read.go

     1  // Copyright 2009 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  	"bytes"
     9  	"encoding"
    10  	"errors"
    11  	"fmt"
    12  	"reflect"
    13  	"runtime"
    14  	"strconv"
    15  	"strings"
    16  )
    17  
    18  // BUG(rsc): Mapping between XML elements and data structures is inherently flawed:
    19  // an XML element is an order-dependent collection of anonymous
    20  // values, while a data structure is an order-independent collection
    21  // of named values.
    22  // See [encoding/json] for a textual representation more suitable
    23  // to data structures.
    24  
    25  // Unmarshal parses the XML-encoded data and stores the result in
    26  // the value pointed to by v, which must be an arbitrary struct,
    27  // slice, or string. Well-formed data that does not fit into v is
    28  // discarded.
    29  //
    30  // Because Unmarshal uses the reflect package, it can only assign
    31  // to exported (upper case) fields. Unmarshal uses a case-sensitive
    32  // comparison to match XML element names to tag values and struct
    33  // field names.
    34  //
    35  // Unmarshal maps an XML element to a struct using the following rules.
    36  // In the rules, the tag of a field refers to the value associated with the
    37  // key 'xml' in the struct field's tag (see the example above).
    38  //
    39  //   - If the struct has a field of type []byte or string with tag
    40  //     ",innerxml", Unmarshal accumulates the raw XML nested inside the
    41  //     element in that field. The rest of the rules still apply.
    42  //
    43  //   - If the struct has a field named XMLName of type Name,
    44  //     Unmarshal records the element name in that field.
    45  //
    46  //   - If the XMLName field has an associated tag of the form
    47  //     "name" or "namespace-URL name", the XML element must have
    48  //     the given name (and, optionally, name space) or else Unmarshal
    49  //     returns an error.
    50  //
    51  //   - If the XML element has an attribute whose name matches a
    52  //     struct field name with an associated tag containing ",attr" or
    53  //     the explicit name in a struct field tag of the form "name,attr",
    54  //     Unmarshal records the attribute value in that field.
    55  //
    56  //   - If the XML element has an attribute not handled by the previous
    57  //     rule and the struct has a field with an associated tag containing
    58  //     ",any,attr", Unmarshal records the attribute value in the first
    59  //     such field.
    60  //
    61  //   - If the XML element contains character data, that data is
    62  //     accumulated in the first struct field that has tag ",chardata".
    63  //     The struct field may have type []byte or string.
    64  //     If there is no such field, the character data is discarded.
    65  //
    66  //   - If the XML element contains comments, they are accumulated in
    67  //     the first struct field that has tag ",comment".  The struct
    68  //     field may have type []byte or string. If there is no such
    69  //     field, the comments are discarded.
    70  //
    71  //   - If the XML element contains a sub-element whose name matches
    72  //     the prefix of a tag formatted as "a" or "a>b>c", unmarshal
    73  //     will descend into the XML structure looking for elements with the
    74  //     given names, and will map the innermost elements to that struct
    75  //     field. A tag starting with ">" is equivalent to one starting
    76  //     with the field name followed by ">".
    77  //
    78  //   - If the XML element contains a sub-element whose name matches
    79  //     a struct field's XMLName tag and the struct field has no
    80  //     explicit name tag as per the previous rule, unmarshal maps
    81  //     the sub-element to that struct field.
    82  //
    83  //   - If the XML element contains a sub-element whose name matches a
    84  //     field without any mode flags (",attr", ",chardata", etc), Unmarshal
    85  //     maps the sub-element to that struct field.
    86  //
    87  //   - If the XML element contains a sub-element that hasn't matched any
    88  //     of the above rules and the struct has a field with tag ",any",
    89  //     unmarshal maps the sub-element to that struct field.
    90  //
    91  //   - An anonymous struct field is handled as if the fields of its
    92  //     value were part of the outer struct.
    93  //
    94  //   - A struct field with tag "-" is never unmarshaled into.
    95  //
    96  // If Unmarshal encounters a field type that implements the Unmarshaler
    97  // interface, Unmarshal calls its UnmarshalXML method to produce the value from
    98  // the XML element.  Otherwise, if the value implements
    99  // [encoding.TextUnmarshaler], Unmarshal calls that value's UnmarshalText method.
