfo != nil && finfo.name != "" {
	 646  		start.Name.Local = finfo.name
	 647  		start.Name.Space = finfo.xmlns
	 648  	} else if typ.Name() != "" {
	 649  		start.Name.Local = typ.Name()
	 650  	} else {
	 651  		// Must be a pointer to a named type,
	 652  		// since it has the Marshaler methods.
	 653  		start.Name.Local = typ.Elem().Name()
	 654  	}
	 655  	return start
	 656  }
	 657  
	 658  // marshalInterface marshals a Marshaler interface value.
	 659  func (p *printer) marshalInterface(val Marshaler, start StartElement) error {
	 660  	// Push a marker onto the tag stack so that MarshalXML
	 661  	// cannot close the XML tags that it did not open.
	 662  	p.tags = append(p.tags, Name{})
	 663  	n := len(p.tags)
	 664  
	 665  	err := val.MarshalXML(p.encoder, start)
	 666  	if err != nil {
	 667  		return err
	 668  	}
	 669  
	 670  	// Make sure MarshalXML closed all its tags. p.tags[n-1] is the mark.
	 671  	if len(p.tags) > n {
	 672  		return fmt.Errorf("xml: %s.MarshalXML wrote invalid XML: <%s> not closed", receiverType(val), p.tags[len(p.tags)-1].Local)
	 673  	}
	 674  	p.tags = p.tags[:n-1]
	 675  	return nil
	 676  }
	 677  
	 678  // marshalTextInterface marshals a TextMarshaler interface value.
	 679  func (p *printer) marshalTextInterface(val encoding.TextMarshaler, start StartElement) error {
	 680  	if err := p.writeStart(&start); err != nil {
	 681  		return err
	 682  	}
	 683  	text, err := val.MarshalText()
	 684  	if err != nil {
	 685  		return err
	 686  	}
	 687  	EscapeText(p, text)
	 688  	return p.writeEnd(start.Name)
	 689  }
	 690  
	 691  // writeStart writes the given start element.
	 692  func (p *printer) writeStart(start *StartElement) error {
	 693  	if start.Name.Local == "" {
	 694  		return fmt.Errorf("xml: start tag with no name")
	 695  	}
	 696  
	 697  	p.tags = append(p.tags, start.Name)
	 698  	p.markPrefix()
	 699  
	 700  	p.writeIndent(1)
	 701  	p.WriteByte('<')
	 702  	p.WriteString(start.Name.Local)
	 703  
	 704  	if start.Name.Space != "" {
	 705  		p.WriteString(` xmlns="`)
	 706  		p.EscapeString(start.Name.Space)
	 707  		p.WriteByte('"')
	 708  	}
	 709  
	 710  	// Attributes
	 711  	for _, attr := range start.Attr {
	 712  		name := attr.Name
	 713  		if name.Local == "" {
	 714  			continue
	 715  		}
	 716  		p.WriteByte(' ')
	 717  		if name.Space != "" {
	 718  			p.WriteString(p.createAttrPrefix(name.Space))
	 719  			p.WriteByte(':')
	 720  		}
	 721  		p.WriteString(name.Local)
	 722  		p.WriteString(`="`)
	 723  		p.EscapeString(attr.Value)
	 724  		p.WriteByte('"')
	 725  	}
	 726  	p.WriteByte('>')
	 727  	return nil
	 728  }
	 729  
	 730  func (p *printer) writeEnd(name Name) error {
	 731  	if name.Local == "" {
	 732  		return fmt.Errorf("xml: end tag with no name")
	 733  	}
	 734  	if len(p.tags) == 0 || p.tags[len(p.tags)-1].Local == "" {
