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		// 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		if strings.HasPrefix(prefix, "xml") {
   349			// xmlanything is reserved.
   350			prefix = "_" + prefix
   351		}
   352		if p.attrNS[prefix] != "" {
   353			// Name is taken. Find a better one.
   354			for p.seq++; ; p.seq++ {
   355				if id := prefix + "_" + strconv.Itoa(p.seq); p.attrNS[id] == "" {
   356					prefix = id
   357					break
   358				}
   359			}
   360		}
   361	
   362		p.attrPrefix[url] = prefix
   363		p.attrNS[prefix] = url
   364	
   365		p.WriteString(`xmlns:`)
   366		p.WriteString(prefix)
   367		p.WriteString(`="`)
   368		EscapeText(p, []byte(url))
   369		p.WriteString(`" `)
   370	
   371		p.prefixes = append(p.prefixes, prefix)
   372	
   373		return prefix
   374	}
   375	
   376	// deleteAttrPrefix removes an attribute name space prefix.
   377	func (p *printer) deleteAttrPrefix(prefix string) {
   378		delete(p.attrPrefix, p.attrNS[prefix])
   379		delete(p.attrNS, prefix)
   380	}
   381	
   382	func (p *printer) markPrefix() {
   383		p.prefixes = append(p.prefixes, "")
   384	}
   385	
   386	func (p *printer) popPrefix() {
   387		for len(p.prefixes) > 0 {
   388			prefix := p.prefixes[len(p.prefixes)-1]
   389			p.prefixes = p.prefixes[:len(p.prefixes)-1]
   390			if prefix == "" {
   391				break
   392			}
   393			p.deleteAttrPrefix(prefix)
   394		}
   395	}
   396	
   397	var (
   398		marshalerType     = reflect.TypeOf((*Marshaler)(nil)).Elem()
   399		marshalerAttrType = reflect.TypeOf((*MarshalerAttr)(nil)).Elem()
   400		textMarshalerType = reflect.TypeOf((*encoding.TextMarshaler)(nil)).Elem()
   401	)
   402	
   403	// marshalValue writes one or more XML elements representing val.
   404	// If val was obtained from a struct field, finfo must have its details.
   405	func (p *printer) marshalValue(val reflect.Value, finfo *fieldInfo, startTemplate *StartElement) error {
   406		if startTemplate != nil && startTemplate.Name.Local == "" {
   407			return fmt.Errorf("xml: EncodeElement of StartElement with missing name")
   408		}
   409	
   410		if !val.IsValid() {
   411			return nil
   412		}
   413		if finfo != nil && finfo.flags&fOmitEmpty != 0 && isEmptyValue(val) {
   414			return nil
   415		}
   416	
   417		// Drill into interfaces and pointers.
   418		// This can turn into an infinite loop given a cyclic chain,
   419		// but it matches the Go 1 behavior.
   420		for val.Kind() == reflect.Interface || val.Kind() == reflect.Ptr {
   421			if val.IsNil() {
   422				return nil
   423			}
   424			val = val.Elem()
   425		}
   426	
   427		kind := val.Kind()
   428		typ := val.Type()
   429	
   430		// Check for marshaler.
   431		if val.CanInterface() && typ.Implements(marshalerType) {
   432			return p.marshalInterface(val.Interface().(Marshaler), defaultStart(typ, finfo, startTemplate))
   433		}
   434		if val.CanAddr() {
   435			pv := val.Addr()
   436			if pv.CanInterface() && pv.Type().Implements(marshalerType) {
   437				return p.marshalInterface(pv.Interface().(Marshaler), defaultStart(pv.Type(), finfo, startTemplate))
   438			}
   439		}
   440	
   441		// Check for text marshaler.
   442		if val.CanInterface() && typ.Implements(textMarshalerType) {
   443			return p.marshalTextInterface(val.Interface().(encoding.TextMarshaler), defaultStart(typ, finfo, startTemplate))
   444		}
   445		if val.CanAddr() {
   446			pv := val.Addr()
   447			if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   448				return p.marshalTextInterface(pv.Interface().(encoding.TextMarshaler), defaultStart(pv.Type(), finfo, startTemplate))
   449			}
   450		}
   451	
   452		// Slices and arrays iterate over the elements. They do not have an enclosing tag.