   100  //
   101  // Unmarshal maps an XML element to a string or []byte by saving the
   102  // concatenation of that element's character data in the string or
   103  // []byte. The saved []byte is never nil.
   104  //
   105  // Unmarshal maps an attribute value to a string or []byte by saving
   106  // the value in the string or slice.
   107  //
   108  // Unmarshal maps an attribute value to an [Attr] by saving the attribute,
   109  // including its name, in the Attr.
   110  //
   111  // Unmarshal maps an XML element or attribute value to a slice by
   112  // extending the length of the slice and mapping the element or attribute
   113  // to the newly created value.
   114  //
   115  // Unmarshal maps an XML element or attribute value to a bool by
   116  // setting it to the boolean value represented by the string. Whitespace
   117  // is trimmed and ignored.
   118  //
   119  // Unmarshal maps an XML element or attribute value to an integer or
   120  // floating-point field by setting the field to the result of
   121  // interpreting the string value in decimal. There is no check for
   122  // overflow. Whitespace is trimmed and ignored.
   123  //
   124  // Unmarshal maps an XML element to a Name by recording the element
   125  // name.
   126  //
   127  // Unmarshal maps an XML element to a pointer by setting the pointer
   128  // to a freshly allocated value and then mapping the element to that value.
   129  //
   130  // A missing element or empty attribute value will be unmarshaled as a zero value.
   131  // If the field is a slice, a zero value will be appended to the field. Otherwise, the
   132  // field will be set to its zero value.
   133  func Unmarshal(data []byte, v any) error {
   134  	return NewDecoder(bytes.NewReader(data)).Decode(v)
   135  }
   136  
   137  // Decode works like [Unmarshal], except it reads the decoder
   138  // stream to find the start element.
   139  func (d *Decoder) Decode(v any) error {
   140  	return d.DecodeElement(v, nil)
   141  }
   142  
   143  // DecodeElement works like [Unmarshal] except that it takes
   144  // a pointer to the start XML element to decode into v.
   145  // It is useful when a client reads some raw XML tokens itself
   146  // but also wants to defer to [Unmarshal] for some elements.
   147  func (d *Decoder) DecodeElement(v any, start *StartElement) error {
   148  	val := reflect.ValueOf(v)
   149  	if val.Kind() != reflect.Pointer {
   150  		return errors.New("non-pointer passed to Unmarshal")
   151  	}
   152  
   153  	if val.IsNil() {
   154  		return errors.New("nil pointer passed to Unmarshal")
   155  	}
   156  	return d.unmarshal(val.Elem(), start, 0)
   157  }
   158  
   159  // An UnmarshalError represents an error in the unmarshaling process.
   160  type UnmarshalError string
   161  
   162  func (e UnmarshalError) Error() string { return string(e) }
   163  
   164  // Unmarshaler is the interface implemented by objects that can unmarshal
   165  // an XML element description of themselves.
   166  //
   167  // UnmarshalXML decodes a single XML element
   168  // beginning with the given start element.
   169  // If it returns an error, the outer call to Unmarshal stops and
   170  // returns that error.
   171  // UnmarshalXML must consume exactly one XML element.
   172  // One common implementation strategy is to unmarshal into
   173  // a separate value with a layout matching the expected XML
   174  // using d.DecodeElement, and then to copy the data from
   175  // that value into the receiver.
   176  // Another common strategy is to use d.Token to process the
   177  // XML object one token at a time.
   178  // UnmarshalXML may not use d.RawToken.
   179  type Unmarshaler interface {
   180  	UnmarshalXML(d *Decoder, start StartElement) error
   181  }
   182  
   183  // UnmarshalerAttr is the interface implemented by objects that can unmarshal
   184  // an XML attribute description of themselves.
   185  //
   186  // UnmarshalXMLAttr decodes a single XML attribute.
   187  // If it returns an error, the outer call to [Unmarshal] stops and
   188  // returns that error.
   189  // UnmarshalXMLAttr is used only for struct fields with the
   190  // "attr" option in the field tag.
   191  type UnmarshalerAttr interface {
   192  	UnmarshalXMLAttr(attr Attr) error
   193  }
   194  
   195  // receiverType returns the receiver type to use in an expression like "%s.MethodName".