	 735  		return fmt.Errorf("xml: end tag </%s> without start tag", name.Local)
	 736  	}
	 737  	if top := p.tags[len(p.tags)-1]; top != name {
	 738  		if top.Local != name.Local {
	 739  			return fmt.Errorf("xml: end tag </%s> does not match start tag <%s>", name.Local, top.Local)
	 740  		}
	 741  		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)
	 742  	}
	 743  	p.tags = p.tags[:len(p.tags)-1]
	 744  
	 745  	p.writeIndent(-1)
	 746  	p.WriteByte('<')
	 747  	p.WriteByte('/')
	 748  	p.WriteString(name.Local)
	 749  	p.WriteByte('>')
	 750  	p.popPrefix()
	 751  	return nil
	 752  }
	 753  
	 754  func (p *printer) marshalSimple(typ reflect.Type, val reflect.Value) (string, []byte, error) {
	 755  	switch val.Kind() {
	 756  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
	 757  		return strconv.FormatInt(val.Int(), 10), nil, nil
	 758  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
	 759  		return strconv.FormatUint(val.Uint(), 10), nil, nil
	 760  	case reflect.Float32, reflect.Float64:
	 761  		return strconv.FormatFloat(val.Float(), 'g', -1, val.Type().Bits()), nil, nil
	 762  	case reflect.String:
	 763  		return val.String(), nil, nil
	 764  	case reflect.Bool:
	 765  		return strconv.FormatBool(val.Bool()), nil, nil
	 766  	case reflect.Array:
	 767  		if typ.Elem().Kind() != reflect.Uint8 {
	 768  			break
	 769  		}
	 770  		// [...]byte
	 771  		var bytes []byte
	 772  		if val.CanAddr() {
	 773  			bytes = val.Slice(0, val.Len()).Bytes()
	 774  		} else {
	 775  			bytes = make([]byte, val.Len())
	 776  			reflect.Copy(reflect.ValueOf(bytes), val)
	 777  		}
	 778  		return "", bytes, nil
	 779  	case reflect.Slice:
	 780  		if typ.Elem().Kind() != reflect.Uint8 {
	 781  			break
	 782  		}
	 783  		// []byte
	 784  		return "", val.Bytes(), nil
	 785  	}
	 786  	return "", nil, &UnsupportedTypeError{typ}
	 787  }
	 788  
	 789  var ddBytes = []byte("--")
	 790  
	 791  // indirect drills into interfaces and pointers, returning the pointed-at value.
	 792  // If it encounters a nil interface or pointer, indirect returns that nil value.
	 793  // This can turn into an infinite loop given a cyclic chain,
	 794  // but it matches the Go 1 behavior.
	 795  func indirect(vf reflect.Value) reflect.Value {
	 796  	for vf.Kind() == reflect.Interface || vf.Kind() == reflect.Ptr {
	 797  		if vf.IsNil() {
	 798  			return vf
	 799  		}
	 800  		vf = vf.Elem()
	 801  	}
	 802  	return vf
	 803  }
	 804  
	 805  func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
	 806  	s := parentStack{p: p}
	 807  	for i := range tinfo.fields {
	 808  		finfo := &tinfo.fields[i]
	 809  		if finfo.flags&fAttr != 0 {
	 810  			continue
	 811  		}
	 812  		vf := finfo.value(val, dontInitNilPointers)
	 813  		if !vf.IsValid() {
	 814  			// The field is behind an anonymous struct field that's
	 815  			// nil. Skip it.