   453		if (kind == reflect.Slice || kind == reflect.Array) && typ.Elem().Kind() != reflect.Uint8 {
   454			for i, n := 0, val.Len(); i < n; i++ {
   455				if err := p.marshalValue(val.Index(i), finfo, startTemplate); err != nil {
   456					return err
   457				}
   458			}
   459			return nil
   460		}
   461	
   462		tinfo, err := getTypeInfo(typ)
   463		if err != nil {
   464			return err
   465		}
   466	
   467		// Create start element.
   468		// Precedence for the XML element name is:
   469		// 0. startTemplate
   470		// 1. XMLName field in underlying struct;
   471		// 2. field name/tag in the struct field; and
   472		// 3. type name
   473		var start StartElement
   474	
   475		if startTemplate != nil {
   476			start.Name = startTemplate.Name
   477			start.Attr = append(start.Attr, startTemplate.Attr...)
   478		} else if tinfo.xmlname != nil {
   479			xmlname := tinfo.xmlname
   480			if xmlname.name != "" {
   481				start.Name.Space, start.Name.Local = xmlname.xmlns, xmlname.name
   482			} else if v, ok := xmlname.value(val).Interface().(Name); ok && v.Local != "" {
   483				start.Name = v
   484			}
   485		}
   486		if start.Name.Local == "" && finfo != nil {
   487			start.Name.Space, start.Name.Local = finfo.xmlns, finfo.name
   488		}
   489		if start.Name.Local == "" {
   490			name := typ.Name()
   491			if name == "" {
   492				return &UnsupportedTypeError{typ}
   493			}
   494			start.Name.Local = name
   495		}
   496	
   497		// Attributes
   498		for i := range tinfo.fields {
   499			finfo := &tinfo.fields[i]
   500			if finfo.flags&fAttr == 0 {
   501				continue
   502			}
   503			fv := finfo.value(val)
   504	
   505			if finfo.flags&fOmitEmpty != 0 && isEmptyValue(fv) {
   506				continue
   507			}
   508	
   509			if fv.Kind() == reflect.Interface && fv.IsNil() {
   510				continue
   511			}
   512	
   513			name := Name{Space: finfo.xmlns, Local: finfo.name}
   514			if err := p.marshalAttr(&start, name, fv); err != nil {
   515				return err
   516			}
   517		}
   518	
   519		if err := p.writeStart(&start); err != nil {
   520			return err
   521		}
   522	
   523		if val.Kind() == reflect.Struct {
   524			err = p.marshalStruct(tinfo, val)
   525		} else {
   526			s, b, err1 := p.marshalSimple(typ, val)
   527			if err1 != nil {
   528				err = err1
   529			} else if b != nil {
   530				EscapeText(p, b)
   531			} else {
   532				p.EscapeString(s)
   533			}
   534		}
   535		if err != nil {
   536			return err
   537		}
   538	
   539		if err := p.writeEnd(start.Name); err != nil {
   540			return err
   541		}
   542	
   543		return p.cachedWriteError()
   544	}
   545	
   546	// marshalAttr marshals an attribute with the given name and value, adding to start.Attr.
   547	func (p *printer) marshalAttr(start *StartElement, name Name, val reflect.Value) error {
   548		if val.CanInterface() && val.Type().Implements(marshalerAttrType) {
   549			attr, err := val.Interface().(MarshalerAttr).MarshalXMLAttr(name)
   550			if err != nil {
   551				return err
   552			}
   553			if attr.Name.Local != "" {
   554				start.Attr = append(start.Attr, attr)
   555			}
   556			return nil
   557		}
   558	
   559		if val.CanAddr() {
   560			pv := val.Addr()
   561			if pv.CanInterface() && pv.Type().Implements(marshalerAttrType) {
   562				attr, err := pv.Interface().(MarshalerAttr).MarshalXMLAttr(name)
   563				if err != nil {
   564					return err
   565				}
   566				if attr.Name.Local != "" {
   567					start.Attr = append(start.Attr, attr)
   568				}
   569				return nil
   570			}
   571		}
   572	
   573		if val.CanInterface() && val.Type().Implements(textMarshalerType) {
   574			text, err := val.Interface().(encoding.TextMarshaler).MarshalText()
   575			if err != nil {
   576				return err
   577			}
   578			start.Attr = append(start.Attr, Attr{name, string(text)})
   579			return nil
   580		}
   581	
   582		if val.CanAddr() {
   583			pv := val.Addr()
   584			if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   585				text, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
   586				if err != nil {
   587					return err
   588				}
   589				start.Attr = append(start.Attr, Attr{name, string(text)})
   590				return nil
   591			}
   592		}
   593	
   594		// Dereference or skip nil pointer, interface values.