   196  func receiverType(val any) string {
   197  	t := reflect.TypeOf(val)
   198  	if t.Name() != "" {
   199  		return t.String()
   200  	}
   201  	return "(" + t.String() + ")"
   202  }
   203  
   204  // unmarshalInterface unmarshals a single XML element into val.
   205  // start is the opening tag of the element.
   206  func (d *Decoder) unmarshalInterface(val Unmarshaler, start *StartElement) error {
   207  	// Record that decoder must stop at end tag corresponding to start.
   208  	d.pushEOF()
   209  
   210  	d.unmarshalDepth++
   211  	err := val.UnmarshalXML(d, *start)
   212  	d.unmarshalDepth--
   213  	if err != nil {
   214  		d.popEOF()
   215  		return err
   216  	}
   217  
   218  	if !d.popEOF() {
   219  		return fmt.Errorf("xml: %s.UnmarshalXML did not consume entire <%s> element", receiverType(val), start.Name.Local)
   220  	}
   221  
   222  	return nil
   223  }
   224  
   225  // unmarshalTextInterface unmarshals a single XML element into val.
   226  // The chardata contained in the element (but not its children)
   227  // is passed to the text unmarshaler.
   228  func (d *Decoder) unmarshalTextInterface(val encoding.TextUnmarshaler) error {
   229  	var buf []byte
   230  	depth := 1
   231  	for depth > 0 {
   232  		t, err := d.Token()
   233  		if err != nil {
   234  			return err
   235  		}
   236  		switch t := t.(type) {
   237  		case CharData:
   238  			if depth == 1 {
   239  				buf = append(buf, t...)
   240  			}
   241  		case StartElement:
   242  			depth++
   243  		case EndElement:
   244  			depth--
   245  		}
   246  	}
   247  	return val.UnmarshalText(buf)
   248  }
   249  
   250  // unmarshalAttr unmarshals a single XML attribute into val.
   251  func (d *Decoder) unmarshalAttr(val reflect.Value, attr Attr) error {
   252  	if val.Kind() == reflect.Pointer {
   253  		if val.IsNil() {
   254  			val.Set(reflect.New(val.Type().Elem()))
   255  		}
   256  		val = val.Elem()
   257  	}
   258  	if val.CanInterface() && val.Type().Implements(unmarshalerAttrType) {
   259  		// This is an unmarshaler with a non-pointer receiver,
   260  		// so it's likely to be incorrect, but we do what we're told.
   261  		return val.Interface().(UnmarshalerAttr).UnmarshalXMLAttr(attr)
   262  	}
   263  	if val.CanAddr() {
   264  		pv := val.Addr()
   265  		if pv.CanInterface() && pv.Type().Implements(unmarshalerAttrType) {
   266  			return pv.Interface().(UnmarshalerAttr).UnmarshalXMLAttr(attr)
   267  		}
   268  	}
   269  
   270  	// Not an UnmarshalerAttr; try encoding.TextUnmarshaler.
   271  	if val.CanInterface() && val.Type().Implements(textUnmarshalerType) {
   272  		// This is an unmarshaler with a non-pointer receiver,
   273  		// so it's likely to be incorrect, but we do what we're told.
   274  		return val.Interface().(encoding.TextUnmarshaler).UnmarshalText([]byte(attr.Value))
   275  	}
   276  	if val.CanAddr() {
   277  		pv := val.Addr()
   278  		if pv.CanInterface() && pv.Type().Implements(textUnmarshalerType) {
   279  			return pv.Interface().(encoding.TextUnmarshaler).UnmarshalText([]byte(attr.Value))
   280  		}
   281  	}
   282  
   283  	if val.Type().Kind() == reflect.Slice && val.Type().Elem().Kind() != reflect.Uint8 {
   284  		// Slice of element values.
   285  		// Grow slice.
   286  		n := val.Len()
   287  		val.Grow(1)
   288  		val.SetLen(n + 1)
   289  
   290  		// Recur to read element into slice.