	 816  			continue
	 817  		}
	 818  
	 819  		switch finfo.flags & fMode {
	 820  		case fCDATA, fCharData:
	 821  			emit := EscapeText
	 822  			if finfo.flags&fMode == fCDATA {
	 823  				emit = emitCDATA
	 824  			}
	 825  			if err := s.trim(finfo.parents); err != nil {
	 826  				return err
	 827  			}
	 828  			if vf.CanInterface() && vf.Type().Implements(textMarshalerType) {
	 829  				data, err := vf.Interface().(encoding.TextMarshaler).MarshalText()
	 830  				if err != nil {
	 831  					return err
	 832  				}
	 833  				if err := emit(p, data); err != nil {
	 834  					return err
	 835  				}
	 836  				continue
	 837  			}
	 838  			if vf.CanAddr() {
	 839  				pv := vf.Addr()
	 840  				if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
	 841  					data, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
	 842  					if err != nil {
	 843  						return err
	 844  					}
	 845  					if err := emit(p, data); err != nil {
	 846  						return err
	 847  					}
	 848  					continue
	 849  				}
	 850  			}
	 851  
	 852  			var scratch [64]byte
	 853  			vf = indirect(vf)
	 854  			switch vf.Kind() {
	 855  			case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
	 856  				if err := emit(p, strconv.AppendInt(scratch[:0], vf.Int(), 10)); err != nil {
	 857  					return err
	 858  				}
	 859  			case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
	 860  				if err := emit(p, strconv.AppendUint(scratch[:0], vf.Uint(), 10)); err != nil {
	 861  					return err
	 862  				}
	 863  			case reflect.Float32, reflect.Float64:
	 864  				if err := emit(p, strconv.AppendFloat(scratch[:0], vf.Float(), 'g', -1, vf.Type().Bits())); err != nil {
	 865  					return err
	 866  				}
	 867  			case reflect.Bool:
	 868  				if err := emit(p, strconv.AppendBool(scratch[:0], vf.Bool())); err != nil {
	 869  					return err
	 870  				}
	 871  			case reflect.String:
	 872  				if err := emit(p, []byte(vf.String())); err != nil {
	 873  					return err
	 874  				}
	 875  			case reflect.Slice:
	 876  				if elem, ok := vf.Interface().([]byte); ok {
	 877  					if err := emit(p, elem); err != nil {
	 878  						return err
	 879  					}
	 880  				}
	 881  			}
	 882  			continue
	 883  
	 884  		case fComment:
	 885  			if err := s.trim(finfo.parents); err != nil {
	 886  				return err
	 887  			}
	 888  			vf = indirect(vf)
	 889  			k := vf.Kind()
	 890  			if !(k == reflect.String || k == reflect.Slice && vf.Type().Elem().Kind() == reflect.Uint8) {
	 891  				return fmt.Errorf("xml: bad type for comment field of %s", val.Type())
	 892  			}
	 893  			if vf.Len() == 0 {
	 894  				continue
	 895  			}
	 896  			p.writeIndent(0)
	 897  			p.WriteString("<!--")
	 898  			dashDash := false
	 899  			dashLast := false
	 900  			switch k {
	 901  			case reflect.String:
	 902  				s := vf.String()
	 903  				dashDash = strings.Contains(s, "--")
	 904  				dashLast = s[len(s)-1] == '-'
	 905  				if !dashDash {
	 906  					p.WriteString(s)
	 907  				}
	 908  			case reflect.Slice:
	 909  				b := vf.Bytes()
	 910  				dashDash = bytes.Contains(b, ddBytes)
	 911  				dashLast = b[len(b)-1] == '-'
	 912  				if !dashDash {
	 913  					p.Write(b)
	 914  				}
	 915  			default:
	 916  				panic("can't happen")
	 917  			}
	 918  			if dashDash {
	 919  				return fmt.Errorf(`xml: comments must not contain "--"`)
	 920  			}
	 921  			if dashLast {
	 922  				// "--->" is invalid grammar. Make it "- -->"
	 923  				p.WriteByte(' ')
	 924  			}
	 925  			p.WriteString("-->")
	 926  			continue
	 927  
	 928  		case fInnerXML:
	 929  			vf = indirect(vf)
	 930  			iface := vf.Interface()
	 931  			switch raw := iface.(type) {
	 932  			case []byte:
	 933  				p.Write(raw)
	 934  				continue