   595		switch val.Kind() {
   596		case reflect.Ptr, reflect.Interface:
   597			if val.IsNil() {
   598				return nil
   599			}
   600			val = val.Elem()
   601		}
   602	
   603		// Walk slices.
   604		if val.Kind() == reflect.Slice && val.Type().Elem().Kind() != reflect.Uint8 {
   605			n := val.Len()
   606			for i := 0; i < n; i++ {
   607				if err := p.marshalAttr(start, name, val.Index(i)); err != nil {
   608					return err
   609				}
   610			}
   611			return nil
   612		}
   613	
   614		if val.Type() == attrType {
   615			start.Attr = append(start.Attr, val.Interface().(Attr))
   616			return nil
   617		}
   618	
   619		s, b, err := p.marshalSimple(val.Type(), val)
   620		if err != nil {
   621			return err
   622		}
   623		if b != nil {
   624			s = string(b)
   625		}
   626		start.Attr = append(start.Attr, Attr{name, s})
   627		return nil
   628	}
   629	
   630	// defaultStart returns the default start element to use,
   631	// given the reflect type, field info, and start template.
   632	func defaultStart(typ reflect.Type, finfo *fieldInfo, startTemplate *StartElement) StartElement {
   633		var start StartElement
   634		// Precedence for the XML element name is as above,
   635		// except that we do not look inside structs for the first field.
   636		if startTemplate != nil {
   637			start.Name = startTemplate.Name
   638			start.Attr = append(start.Attr, startTemplate.Attr...)
   639		} else if finfo != nil && finfo.name != "" {
   640			start.Name.Local = finfo.name
   641			start.Name.Space = finfo.xmlns
   642		} else if typ.Name() != "" {
   643			start.Name.Local = typ.Name()
   644		} else {
   645			// Must be a pointer to a named type,
   646			// since it has the Marshaler methods.
   647			start.Name.Local = typ.Elem().Name()
   648		}
   649		return start
   650	}
   651	
   652	// marshalInterface marshals a Marshaler interface value.
   653	func (p *printer) marshalInterface(val Marshaler, start StartElement) error {
   654		// Push a marker onto the tag stack so that MarshalXML
   655		// cannot close the XML tags that it did not open.
   656		p.tags = append(p.tags, Name{})
   657		n := len(p.tags)
   658	
   659		err := val.MarshalXML(p.encoder, start)
   660		if err != nil {
   661			return err
   662		}
   663	
   664		// Make sure MarshalXML closed all its tags. p.tags[n-1] is the mark.
   665		if len(p.tags) > n {
   666			return fmt.Errorf("xml: %s.MarshalXML wrote invalid XML: <%s> not closed", receiverType(val), p.tags[len(p.tags)-1].Local)
   667		}
   668		p.tags = p.tags[:n-1]
   669		return nil
   670	}
   671	
   672	// marshalTextInterface marshals a TextMarshaler interface value.
   673	func (p *printer) marshalTextInterface(val encoding.TextMarshaler, start StartElement) error {
   674		if err := p.writeStart(&start); err != nil {
   675			return err
   676		}
   677		text, err := val.MarshalText()
   678		if err != nil {
   679			return err
   680		}
   681		EscapeText(p, text)
   682		return p.writeEnd(start.Name)
   683	}
   684	
   685	// writeStart writes the given start element.