   291  		if err := d.unmarshalAttr(val.Index(n), attr); err != nil {
   292  			val.SetLen(n)
   293  			return err
   294  		}
   295  		return nil
   296  	}
   297  
   298  	if val.Type() == attrType {
   299  		val.Set(reflect.ValueOf(attr))
   300  		return nil
   301  	}
   302  
   303  	return copyValue(val, []byte(attr.Value))
   304  }
   305  
   306  var (
   307  	attrType            = reflect.TypeFor[Attr]()
   308  	unmarshalerType     = reflect.TypeFor[Unmarshaler]()
   309  	unmarshalerAttrType = reflect.TypeFor[UnmarshalerAttr]()
   310  	textUnmarshalerType = reflect.TypeFor[encoding.TextUnmarshaler]()
   311  )
   312  
   313  const (
   314  	maxUnmarshalDepth     = 10000
   315  	maxUnmarshalDepthWasm = 5000 // go.dev/issue/56498
   316  )
   317  
   318  var errUnmarshalDepth = errors.New("exceeded max depth")
   319  
   320  // Unmarshal a single XML element into val.
   321  func (d *Decoder) unmarshal(val reflect.Value, start *StartElement, depth int) error {
   322  	if depth >= maxUnmarshalDepth || runtime.GOARCH == "wasm" && depth >= maxUnmarshalDepthWasm {
   323  		return errUnmarshalDepth
   324  	}
   325  	// Find start element if we need it.
   326  	if start == nil {
   327  		for {
   328  			tok, err := d.Token()
   329  			if err != nil {
   330  				return err
   331  			}
   332  			if t, ok := tok.(StartElement); ok {
   333  				start = &t
   334  				break
   335  			}
   336  		}
   337  	}
   338  
   339  	// Load value from interface, but only if the result will be
   340  	// usefully addressable.
   341  	if val.Kind() == reflect.Interface && !val.IsNil() {
   342  		e := val.Elem()
   343  		if e.Kind() == reflect.Pointer && !e.IsNil() {
   344  			val = e
   345  		}
   346  	}
   347  
   348  	if val.Kind() == reflect.Pointer {
   349  		if val.IsNil() {
   350  			val.Set(reflect.New(val.Type().Elem()))
   351  		}
   352  		val = val.Elem()
   353  	}
   354  
   355  	if val.CanInterface() && val.Type().Implements(unmarshalerType) {
   356  		// This is an unmarshaler with a non-pointer receiver,
   357  		// so it's likely to be incorrect, but we do what we're told.
   358  		return d.unmarshalInterface(val.Interface().(Unmarshaler), start)
   359  	}
   360  
   361  	if val.CanAddr() {
   362  		pv := val.Addr()
   363  		if pv.CanInterface() && pv.Type().Implements(unmarshalerType) {
   364  			return d.unmarshalInterface(pv.Interface().(Unmarshaler), start)
   365  		}
   366  	}
   367  
   368  	if val.CanInterface() && val.Type().Implements(textUnmarshalerType) {
   369  		return d.unmarshalTextInterface(val.Interface().(encoding.TextUnmarshaler))
   370  	}
   371  
   372  	if val.CanAddr() {
   373  		pv := val.Addr()
   374  		if pv.CanInterface() && pv.Type().Implements(textUnmarshalerType) {
   375  			return d.unmarshalTextInterface(pv.Interface().(encoding.TextUnmarshaler))
   376  		}
   377  	}
   378  
   379  	var (
   380  		data         []byte
   381  		saveData     reflect.Value
   382  		comment      []byte
   383  		saveComment  reflect.Value
   384  		saveXML      reflect.Value
   385  		saveXMLIndex int
   386  		saveXMLData  []byte
   387  		saveAny      reflect.Value
   388  		sv           reflect.Value
   389  		tinfo        *typeInfo
   390  		err          error
   391  	)
   392  
   393  	switch v := val; v.Kind() {
   394  	default:
   395  		return errors.New("unknown type " + v.Type().String())
   396  
   397  	case reflect.Interface:
   398  		// TODO: For now, simply ignore the field. In the near
   399  		//       future we may choose to unmarshal the start
   400  		//       element on it, if not nil.
   401  		return d.Skip()
   402  
   403  	case reflect.Slice:
   404  		typ := v.Type()
   405  		if typ.Elem().Kind() == reflect.Uint8 {
   406  			// []byte
   407  			saveData = v
   408  			break
   409  		}
   410  
   411  		// Slice of element values.
   412  		// Grow slice.
   413  		n := v.Len()
   414  		v.Grow(1)
   415  		v.SetLen(n + 1)
   416  
   417  		// Recur to read element into slice.