	 935  			case string:
	 936  				p.WriteString(raw)
	 937  				continue
	 938  			}
	 939  
	 940  		case fElement, fElement | fAny:
	 941  			if err := s.trim(finfo.parents); err != nil {
	 942  				return err
	 943  			}
	 944  			if len(finfo.parents) > len(s.stack) {
	 945  				if vf.Kind() != reflect.Ptr && vf.Kind() != reflect.Interface || !vf.IsNil() {
	 946  					if err := s.push(finfo.parents[len(s.stack):]); err != nil {
	 947  						return err
	 948  					}
	 949  				}
	 950  			}
	 951  		}
	 952  		if err := p.marshalValue(vf, finfo, nil); err != nil {
	 953  			return err
	 954  		}
	 955  	}
	 956  	s.trim(nil)
	 957  	return p.cachedWriteError()
	 958  }
	 959  
	 960  // return the bufio Writer's cached write error
	 961  func (p *printer) cachedWriteError() error {
	 962  	_, err := p.Write(nil)
	 963  	return err
	 964  }
	 965  
	 966  func (p *printer) writeIndent(depthDelta int) {
	 967  	if len(p.prefix) == 0 && len(p.indent) == 0 {
	 968  		return
	 969  	}
	 970  	if depthDelta < 0 {
	 971  		p.depth--
	 972  		if p.indentedIn {
	 973  			p.indentedIn = false
	 974  			return
	 975  		}
	 976  		p.indentedIn = false
	 977  	}
	 978  	if p.putNewline {
	 979  		p.WriteByte('\n')
	 980  	} else {
	 981  		p.putNewline = true
	 982  	}
	 983  	if len(p.prefix) > 0 {
	 984  		p.WriteString(p.prefix)
	 985  	}
	 986  	if len(p.indent) > 0 {
	 987  		for i := 0; i < p.depth; i++ {
	 988  			p.WriteString(p.indent)
	 989  		}
	 990  	}
	 991  	if depthDelta > 0 {
	 992  		p.depth++
	 993  		p.indentedIn = true
	 994  	}
	 995  }
	 996  
	 997  type parentStack struct {
	 998  	p		 *printer
	 999  	stack []string
	1000  }
	1001  
	1002  // trim updates the XML context to match the longest common prefix of the stack
	1003  // and the given parents. A closing tag will be written for every parent
	1004  // popped. Passing a zero slice or nil will close all the elements.
	1005  func (s *parentStack) trim(parents []string) error {
	1006  	split := 0
	1007  	for ; split < len(parents) && split < len(s.stack); split++ {
	1008  		if parents[split] != s.stack[split] {
	1009  			break
	1010  		}
	1011  	}
	1012  	for i := len(s.stack) - 1; i >= split; i-- {
	1013  		if err := s.p.writeEnd(Name{Local: s.stack[i]}); err != nil {
	1014  			return err
	1015  		}
	1016  	}
	1017  	s.stack = s.stack[:split]
	1018  	return nil
	1019  }
	1020  
	1021  // push adds parent elements to the stack and writes open tags.
	1022  func (s *parentStack) push(parents []string) error {
	1023  	for i := 0; i < len(parents); i++ {
	1024  		if err := s.p.writeStart(&StartElement{Name: Name{Local: parents[i]}}); err != nil {
	1025  			return err
	1026  		}
	1027  	}
	1028  	s.stack = append(s.stack, parents...)
	1029  	return nil
	1030  }
	1031  
	1032  // UnsupportedTypeError is returned when Marshal encounters a type
	1033  // that cannot be converted into XML.
	1034  type UnsupportedTypeError struct {
	1035  	Type reflect.Type
	1036  }
	1037  
	1038  func (e *UnsupportedTypeError) Error() string {
	1039  	return "xml: unsupported type: " + e.Type.String()
	1040  }
	1041  
	1042  func isEmptyValue(v reflect.Value) bool {
	1043  	switch v.Kind() {
	1044  	case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
	1045  		return v.Len() == 0
	1046  	case reflect.Bool:
	1047  		return !v.Bool()
	1048  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
	1049  		return v.Int() == 0
	1050  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
	1051  		return v.Uint() == 0
	1052  	case reflect.Float32, reflect.Float64:
	1053  		return v.Float() == 0
	1054  	case reflect.Interface, reflect.Ptr:
	1055  		return v.IsNil()
	1056  	}
	1057  	return false
	1058  }
	1059  

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