   686	func (p *printer) writeStart(start *StartElement) error {
   687		if start.Name.Local == "" {
   688			return fmt.Errorf("xml: start tag with no name")
   689		}
   690	
   691		p.tags = append(p.tags, start.Name)
   692		p.markPrefix()
   693	
   694		p.writeIndent(1)
   695		p.WriteByte('<')
   696		p.WriteString(start.Name.Local)
   697	
   698		if start.Name.Space != "" {
   699			p.WriteString(` xmlns="`)
   700			p.EscapeString(start.Name.Space)
   701			p.WriteByte('"')
   702		}
   703	
   704		// Attributes
   705		for _, attr := range start.Attr {
   706			name := attr.Name
   707			if name.Local == "" {
   708				continue
   709			}
   710			p.WriteByte(' ')
   711			if name.Space != "" {
   712				p.WriteString(p.createAttrPrefix(name.Space))
   713				p.WriteByte(':')
   714			}
   715			p.WriteString(name.Local)
   716			p.WriteString(`="`)
   717			p.EscapeString(attr.Value)
   718			p.WriteByte('"')
   719		}
   720		p.WriteByte('>')
   721		return nil
   722	}
   723	
   724	func (p *printer) writeEnd(name Name) error {
   725		if name.Local == "" {
   726			return fmt.Errorf("xml: end tag with no name")
   727		}
   728		if len(p.tags) == 0 || p.tags[len(p.tags)-1].Local == "" {
   729			return fmt.Errorf("xml: end tag </%s> without start tag", name.Local)
   730		}
   731		if top := p.tags[len(p.tags)-1]; top != name {
   732			if top.Local != name.Local {
   733				return fmt.Errorf("xml: end tag </%s> does not match start tag <%s>", name.Local, top.Local)
   734			}
   735			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)
   736		}
   737		p.tags = p.tags[:len(p.tags)-1]
   738	
   739		p.writeIndent(-1)
   740		p.WriteByte('<')
   741		p.WriteByte('/')
   742		p.WriteString(name.Local)
   743		p.WriteByte('>')
   744		p.popPrefix()
   745		return nil
   746	}
   747	
   748	func (p *printer) marshalSimple(typ reflect.Type, val reflect.Value) (string, []byte, error) {
   749		switch val.Kind() {
   750		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   751			return strconv.FormatInt(val.Int(), 10), nil, nil
   752		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   753			return strconv.FormatUint(val.Uint(), 10), nil, nil
   754		case reflect.Float32, reflect.Float64:
   755			return strconv.FormatFloat(val.Float(), 'g', -1, val.Type().Bits()), nil, nil
   756		case reflect.String:
   757			return val.String(), nil, nil
   758		case reflect.Bool:
   759			return strconv.FormatBool(val.Bool()), nil, nil
   760		case reflect.Array:
   761			if typ.Elem().Kind() != reflect.Uint8 {
   762				break
   763			}
   764			// [...]byte
   765			var bytes []byte
   766			if val.CanAddr() {
   767				bytes = val.Slice(0, val.Len()).Bytes()
   768			} else {
   769				bytes = make([]byte, val.Len())
   770				reflect.Copy(reflect.ValueOf(bytes), val)
   771			}
   772			return "", bytes, nil
   773		case reflect.Slice:
   774			if typ.Elem().Kind() != reflect.Uint8 {
   775				break
   776			}
   777			// []byte
   778			return "", val.Bytes(), nil
   779		}
   780		return "", nil, &UnsupportedTypeError{typ}
   781	}
   782	
   783	var ddBytes = []byte("--")
   784	
   785	// indirect drills into interfaces and pointers, returning the pointed-at value.
   786	// If it encounters a nil interface or pointer, indirect returns that nil value.
   787	// This can turn into an infinite loop given a cyclic chain,
   788	// but it matches the Go 1 behavior.