   418  		if err := d.unmarshal(v.Index(n), start, depth+1); err != nil {
   419  			v.SetLen(n)
   420  			return err
   421  		}
   422  		return nil
   423  
   424  	case reflect.Bool, reflect.Float32, reflect.Float64, reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr, reflect.String:
   425  		saveData = v
   426  
   427  	case reflect.Struct:
   428  		typ := v.Type()
   429  		if typ == nameType {
   430  			v.Set(reflect.ValueOf(start.Name))
   431  			break
   432  		}
   433  
   434  		sv = v
   435  		tinfo, err = getTypeInfo(typ)
   436  		if err != nil {
   437  			return err
   438  		}
   439  
   440  		// Validate and assign element name.
   441  		if tinfo.xmlname != nil {
   442  			finfo := tinfo.xmlname
   443  			if finfo.name != "" && finfo.name != start.Name.Local {
   444  				return UnmarshalError("expected element type <" + finfo.name + "> but have <" + start.Name.Local + ">")
   445  			}
   446  			if finfo.xmlns != "" && finfo.xmlns != start.Name.Space {
   447  				e := "expected element <" + finfo.name + "> in name space " + finfo.xmlns + " but have "
   448  				if start.Name.Space == "" {
   449  					e += "no name space"
   450  				} else {
   451  					e += start.Name.Space
   452  				}
   453  				return UnmarshalError(e)
   454  			}
   455  			fv := finfo.value(sv, initNilPointers)
   456  			if _, ok := fv.Interface().(Name); ok {
   457  				fv.Set(reflect.ValueOf(start.Name))
   458  			}
   459  		}
   460  
   461  		// Assign attributes.
   462  		for _, a := range start.Attr {
   463  			handled := false
   464  			any := -1
   465  			for i := range tinfo.fields {
   466  				finfo := &tinfo.fields[i]
   467  				switch finfo.flags & fMode {
   468  				case fAttr:
   469  					strv := finfo.value(sv, initNilPointers)
   470  					if a.Name.Local == finfo.name && (finfo.xmlns == "" || finfo.xmlns == a.Name.Space) {
   471  						if err := d.unmarshalAttr(strv, a); err != nil {
   472  							return err
   473  						}
   474  						handled = true
   475  					}
   476  
   477  				case fAny | fAttr:
   478  					if any == -1 {
   479  						any = i
   480  					}
   481  				}
   482  			}
   483  			if !handled && any >= 0 {
   484  				finfo := &tinfo.fields[any]
   485  				strv := finfo.value(sv, initNilPointers)
   486  				if err := d.unmarshalAttr(strv, a); err != nil {
   487  					return err
   488  				}
   489  			}
   490  		}
   491  
   492  		// Determine whether we need to save character data or comments.
   493  		for i := range tinfo.fields {
   494  			finfo := &tinfo.fields[i]
   495  			switch finfo.flags & fMode {
   496  			case fCDATA, fCharData:
   497  				if !saveData.IsValid() {
   498  					saveData = finfo.value(sv, initNilPointers)
   499  				}
   500  
   501  			case fComment:
   502  				if !saveComment.IsValid() {
   503  					saveComment = finfo.value(sv, initNilPointers)
   504  				}
   505  
   506  			case fAny, fAny | fElement:
   507  				if !saveAny.IsValid() {
   508  					saveAny = finfo.value(sv, initNilPointers)
   509  				}
   510  
   511  			case fInnerXML:
   512  				if !saveXML.IsValid() {
   513  					saveXML = finfo.value(sv, initNilPointers)
   514  					if d.saved == nil {
   515  						saveXMLIndex = 0
   516  						d.saved = new(bytes.Buffer)
   517  					} else {
   518  						saveXMLIndex = d.savedOffset()
   519  					}
   520  				}
   521  			}
   522  		}
   523  	}
   524  
   525  	// Find end element.
   526  	// Process sub-elements along the way.
   527  Loop:
   528  	for {
   529  		var savedOffset int
   530  		if saveXML.IsValid() {
   531  			savedOffset = d.savedOffset()
   532  		}
   533  		tok, err := d.Token()
   534  		if err != nil {
   535  			return err
   536  		}
   537  		switch t := tok.(type) {
   538  		case StartElement:
   539  			consumed := false
   540  			if sv.IsValid() {
   541  				// unmarshalPath can call unmarshal, so we need to pass the depth through so that
   542  				// we can continue to enforce the maximum recursion limit.