   789	func indirect(vf reflect.Value) reflect.Value {
   790		for vf.Kind() == reflect.Interface || vf.Kind() == reflect.Ptr {
   791			if vf.IsNil() {
   792				return vf
   793			}
   794			vf = vf.Elem()
   795		}
   796		return vf
   797	}
   798	
   799	func (p *printer) marshalStruct(tinfo *typeInfo, val reflect.Value) error {
   800		s := parentStack{p: p}
   801		for i := range tinfo.fields {
   802			finfo := &tinfo.fields[i]
   803			if finfo.flags&fAttr != 0 {
   804				continue
   805			}
   806			vf := finfo.value(val)
   807	
   808			switch finfo.flags & fMode {
   809			case fCDATA, fCharData:
   810				emit := EscapeText
   811				if finfo.flags&fMode == fCDATA {
   812					emit = emitCDATA
   813				}
   814				if err := s.trim(finfo.parents); err != nil {
   815					return err
   816				}
   817				if vf.CanInterface() && vf.Type().Implements(textMarshalerType) {
   818					data, err := vf.Interface().(encoding.TextMarshaler).MarshalText()
   819					if err != nil {
   820						return err
   821					}
   822					if err := emit(p, data); err != nil {
   823						return err
   824					}
   825					continue
   826				}
   827				if vf.CanAddr() {
   828					pv := vf.Addr()
   829					if pv.CanInterface() && pv.Type().Implements(textMarshalerType) {
   830						data, err := pv.Interface().(encoding.TextMarshaler).MarshalText()
   831						if err != nil {
   832							return err
   833						}
   834						if err := emit(p, data); err != nil {
   835							return err
   836						}
   837						continue
   838					}
   839				}
   840	
   841				var scratch [64]byte
   842				vf = indirect(vf)
   843				switch vf.Kind() {
   844				case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   845					if err := emit(p, strconv.AppendInt(scratch[:0], vf.Int(), 10)); err != nil {
   846						return err
   847					}
   848				case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   849					if err := emit(p, strconv.AppendUint(scratch[:0], vf.Uint(), 10)); err != nil {
   850						return err
   851					}
   852				case reflect.Float32, reflect.Float64:
   853					if err := emit(p, strconv.AppendFloat(scratch[:0], vf.Float(), 'g', -1, vf.Type().Bits())); err != nil {
   854						return err
   855					}
   856				case reflect.Bool:
   857					if err := emit(p, strconv.AppendBool(scratch[:0], vf.Bool())); err != nil {
   858						return err
   859					}
   860				case reflect.String:
   861					if err := emit(p, []byte(vf.String())); err != nil {
   862						return err
   863					}
   864				case reflect.Slice:
   865					if elem, ok := vf.Interface().([]byte); ok {
   866						if err := emit(p, elem); err != nil {
   867							return err
   868						}
   869					}
   870				}
   871				continue
   872	
   873			case fComment:
   874				if err := s.trim(finfo.parents); err != nil {
   875					return err
   876				}
   877				vf = indirect(vf)
   878				k := vf.Kind()
   879				if !(k == reflect.String || k == reflect.Slice && vf.Type().Elem().Kind() == reflect.Uint8) {
   880					return fmt.Errorf("xml: bad type for comment field of %s", val.Type())
   881				}
   882				if vf.Len() == 0 {
   883					continue
   884				}
   885				p.writeIndent(0)
   886				p.WriteString("<!--")
   887				dashDash := false
   888				dashLast := false
   889				switch k {
   890				case reflect.String:
   891					s := vf.String()
   892					dashDash = strings.Contains(s, "--")
   893					dashLast = s[len(s)-1] == '-'
   894					if !dashDash {
   895						p.WriteString(s)
   896					}
   897				case reflect.Slice:
   898					b := vf.Bytes()
   899					dashDash = bytes.Contains(b, ddBytes)
   900					dashLast = b[len(b)-1] == '-'
   901					if !dashDash {
   902						p.Write(b)
   903					}
   904				default:
   905					panic("can't happen")
   906				}
   907				if dashDash {
   908					return fmt.Errorf(`xml: comments must not contain "--"`)
   909				}
   910				if dashLast {
   911					// "--->" is invalid grammar. Make it "- -->"
   912					p.WriteByte(' ')
   913				}