   543  				consumed, err = d.unmarshalPath(tinfo, sv, nil, &t, depth)
   544  				if err != nil {
   545  					return err
   546  				}
   547  				if !consumed && saveAny.IsValid() {
   548  					consumed = true
   549  					if err := d.unmarshal(saveAny, &t, depth+1); err != nil {
   550  						return err
   551  					}
   552  				}
   553  			}
   554  			if !consumed {
   555  				if err := d.Skip(); err != nil {
   556  					return err
   557  				}
   558  			}
   559  
   560  		case EndElement:
   561  			if saveXML.IsValid() {
   562  				saveXMLData = d.saved.Bytes()[saveXMLIndex:savedOffset]
   563  				if saveXMLIndex == 0 {
   564  					d.saved = nil
   565  				}
   566  			}
   567  			break Loop
   568  
   569  		case CharData:
   570  			if saveData.IsValid() {
   571  				data = append(data, t...)
   572  			}
   573  
   574  		case Comment:
   575  			if saveComment.IsValid() {
   576  				comment = append(comment, t...)
   577  			}
   578  		}
   579  	}
   580  
   581  	if saveData.IsValid() && saveData.CanInterface() && saveData.Type().Implements(textUnmarshalerType) {
   582  		if err := saveData.Interface().(encoding.TextUnmarshaler).UnmarshalText(data); err != nil {
   583  			return err
   584  		}
   585  		saveData = reflect.Value{}
   586  	}
   587  
   588  	if saveData.IsValid() && saveData.CanAddr() {
   589  		pv := saveData.Addr()
   590  		if pv.CanInterface() && pv.Type().Implements(textUnmarshalerType) {
   591  			if err := pv.Interface().(encoding.TextUnmarshaler).UnmarshalText(data); err != nil {
   592  				return err
   593  			}
   594  			saveData = reflect.Value{}
   595  		}
   596  	}
   597  
   598  	if err := copyValue(saveData, data); err != nil {
   599  		return err
   600  	}
   601  
   602  	switch t := saveComment; t.Kind() {
   603  	case reflect.String:
   604  		t.SetString(string(comment))
   605  	case reflect.Slice:
   606  		t.Set(reflect.ValueOf(comment))
   607  	}
   608  
   609  	switch t := saveXML; t.Kind() {
   610  	case reflect.String:
   611  		t.SetString(string(saveXMLData))
   612  	case reflect.Slice:
   613  		if t.Type().Elem().Kind() == reflect.Uint8 {
   614  			t.Set(reflect.ValueOf(saveXMLData))
   615  		}
   616  	}
   617  
   618  	return nil
   619  }
   620  
   621  func copyValue(dst reflect.Value, src []byte) (err error) {
   622  	dst0 := dst
   623  
   624  	if dst.Kind() == reflect.Pointer {
   625  		if dst.IsNil() {
   626  			dst.Set(reflect.New(dst.Type().Elem()))
   627  		}
   628  		dst = dst.Elem()
   629  	}
   630  
   631  	// Save accumulated data.
   632  	switch dst.Kind() {
   633  	case reflect.Invalid:
   634  		// Probably a comment.
   635  	default:
   636  		return errors.New("cannot unmarshal into " + dst0.Type().String())
   637  	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
   638  		if len(src) == 0 {
   639  			dst.SetInt(0)
   640  			return nil
   641  		}
   642  		itmp, err := strconv.ParseInt(strings.TrimSpace(string(src)), 10, dst.Type().Bits())
   643  		if err != nil {
   644  			return err
   645  		}
   646  		dst.SetInt(itmp)
   647  	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
   648  		if len(src) == 0 {
   649  			dst.SetUint(0)
   650  			return nil
   651  		}
   652  		utmp, err := strconv.ParseUint(strings.TrimSpace(string(src)), 10, dst.Type().Bits())
   653  		if err != nil {
   654  			return err
   655  		}
   656  		dst.SetUint(utmp)
   657  	case reflect.Float32, reflect.Float64:
   658  		if len(src) == 0 {
   659  			dst.SetFloat(0)
   660  			return nil
   661  		}
   662  		ftmp, err := strconv.ParseFloat(strings.TrimSpace(string(src)), dst.Type().Bits())
   663  		if err != nil {
   664  			return err
   665  		}
   666  		dst.SetFloat(ftmp)
   667  	case reflect.Bool:
   668  		if len(src) == 0 {
   669  			dst.SetBool(false)
   670  			return nil
   671  		}
   672  		value, err := strconv.ParseBool(strings.TrimSpace(string(src)))
   673  		if err != nil {
   674  			return err
   675  		}
   676  		dst.SetBool(value)
   677  	case reflect.String:
   678  		dst.SetString(string(src))
   679  	case reflect.Slice:
   680  		if len(src) == 0 {
   681  			// non-nil to flag presence
   682  			src = []byte{}
   683  		}
   684  		dst.SetBytes(src)
   685  	}
   686  	return nil
   687  }
   688  
   689  // unmarshalPath walks down an XML structure looking for wanted
   690  // paths, and calls unmarshal on them.
   691  // The consumed result tells whether XML elements have been consumed
   692  // from the Decoder until start's matching end element, or if it's
   693  // still untouched because start is uninteresting for sv's fields.
   694  func (d *Decoder) unmarshalPath(tinfo *typeInfo, sv reflect.Value, parents []string, start *StartElement, depth int) (consumed bool, err error) {
   695  	recurse := false
   696  Loop:
   697  	for i := range tinfo.fields {
   698  		finfo := &tinfo.fields[i]
   699  		if finfo.flags&fElement == 0 || len(finfo.parents) < len(parents) || finfo.xmlns != "" && finfo.xmlns != start.Name.Space {
   700  			continue
   701  		}
   702  		for j := range parents {
   703  			if parents[j] != finfo.parents[j] {
   704  				continue Loop
   705  			}
   706  		}
   707  		if len(finfo.parents) == len(parents) && finfo.name == start.Name.Local {
   708  			// It's a perfect match, unmarshal the field.
   709  			return true, d.unmarshal(finfo.value(sv, initNilPointers), start, depth+1)
   710  		}
   711  		if len(finfo.parents) > len(parents) && finfo.parents[len(parents)] == start.Name.Local {
   712  			// It's a prefix for the field. Break and recurse
   713  			// since it's not ok for one field path to be itself
   714  			// the prefix for another field path.
   715  			recurse = true
   716  
   717  			// We can reuse the same slice as long as we
   718  			// don't try to append to it.
   719  			parents = finfo.parents[:len(parents)+1]
   720  			break
   721  		}
   722  	}
   723  	if !recurse {
   724  		// We have no business with this element.
   725  		return false, nil
   726  	}
   727  	// The element is not a perfect match for any field, but one
   728  	// or more fields have the path to this element as a parent
   729  	// prefix. Recurse and attempt to match these.
   730  	for {
   731  		var tok Token
   732  		tok, err = d.Token()
   733  		if err != nil {
   734  			return true, err
   735  		}
   736  		switch t := tok.(type) {
   737  		case StartElement:
   738  			// the recursion depth of unmarshalPath is limited to the path length specified
   739  			// by the struct field tag, so we don't increment the depth here.
   740  			consumed2, err := d.unmarshalPath(tinfo, sv, parents, &t, depth)
   741  			if err != nil {
   742  				return true, err
   743  			}
   744  			if !consumed2 {
   745  				if err := d.Skip(); err != nil {
   746  					return true, err
   747  				}
   748  			}
   749  		case EndElement:
   750  			return true, nil
   751  		}
   752  	}
   753  }
   754  
   755  // Skip reads tokens until it has consumed the end element
   756  // matching the most recent start element already consumed,
   757  // skipping nested structures.
   758  // It returns nil if it finds an end element matching the start
   759  // element; otherwise it returns an error describing the problem.
   760  func (d *Decoder) Skip() error {
   761  	var depth int64
   762  	for {
   763  		tok, err := d.Token()
   764  		if err != nil {
   765  			return err
   766  		}
   767  		switch tok.(type) {
   768  		case StartElement:
   769  			depth++
   770  		case EndElement:
   771  			if depth == 0 {
   772  				return nil
   773  			}
   774  			depth--
   775  		}
   776  	}
   777  }
   778
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