   914				p.WriteString("-->")
   915				continue
   916	
   917			case fInnerXml:
   918				vf = indirect(vf)
   919				iface := vf.Interface()
   920				switch raw := iface.(type) {
   921				case []byte:
   922					p.Write(raw)
   923					continue
   924				case string:
   925					p.WriteString(raw)
   926					continue
   927				}
   928	
   929			case fElement, fElement | fAny:
   930				if err := s.trim(finfo.parents); err != nil {
   931					return err
   932				}
   933				if len(finfo.parents) > len(s.stack) {
   934					if vf.Kind() != reflect.Ptr && vf.Kind() != reflect.Interface || !vf.IsNil() {
   935						if err := s.push(finfo.parents[len(s.stack):]); err != nil {
   936							return err
   937						}
   938					}
   939				}
   940			}
   941			if err := p.marshalValue(vf, finfo, nil); err != nil {
   942				return err
   943			}
   944		}
   945		s.trim(nil)
   946		return p.cachedWriteError()
   947	}
   948	
   949	// return the bufio Writer's cached write error
   950	func (p *printer) cachedWriteError() error {
   951		_, err := p.Write(nil)
   952		return err
   953	}
   954	
   955	func (p *printer) writeIndent(depthDelta int) {
   956		if len(p.prefix) == 0 && len(p.indent) == 0 {
   957			return
   958		}
   959		if depthDelta < 0 {
   960			p.depth--
   961			if p.indentedIn {
   962				p.indentedIn = false
   963				return
   964			}
   965			p.indentedIn = false
   966		}
   967		if p.putNewline {
   968			p.WriteByte('\n')
   969		} else {
   970			p.putNewline = true
   971		}
   972		if len(p.prefix) > 0 {
   973			p.WriteString(p.prefix)
   974		}
   975		if len(p.indent) > 0 {
   976			for i := 0; i < p.depth; i++ {
   977				p.WriteString(p.indent)
   978			}
   979		}
   980		if depthDelta > 0 {
   981			p.depth++
   982			p.indentedIn = true
   983		}
   984	}
   985	
   986	type parentStack struct {
   987		p     *printer
   988		stack []string
   989	}
   990	
   991	// trim updates the XML context to match the longest common prefix of the stack
   992	// and the given parents. A closing tag will be written for every parent
   993	// popped. Passing a zero slice or nil will close all the elements.
   994	func (s *parentStack) trim(parents []string) error {
   995		split := 0
   996		for ; split < len(parents) && split < len(s.stack); split++ {
   997			if parents[split] != s.stack[split] {
   998				break
   999			}
  1000		}
  1001		for i := len(s.stack) - 1; i >= split; i-- {
  1002			if err := s.p.writeEnd(Name{Local: s.stack[i]}); err != nil {
  1003				return err
  1004			}
  1005		}
  1006		s.stack = s.stack[:split]
  1007		return nil
  1008	}
  1009	
  1010	// push adds parent elements to the stack and writes open tags.
  1011	func (s *parentStack) push(parents []string) error {
  1012		for i := 0; i < len(parents); i++ {
  1013			if err := s.p.writeStart(&StartElement{Name: Name{Local: parents[i]}}); err != nil {
  1014				return err
  1015			}
  1016		}
  1017		s.stack = append(s.stack, parents...)
  1018		return nil
  1019	}
  1020	
  1021	// UnsupportedTypeError is returned when Marshal encounters a type
  1022	// that cannot be converted into XML.
  1023	type UnsupportedTypeError struct {
  1024		Type reflect.Type
  1025	}
  1026	
  1027	func (e *UnsupportedTypeError) Error() string {
  1028		return "xml: unsupported type: " + e.Type.String()
  1029	}
  1030	
  1031	func isEmptyValue(v reflect.Value) bool {
  1032		switch v.Kind() {
  1033		case reflect.Array, reflect.Map, reflect.Slice, reflect.String:
  1034			return v.Len() == 0
  1035		case reflect.Bool:
  1036			return !v.Bool()
  1037		case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
  1038			return v.Int() == 0
  1039		case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
  1040			return v.Uint() == 0
  1041		case reflect.Float32, reflect.Float64:
  1042			return v.Float() == 0
  1043		case reflect.Interface, reflect.Ptr:
  1044			return v.IsNil()
  1045		}
  1046		return false
  1047	}
  1048	

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